Tropical Storm Linda

Tropical Storm Linda Track 1100 Hours August 19 2021
Tropical Storm Linda Track 1100 Hours August 19 2021

Tropical Storm Linda Wind Speed FieldTropical Storm LindaNWS National Hurricane Center Miami FL 1100 AM HST Thu Aug 19, 2021 (see Thursday video below)

Linda continues to come unhinged. Dry and stable air has wrapped almost completely into the cyclone’s circulation, as indicated by the low-level stratocumulus cloud field that now primarily characterizes the system. Linda has now lacked organized deep convection for nearly 6 h. A blend of the T- and CI- numbers from the latest subjective Dvorak intensity estimates suggest that the cyclone’s initial intensity has decreased to 45 kt. Cool SSTs of 24-25 C and dry, stable air should prevent any significant deep convection from returning over the next couple of days. Therefore, Linda could be declared post-tropical by tonight. The low will reach warmer waters in a few days. However, by that time, strong southwesterly shear within a dry environment should inhibit regeneration of the cyclone, and the low should should open into a trough early next week. The latest NHC intensity forecast remains near the HCCA and IVCN consensus.

Over the past several hours Linda has moved almost due west with a 12 h motion of about 275/15 kt. Steered by a low- mid-level ridge to its north, a general westward motion is expected until the system dissipates. The latest NHC track forecast is little changed from the previous one, and is close to the tightly packed track guidance.

Linda is crossing into the central Pacific basin, and this will be the final NHC advisory on this system. Future information on Linda can be found in Forecast/Advisories issued by the Central Pacific Hurricane Center beginning at 0300 UTC under AWIPS header HFOTCMCP3 and WMO header WTPA23 PHFO.

FORECAST POSITIONS AND MAX WINDS

INIT  19/2100Z 19.7N 139.5W   45 KT  50 MPH - Tropical Storm (ENE Hilo,Hawaii)
 12H  20/0600Z 19.9N 141.8W   35 KT  40 MPH - Post Tropical(ENE Hilo,Hawaii)
 24H  20/1800Z 20.2N 144.7W   30 KT  35 MPH - Post Tropical(ENE Hilo,Hawaii)
 36H  21/0600Z 20.4N 147.2W   30 KT  35 MPH - Post Tropical(ENE Hilo,Hawaii)
 48H  21/1800Z 20.8N 149.5W   30 KT  35 MPH - Post Tropical(ENE Hilo,Hawaii)
 60H  22/0600Z 21.1N 151.7W   30 KT  35 MPH - Post Tropical(ENE Hilo,Hawaii)
 72H  22/1800Z 21.5N 153.9W   30 KT  35 MPH - Post Tropical(ENE Kahului,Hawaii)
 96H  23/1800Z 22.0N 158.4W   25 KT  30 MPH - Post Tropical(WNW Honolulu,Hawaii)
120H  24/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 AM HST Thu Aug 19, 2021 

Linda has weakened rapidly over the past several hours. The cyclone no longer has an eye, and its deep convection is dissipating and becoming confined mainly to the north of the low-level center. The latest Dvorak intensity estimates from TAFB and SAB both indicate that the initial intensity has decreased to 60 kt, making Linda a tropical storm.

The initial motion estimate is now 280/14 kt. This general motion is forecast to continue for the next several days as the cyclone remains in the flow to the south of a strong subtropical ridge. The model track guidance is in very good agreement, and the latest NHC track forecast lies near the various consensus model solutions.

The cooler waters of 24-25 C and dry, stable air are taking their toll on Linda. These conditions are not supportive of the return of deep convection, and therefore the cyclone should continue to quickly weaken in the short term. Based on the convective trends, there is a possibility that Linda could degenerate into a post-tropical gale within the next couple of days. The NHC forecast is conservative and shows Linda remaining a tropical cyclone through Saturday. The latest NHC intensity forecast remains similar to the IVCN and HCCA intensity consensus models.

FORECAST POSITIONS AND MAX WINDS

INIT  19/1500Z 19.9N 137.6W   60 KT  70 MPH - Tropical Storm (ENE Hilo,Hawaii)
 12H  20/0000Z 20.3N 139.9W   50 KT  60 MPH - Tropical Storm (ENE Hilo,Hawaii)
 24H  20/1200Z 20.7N 142.9W   40 KT  45 MPH - Tropical Storm (ENE Hilo,Hawaii)
 36H  21/0000Z 21.0N 145.6W   35 KT  40 MPH - Tropical Storm (ENE Hilo,Hawaii)
 48H  21/1200Z 21.3N 148.0W   35 KT  40 MPH - Tropical Storm (ENE Hilo,Hawaii)
 60H  22/0000Z 21.7N 150.3W   35 KT  40 MPH - Post Tropical(ENE Hilo,Hawaii)
 72H  22/1200Z 22.0N 152.4W   35 KT  40 MPH - Post Tropical (ENE Lahaina,Hawaii)
 96H  23/1200Z 22.7N 157.0W   30 KT  35 MPH - Post Tropical (ENE Honolulu,Hawaii)
120H  24/1200Z 23.2N 162.3W   30 KT  35 MPH - Post Tropical (WNW Princeville,Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Wed Aug 18, 2021 

The convective structure associated with long-lived Hurricane Linda continues to gradually decay, especially on its western flank. In fact, earlier visible satellite imagery showed that the mid-level eye was starting to become displaced to the northeast of the low-level center, a possible consequence of some sneaky westerly mid-level shear impinging on the storm and importing very dry mid-level air into the circulation from that direction. The latest round of subjective Dvorak CI intensity estimates were both 5.0/90 kt from SAB and TAFB, respectively, but their data T numbers have started to decline. The latest NHC intensity estimate was lowered to 80 kt for this advisory given additional deterioration of the hurricane’s structure since that time.

Now that Linda is finally starting to lose its stable eyewall structure it has maintained for the last 4-5 days, weakening should begin in earnest under cooling sea-surface temperatures. While the deep-layer shear in the SHIPS guidance remains low, there also appears to be some mid-level westerly shear undercutting the outflow layer, allowing very dry mid-level air below 40 percent to get entrained into the circulation. As sea-surface temperatures decrease to near 24 C in 24 hours the weakening rate should increase, and the latest NHC intensity forecast has a faster rate of weakening than in the previous one, following the HCCA guidance aid closely. Both the ECMWF and GFS show Linda becoming devoid of deep convection between 48 to 60 hours, and the latest forecast makes Linda post-tropical by that time.

The current motion of Linda continues off to the west-northwest, but a little faster, at 285/14 kt. This general motion is expected to continue throughout the forecast period as Linda remains steered by a prominent mid-level ridge, which is expected to build-in west along with the cyclone. The latest track guidance remains tightly clustered pretty close to the previous NHC forecast track and only a slight southward adjustment was made , following the HCCA guidance aid. On the current track, Linda will be crossing over in the Central Pacific basin in less than 24 hours, by 0000 UTC Friday.

FORECAST POSITIONS AND MAX WINDS

INIT  19/0300Z 19.2N 134.7W   80 KT  90 MPH - Category 1 (ESE Hilo,Hawaii)
 12H  19/1200Z 19.7N 137.0W   70 KT  80 MPH - Category 1 (ESE Hilo,Hawaii)
 24H  20/0000Z 20.4N 140.1W   55 KT  65 MPH - Tropical Storm (ENE Hilo,Hawaii)
 36H  20/1200Z 20.8N 143.2W   45 KT  50 MPH - Tropical Storm (ENE Hilo,Hawaii)
 48H  21/0000Z 21.1N 145.8W   40 KT  45 MPH - Tropical Storm (ENE Hilo,Hawaii)
 60H  21/1200Z 21.5N 148.1W   40 KT  45 MPH - Post Tropical(ENE Hilo,Hawaii)
 72H  22/0000Z 21.9N 150.4W   40 KT  45 MPH - Post Tropical(ENE Lahaina,Hawaii)
 96H  23/0000Z 22.8N 154.9W   35 KT  40 MPH - Post Tropical(ENE Honolulu,Hawaii)
120H  24/0000Z 23.5N 160.1W   30 KT  35 MPH - Post Tropical(WNW Princeville,Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Wed Aug 18, 2021 

Since the time of the previous advisory, satellite images show that Linda’s cloud tops have warmed and are less prevalent on its west side. Visible imagery has also shown an increase in the low-level cloud cover inside the eye, though Linda still displays a fairly well-defined eye in infrared imagery. Dvorak T-numbers from TAFB and SAB have decreased, and the initial intensity has been lowered to 85 kt for this advisory.

Linda is currently over SSTs near 26 C, but SSTs along the path of the cyclone will decrease to below 25 C in about 6 hours, then remain in the 24-25 C range between 6 to 48 hours. Vertical wind shear will remain low through 48 h, then steadily increase during the day 3 to 5 period as Linda approaches a potent upper-level trough located to the northwest of Oahu. Perhaps even more detrimental than the gradually increasing wind shear is the dry airmass that Linda is embedded in, with environmental mid-level relative humidity values of less than 40 percent. Mid-level moisture is forecast to decrease further over the next 48 hours. A combination of these environmental factors will ultimately lead to the loss of deep convection, and Linda is forecast to become a post-tropical gale by Saturday. Although the intensity forecast reasoning has not changed appreciably, a slightly faster weakening rate is forecast through the first 36 hours. However, the new NHC intensity forecast still lies at the high end of the guidance during that time. Beyond 36 h, little change has been made to the previous forecast.

The initial motion is 285/12 kt. A well-established subtropical ridge should steer Linda in a westward to west-northwestward fashion during the next 5 days. There is essentially no change to the forecast track through 72 hours. Thereafter, a slight southward nudge was made, but still lies just to the north of the TVCE and HCCA consensus aids. Linda is forecast to cross into the Central Pacific in about 30 h and is expected to pass to the north of the Hawaiian Islands as a post-tropical gale late Sunday into Monday.

FORECAST POSITIONS AND MAX WINDS

INIT  18/2100Z 18.7N 133.2W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  19/0600Z 19.3N 135.3W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 24H  19/1800Z 20.0N 138.3W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  20/0600Z 20.6N 141.4W   55 KT  65 MPH - Tropical Storm (ENE Hilo,Hawaii)
 48H  20/1800Z 21.0N 144.2W   50 KT  60 MPH - Tropical Storm (ENE Hilo,Hawaii)
 60H  21/0600Z 21.3N 146.7W   45 KT  50 MPH - Tropical Storm (ENE Hilo,Hawaii)
 72H  21/1800Z 21.8N 149.0W   40 KT  45 MPH - Post Tropical (ENE Hilo,Hawaii)
 96H  22/1800Z 22.7N 153.5W   35 KT  40 MPH - Post Tropical (ENE Honolulu,Hawaii)
120H  23/1800Z 23.4N 158.5W   30 KT  35 MPH - Post Tropical (ENE Princeville,Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST  Wed Aug 18, 2021 

Satellite images indicate that Linda has been maintaining its intensity over the past 12 h or so. The hurricane has begun to lose some of its annular characteristics, as cloud tops in the northern semicircle are warmer than in the southern semicircle. However, the eye remains clear, and the overall structure has not changed much in the last 6 h. Final-T numbers from TAFB and SAB were both T-5.0/90 kt. Therefore, the initial intensity remains 90 kt for this advisory.

Linda is currently over SSTs near 26C, but SSTs along the path of the cyclone will decrease to below 25C in about 12 h, then remain in the 24-25C range during the 12 to 48 h period. Vertical wind shear will remain low through 48 h, but mid-level relative humidity will decrease and become very dry over the next 48 h. Despite the favorable dynamics through 48 h, the unfavorable thermodynamics will likely cause weakening to below hurricane strength by 48 h. By 72 h, wind shear is forecast to increase and become strong by day 4 as Linda approaches a potent upper-level trough located to the northwest of Oahu. This will ultimately lead to the loss of deep convection, despite a slight increase in water temperatures along the cyclone’s path at that time. Linda is forecast to become a post-tropical gale by Saturday morning. The NHC intensity forecast is essentially unchanged from the previous forecast and is in best agreement with the DSHP statistical-dynamical guidance.

The initial motion is 280/11, which is unchanged from 6 h ago. There is no significant change to the previous forecast track or reasoning. A well-established subtropical ridge should steer Linda in a westward to west-northwestward fashion during the next 5 days. The new NHC forecast track is virtually unchanged from the previous one and is in best agreement with the TVCN and HCCA consensus models. Linda is forecast to cross into the Central Pacific in about 36 h and is expected to pass to the north of the Hawaiian Islands as a post-tropical gale late Sunday into Monday.

FORECAST POSITIONS AND MAX WINDS

INIT  18/1500Z 18.2N 131.8W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  19/0000Z 18.9N 133.9W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  19/1200Z 19.7N 136.9W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  20/0000Z 20.3N 140.0W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  20/1200Z 20.8N 142.9W   55 KT  65 MPH - Tropical Storm (WSW Hilo,Hawaii)
 60H  21/0000Z 21.2N 145.6W   45 KT  50 MPH - Tropical Storm (WNW Hilo,Hawaii)
 72H  21/1200Z 21.6N 148.0W   40 KT  45 MPH - Post Tropical (WNW Hilo,Hawaii)
 96H  22/1200Z 22.6N 152.5W   35 KT  40 MPH - Post Tropical (WNW Hilo,Hawaii)
120H  23/1200Z 23.5N 157.3W   35 KT  40 MPH - Post Tropical (WNW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Tue Aug 17, 2021

Linda has made a bit of a comeback over the last 6-12 hours. While the eye continues to remain clear and warm, the eyewall convection has been gradually cooling over the course of the day, with a thickening ring of -60 to -65 C cloud top temperatures occasionally surrounding the eye. This has led to an increase in the most recent subjective Dvorak intensity estimates which at 0000 UTC were T5.5/102 kt from SAB and T5.0/90 kt from TAFB. The latest objective UW-CIMSS ADT estimate is up to T5.3/97 kt though the most recent SATCON estimate was only 79 kt. Taking a blend of these data yields an estimated intensity of 90 kt for this advisory.

Linda is starting to gain some latitude, with the estimated motion now at 280/10 kt. The track guidance philosophy remains the same, with a mid-level ridge well-established across the North Pacific expected to keep Linda moving on a west-northwestward track thorough the forecast period. Once again, the guidance has shifted a bit faster over the forecast period, and the latest NHC track forecast has also been nudged a little faster. Based on the latest forecast, Linda should be crossing into the Central Pacific in about 48 hours, and is expected to pass by to the north of the Hawaiian Islands as a post-tropical gale late in the weekend.

Linda’s recent increase in intensity could be related to the cyclone moving over a small finger of warmer sea-surface temperatures (SSTs) currently. The storm has continued to maintain its stable annular structure, and little change in strength is expected during the next 12 h. However, SSTs will soon begin to decrease once again and should drop below 25 C beyond 24 hours. While the deep-layer vertical wind shear diagnosed by SHIPS is expected to remain low for the next 72 hours, a bit more westerly mid-level shear could begin to undercut the outflow layer in 24-36 hours. For these reasons, Linda should begin a more pronounced weakening trend after 24 hours, with the tropical cyclone forecast to finally drop below hurricane intensity Thursday Night. The latest NHC intensity forecast remains on the high side of the guidance for the first 24 hours, but then is brought down to the guidance mean afterwards, in best agreement with the HFIP Corrected Consensus Approach (HCCA) guidance. While SSTs do begin to increase again after 72 hours, an increase in southwesterly shear is expected to prevent organized convection from redeveloping near the center, and Linda is forecast to become a post-tropical gale by that time.

FORECAST POSITIONS AND MAX WINDS

INIT  18/0300Z 17.9N 129.5W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  18/1200Z 18.4N 131.2W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  19/0000Z 19.2N 133.9W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  19/1200Z 20.0N 136.9W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  20/0000Z 20.7N 140.0W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 60H  20/1200Z 21.3N 142.9W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
 72H  21/0000Z 21.6N 145.6W   40 KT  45 MPH - Post Tropical (WSW Hilo,Hawaii)
 96H  22/0000Z 22.2N 150.0W   35 KT  40 MPH - Post Tropical (WSW Hilo,Hawaii)
120H  23/0000Z 22.7N 154.2W   35 KT  40 MPH - Post Tropical (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Tue Aug 17, 2021

Linda still has annular characteristics with a large circular eye evident in satellite images and a ring of deep convection surrounding that feature. Visible satellite images show mesovorticies rotating around in the hurricane’s eye. The Dvorak classifications have nudged back up this cycle and range from 75 to 90 kt. Based on these estimates, the initial intensity is raised a little to 80 kt.

Linda has moved over slightly warmer waters during the past few hours and is now hugging the 26 deg C isotherm. Annular hurricanes like Linda typically hold their intensity or weaken at a slower pace over cool waters than what is climatological, and it appears that Linda is accomplishing that. Nonetheless, a combination of cool SSTs and drier air should eventually cause a slow weakening trend during the next several days. The models suggest that an increase in southerly shear is likely toward the end of the forecast period, and that could assist in the storm becoming post-tropical by then. The NHC intensity forecast remains near the high end of the guidance in the short term and then falls in line with the majority of the guidance from days 3-5.

Linda is moving due westward at 270/9 kt. The track forecast reasoning is unchanged. A mid-level ridge is expected to remain anchored to the north of Linda, which should keep the storm on a westward to west-northwestward track during the next several days. The models have trended a little faster this cycle, and the NHC track forecast has followed suit. Based on this prediction, Linda is expected to cross into the Central Pacific basin in 48-60 h and be located to the north or northeast of the Hawaiian Islands late this weekend and early next week.

FORECAST POSITIONS AND MAX WINDS

INIT  17/2100Z 17.6N 128.3W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 12H  18/0600Z 18.1N 129.9W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 24H  18/1800Z 18.7N 132.4W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  19/0600Z 19.6N 135.2W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  19/1800Z 20.4N 138.0W   55 KT  65 MPH - Tropical Storm (WSW Hilo,Hawaii)
 60H  20/0600Z 21.0N 141.0W   45 KT  50 MPH - Tropical Storm (WSW Hilo,Hawaii)
 72H  20/1800Z 21.5N 143.9W   40 KT  45 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  21/1800Z 22.1N 148.6W   35 KT  40 MPH - Post Tropical (WSW Hilo,Hawaii)
120H  22/1800Z 22.6N 152.8W   35 KT  40 MPH - Post Tropical (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Tue Aug 17, 2021 

Linda has not changed much during the past several hours. The system still has characteristics of an annular hurricane with a large circular eye (a little more than 30 n mi in diameter) and a ring of deep convection completely surrounding that feature. The convection in the eyewall appears a little less symmetric than it was a few hours ago, however. A blend of the latest Dvorak estimates from TAFB, SAB, and automated values from CIMSS at the University of Wisconsin support nudging the intensity down to 75 kt.

Even though Linda is over cool 25-26 deg C waters, research has proven that tropical cyclones that are characterized by an annular cloud pattern usually weaken more slowly than the climatological rate in the eastern Pacific, and we expect Linda to be in that category during the next day or so. Nonetheless, a combination of cool SSTs and drier air should induce a slow weakening trend. The models suggest that an increase in southerly shear is likely toward the end of the forecast period, and that could assist in the storm becoming post-tropical by then. The NHC intensity forecast lies near the high end of the guidance in the short term and then falls in line with the majority of the guidance from days 3-5.

Linda is moving nearly due westward at 265/9 kt. The track forecast reasoning appears fairly straightforward. A mid-level ridge is expected to remain anchored to the north of Linda, which should keep the storm on a westward to west-northwestward track during the next several days. The models are tightly clustered, and only small changes were made to the previous track forecast. Based on this prediction, Linda is expected to cross into the Central Pacific basin in 60-72 h and be located to the north or northeast of the Hawaiian Islands late this weekend and early next week.

FORECAST POSITIONS AND MAX WINDS

INIT  17/1500Z 17.5N 127.4W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 12H  18/0000Z 17.8N 128.8W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 24H  18/1200Z 18.3N 131.0W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  19/0000Z 19.1N 133.7W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  19/1200Z 20.1N 136.5W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 60H  20/0000Z 20.8N 139.4W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
 72H  20/1200Z 21.3N 142.1W   40 KT  45 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  21/1200Z 22.0N 147.3W   35 KT  40 MPH - Post Tropical (ENE Hilo,Hawaii)
120H  22/1200Z 22.5N 151.4W   35 KT  40 MPH - Post Tropical (ENE Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Mon Aug 16, 2021

This evening’s conventional satellite images indicate that the cloud pattern hasn’t changed that much during the past 6 hours. If anything, the eyewall cloud top temperatures continue to gradually warm, however, the convective MG (-51 to -53C) ring is showing less erosion in the west quadrant as noted earlier. A blend of the objective and subjective satellite intensity estimates supports maintaining 85 kt for this advisory.

Finally, Linda has begun moving over cooler 25C waters, so we could see some weakening overnight. NOAA’s daily Real-Time Global Sea Surface temperature analysis, however, reveals a marginally warm pool of water just to the west of the hurricane. Consequently, little change in strength, or possibly some restrengthening could occur on Tuesday. Toward the end of the week, Linda is forecast to traverse even cooler oceanic temperatures which should induce a more rapid weakening as the cyclone crosses into the central Pacific. The NHC forecast follows the statistical SHIPS intensity model through 60 hours, then stays close to the IVCN consensus aid.

Linda is embedded in the deep easterly flow provided by high pressure located over the northeast Pacific, and the initial motion is 265/8 kt. The hurricane should be bending back to the right (west-northwestward) around early Wednesday as the aforementioned ridge builds to the northeast, behind a mid- to upper-level trough approaching the U.S. west coast and the Baja California peninsula. Global and regional models are in agreement that Linda should continue moving toward the west-northwest through day 5, and the official forecast follows suit. The track forecast is near the middle of the guidance envelope, and is in best agreement with the TVCN multi-model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  17/0300Z 17.7N 125.4W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  17/1200Z 17.7N 126.7W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  18/0000Z 17.9N 128.7W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  18/1200Z 18.6N 130.9W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  19/0000Z 19.4N 133.5W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  19/1200Z 20.3N 136.2W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 72H  20/0000Z 21.1N 139.0W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  21/0000Z 22.1N 144.2W   40 KT  45 MPH - Post Tropical (ENE Hilo,Hawaii)
120H  22/0000Z 22.9N 148.1W   35 KT  40 MPH - Post Tropical (ENE Hilo,Hawaii)

NWS National Hurricane Center Miami FL 1100 AM HST Mon Aug 16, 2021 

Linda still has a very striking appearance on visible satellite imagery, with a well-defined large eye, and multiple eyewall mesovorticies rotating about the mean center. However, the ring of cold cloud tops associated with the eyewall has become just a touch more ragged over the last few hours, and an earlier SSMIS microwave pass at 1518 UTC showed a break in the singular eyewall on the south side. The 1800 UTC Dvorak CI numbers were steady from SAB and TAFB, but the data-T numbers have decreased a bit from earlier today. In addition, the latest UW-CIMSS ADT intensity estimate was down to T4.8/85-kt. Therefore, Linda is estimated to be a bit weaker this advisory, with maximum sustained winds near 85-kt.

The initial motion is beginning to turn a bit more westward, now at 260/8 kt. A well-established mid-level ridge north of Linda is expected to build in gradually to the northeast, allowing the storm to begin gaining latitude starting tomorrow. This west-northwest track is then expected to continue through the forecast period. The latest NHC track forecast is very close to the previous one, and is closest to the GEFX consensus, which is a simple blend of the most recent GFS and ECMWF forecasts.

As discussed in previous advisories, Linda is expected to remain in a low deep-layer vertical-wind-shear environment (below 10 kt) for the next 4-5 days. Thus, Linda’s intensity forecast is expected to be driven by a combination of thermodynamic factors and the cyclone’s stable annular inner-core structure. While sea-surface temperatures (SSTs) are only between 25-26 C under the hurricane right now, the forecast track takes Linda back over slightly warmer SSTs in the 12-36 h period, and this could delay weakening in the short-term.

The NHC intensity forecast continues to be above much of the intensity guidance, showing little change in intensity over the next 24-36 hours. In fact, when Linda moves over slightly warmer SSTs tomorrow, it would not be surprising to see a bit of restrengthening, assuming nearby dry-air does not disrupt the stable eyewall structure. However by 48 hours, SSTs decrease below 26 C in earnest and Linda is expected to begin a pronounced weakening trend. Towards the end of the forecast, Linda should become devoid of deep convection as indicated by the latest GFS and ECMWF IR brightness temperature forecast, and Linda is expected to become a post-tropical gale by Friday.

FORECAST POSITIONS AND MAX WINDS

INIT  16/2100Z 17.7N 124.6W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  17/0600Z 17.6N 125.9W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  17/1800Z 17.7N 127.7W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  18/0600Z 18.2N 129.8W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 48H  18/1800Z 19.0N 132.2W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  19/0600Z 19.9N 134.8W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 72H  19/1800Z 20.7N 137.5W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  20/1800Z 22.0N 142.6W   40 KT  45 MPH - Post Tropical (ENE Hilo,Hawaii)
120H  21/1800Z 23.0N 146.8W   35 KT  40 MPH - Post Tropical (ENE Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Mon Aug 16, 2021 

There has been little notable change in Linda’s structure on satellite imagery. The hurricane continues to possess annular characteristics, with a well-defined warm eye up to +15 C surrounded by a ring of -60 to -65 C cloud top temperatures associated with the eyewall. The eyewall was also well-defined on a recent 1003 UTC AMSR-2 microwave pass. The most recent subjective Dvorak classifications from SAB and TAFB were T5.5/102 kt and T5.0/90 kt, while the latest UW-CIMSS ADT estimate was T5.1/92 kt. Thus, Linda is being maintained as a 90-kt hurricane for this advisory, though this might be a bit on the conservative side.

The initial motion estimate continues off to the west-southeast, at 255/8 kt. The most recent track forecast is mostly just an update of the previous one. Linda is expected to gradually make a rightward turn from the west-southwest to the west-northwest as a strong mid-level ridge to the north shifts its orientation. The latest NHC track forecast remains is good agreement with the track consensus guidance, blending the TVCN and HCCA aids.

Linda remains in a very low wind shear environment, with SHIPS guidance diagnosing less than 5-kt of shear over the hurricane currently. Even though sea-surface temperatures remain only marginally warm along Linda’s forecast track, its continued annular structure argues for only very gradual weakening over the next 48 hours. Afterwards, Linda will cross over the 26 C isotherm into cooler waters, and a faster rate of weakening is anticipated after that time. The latest NHC intensity forecast over the first couple of days remains higher than the majority of the model guidance, and is closest to the ECMWF forecast. After Linda begins to move over cooler waters in 60 h, the intensity forecast is brought back down towards the intensity consensus. At the end of the forecast period, Linda is expected to become a post-tropical gale once deep organized convection ceases, as suggested by the GFS and ECMWF simulated brightness temperature at that time frame.

FORECAST POSITIONS AND MAX WINDS

INIT  16/1500Z 17.9N 123.7W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  17/0000Z 17.6N 124.9W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  17/1200Z 17.5N 126.7W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  18/0000Z 17.9N 128.6W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  18/1200Z 18.5N 130.9W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  19/0000Z 19.2N 133.4W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  19/1200Z 20.1N 136.0W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  20/1200Z 21.6N 141.3W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
120H  21/1200Z 22.6N 146.0W   40 KT  45 MPH - Post Tropical (WNW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 PM HST Sun Aug 15, 2021 

This evening’s satellite presentation reveals little change in Linda’s annular cloud pattern. The eyewall consists of -60 to -65C cloud tops and the 38-n-mi-diameter obscured eye temperature is a warm +12C. Once again, using a consensus of the Final T- and CI- Dvorak satellite intensity estimates from TAFB and SAB along with a blend of an earlier SATCON and UW-CIMSS ADT estimates, the initial intensity is held at 95 kt.

While Linda is expected to move in a generally west-southwestward to westward motion during the next couple of days, the annular hurricane will essentially be paralleling an oceanic temperature gradient while remaining over 26-27C waters. Since the wind shear component is forecast to remain low throughout the entire forecast, only invading drier more stable air will negatively affect the cyclone’s intensity. Intensive research in the past has proven that these truck-tire-shaped tropical cyclones tend to weaken slower than the climatological rate recognized in the eastern Pacific. Therefore, only slow weakening is forecast through the 60-hour period. Afterward, Linda will move over a steep sea-surface temperature gradient (sub-24C) which should induce a more rapid weakening pace. The NHC intensity forecast is hedged closely to the Decay-SHIPS model through 60 hours, then uses a blend of the global models and the IVCN/HCCA consensus aids through day 5.

The initial motion estimate is west-southwestward, or 255/9 kt, and this general heading should continue through Monday night. A subsequent turn back to the west is forecast as mid-tropospheric high pressure over the northeastern Pacific builds southward along 135W. At the 48-hour period, a turn toward the west-northwest is expected as Linda rounds the southwestern periphery of the aforementioned ridge. The latest NHC track forecast is basically just an update of the previous one through day 3, and then is adjusted slightly to the left closer to the TVCN consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  16/0300Z 18.6N 122.0W   95 KT 110 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  16/1200Z 18.2N 123.3W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  17/0000Z 17.8N 124.9W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  17/1200Z 17.7N 126.8W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  18/0000Z 18.1N 128.8W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  18/1200Z 18.6N 130.8W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  19/0000Z 19.5N 133.4W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  20/0000Z 21.1N 138.3W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
120H  21/0000Z 22.3N 142.8W   35 KT  40 MPH - Post Tropical (WNW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 500 AM HST Sun Aug 15, 2021 

As was hypothesized in the previous advisory, it appears that Linda is completing an eyewall replacement. An 0918 UTC GCOM AMSR2 pass revealed the last-remaining vestiges of an inner eyewall decaying within a newer, larger eye, which is estimated to be 35 n mi in diameter based on the 89-GHz channel imagery. While the microwave data still showed a few banding features on the western side of the circulation, the hurricane has taken on annular characteristics, with a relatively thick, solid ring of deep convection surrounding the eye. This evolution is confirmed by the objective annular hurricane screening algorithm. Cloud-top and eye temperatures have not changed much since the previous advisory, with Dvorak CI numbers ranging between 100-115 kt and objective estimates ranging between 90-100 kt. Therefore, the initial intensity remains 100 kt.

Linda has begun to lose some latitude, and the initial motion is south of due west, or 265/10 kt. A strong mid-tropospheric high centered over the western United States is forecast to slide westward and southwestward over the Pacific during the next couple of days, which should push Linda toward the west-southwest during the next 36-48 hours. After that time, the ridge merges with another high farther north, which will likely allow Linda to turn back toward the west-northwest on days 3 through 5. The track models are showing a near to below-normal amount of spread, and therefore the NHC track forecast is of high confidence, lying near the middle of the guidance envelope.

Vertical shear over Linda is expected to be less than 10 kt for the next 5 days. Therefore, the hurricane’s future intensity is likely to be driven by thermodynamic factors, and its annular structure will come into play. Linda is expected to move over near-constant or gradually decreasing sea surface temperatures of 26-27 degrees Celsius for the next several days, a scenario which is typical of the gradual weakening noted by most annular hurricanes. Therefore, the NHC intensity forecast is above the consensus aids and keeps Linda at hurricane strength for the next 3 days. The weakening trend could be even more gradual than indicated here, if the statistical-dynamical SHIPS guidance ends up being correct.

FORECAST POSITIONS AND MAX WINDS

INIT  15/1500Z 19.0N 120.2W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 12H  16/0000Z 18.7N 121.7W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  16/1200Z 18.1N 123.5W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  17/0000Z 17.7N 125.2W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  17/1200Z 17.6N 126.9W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  18/0000Z 18.0N 128.7W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  18/1200Z 18.6N 130.9W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  19/1200Z 20.4N 135.7W   55 KT  65 MPH - Tropical Storm (WSW Hilo,Hawaii)
120H  20/1200Z 22.3N 140.2W   40 KT  45 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 800 PM PDT Sat Aug 14, 2021 

Although Linda is still quite an impressive and powerful hurricane, inner-core cloud tops have been warming during the past several hours. Furthermore, the eye has become more obscured during the past few hours, with convoluted cloud elements and a few mesovortices identifiable in High resolution visible imagery. A series of microwave images from earlier today, suggest a concentric, outer convective ring may be forming, usually indicative of an eyewall replacement cycle. The latest subjective and objective satellite intensity estimates indicate that Linda has weakened to 110 kt, and the initial intensity is lowered to this value for this advisory.

With the possibility that Linda maybe undergoing an eyewall replacement cycle, fluctuations in strength are possible during the next few hours. Regardless of any inner-core structural changes, Linda will be moving over gradually decreasing oceanic temperatures and into a more statically stable and drier surrounding environment during the next several days. Based on the statistical GFS and ECMWF SHIPS intensity guidance and the large-scale and regional models, Linda should begin a weakening trend soon, if it hasn’t started already. The NHC intensity forecast resembles the previous advisory, and is in best agreement with the HCCA and IVCN intensity consensus aids.

Linda is embedded within the mid-tropospheric south peripheral flow of a strengthening ridge to the north, and the initial motion is estimated to be west-northwestward, or 285/12 kt. This subtropical ridge is forecast to build back westward to the northwest of Linda during the next 24-36 h, inducing a turn toward the west-southwest. Around early Tuesday, the hurricane is expected to turn back toward the west and west-northwest in response to a mid-level cut-off low forming west of the Baja California peninsula. The official track forecast is based primarily on the TVCN consensus model and is quite similar to the previous NHC forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  15/0300Z 19.3N 118.2W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 12H  15/1200Z 19.4N 119.9W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  16/0000Z 19.1N 121.9W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  16/1200Z 18.6N 123.7W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  17/0000Z 18.1N 125.4W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  17/1200Z 18.0N 127.1W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  18/0000Z 18.2N 128.9W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
 96H  19/0000Z 19.6N 133.2W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)
120H  20/0000Z 21.6N 137.9W   40 KT  45 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 200 PM PDT Sat Aug 14, 2021

Linda is maintaining category 4 strength this afternoon. The hurricane continues to exhibit a well-defined eye of about 15 n mi in diameter, with some mesoscale vortices noted within the eye on visible imagery. Linda also has a fairly symmetrical convective cloud and upper-level outflow pattern. The current intensity estimate remains at 130 kt in agreement with the latest subjective Dvorak estimates from TAFB and SAB.

Some short-term fluctuations in intensity are still possible through tonight due to eyewall replacements. Vertical shear remains weak over the system and the dynamical guidance indicates that it will remain weak throughout the forecast period. However, the hurricane will be moving over gradually cooling ocean waters with some drier mid-tropospheric air in the environment during the next several days. This should cause the powerful hurricane to begin to gradually weaken. The official intensity forecast continues to follow the NOAA Corrected Consensus prediction.

The direction of motion is gradually bending to the left, and the initial motion is 285/11 kt. The track forecast philosophy remains essentially the same as in the previous advisory package. A mid-tropospheric ridge is predicted by the global models to build to the northwest of Linda, and this should cause the system to turn toward the west-southwest within the next couple of days. Later in the forecast period, Linda is expect to turn back to the west-northwest as the ridge shifts a little northward and becomes more zonally-oriented. The official track forecast is very similar to the previous one and is also very close to the dynamical model consensus, TVCE.

FORECAST POSITIONS AND MAX WINDS

INIT  14/2100Z 19.1N 117.0W  115 KT 130 MPH - Category 4 (WSW Puerto Vallarta, MX)
 12H  15/0600Z 19.4N 118.7W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  15/1800Z 19.3N 120.8W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  16/0600Z 18.8N 122.6W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  16/1800Z 18.3N 124.5W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  17/0600Z 18.1N 126.3W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  17/1800Z 18.0N 128.2W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  18/1800Z 19.2N 132.2W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)
120H  19/1800Z 21.1N 136.9W   45 KT  50 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 800 AM PDT Sat Aug 14, 2021 

Linda is maintaining a well-defined 15-n mi wide eye, and a quite symmetric surrounding convective cloud pattern. Taking a blend of the latest subjective and objective Dvorak estimates gives a current intensity estimate of about 115 kt, i.e. category 4 strength.

Linda may undergo an eyewall replacement later today, which is typical for intense hurricanes, and this could cause some short-term fluctuations in intensity. The hurricane is currently in a low-vertical shear environment, and the dynamical guidance indicates that the shear will remain low for the next few days. However, SSTs beneath Linda should gradually lower along with decreasing environmental mid-level humidities during the next several days. Thus a slow weakening trend should commence by tonight. The official intensity forecast is a blend of the corrected and simple model consensus predictions.

The initial motion is estimated to be west-northwestward, or 290/11 kt. There is little change to the expected steering scenario. Linda is moving along the southern side of a pronounced subtropical ridge. The ridge is predicted by the global models to build westward to the northwest of the hurricane during the next couple of days. This should cause Linda to turn toward the west-southwest within the next day or two. Late in the forecast period, as the ridge weakens, the cyclone is forecast to turn westward. The NHC track forecast is very close to the previous one and in good agreement with the latest dynamical model consensus.

FORECAST POSITIONS AND MAX WINDS

INIT  14/1500Z 18.8N 116.1W  115 KT 130 MPH - Category 4 (WSW Puerto Vallarta, MX)
 12H  15/0000Z 19.1N 117.7W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  15/1200Z 19.2N 119.8W   95 KT 110 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  16/0000Z 19.0N 121.8W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 48H  16/1200Z 18.5N 123.8W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  17/0000Z 18.0N 125.6W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  17/1200Z 17.9N 127.5W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  18/1200Z 18.5N 131.5W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  19/1200Z 20.5N 136.0W   55 KT  65 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS NATIONAL HURRICANE CENTER MIAMI FL 900 PM MDT FRI AUG 13 2021

Enhanced BD-curve infrared satellite imagery shows that Linda’s inner core has become much better organized during the past few hours. The eye temperature has warmed to about 13c and the eyewall temperatures have cooled to -66 to -69c, and in fact, this thick black ring is a little more than 80 percent closed. Based on these inner cloud pattern improvements, the initial intensity for this advisory is adjusted up to 105 kt.

Linda still has a chance through early saturday to strengthen some more, and this is indicated in the forecast. By Saturday night, Linda is expected to move over decreasing oceanic temperatures (25-26c) and enter a more stable and drier thermodynamic surrounding environment. These inhibiting contributions should induce a steady weakening trend through day 3. For the remaining portion of the forecast, the cyclone should weaken a little more rapidly as it moves over even cooler (sub 24c) sea surface temperatures. The NHC intensity forecast is based on a blend of the NOAA HCCA and IVCN consensus aids, and is just below the decay SHIPS model.

The initial motion is estimated to be west-northwestward, or 300/11 kt. Linda is forecast to move in a west-northwestward to westward motion during the next couple of days. Afterward, the large-scale models show a mid-tropospheric high pressure anchored over the southwestern united states building westward over the eastern pacific and to the northwest of the cyclone. In response to the changing synoptic steering pattern, Linda is expected to turn west-southwestward by early next week. The official track forecast has not changed much at all, and closely follows the better performing TVCN multi-model consensus.

Slight adjustments were made to Linda’s wind radii based on earlier METOP-A and B scatterometer overpasses.

FORECAST POSITIONS AND MAX WINDS

INIT  14/0300Z 17.9N 113.9W  105 KT 120 MPH - Category 3 (WSW Puerto Vallarta, MX)
 12H  14/1200Z 18.5N 115.6W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  15/0000Z 19.1N 117.8W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 36H  15/1200Z 19.2N 120.0W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 48H  16/0000Z 18.9N 121.9W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 60H  16/1200Z 18.5N 123.8W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  17/0000Z 18.1N 125.6W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  18/0000Z 18.1N 129.5W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  19/0000Z 19.5N 134.1W   50 KT  60 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 300 PM MDT Fri Aug 13, 2021 

Linda has become an impressive looking hurricane this afternoon. The eye that first became evident on geostationary satellite imagery this morning has continued to clear out and warm while the surrounding cold convection associated with the eyewall wraps around the eye. The convective structure on microwave imagery has also improved, with a distinct eye and closed eyewall apparent in an earlier 1417 UTC SSMIS pass. The 1800 UTC subjective and objective Dvorak estimates were in unanimous agreement with T5.5/102 kt provided by SAB, TAFB, and ADT sources. Therefore, the initial intensity has been increased to 100 kt this advisory, making Linda a major hurricane.

Linda continues to move steadily to the west-northwest, at 300/12 kt. The track philosophy has not changed much over the past 24 hours. A mid- to upper-level ridge currently centered over the southwestern United States is expected to expand westward, building in to the northwest of the hurricane. This evolution should result in Lisa’s motion bending left, first to the west, and then to the west-southwest over the next 2-3 days. The track guidance remains tightly clustered near and just slightly poleward of the previous forecast track. The latest NHC track forecast was nudged just slightly northward over the first few days, but is nearly on top of the previous forecast by the end of the period.

Linda has rapidly intensified, with a 35-kt increase over the past 24 hours, and the hurricane still has an opportunity to intensify a bit more over the next 12 hours. After 24 hours, Linda will begin to cross over gradually decreasing sea-surface temperatures and into a and drier mid-level environment. These factors should lead to gradual weakening. One fly in the ointment is that the shear diagnosed by SHIPS guidance is expected to remain low and easterly while sea-surface temperatures remain between 26-27 C through 60 hours. Both the ECMWF and HWRF simulated brightness temperatures during that time suggest that Linda could develop a stable annular structure, which often results in a slower than expected weakening rate. For this reason, the latest intensity forecast only shows gradual weakening through 60 hours, which is a bit above the HCCA consensus aid. More rapid weakening is likely at the end of the forecast period when Linda will move over sub 25 C water.

FORECAST POSITIONS AND MAX WINDS

INIT  13/2100Z 17.5N 112.9W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 12H  14/0600Z 18.2N 114.6W  110 KT 125 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  14/1800Z 18.9N 116.9W  105 KT 120 MPH - Category 3 (WSW Puerto Vallarta, MX)
 36H  15/0600Z 19.2N 119.2W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 48H  15/1800Z 19.1N 121.3W   95 KT 110 MPH - Category 2 (WSW Puerto Vallarta, MX)
 60H  16/0600Z 18.7N 123.3W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 72H  16/1800Z 18.2N 125.2W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  17/1800Z 17.9N 129.0W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  18/1800Z 19.0N 133.0W   55 KT  65 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 900 AM MDT Fri Aug 13, 2021

Linda’s structure has continued to improve since early this morning. An eye was evident in longwave and shortwave IR imagery from GOES-17 and GOES-15 near 1200 UTC, though it has since become obscured by cold cloud tops associated with eyewall convection. An earlier AMSR overpass showed evidence of a ring of shallow to moderate convection, often associated with rapidly intensifying cyclones. Intensity estimates at 1200 UTC ranged from 77 kt to 97 kt, so the initial intensity was set at 90 kt, in closest agreement with the U-W CIMSS SATCON. It is worth noting that Linda’s intensity is in a range where estimates can range greatly, so confidence in that assessment is not particularly high.

Computational problems with the GFS this morning has limited the guidance available for the forecast, particularly with respect to the intensity. Therefore, despite the higher initial intensity and recent improvement in convective structure, the official intensity forecast was only modestly increased in the short term. It does not appear that wind shear will be a major inhibiting factor during the next day or two. Environmental moisture and SSTs should also be sufficient for further strengthening. The NHC forecast is a little above the model consensus and previous forecast for the next 24-36 h. After that time, Linda should move over cooler SSTs which should cause at least gradual weakening. By the end of the 5-day period, the NHC forecast is in line with the consensus and identical to the previous advisory.

Only small tweaks were made to the NHC track forecast. Linda continues to move toward the west-northwest with an estimated forward speed of 11 kt. The global models unanimously forecast that a deep-layer ridge to the north of Linda will build over the weekend, causing the hurricane to turn westward, and then west-southwestward by early next week. Confidence in the track forecast is quite high due to the agreement among the track models.

FORECAST POSITIONS AND MAX WINDS

INIT  13/1500Z 16.9N 111.8W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 12H  14/0000Z 17.6N 113.6W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 24H  14/1200Z 18.4N 115.9W  105 KT 120 MPH - Category 3 (WSW Puerto Vallarta, MX)
 36H  15/0000Z 18.8N 118.2W  105 KT 120 MPH - Category 3 (WSW Puerto Vallarta, MX)
 48H  15/1200Z 18.8N 120.3W  100 KT 115 MPH - Category 3 (WSW Puerto Vallarta, MX)
 60H  16/0000Z 18.6N 122.3W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 72H  16/1200Z 18.2N 124.2W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  17/1200Z 17.5N 128.0W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  18/1200Z 18.5N 132.0W   60 KT  70 MPH - Tropical Storm (WSW Hilo,Hawaii)

NWS National Hurricane Center Miami FL 900 PM MDT Thu Aug 12, 2021

Linda is starting to intensify more in earnest. This evening, the Central Dense Overcast has expanded some, especially to the northwest which had previously been more restricted by moderate northerly shear. A warm spot has been intermittently appearing on infrared satellite imagery, suggesting the development of a more well-defined eye. A SSMIS 2348 UTC microwave pass also indicated a closed mid-level eyewall had developed on the 91 GHz channel, though the 37 GHz channel still suggested the low-level eyewall may still be open to the west. Objective satellite estimates this evening have been steadily increasing with the latest UW-CIMSS ADT estimate up to T4.6/80 kt and the most recent SATCON estimate up to 76 kt. However, subjective Dvorak estimates from SAB and TAFB were lower. Given the improvement in Linda’s structure this evening, the intensity is raised to 75-kt for this advisory.

Linda continues to move to the west-northwest, with a slightly faster forward motion at 300/11 kt. Linda should continue a general west-northwest motion for the next several days as a mid-level ridge remains parked over Mexico and the southwestern United States. After 48 hours, this ridge is forecast to build westward and become reoriented west-southwest to east-northeast ahead of Linda. This synoptic evolution should result in Linda turning to the west or even west-southwest after 72 hours through the end of the forecast period. The latest NHC track forecast is very similar to the previous forecast for the first 48-72 hours, but has been shifted a little further south thereafter. However, this forecast track is still poleward of the GFS, ECMWF, and reliable HCCA consensus guidance, and further southward adjustments may be needed in subsequent forecasts.

Northerly vertical wind shear, which has slowed Linda’s intensification rate over the last day or so, appears to be slowly subsiding, and the ECMWF-SHIPS guidance suggests this shear will gradually decrease to under 10 kt by 48 hours. During this period, Linda should remain in a moist environment and over 27-28 C sea-surface temperatures. These factors favor strengthening, and the improvement in Linda’s inner-core structure argues for a faster rate of intensification over the next 12-24 hours. The latest intensity forecast was raised in the short-term, following the latest HCCA guidance, and calls for a peak intensity of 95 kt in 36-48 hours. It remains possible Linda could intensify a bit more than expected, as the latest HWRF, HMON, and COAMPS-TC regional hurricane models still show a peak intensity as a major hurricane. After 48 hours, Linda will be moving over sub 27 C sea-surface temperatures and into a drier environment, which should result in gradual weakening through the end of the forecast period.

FORECAST POSITIONS AND MAX WINDS

INIT  13/0300Z 15.8N 109.6W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 12H  13/1200Z 16.6N 111.2W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 24H  14/0000Z 17.6N 113.5W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 36H  14/1200Z 18.5N 115.8W   95 KT 110 MPH - Category 2 (WSW Puerto Vallarta, MX)
 48H  15/0000Z 18.9N 118.0W   95 KT 110 MPH - Category 2 (WSW Puerto Vallarta, MX)
 60H  15/1200Z 19.0N 120.0W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 72H  16/0000Z 18.9N 121.9W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  17/0000Z 18.3N 125.4W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  18/0000Z 18.1N 129.4W   60 KT  70 MPH - Tropical Storm (ESE Hilo,Hawaii)

NWS National Hurricane Center Miami FL 300 PM MDT Thu Aug 12, 2021 

There hasn’t been much change to Linda’s structure since this morning. The hurricane’s center is embedded within a small Central Dense Overcast, and a dimple is evident in visible satellite images where an eye would be likely to form. For the most part, satellite intensity estimates have not changed from this morning, and a 1550 UTC ASCAT-A pass showed peak winds in the 55-60 kt range. Given that instrument’s typical undersampling, especially for a small cyclone, the 65-kt initial intensity still seems appropriate.

Linda is moving toward the west-northwest, or 300/8 kt, to the south of a mid-tropospheric ridge located over northern Mexico. This ridge, and a stronger mid-level high developing over the western United States, are expected to continue driving Linda toward the west-northwest for the next 2-3 days. By days 4 and 5, another mid-level high is forecast to develop between Hawaii and Alaska, and that feature is likely to block Linda’s northward progress, and possibly even cause a south-of-due-west motion by the end of the forecast period. The track guidance is in good agreement on this scenario, and the updated NHC track forecast has been nudged southward mainly on days 4 and 5. It should be noted that this new forecast is not as far south as several of the track models, and additional southward adjustments may be required in subsequent forecasts.

Various shear analyses suggest that the northerly shear affecting Linda may have decreased slightly, with the magnitude now on the order of 10-15 kt. SHIPS diagnostics indicate that this level of shear is likely to continue for another 24 hours or so, and then it could decrease further and enable some gradual strengthening. Models generally show Linda’s intensity peaking and leveling off in the 36-60 hour window. After 60 hours, Linda is expected to move into a less favorable thermodynamic environment, highlighted by colder sea surface temperatures and drier, more stable air, and weakening is therefore shown on days 3-5. One important note is that further southward shifts in the forecast track would keep Linda over warmer waters and potentially slow the cyclone’s weakening trend.

FORECAST POSITIONS AND MAX WINDS

INIT  12/2100Z 15.3N 108.7W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 12H  13/0600Z 16.0N 110.3W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 24H  13/1800Z 17.0N 112.4W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  14/0600Z 17.9N 114.6W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  14/1800Z 18.7N 116.8W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  15/0600Z 19.0N 118.8W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  15/1800Z 19.0N 120.8W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  16/1800Z 18.6N 124.5W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  17/1800Z 18.5N 128.3W   55 KT  65 MPH - Tropical Storm (ESE Hilo,Hawaii)

NWS National Hurricane Center Miami FL 900 AM MDT Thu Aug 12, 2021 

Linda has been trying to form an eye in conventional satellite imagery during the past few hours, but that feature has been obscured by the development of new convective bursts near the center. An AMSR2 microwave pass from 0850 UTC indicated that the structure remains well organized, if not a little tilted with height due to shear, and a ragged mid-level eye feature was noted. Objective intensity estimates are at hurricane strength–T4.4/75 kt from the UW-CIMSS ADT and 66 kt from SATCON–but subjective CI numbers from TAFB and SAB remain at 3.5/55 kt. Given the continued attempts at eye formation, I have elected to lean on the side of the objective numbers and increase the initial intensity to 65 kt, making Linda a hurricane.

The AMSR2 pass revealed that Linda has been moving a little to the right of the previous forecast track, and the initial motion is estimated to be west-northwestward, or 300/7 kt. Mid-tropospheric ridging located over northern Mexico should keep Linda on a west-northwestward track for the next 2 to 3 days. After that time, another ridge is forecast to slide westward from California out over the Pacific, which should have a blocking influence on Linda and cause it to turn back toward the west. In fact, by day 5, most of the track models are showing a south-of-due-west motion. On the whole, the guidance is showing a normal amount of spread, and the NHC track forecast has only been shifted slightly eastward and northward through day 3 to account for the adjustment of the initial position. This solution is very close to the HCCA and TVCE consensus aids.

Moderate northerly to north-northeasterly shear continues to affect the cyclone, and the effect of this shear was seen in the slight offset of the low- and mid-level centers in microwave imagery. The shear is forecast to subside slightly during the next couple of days while the hurricane moves over warm waters of 28-29 degrees Celsius and within an environment of upper-level divergence. The limiting effects of the shear are likely to support gradual strengthening during the next couple of days, and the NHC intensity forecast is within the relatively tightly packed guidance suite during that time. During the 3-5 day period, shear is expected to decrease substantially, but less conducive thermodynamic conditions should cause Linda to gradually lose intensity, potentially weakening to a tropical storm by day 5.

FORECAST POSITIONS AND MAX WINDS

INIT  12/1500Z 14.8N 107.7W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 12H  13/0000Z 15.6N 109.1W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
 24H  13/1200Z 16.6N 111.2W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)
 36H  14/0000Z 17.7N 113.4W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 48H  14/1200Z 18.6N 115.5W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 60H  15/0000Z 19.2N 117.6W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
 72H  15/1200Z 19.4N 119.6W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
 96H  16/1200Z 19.1N 123.4W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  17/1200Z 19.0N 127.2W   55 KT  65 MPH - Tropical Storm (WSW Puerto Vallarta, MX)

NWS National Hurricane Center Miami FL 900 PM MDT Wed Aug 11, 2021

While deep convection continues to pulse near and just south of the estimated center of Linda, recent satellite imagery suggests the center is now along the northwestern edge of the cirrus canopy. A series of microwave passes, first from AMSR-2 at 2036 UTC and then SSMIS at 2340 UTC indicated that the mid-level eye that was observed earlier today has become poorly defined. This degradation in structure could be attributed to dry air being imported into the inner core of Linda by persistent 15-20 kt of northerly vertical wind shear. The current intensity this advisory is held at 60 kt, taking a blend of the latest subjective intensity estimates from TAFB (T3.5/55 kt) and SAB (T4.0/65 kt), though this might be somewhat generous given that the most recent UW-CIMSS ADT estimate is down to T3.1/47 kt.

Linda appears to be back on a due west heading, though a bit slower at 270/6 kt. Linda is reaching the western extent of a large deep-layer ridge located poleward over the western United States, which is also forecast to become eroded by a mid-tropospheric trough located just offshore California. Thus, Linda is forecast to start gaining latitude tomorrow, remaining on a track to the west-northwest for the next 2-3 days. The track guidance remains in good agreement on this forecast evolution, and the latest NHC track forecast lies close to the HCCA consensus aid. This track forecast roughly splits the difference between the further south and west ECMWF and north and east GFS forecast, and is just slightly further north compared to the previous track forecast.

After intensifying today despite continued moderate northerly vertical wind shear, Linda appears to be taking a pause as dry air has been entrained into its inner core, disrupting its convective structure. Over the next 24-36 hours, this shear is expected to slowly decrease as diagnosed by the ECMWF-SHIPS guidance, and should provide an opportunity for Linda to intensify, especially as the storm remains in a moist environment and over sea-surface temperatures above 28 C. However, given the current structure, only slow intensification is now anticipated over the next 24 hours. Linda is forecast to peak around 85 kt between 48-72 hours, though it remains possible the storm could become stronger as suggested in the latest HWRF and HMON forecasts. The latest NHC intensity forecast is slightly under the HCCA consensus aid over the first 24 hours, but is now near the peak intensity of this guidance aid. After 72 hours, gradual weakening is anticipated as Linda begins to move over cooler ocean waters.

FORECAST POSITIONS AND MAX WINDS

INIT  12/0300Z 13.6N 106.5W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, MX)
 12H  12/1200Z 14.1N 107.8W   65 KT  75 MPH - Category 1 (WSW Acapulco, MX)
 24H  13/0000Z 15.0N 109.7W   70 KT  80 MPH - Category 1 (WSW Acapulco, MX)
 36H  13/1200Z 16.0N 111.7W   80 KT  90 MPH - Category 1 (WSW Acapulco, MX)
 48H  14/0000Z 17.0N 113.9W   85 KT 100 MPH - Category 2 (WSW Acapulco, MX)
 60H  14/1200Z 17.9N 115.9W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 72H  15/0000Z 18.5N 118.1W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
 96H  16/0000Z 18.9N 122.1W   75 KT  85 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  17/0000Z 18.9N 125.5W   60 KT  70 MPH - Tropical Storm (WSW Puerto Vallarta, MX)

NWS National Hurricane Center Miami FL 300 PM MDT Wed Aug 11, 2021 

After the issuance of the previous advisory, Linda showed hints of an eye in visible and infrared satellite imagery. That feature is no longer apparent, and it appears that some dry air has infiltrated into the circulation. That being said, earlier microwave data indicated that the storm has a robust structure, and new convection is developing near the center. The latest Dvorak T-numbers are T3.5 from TAFB and T4.0 from SAB, and as a result, the initial intensity is raised to 60 kt.

Linda has been losing latitude for the past 12-18 hours, and the initial motion is south of due west, or 260/8 kt. The mid-level ridge that is steering Linda extends over northern Mexico, reaching as far as the Baja California peninsula. With Linda approaching the western edge of the ridge, it should begin to gain latitude again soon and turn toward the west-northwest by 24 hours. General ridging should remain in control through the 5-day forecast period, maintaining Linda on a west-northwestward or westward track with minimal changes in speed. There were no noteworthy changes to the guidance on this cycle, and the updated NHC track forecast is very close to the HCCA consensus aid and not too different from the previous forecast.

As mentioned earlier today, the environment ahead of Linda consists of a mix of positives and negatives for intensification. North-northeasterly shear of 15-20 kt is not expected to decrease much in the coming days, which could allow some dry air to continue penetrating into the circulation. On the other hand, Linda’s track will keep it over warm 28 degree Celsius waters for several days, and strong upper-level divergence should support deep convective development for another couple of days. Therefore, steady strengthening is shown in the official forecast, which indicates a slightly higher peak intensity compared to this morning’s forecast. An important note is that several dynamical and statistical models are showing the intensity peaking near or at major hurricane intensity in 2 to 3 days. However, given the presence of the shear, I’d prefer to keep the forecast on the conservative side and only nudge the forecast up for now. Future upward adjustments may be required if Linda strengthens more in the short term than what is shown in the official forecast. Weakening should occur by days 4 and 5 due to Linda moving over cooler waters.

FORECAST POSITIONS AND MAX WINDS

INIT  11/2100Z 13.6N 106.2W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, MX)
 12H  12/0600Z 13.8N 107.2W   70 KT  80 MPH - Category 1 (WSW Acapulco, MX)
 24H  12/1800Z 14.5N 109.0W   80 KT  90 MPH - Category 1 (WSW Acapulco, MX)
 36H  13/0600Z 15.4N 110.9W   85 KT 100 MPH - Category 2 (WNW Acapulco, MX)
 48H  13/1800Z 16.4N 112.9W   90 KT 105 MPH - Category 2 (WNW Acapulco, MX)
 60H  14/0600Z 17.4N 115.0W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 72H  14/1800Z 18.1N 117.0W   90 KT 105 MPH - Category 2 (WSW Puerto Vallarta, MX)
 96H  15/1800Z 18.7N 120.9W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  16/1800Z 18.9N 124.6W   65 KT  75 MPH - Category 1 (WSW Puerto Vallarta, MX)

NWS National Hurricane Center Miami FL 1000 AM CDT Wed Aug 11, 2021 

Despite a continuation of moderate deep-layer shear, Linda is becoming better organized. Upper-level outflow appears to be expanding over the system, but even more notably, an 1109 UTC SSMIS microwave pass revealed that a well-defined mid-level eye has formed. Dvorak T-numbers have increased to T3.5 from both TAFB and SAB, and given the significantly improved microwave structure, Linda’s initial intensity has been increased to 55 kt.

The latest fixes, including from the microwave pass, indicate that Linda is moving a little faster and more south of due west, or 265/10 kt. This motion is being caused by a large mid-level ridge located over Mexico, and the ridging is expected to maintain Linda on a westward and then west-northwestward track for the next 5 days. There is very tight clustering among the track models for the entire forecast period, and the updated NHC track forecast lies very close to the HCCA consensus aid. This new forecast has been shifted a bit to the left of the previous official forecast to account for the updated initial position.

Linda will be moving through an environment of mixed favorability for strengthening. On the positive side, sea surface temperatures will hover around 28 degrees Celsius, mid-level moisture will remain high, and upper-level divergence should be strong for the next day or two. On the negative side, the deep-layer shear is not expected to abate much for several days. That being said, the system has still been able to strengthen, and the intensity models support further intensification. The NHC intensity forecast generally lies between the HCCA aid and the IVCN consensus, and brings Linda to hurricane strength tonight with a peak intensity occurring in 2-3 days.

FORECAST POSITIONS AND MAX WINDS

INIT  11/1500Z 13.8N 105.9W   55 KT  65 MPH - Tropical Storm (WSW Acapulco, MX)
 12H  12/0000Z 13.8N 106.9W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, MX)
 24H  12/1200Z 14.3N 108.4W   70 KT  80 MPH - Category 1 (WSW Acapulco, MX)
 36H  13/0000Z 15.2N 110.1W   75 KT  85 MPH - Category 1 (WSW Acapulco, MX)
 48H  13/1200Z 16.2N 112.0W   80 KT  90 MPH - Category 1 (WSW Acapulco, MX)
 60H  14/0000Z 17.2N 114.1W   85 KT 100 MPH - Category 2 (WSW Acapulco, MX)
 72H  14/1200Z 17.9N 116.2W   85 KT 100 MPH - Category 2 (WSW Acapulco, MX)
 96H  15/1200Z 18.7N 120.0W   80 KT  90 MPH - Category 1 (WSW Acapulco, MX)
120H  16/1200Z 19.1N 123.8W   65 KT  75 MPH - Category 1 (WSW Acapulco, MX)

NWS National Hurricane Center Miami FL 1000 PM CDT Tue Aug 10, 2021

Linda appears to be on an intensification trend this evening. The low-level center, after being partially exposed to the north earlier today, has recently become obscured by a large convective burst. There is also some evidence of banding on the northwest side of the center as well. The most recent 0000 UTC TAFB Dvorak estimate was T3.0/45 kt and given the improvement in structure on satellite imagery, the initial intensity was set to 45 kt for this advisory.

Linda appears to be starting a turn to the west, with the latest motion now estimated at 285/8 kt. A more westward motion appears likely in the short term as a deep-layer ridge builds in to the north of the tropical storm. Afterwards, the guidance remains tightly clustered on a resumption of a west-northwest track between 36-72 hours. The latest NHC track forecast is quite similar to the previous one, except for a bit more westward motion in the short-term. The overall track forecast remains in excellent agreement with the track guidance consensus, and is roughly a blend between the HFIP corrected consensus approach (HCCA) and TVCE consensus aids.

The moderate northerly shear that has been affecting Linda today does not appear to be hindering the storm from intensifying currently. In fact, the ongoing convective burst may help to better align the low and mid-level centers, which could allow for a faster rate of intensification in the short-term. For this reason, the intensity forecast for the next 48 hours has been increased, with Linda now forecast to peak as a 90 knot hurricane in 60 hours. Thereafter, while vertical wind shear and mid-level moisture are expected to remain favorable, sea-surface temperatures will begin to gradually decrease. Linda will also be traversing the same location that the large wind field of Kevin is currently over, and Kevin’s large 34-kt wind radii may also lower the sea-surface temperatures along the path of Linda. The latest NHC intensity forecast is now around the mean of the guidance envelope through the first 48 hours, but still remains lower than the reliable HCCA guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  11/0300Z 14.3N 103.5W   45 KT  50 MPH - Tropical Storm (WSW Acapulco, MX)
 12H  11/1200Z 14.3N 104.5W   55 KT  65 MPH - Tropical Storm (WSW Acapulco, MX)
 24H  12/0000Z 14.5N 106.0W   65 KT  75 MPH - Category 1 (WSW Acapulco, MX)
 36H  12/1200Z 15.1N 107.2W   75 KT  85 MPH - Category 1 (WSW Acapulco, MX)
 48H  13/0000Z 16.1N 108.9W   85 KT 100 MPH - Category 2 (WSW Acapulco, MX)
 60H  13/1200Z 17.2N 110.9W   90 KT 105 MPH - Category 2 (WSW Acapulco, MX)
 72H  14/0000Z 18.0N 112.7W   90 KT 105 MPH - Category 2 (WSW Lázaro Cárdenas, MX)
 96H  15/0000Z 19.3N 116.5W   80 KT  90 MPH - Category 1 (WSW Puerto Vallarta, MX)
120H  16/0000Z 19.7N 120.8W   70 KT  80 MPH - Category 1 (WSW Puerto Vallarta, MX)

NWS National Hurricane Center Miami FL 400 PM CDT Tue Aug 10, 2021

A recent ASCAT-B overpass revealed tropical-storm-force winds in both the northern and southern semicircles of the cyclone, with believable peak winds of 38 kt. Therefore, the depression has been upgraded to a 40-kt tropical storm.

Moderate to strong northerly shear over Linda is keeping the bulk of the deep convection confined to the southern portion of the cyclone’s circulation, resulting in a partially exposed low-level center. This shear is forecast to persist over the storm for the next day or so. Therefore, despite a moist, unstable environment with ample oceanic heat content, only slow strengthening is expected in the short term. If the shear decreases as anticipated, a faster rate of intensification should occur for a couple of days. The latest NHC intensity forecast is on the low end of the guidance through 24-36 h due to the anticipated affects of the shear, and then trends to near the various intensity consensus values thereafter.

The estimated motion of Linda remains 295/9 kt. The cyclone is expected to turn westward tonight as a ridge builds to its north, and then resume a west-northwestward motion by later this week as it begins to move along the southwestern periphery of this ridge. This track is roughly parallel to, but well offshore of, the southwestern coast of Mexico over the next couple of days. Thereafter, the depression is forecast to move away from the coast of Mexico. The latest NHC forecast track is little changed from the previous one, and lies near the consensus track guidance.

FORECAST POSITIONS AND MAX WINDS

INIT  10/2100Z 14.4N 102.8W   40 KT  45 MPH - Tropical Storm (WSW Acapulco, MX)
 12H  11/0600Z 14.8N 104.0W   45 KT  50 MPH - Tropical Storm (WSW Acapulco, MX)
 24H  11/1800Z 15.0N 105.6W   50 KT  60 MPH - Tropical Storm (WSW Acapulco, MX)
 36H  12/0600Z 15.3N 106.9W   60 KT  70 MPH - Tropical Storm (WSW Acapulco, MX)
 48H  12/1800Z 16.0N 108.3W   70 KT  80 MPH - Category 1 (WSW Acapulco, MX)
 60H  13/0600Z 16.9N 110.0W   80 KT  90 MPH - Category 1 (WSW Lázaro Cárdenas, MX)
 72H  13/1800Z 17.8N 112.0W   85 KT 100 MPH - Category 2 (WSW Manzanillo, MX)
 96H  14/1800Z 19.3N 116.0W   85 KT 100 MPH - Category 2 (WSW Puerto Vallarta, MX)
120H  15/1800Z 20.0N 120.0W   75 KT  85 MPH - Category 1 (WNW Puerto Vallarta, MX)

NWS National Hurricane Center Miami FL 1000 AM CDT Tue Aug 10, 2021

The depression is slowly getting better organized, with deep convection becoming a bit more concentrated. However, the system appears to be undergoing moderate to strong northerly shear, which is keeping this convection mainly confined to the southern portion of the cyclone’s circulation. The initial intensity is being held at 30 kt, which is in agreement with the latest Dvorak T-number from TAFB.

The estimated motion of the depression is 295/9 kt. The cyclone is expected to turn westward by Wednesday as a ridge builds to its north, and then resume a west-northwestward motion by late this week as it begins to move along the southwestern periphery of this ridge. This track is roughly parallel to, but well offshore of, the southwestern coast of Mexico over the next couple of days. Thereafter, the depression is forecast to move away from the coast of Mexico. The latest NHC forecast track is little changed from the previous one, and lies near the consensus guidance tracks.

The depression is within a moist, unstable environment with ample oceanic heat content to fuel strengthening during the next few days. However, ongoing northerly vertical wind shear will likely slow the rate of intensification of this system over the next day or so. The shear is forecast to diminish somewhat after 24 h, which should allow for a faster rate of intensification for a couple of days. Late in the forecast period, the cyclone is expected to reach cooler waters, which should begin to weaken the system. The official NHC intensity forecast is near the IVCN consensus through 60 h, and is then near the HFIP corrected consensus HCCA thereafter. Based on this forecast, the depression should become a tropical storm by tonight and a hurricane on Thursday.

FORECAST POSITIONS AND MAX WINDS

INIT  10/1500Z 13.4N 101.5W   30 KT  35 MPH - Depression (WSW Acapulco, MX)
 12H  11/0000Z 14.0N 102.8W   35 KT  40 MPH - Tropical Storm (WSW Acapulco, MX)
 24H  11/1200Z 14.3N 104.6W   45 KT  50 MPH - Tropical Storm (WSW Acapulco, MX)
 36H  12/0000Z 14.5N 105.8W   55 KT  65 MPH - Tropical Storm (WSW Acapulco, MX)
 48H  12/1200Z 14.9N 107.1W   65 KT  75 MPH - Category 1 (WSW Acapulco, MX)
 60H  13/0000Z 15.8N 108.6W   75 KT  85 MPH - Category 1 (WSW Cabo San Lucas, MX)
 72H  13/1200Z 16.8N 110.4W   80 KT  90 MPH - Category 1 (WSW Cabo San Lucas, MX)
 96H  14/1200Z 18.4N 114.5W   80 KT  90 MPH - Category 1 (WSW Cabo San Lucas, MX)
120H  15/1200Z 19.2N 118.3W   75 KT  85 MPH - Category 1 (WSW Cabo San Lucas, MX)

NWS National Hurricane Center Miami FL 500 PM PDT Mon Aug 9, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on Tropical Storm Kevin, located several hundred miles south-southwest of the southern tip of the Baja California peninsula.

  • 1. Satellite data indicate that a large low pressure system located about 300 miles south of Acapulco, Mexico, is becoming better defined. In addition, showers and thunderstorms are beginning to show signs of organization, and environmental conditions are conducive for further development. A tropical depression is likely to form later tonight or early Tuesday while the low moves west-northwestward to westward at 10 to 15 mph through midweek, parallel to and well offshore the coasts of southern and southwestern Mexico. Additional information on this system can be found in high seas forecasts issued by the NOAA National Weather Service. * Formation chance through 48 hours…high…90 percent. * Formation chance through 5 days…high...90 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Mon Aug 9, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on Tropical Storm Kevin, located several hundred miles south of the southern tip of the Baja California peninsula.

  • 1. A broad area of low pressure located a few hundred miles south of the Gulf of Tehuantepec continues to produce disorganized showers and a few thunderstorms. Environmental conditions are conducive for development of this disturbance, and a tropical depression is expected to form within the next couple of days. This system is forecast to move westward to west-northwestward at about 10 mph through midweek, parallel to and offshore of the coast of southern Mexico. * Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Sun Aug 8, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on Tropical Storm Kevin, located several hundred miles south of the southern tip of the Baja California peninsula.

  • 1. A broad area of low pressure located a few hundred miles south of the Gulf of Tehuantepec continues to produce disorganized showers and thunderstorms. Environmental conditions are conducive for development of this disturbance, and a tropical depression is expected to form during the next two or three days. This system is forecast to move westward to west-northwestward at about 10 mph during the next several days, parallel to and offshore of the coast of southern Mexico. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 1100 AM PDT Sun Aug 8, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on Tropical Storm Kevin, located several hundred miles south of the southern tip of the Baja California peninsula.

  • 1. A broad area of low pressure is producing disorganized shower activity a few hundred miles offshore of the coasts of southern Mexico and Guatemala. Environmental conditions are expected to be conducive for development of this disturbance, and a tropical depression is likely to form during the early or middle portions of the week. This system is expected to move westward to west-northwestward at about 10 mph during the next several days, parallel to and offshore of the coast of southern Mexico. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…90 percent.

NWS National Hurricane Center Miami FL 500 AM PDT Sun Aug 8, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane Center is issuing advisories on Tropical Storm Kevin, located several hundred miles south of the southern tip of the Baja California peninsula.

  • 1. A broad area of low pressure is producing some disorganized shower activity a few hundred miles offshore of the coasts of southern Mexico, Guatemala, and El Salvador. Environmental conditions are expected to be conducive for development of this system, and a tropical depression is likely to form during the early or middle portions of the week. This system is expected to move westward to west-northwestward at about 10 mph during the next several days, parallel to and offshore of the coast of southern Mexico. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Sat Aug 7, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

The National Hurricane center is issuing advisories on recently upgraded Tropical Storm Kevin, located a couple of hundred miles southwest of Manzanillo, Mexico.

  • 1. A broad area of low pressure is forming a few hundred miles south of the coast of Guatemala. Environmental conditions are forecast to be conducive for development of this system, and a tropical depression is likely to form during the early or middle portions of next week. This system is expected to move west-northwestward at about 10 mph, parallel to and offshore of the coast of southern Mexico during the next several days. * Formation chance through 48 hours…low…20 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 500 PM PDT Fri Aug 6, 2021

For the eastern North Pacific…east of 140 degrees west longitude:

Recently downgraded Tropical Depression Jimena has crossed into the Central Pacific basin and is located about 1000 miles east of Hilo, Hawaii. The Central Pacific Hurricane Center in Honolulu, Hawaii, will be issuing the next advisory on Jimena at 500 PM HST.

  • 1. Showers and thunderstorms are beginning to show some signs of organization in association with a broad area of low pressure located a couple of hundred miles south of the coast of southwestern Mexico. Environmental conditions are conducive for additional development, and a tropical depression is expected to form late this weekend or early next week while the system moves west-northwestward at about 10 mph. * Formation chance through 48 hours…medium…40 percent. * Formation chance through 5 days…high...90 percent.
  • 2. An area of low pressure is expected to develop a few hundred miles south of the Gulf of Tehuantepec by early next week. Environmental conditions are forecast to be conducive for gradual development thereafter while the system moves west-northwestward at about 10 mph, parallel to and offshore of the coast of southern Mexico. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…low…30 percent.

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