Tropical Storm Kate

Tropical Depression Kate Track 1100 Hours September 1 2021
Tropical Depression Kate Track 1100 Hours September 1 2021

Tropical Storm Kate Wind Speed FieldTropical Storm KateNWS National Hurricane Center Miami FL 1100 AM AST Wed Sep 01, 2021 (see Wednesday video below)

It has been difficult to pinpoint where the low-level circulation of Kate is this morning. After last night’s diurnal convective maximum, the remaining convection has taken on a very disorganized structure, with a mid-level vortex being left behind to the south, while deeper, but more outflow driven convection is racing off to the north, ahead of the estimated low-level center position. A recently received 1211 UTC ASCAT-A pass indicated that Kate’s low-level circulation is still closed, but just barely. The scatterometer wind data supports maintaining the current intensity at 30-kt, which also agrees with the latest subjective and objective Dvorak estimates.

The estimated motion is continuing off to the north-northwest, at 340/9 kt. Kate appears to now be primarily steered by the low-level flow around a subtropical ridge located to its east. A general north-northwest motion is expected to continue today, followed by a turn to the north and north-northeast around the periphery of this ridge. The latest NHC track guidance has been adjusted a bit right of the previous track, shifting towards the latest consensus guidance (TVCN) that can still track the cyclone beyond 24 hours.

A 0958 UTC SSMIS microwave pass suggested that the better organized structure observed last night has decayed, with the low- and mid-level centers quite misaligned. Vertical wind shear diagnosed by SHIPS is now between 15-20 kt out of the north. This shear is likely contributing to the vortex tilt, while also helping to import very dry mid-level air, preventing Kate’s convective activity from organizing. The bulk of the intensity guidance is in agreement that gradual spin down of the low-level circulation will occur over the next several days, with the deterministic ECMWF model suggesting Kate could open up to a trough as soon as tomorrow. The latest NHC intensity forecast makes Kate a remnant low in 36 hours, with dissipation after 48 hours. However, given the current structure, this could occur sooner than forecast.

FORECAST POSITIONS AND MAX WINDS

INIT  01/1500Z 26.8N  52.3W   30 KT  35 MPH - Depression  (WSW St. George's,Bermuda)
 12H  02/0000Z 27.9N  52.7W   25 KT  30 MPH - Depression (WSW St. George's,Bermuda)
 24H  02/1200Z 29.6N  53.1W   25 KT  30 MPH - Depression (WSW St. George's,Bermuda)
 36H  03/0000Z 31.1N  53.2W   20 KT  25 MPH - Post Tropical (WSW St. George's,Bermuda)
 48H  03/1200Z 32.4N  52.5W   20 KT  25 MPH - Post Tropical (WNW St. George's,Bermuda)
 60H  04/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Tue Aug 31, 2021

Some bursts of convection have been forming within Kate’s small circulation during the past several hours, but none of it has any real significant organization. In addition, the low clouds appear to be losing definition, and a very-recent ASCAT-B pass showed that the maximum winds are now only about 25 kt. It’s going to be difficult for Kate to make much of a comeback, if at all. Moderate northerly shear, dry mid-level air, upper-level convergence, and an increasingly anticyclonic low-level environment are likely to cause the circulation to spin down further and make it hard for deep convection to persist. Therefore, the NHC official forecast now calls for additional weakening, with Kate likely becoming a remnant low by 36 hours (if not sooner) and dissipating by 72 hours. This scenario is closest to the GFS, HWRF, and HMON solutions.

Located on the southwestern periphery of a low-level area of high pressure, Kate is moving toward the north-northwest (345/9 kt). The depression is forecast to turn toward the northwest by morning, but then recurve around the high toward the north and north-northeast in a couple of days. The NHC track forecast remains close to the consensus aids and is generally just an update from the previous advisory.

FORECAST POSITIONS AND MAX WINDS

INIT  01/0300Z 25.4N  51.3W   25 KT  30 MPH - Depression (WSW St. George's,Bermuda)
 12H  01/1200Z 26.4N  52.1W   25 KT  30 MPH - Depression (WSW St. George's,Bermuda)
 24H  02/0000Z 27.9N  53.1W   25 KT  30 MPH - Depression (WSW St. George's,Bermuda)
 36H  02/1200Z 29.8N  53.8W   20 KT  25 MPH - Post Tropical (WSW St. George's,Bermuda)
 48H  03/0000Z 31.6N  54.1W   20 KT  25 MPH - Post Tropical (WSW St. George's,Bermuda)
 60H  03/1200Z 33.1N  53.7W   20 KT  25 MPH - Post Tropical (WNW St. George's,Bermuda)
 72H  04/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Tue Aug 31, 2021 

Strong west-northwesterly shear continues to displace the limited convective activity associated with Kate well to the east of its center, which is fully exposed and becoming less well-defined in visible satellite imagery. A small burst of deep convection from earlier this morning appears to be waning, as infrared cloud top temperatures are warming to the east of Kate’s center. Consensus T2.0/30 kt Dvorak classifications from TAFB and SAB, in addition to the latest objective UW-CIMSS ADT estimates, suggest that Kate is now likely a tropical depression. Therefore, the initial intensity is lowered to 30 kt for this advisory.

Kate’s center has jogged a little east of due north this morning, and its initial estimated 12-h motion is northward, or 010/4 kt. A mid-level ridge is forecast to build to the northeast and east of Kate later today through Wednesday, which should steer the cyclone more north-northwestward through midweek. Then, Kate should turn toward the north on Thursday night and early Friday within the flow associated with a mid- to upper-level trough that will be moving across the western Atlantic. The official NHC forecast track is very similar to the previous one, and it lies near the reliable consensus aids TVCA and HCCA. The only minor track adjustment has Kate turning a little earlier and faster toward the north late this week.

Even though the vertical shear is expected to diminish over Kate during the next 12-24 h, the cyclone remains embedded within a relatively dry mid-level environment. This will make it difficult for Kate to sustain enough organized convection to strengthen much. In fact, numerous models including the GFS, HWRF, and HMON show the low weakening in the coming days, as the model simulated satellite imagery suggests only sporadic bursts of convection will occur even after the shear subsides. However, the possibility of Kate briefly re-intensifying into a weak tropical storm cannot be completely ruled out, since the cyclone will remain over warm SSTs around 28 deg C for at least the next couple of days. The official NHC intensity forecast remains consistent with the consensus aids IVCN and HCCA and shows no explicit change in intensity, although some fluctuation is possible. If Kate survives this week, the global models indicate that it will likely open up into a trough by Saturday morning, shortly before being absorbed by an approaching frontal system.

FORECAST POSITIONS AND MAX WINDS

INIT  31/1500Z 23.5N  50.8W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  01/0000Z 24.3N  51.0W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 24H  01/1200Z 25.7N  51.7W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 36H  02/0000Z 27.3N  52.7W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 48H  02/1200Z 29.0N  53.6W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 60H  03/0000Z 30.7N  54.1W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 72H  03/1200Z 32.5N  53.9W   30 KT  35 MPH - Depression (WNW St. George's,Bermuda)
 96H  04/1200Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 PM AST Mon Aug 30, 2021

Kate is a strongly sheared and poorly organized tropical cyclone. Satellite images show an exposed low-level center with a few patches of deep convection on the system’s east side. The latest Dvorak classifications range from 25-35 kt, and the initial intensity is held at a possibly generous 35 kt for this advisory. Unfortunately, ASCAT missed the circulation this evening.

Strong west-northwesterly shear of about 30 kt is expected to persist into early Tuesday, and that could cause some weakening in the short term. Although the shear is expected to lessen after that, Kate will be moving into a drier and more stable airmass. None of the intensity models show much strengthening, and the global models suggest that Kate could dissipate sometime within the next couple of days. The official forecast is again nudged downward and generally shows little change in strength during the next 4 days. Kate, or its remnants, are likely to merge with an extratropical low and associated front in 4 to 5 days.

The tropical storm has moved little during the past few hours, but a 12-hour motion yields an estimate of 360/5 kt. The storm is moving toward a weakness in the ridge caused by a deep-layer low over the North Atlantic, and that motion should continue into Tuesday. By Wednesday, mid-level ridging building to the northeast of the system should cause it to turn northwestward. However, another trough moving eastward over the western Atlantic is expected to cause Kate to turn northward again toward the end of the week. The NHC track forecast follows the various consensus aids and is similar to the previous one.

FORECAST POSITIONS AND MAX WINDS

INIT  31/0300Z 22.7N  50.9W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 12H  31/1200Z 23.6N  50.7W   30 KT  35 MPH - Tropical Storm (WSW St. George's,Bermuda)
 24H  01/0000Z 24.8N  50.9W   30 KT  35 MPH - Tropical Storm (WSW St. George's,Bermuda)
 36H  01/1200Z 26.1N  51.8W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 48H  02/0000Z 27.6N  52.9W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 60H  02/1200Z 29.1N  54.0W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  03/0000Z 30.4N  54.8W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  04/0000Z 33.9N  54.6W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  05/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 500 PM AST Mon Aug 30, 2021

The low-level center of Kate is exposed in visible satellite imagery this afternoon. Its deep convection collapsed late this morning, and the sheared tropical cyclone is now only producing a small area of convection over 60 n mi east of its center. A partial 1321 UTC ASCAT-B pass still showed numerous 30-kt wind vectors in the eastern semicircle, even with little to no active convection. The initial intensity is conservatively lowered to 35 kt for this advisory.

The subtropical jet stream across the central Atlantic will continue to impart strong west-northwesterly vertical wind shear on Kate during the next day or so. If the struggling tropical cyclone can survive these hostile conditions, some modest strengthening could occur later this week over warm SSTs of 28 deg C or so. However, the lack of mid-level moisture in the surrounding environment may limit convective development even under these more favorable conditions, and there is no guarantee that Kate will survive that long. In fact, simulated satellite imagery from the GFS and ECMWF suggest that Kate may continue to only produce sporadic bursts of convection over the next couple of days, which jeopardizes its chances of surviving through the week. The official NHC intensity forecast has been adjusted downward based on the latest guidance trends and the uncertainties discussed above. Minor fluctuations in intensity could occur over the next 24-36 h as convective pulsing causes the cyclone’s intensity to hover around tropical-storm-force strength.

Kate is moving a little faster toward the north, or 355/9 kt, within a weakness in the subtropical ridge. A northward motion is expected to continue through early Tuesday. The subtropical ridge is expected to become reestablished over the central Atlantic Tuesday night into Wednesday, which should turn Kate toward the northwest through midweek. Thereafter, Kate is forecast to accelerate northward or north-northeastward ahead of an approaching deep-layer trough that will move across the western Atlantic late this week. Assuming Kate is still around by day 5, the cyclone is forecast to become absorbed by a larger extratropical low near Atlantic Canada.

FORECAST POSITIONS AND MAX WINDS

INIT  30/2100Z 22.7N  50.9W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 12H  31/0600Z 23.7N  50.7W   30 KT  35 MPH - Tropical Storm (WSW St. George's,Bermuda)
 24H  31/1800Z 24.7N  50.7W   30 KT  35 MPH - Tropical Storm (WSW St. George's,Bermuda)
 36H  01/0600Z 25.8N  51.1W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 48H  01/1800Z 27.0N  52.1W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 60H  02/0600Z 28.4N  53.5W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  02/1800Z 30.1N  54.7W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  03/1800Z 34.5N  55.0W   40 KT  45 MPH - Tropical Storm (WNW St. George's,Bermuda)
120H  04/1800Z...DISSIPATED

NWS National Hurricane Center Miami FL 1100 AM AST Mon Aug 30, 2021 

Although strong upper-level westerly shear continues to plague the cyclone, its satellite presentation improved early this morning as its center moved closer to the edge of the convective cloud mass to its east. An ASCAT-A pass from 1100 UTC revealed an area of 30 to 40-kt winds in the eastern semicircle of the cyclone, with some slightly stronger winds possibly rain contaminated underneath the deep convection. Additionally, UW-CIMSS ADT objective estimates have risen to around 40 kt within the past few hours, and TAFB gave a T2.5/35 kt subjective Dvorak classification at 12 UTC. These data support upgrading the depression to Tropical Storm Kate. Its initial intensity is set at 40 kt for this advisory, although that could be a bit generous given recent satellite trends.

A weakness in the subtropical ridge is allowing Kate to move just west of due north, or 355/7 kt. This general motion should continue for the next day or so before the subtropical ridge becomes reestablished over the central Atlantic Ocean. Thereafter, the cyclone should move northwestward on Wednesday and Thursday along the southwestern periphery of the ridge. By Friday, an approaching deep-layer trough should cause the cyclone to accelerate northward or north-northeastward through the rest of the forecast period. The track guidance has shifted a little left of the previous NHC track, and so the official forecast has been adjusted in that direction to bring it closer to the TVCA and HCCA consensus aids.

The near-term intensity forecast is tricky, as the subtropical jet stream will maintain strong west-northwesterly shear over Kate during the next 24 to 36 h. In fact, recent satellite imagery of the cyclone shows the center is already more exposed than earlier this morning as the convection is waning. Kate is likely to continue exhibiting a bursting convective pattern over the next couple of days, which would likely result in some intensity fluctuations that hover around the tropical-storm-force threshold. The official NHC intensity forecast shows Kate as a 35-kt tropical storm during the first 36 h of the forecast. If Kate survives the hostile shear conditions, some modest intensification will be possible while the cyclone remains over 28 deg C waters. However, Kate will encounter a drier mid-level environment as it gains latitude, so significant strengthening does not appear likely at this time. The official intensity forecast is similar to the previous one beyond 48 h, as it shows only modest strengthening with time. By day 5, the global models suggest that Kate could be becoming absorbed by a larger extratropical low expected to form and deepen near Atlantic Canada.

FORECAST POSITIONS AND MAX WINDS

INIT  30/1500Z 21.5N  50.9W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 12H  31/0000Z 22.3N  50.7W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 24H  31/1200Z 23.3N  50.5W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 36H  01/0000Z 24.3N  50.6W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 48H  01/1200Z 25.5N  51.5W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 60H  02/0000Z 26.9N  52.7W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  02/1200Z 28.4N  54.2W   45 KT  50 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  03/1200Z 32.0N  55.5W   50 KT  60 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  04/1200Z 37.0N  53.4W   55 KT  65 MPH - Tropical Storm (WSW St. George's,Bermuda)

NWS National Hurricane Center Miami FL 500 AM AST Mon Aug 30 2021

The deep convection with Tropical Depression Ten is in a sheared bursting pattern this morning, associated with overshooting cloud top temperatures below -80 C. A 0518 UTC AMSR-2 microwave pass did show a bit of banding associated with this activity on the 37 GHz low-level channel. However, Proxy-Vis satellite imagery indicates this convective activity remains located downshear of the low-level center thanks to very strong 30-50 kt northwesterly flow associated with a subtropical jet at 200 mb. The latest round of subjective Dvorak estimates were 25 kt from SAB and 35 kt from TAFB. Taking a blend of these estimates and the earlier ASCAT wind data supports keeping the intensity at 30 kt for this advisory.

The depression has resumed a northward motion this morning, with the latest estimate at 360 degrees at 7 kt. A deep-layer trough passing by well to the north is continuing to provide a weakness in the subtropical ridge, allowing the cyclone to escape northward. The system could even move a bit east of due north over the next 24-36 hours if down-shear convective bursts help to drag the low-level center a bit right of the steering flow. After 36 hours, the deep-layer trough moves eastward, allowing the subtropical ridge to build back in. The net result is that the depression should turn leftward and begin a more northwestward motion by the latter part of this week. The latest track guidance has once again made another westward shift this cycle after 36 hours, and the NHC track forecast has been nudged in that direction as well. However, the latest track is still not as far west as the GFS & ECMWF models, and further westward adjustments may be needed in subsequent forecasts.

Strong upper-level flow is the primary hindrance for the depression currently. In fact, both GFS & ECMWF-based SHIPS guidance shows the vertical wind shear remaining above 30 kt for the next 24 hours as the cyclone moves through the core of a subtropical jet streak. Interestingly, this shearing flow seems to be mostly based in the upper-levels, with much lower mid-level shear diagnosed by UW-CIMSS. This lower mid-level shear may help explain why deep-convection has not yet been completely stripped away from the low-level center. After 36 hours, most of the guidance agrees that an upper-level low will cut off to the southwest of the depression, providing a more favorable upper-level environment over the system.

However, it remains unclear what will be left of the depression by that time, and the latest 00z ECMWF, HWRF, and HMON runs suggest the vortex will be too weak and diffuse to take advantage of the more favorable conditions. For now, the latest NHC intensity forecast will maintain the current intensity through 48 hours, with only modest intensification beginning after that time assuming the circulation is coherent enough to take advantage of the more favorable environment. The latest intensity forecast is just a bit lower than the previous forecast, and is also lower than the HCCA and IVCN consensus aids. It remains distinctly possible that the depression could become a remnant low if its convection is completely stripped away.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0900Z 20.8N  50.6W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  30/1800Z 21.7N  50.6W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 24H  31/0600Z 22.6N  50.3W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 36H  31/1800Z 23.6N  50.1W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 48H  01/0600Z 24.8N  50.7W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 60H  01/1800Z 26.1N  51.7W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  02/0600Z 27.6N  53.1W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  03/0600Z 30.8N  55.3W   45 KT  50 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  04/0600Z 35.1N  53.6W   50 KT  60 MPH - Tropical Storm (WSW St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Sun Aug 29, 2021

The depression is looking poorly organized this evening, with the low-level center exposed for the past several hours, and only a small area of convection located over 50 n mi east of the center. Strong west-northwesterly shear on the order of 20 to 30 kt due to a nearby subtropical jet stream has been impacting the cyclone since earlier today. A recent ASCAT pass showed peak winds of 29 kt, so the initial advisory intensity is being kept at 30 kt. The shear is forecast to increase even more later tonight and persist through Monday night. If the depression survives through that time period, then it may have an opportunity to strengthen in a few days when the cyclone moves north of the jet stream. The official NHC intensity forecast was little changed from the previous one, and is close to the HCCA and IVCN consensus.

The lack of deep convection has likely been the cause of a wobble to the northwest over the past several hours, as the shallow depression has been steered primarily the low-level trade wind flow. The overall motion over the past 12 h is 350/7 kt. A weakness in the subtropical ridge to the north of the depression should induce a generally northward motion over the next few days. By the middle of this week, the weakness in the ridge is forecast to fill in, and force the cyclone on more of a northwestward path. The guidance continues to shift to the west with their solutions, as they come into better agreement on the strength of the ridge, and the NHC foreast has followed suit with a shift to the west. However, the latest NHC track forecast remains to the east of all of the consensus track guidance. Therefore, further future adjustments to the track may be necessary.

FORECAST POSITIONS AND MAX WINDS

INIT  30/0300Z 20.1N  50.6W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  30/1200Z 21.1N  50.8W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 24H  31/0000Z 22.4N  50.4W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 36H  31/1200Z 23.5N  50.0W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 48H  01/0000Z 24.5N  50.3W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 60H  01/1200Z 25.6N  51.0W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  02/0000Z 27.0N  51.9W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  03/0000Z 30.0N  53.7W   45 KT  50 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  04/0000Z 34.0N  53.3W   55 KT  65 MPH - Tropical Storm (WNW St. George's,Bermuda)

NWS National Hurricane Center Miami FL 500 PM AST Sun Aug 29, 2021

The depression’s center has again scooted northwestward away from the associated deep convection due to continuing 20-25 kt of northwesterly shear. Since there has been no appreciable change to the various intensity estimates from this morning, the estimated maximum winds remain 30 kt for this advisory. The source of the shear can be seen in water vapor imagery, with high-level clouds emanating from the eastern Caribbean Sea and blowing directly into the depression. In fact, model guidance is now indicating that the shear may increase as high as 35-40 kt during the next 24 hours while the depression moves beneath the subtropical jet stream, and the NHC intensity forecast therefore now shows no intensity change through 36 hours. By 48 hours, the system should have moved north of the subtropical jet, and lower shear and relatively warm waters should finally allow for some strengthening. During the latter part of the forecast period, the NHC intensity forecast is very close to the HCCA and IVCN consensus aids. Much of this forecast is contingent on the depression actually surviving the next 24-36 hours, however.

The depression is moving just west of due north (355/10 kt), but the system is expected to slow down and turn slightly toward the north-northeast within 24 hours, ahead of the tail end of a deep-layer trough which extends over much of the central Atlantic. Beginning in about 48 hours, a piece of the east Atlantic subtropical ridge is forecast to pinch off and block the depression, causing it to turn back to the north and north-northwest through the end of the 5-day forecast period. This developing high looks like it will be a little stronger than previously thought, and most of the models have shifted significantly westward after 48 hours. The new NHC track forecast has been adjusted westward as well, but it is not as far west as the deterministic models and the consensus aids. Therefore, additional adjustment may be required in subsequent advisories.

FORECAST POSITIONS AND MAX WINDS

INIT  29/2100Z 19.7N  50.4W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  30/0600Z 20.7N  50.3W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 24H  30/1800Z 22.1N  49.9W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 36H  31/0600Z 23.3N  49.4W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 48H  31/1800Z 24.5N  49.3W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 60H  01/0600Z 25.8N  49.8W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  01/1800Z 27.4N  50.6W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  02/1800Z 30.4N  51.9W   50 KT  60 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  03/1800Z 33.7N  52.0W   55 KT  65 MPH - Tropical Storm (WNW St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 AM AST Sun Aug 29, 2021

The center of the depression has become a little more exposed to the northwest of the deep convection during the past few hours as a result of continued 25-30 kt of northwesterly shear. The latest Dvorak estimates are T2.5 from TAFB and T1.0/2.0 from SAB, so the initial intensity remains 30 kt. The system is expected to continue moving through a region of strong northwesterly to westerly shear for the next 2 days or so, and little to no strengthening is anticipated during that time. However, if the convection is able to remain fairly close to the center, then the system could eke into tropical storm status at any time. After 48 hours, a significant decrease in shear, along with warm waters of 27-28 degrees Celsius, should allow for a steady strengthening trend. The NHC intensity forecast has been nudged upward on days 3 through 5, although much of the guidance is even higher, suggesting that further adjustments could be required in subsequent advisories.

The depression is moving northward (350/10 kt) through a break in the ridge created by a large deep-layer trough extending south of Newfoundland over the central Atlantic. This trough, along with a strengthening mid-level ridge over the eastern Atlantic on days 3-5, are expected to keep the cyclone on a curvy northward track during the entire forecast period. There is high confidence in the track forecast given low spread among the track models, and the NHC official forecast generally lies between the TVCA and HCCA consensus aids.

FORECAST POSITIONS AND MAX WINDS

INIT  29/1500Z 18.8N  50.2W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  30/0000Z 20.0N  50.3W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 24H  30/1200Z 21.4N  50.1W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 36H  31/0000Z 22.7N  49.5W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 48H  31/1200Z 24.1N  49.1W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 60H  01/0000Z 25.6N  49.2W   40 KT  45 MPH - Tropical Storm (WSW St. George's,Bermuda)
 72H  01/1200Z 27.4N  49.8W   45 KT  50 MPH - Tropical Storm (WSW St. George's,Bermuda)
 96H  02/1200Z 30.6N  50.6W   50 KT  60 MPH - Tropical Storm (WSW St. George's,Bermuda)
120H  03/1200Z 33.5N  50.7W   55 KT  65 MPH - Tropical Storm (WNW St. George's,Bermuda)

NWS National Hurricane Center Miami FL 1100 PM AST Sat Aug 28, 2021

Before sunset this evening, visible satellite images showed that a well-defined low-level circulation was developing in association with the disturbance over the subtropical central Atlantic. However, up until a couple of hours ago, the system lacked sufficient organized deep convection to be considered a tropical cyclone by definition. Since that time, a deep convective burst has increased in size near, and to the east of the estimated center. In addition, a curved band has begun to develop over the southeastern portion of the circulation. Based on this increase in convective organization, advisories are being initiated on Tropical Depression Eleven. There was no ASCAT data this evening over the cyclone, so the initial intensity of 30 kt is based on the latest Dvorak CI number from TAFB.

The initial motion of the depression is 050/10 kt. The cyclone is embedded in southwesterly flow to the southeast of a mid- to upper-level trough and an associated cold front. This flow is forecast to increase as the cold front approaches the cyclone, resulting in the system accelerating northeastward over the next day or so. Once the cyclone interacts with this frontal boundary in a couple of days, a turn to the north is expected. The model guidance is in very good agreement on this scenario, and the NHC track forecast lies in the middle of the consensus tracks.

Baroclinic forcing and upper-level diffluence should aid in intensifying the depression over the next 24 h, despite increasing shear. By 36 h, the combination of interaction with the cold front and passage over much cooler waters should result in extratropical transition. The system is then forecast to become absorbed by a larger low pressure system by midweek. The NHC intensity forecast is near the various multi-model consensus solutions.

FORECAST POSITIONS AND MAX WINDS

INIT  29/0300Z 33.0N  49.7W   30 KT  35 MPH - Depression (WSW St. George's,Bermuda)
 12H  29/1200Z 34.6N  47.1W   35 KT  40 MPH - Tropical Storm (WSW St. George's,Bermuda)
 24H  30/0000Z 36.8N  43.4W   45 KT  50 MPH - Tropical Storm (WSW Ponta Delgada,Azores)
 36H  30/1200Z 39.5N  39.2W   50 KT  60 MPH - Post Tropical (WSW Vila do Corvo,Azores)
 48H  31/0000Z 43.4N  36.4W   45 KT  50 MPH - Post Tropical (WSW São Miguel Island,Azores)
 60H  31/1200Z 47.9N  36.3W   40 KT  45 MPH - Post Tropical (WSW St. John's,NF Canada)
 72H  01/0000Z...DISSIPATED

NWS National Hurricane Center Miami FL 800 PM EDT Sat Aug 28 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Ida, located over the east-central Gulf of Mexico, and on Tropical Depression Ten, located over the central tropical Atlantic.

  • 1. Showers and thunderstorms continue to show signs of organization in association with an area of low pressure located over the central Atlantic. Although environmental conditions remain only marginally conducive for further development, only a slight increase in organization would result in the formation of a tropical depression later tonight or on Sunday. In a couple of days, the system is forecast to be absorbed by a frontal system. The disturbance is expected to drift eastward through tonight, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent.
  • 2. A tropical wave is expected to emerge off the coast of west Africa by the middle of next week. Thereafter, environmental conditions appear conducive for gradual development, and a tropical depression is likely to form toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…high…70 percent.

NWS National Hurricane Center Miami FL 200 PM EDT Sat Aug 28 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Ida, located over the southeastern Gulf of Mexico, and on Tropical Depression Ten, located over the central tropical Atlantic.

1. Showers and thunderstorms continue to show signs of organization in association with an area of low pressure located over the central Atlantic. In addition, satellite wind data indicate that the circulation has become a little better defined. Although environmental conditions remain only marginally conducive for further development, only a slight increase in organization would result in the formation of a tropical depression later today or tonight. In a couple of days, the system is forecast to be absorbed by a frontal system. The disturbance is expected to drift eastward through today, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…high…80 percent. * Formation chance through 5 days…high…80 percent. 2. A tropical wave is expected to emerge off the coast of west Africa by the middle of next week. Thereafter, environmental conditions appear somewhat conducive for gradual development toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium…60 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Sat Aug 28, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Hurricane Ida, located over the southeastern Gulf of Mexico, and on newly formed Tropical Depression Ten, located over the central tropical Atlantic.

  • 1. Showers and thunderstorms associated with an elongated area of low pressure located over the central Atlantic has become a little better organized overnight. Environmental conditions are expected to be only marginally conducive for further development. However, a tropical depression could still form wtihin the next couple of days. By midweek, the system is forecast to be absorbed by a frontal system. The disturbance is expected to drift eastward through today, then accelerate northeastward Sunday toward the central north Atlantic. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…medium…60 percent.
  • 2. A tropical wave is expected to emerge off the coast of west Africa by the middle of next week. Thereafter, environmental conditions appear somewhat conducive for gradual development toward the end of next week as the system moves west-northwestward to northwestward at 10 to 15 mph. * Formation chance through 48 hours…low…near 0 percent. * Formation chance through 5 days…medium...50 percent.

NWS National Hurricane Center Miami FL 800 AM EDT Fri Aug 27, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical Storm Ida, located over the northwestern Caribbean Sea near the Cayman Islands.

  • 1. An elongated area of low pressure located over the central Atlantic about 600 miles east of Bermuda is producing showers and thunderstorms. Environmental conditions are expected to be marginally conducive for development, however, a tropical depression could still form over the weekend. The system is expected to drift eastward today and Saturday, then accelerate northeastward on Sunday toward the central-north Atlantic. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…medium…60 percent.
  • 2. A tropical wave located about midway between the Cabo Verde Islands and the Lesser Antilles is producing limited showers and thunderstorms. Gradual development of this system is expected, however, and a tropical depression is likely to form during the next couple of days before it moves into an environment of stronger upper-level winds and slightly cooler waters. The disturbance is forecast to move west-northwestward today, then turn northward Saturday. * Formation chance through 48 hours…high…70 percent. * Formation chance through 5 days…high…80 percent.

NWS National Hurricane Center Miami FL 800 PM EDT Thu Aug 26, 2021

For the North Atlantic…Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on recently upgraded Tropical Storm Ida, located over the northwestern Caribbean Sea.

  • 1. An elongated area of low pressure located over the central Atlantic about 650 miles east of Bermuda is producing disorganized showers and thunderstorms. Environmental conditions are forecast to be generally conducive for development, and a tropical depression is likely to form over the weekend. The system is expected to move slowly eastward during the next day or two, but a faster northeastward motion is forecast to begin on Sunday. * Formation chance through 48 hours…medium…50 percent. * Formation chance through 5 days…high…70 percent.
  • 2. A tropical wave located about midway between the Cabo Verde Islands and the Lesser Antilles continues to produce a large area of disorganized showers and thunderstorms. Gradual development of this system is expected, and a tropical depression is likely to form during the next couple of days before it moves into an environment of stronger upper-level winds and slightly cooler waters. The disturbance is forecast to move west-northwestward for another day or so and then turn northward over the weekend. * Formation chance through 48 hours…medium…60 percent. * Formation chance through 5 days…high…70 percent.

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