Tropical Storm Walaka

Post-Tropical Storm Walaka Track 0800 Hours October 6 2018
Post-Tropical Storm Walaka Track 0800 Hours October 6 2018

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sat Oct 06 2018

Post-Tropical Storm Walaka’s  (see 13 videos below) low-level circulation center (LLCC) remains completely devoid of deep convection early this morning. The last few thunderstorms associated with the system are slightly more than 90 n mi southeast of the exposed LLCC. ASCAT passes over Walaka at 0735Z and 0838Z showed the system was stronger than expected, with surface wind speeds up to 45 kt. It was also apparent the center of the system was becoming elongated instead of circular. In addition, the wind field was highly asymmetric, with the strongest winds in a broad area covering the southeastern semicircle, while the winds were much weaker over most of the northwestern semicircle. Based on this evidence, Walaka has already transitioned to an extratropical gale low this morning. The initial intensity for this advisory is 45 kt due to the ASCAT data from last evening.

The initial motion for this advisory is 035/23 kt. Walaka is being steered by the deep southwesterly flow associated with an advancing upper-level trough. As a result, it will likely continue to move toward the northeast or north-northeast at an increasing forward speed this weekend. The latest track forecast has been adjusted slightly to the left compared with the previous advisory package. This follows a blend of the track guidance based on the latest operational runs and the ensemble means from the GFS and ECMWF models.

The baroclinic processes driving Walaka’s new life as an extratropical system will likely maintain an area of gale force winds over the southeastern semicircle during the next 36 hours. The latest intensity forecast has been adjusted up compared with the previous advisory package to account for these gales. This intensity forecast is based on a blend of the most recent GFS and ECMWF models, which are in good agreement through 24 hours. The ECMWF maintains 35 kt winds for the 36 hour time period, while the GFS output indicates the winds may drop below gale force by that time. Both models continue to insist the system will be absorbed by a larger extratropical low after 36 hours. Therefore, dissipation will occur by the 48 hour time period.Post-Tropical Storm Walaka Distances 0500 Hours October 6 2018

This is the last Tropical Cyclone Discussion issued by the Central Pacific Hurricane Center on this system.

FORECAST POSITIONS AND MAX WINDS
 
INIT  06/1500Z 36.2N 163.5W   45 KT  50 MPH - POST-TROPICAL (ENE Midway Atoll)
 12H  07/0000Z 41.0N 160.5W   40 KT  45 MPH - POST-TROPICAL (ESE Coos Bay, Oregon)
 24H  07/1200Z 48.0N 154.0W   35 KT  40 MPH - POST-TROPICAL (ENE POrtland, Oregon)
 36H  08/0000Z 55.0N 148.0W   35 KT  40 MPH - POST-TROPICAL (ESE Old Harbor, Alaska)
 48H  08/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Fri Oct 05 2018

Tropical Storm Walaka which has been deteriorating steadily all night, is now coming apart at the seams in satellite imagery. The exposed low level circulation center (LLCC) is beginning to open up to the west, with layered clouds and possibly a single warm-topped cumulonimbus sputtering within the eastern quadrant. The latest Dvorak current intensity estimates range from 1.5/25 kt from JTWC to 3.0/45 kt from PHFO. SAB estimated 2.0/30 kt while UW-CIMSS ADT was 39 kt. Based on these estimates, and with a nod to continuity, we will assign an initial intensity of 45 kt for this advisory. However, this may be generous given the poor satellite presentation and the Dvorak constraints keeping the PHFO estimate high.

This weakening system is tracking just east of due north, with initial motion of 030/10 kt. After moving northward over the past few days along the western fringe of the subtropical ridge, Walaka is beginning to respond to southwesterly steering ahead of a broad north Pacific upper trough moving in from the northwest. This will pick Walaka up and accelerate it off to the northeast through early Sunday. Walaka is expected to begin extra-tropical transition Saturday. The official forecast track is very close to that of the previous advisory, staying within the very tight guidance envelope centered along HWRF. The track terminates at 48 hours as Walaka becomes absorbed by a mid-latitude low.

Walaka will move over increasingly cooler water along its truncated track, while vertical wind shear dramatically ramps up, reaching 34 kt at 36 hours and 44 kt by 48 hours. Global models show Walaka will be absorbed by a mid-latitude low by 48 hours, with weakening and extratropical transition occurring simultaneously from 24 hours through system dissipation at 48 hours. Our forecast follows the HCCA weakening trend, which is also quite close to the IVCN curve.

Note: (Below)[Midway Atoll is a critical habitat in the central Pacific Ocean which includes breeding habitat for 17 seabird species. A number of native species rely on the island, which is now home to 67–70% of the world’s Laysan albatross population, and 34–39% of the global population of black-footed albatross. Midway Atoll, in common with all the Hawaiian Islands, receives substantial amounts of marine debris from the Great Pacific Garbage Patch. Consisting of ninety percent plastic, this debris accumulates on the beaches of Midway. This garbage represents a hazard to the bird population of the island. Twenty tons of plastic debris washes up on Midway every year, with five tons of that debris being fed to Albatross chicks.The U.S. Fish & Wildlife Service estimates at least 100 pounds (45 kg) of plastic washes up every week]Tropical Storm Walaka Distances 1100 Hours October 5 2018

FORECAST POSITIONS AND MAX WINDS
 
INIT  05/2100Z 32.2N 167.8W   45 KT  50 MPH - Tropical Storm (ENE Midway Atoll)
 12H  06/0600Z 34.7N 166.2W   40 KT  45 MPH - Tropical Storm (ENE Midway Atoll)
 24H  06/1800Z 39.4N 162.6W   35 KT  40 MPH - Tropical Storm (WSW Brookings, Oregon)
 36H  07/0600Z 45.7N 157.2W   30 KT  35 MPH - Tropical Storm (WSW POrtland, Oregon)
 48H  07/1800Z...DISSIPATED


NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Fri Oct 05 2018

Tropical Storm Walaka –  The satellite appearance of Walaka has deteriorated overnight, with the low level circulation center now becoming exposed. The latest satellite intensity estimates were 3.5 (55 knots) from PHFO, 2.5 (35 knots) from SAB, while the ADT came in at 2.9 (43 knots). A 0755Z ASCAT pass caught a portion of the western edge of the circulation and showed a 43 knot wind barb. Given the data from the ASCAT only sampling the weaker western side of the circulation along with support from the PHFO intensity estimate, the initial intensity of Walaka was lowered to 55 knots for this advisory. The initial motion was set at 010/07 knots.

Walaka continues to interact with a deep mid-upper level low in the vicinity of 27/28N 167W. This mid-upper low is forecast to fill today as a broad north Pacific upper trough moves in from the northwest. This should pick Walaka up and accelerate the cyclone off to the northeast through Saturday night, with Walaka expected to undergo the extra-tropical transition late Saturday or Saturday night. The official forecast track is very close to that of the previous advisory and is very close to the TVCE, GFEX, and HCCA consensus guidance.

Walaka will be over cool sea surface temperatures below 25C throughout the duration of its journey across the north Pacific, with vertical wind shear expected to increase substantially tonight and Saturday. Although conditions will become increasingly hostile, the transition over to an extra-tropical low will likely keep the intensity from dropping off too much during the next couple of days. As a result, the official intensity forecast calls for slow and steady weakening and closely follows a blend of the dynamical guidance. Walaka is expected to become an extra-tropical low late Saturday or Saturday night, with dissipation by forecast hour 72.

FORECAST POSITIONS AND MAX WINDS
 
INIT  05/1500Z 31.5N 168.3W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 12H  06/0000Z 32.8N 167.2W   50 KT  60 MPH - Tropical Storm (ENE Midway Atoll)
 24H  06/1200Z 36.2N 164.5W   50 KT  60 MPH - Tropical Storm (ENE Midway Atoll)
 36H  07/0000Z 42.2N 160.0W   45 KT  50 MPH - Tropical Storm (WSW Eureka, California)
 48H  07/1200Z 49.1N 153.6W   40 KT  45 MPH - Tropical Storm (WSW Kodiak, Alaska)
 72H  08/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Thu Oct 04 2018

Hurricane Walaka  – The satellite presentation of Walaka has degraded significantly under persistent southwesterly vertical wind shear. The low level circulation center has become partially exposed, with deep convection displaced to the northeast and east. Subjective Dvorak current intensity estimates were 4.0/65 kt from SAB and 4.5/77 kt out of HFO. CIMSS ADT yielded 82 kt, and a 1747Z CIMSS SATCON estimate was at 77 kt. Given these inputs, the initial intensity will be lowered to 80 kt, which could be generous.

Walaka is interacting with a deep, mid- to upper-level low to its west, and the initial motion of the hurricane is toward the north at 19 kt. As this interaction continues into tonight, Walaka will lose forward speed and make a turn toward the north-northwest. A broad North Pacific trough moving in from the northwest will pick up Walaka on Friday and cause it to accelerate toward the northeast. On late Saturday and Sunday, the extratropical low of Walaka will race toward the cold waters of the Gulf of Alaska. The forecast track was changed little from previous advisory and is near the middle of a tightly clustered guidance envelope near TVCE.

Continued weakening is expected. Even though vertical wind shear will decline later today, SSTs will drop below 26C, and continued interaction with the deep low should maintain the weakening trend. Vertical wind shear will steadily rise on Friday and Saturday, and as Walaka accelerates over increasingly colder waters, transition to an extratropical low could occur late Saturday or Sunday. For this advisory, the rate of weakening was increased slightly to be in better line with recent satellite trends, though still not as aggressive as the statistical guidance. The intensity forecast is in the middle of the guidance envelope near ICON and closest to HMON.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/2100Z 28.8N 166.3W   80 KT  90 MPH - Category 1 (ENE Midway Atoll)
 12H  05/0600Z 30.6N 167.0W   70 KT  80 MPH - Category 1 (ENE Midway Atoll)
 24H  05/1800Z 32.6N 166.6W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 36H  06/0600Z 35.2N 164.5W   45 KT  50 MPH - Tropical Storm (WNW Puʻuwai, Hawaii)
 48H  06/1800Z 40.1N 160.5W   40 KT  45 MPH - Tropical Storm (WSW Eureka, California)
 72H  07/1800Z 53.0N 149.0W   35 KT  40 MPH - Tropical Storm (ESE Kodiak. Alaska)
 96H  08/1800Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Thu Oct 04 2018

Hurricane Walaka  partially exposed low-level circulation center (LLCC) is evident southwest of an area of deep convection. Strong vertical wind shear from the southwest is likely responsible for this. As a result of this persistent weakening, the latest subjective Dvorak current intensity estimates were 5.0/90 kt from JTWC and PHFO, and 4.5/77 kt from SAB. The latest UW-CIMSS ADT estimate around 1330Z has lowered to 5.2/95 kt. Therefore, the initial intensity for this advisory is 95 kt.

Walaka’s initial motion for this advisory is 360/17 kt. The track forecast guidance remains rather tightly clustered. We have had to make some minor adjustments in the latest track forecast compared with the previous advisory during the 12 to 48 hour time periods. This is primarily due to the way the models are handling Walaka’s interaction with a deep layer low now centered near 29N 171W. Since there remains a great deal of uncertainty about how warm core Walaka will respond to the close encounter with this baroclinic feature, we are assuming it will survive the event intact. So with this uncertainty in mind, Walaka is expected to move northward at a slower speed within the next 12 hours, followed by a turn toward the north-northwest between 12 and 24 hours. After that, again assuming Walaka is a viable system, it is expected to turn toward the north-northeast between the 24 and 36 hour time periods. An accelerating north-northeast motion is forecast during the 48 to 72 hour time periods.

With continued strong vertical wind shear , sea surface temperatures (SST) dropping below 27 degrees C, and reduced ocean heating content today, Walaka will likely experience a rather rapid weakening trend. By tonight, the guidance continues to suggest the vertical wind shear may relax somewhat. However, water temperatures will become a limiting factor, since the SST would likely cool to 24-25 degrees C. As was mentioned above, we are still not certain how the interaction with the cold core low will affect Walaka. Assuming it survives intact as a warm core system, we continue to maintain it as a tropical storm between 36 and 48 hours. After that, extratropical transition will likely occur, so that Walaka will likely be an extratropical gale low by day 3.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/1500Z 26.8N 166.5W   95 KT 110 MPH - Category 2 (ESE Midway Atoll)
 12H  05/0000Z 29.4N 166.8W   80 KT  90 MPH - Category 1 (ENE Midway Atoll)
 24H  05/1200Z 31.8N 167.2W   65 KT  75 MPH - Category 1 (ENE Midway Atoll)
 36H  06/0000Z 34.4N 165.8W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 48H  06/1200Z 38.9N 162.2W   50 KT  60 MPH - Tropical Storm (ENE Midway Atoll)
 72H  07/1200Z 51.0N 151.0W   40 KT  45 MPH - Tropical Storm (ESE Moresby Island, BC Canada)
 96H  08/1200Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Wed Oct 03 2018

Hurricane Walaka  appearance has continued to degrade this evening, with no signs of an eye. Strong vertical wind shear is likely to blame for this. Fortunately, a plethora of microwave images were available from the FNMOC and NRL web sites earlier this evening. These passes, which were useful for determining the location of the low-level circulation center (LLCC), indicated the eyewall structure appeared to remain somewhat intact, although there has been some degradation in the southeastern quadrant. As a result of this continued weakening, the latest subjective Dvorak current intensity estimates were 5.5/102 kt from JTWC and PHFO, and 4.5/77 kt from SAB. The latest UW-CIMSS ADT estimate was 5.8/110 kt. The initial intensity for this advisory is 110 kt.

Walaka’s initial motion for this advisory is 025/19 kt. The track forecast guidance remains tightly clustered, but it has shifted slightly to the left during the 12 to 36 hour time periods. Therefore, we have had to make some minor adjustments in the current track forecast compared with the previous advisory during the 12 to 48 hour time periods. This is primarily due to the way the models are handling the much anticipated interaction with a deep layer low centered near 30N 170W this evening. Since there is a great deal of uncertainty about how warm core Walaka will respond to the close encounter with this baroclinic feature, we are assuming it will survive the event intact. So with this uncertainty in mind, we have Walaka moving northward at a slower speed within the next 12 hours, followed by a turn toward the north-northwest between 12 and 24 hours. After that, again assuming Walaka is a viable system, it is expected to turn toward the north-northeast by the 36 hour time period. An accelerating north-northeast motion is forecast during the 48 to 72 hour time periods.Hurricane Walaka Distances 0200 Hours October 4 2018

With continued strong vertical wind shear into Thursday and sea surface temperatures (SST) dropping to around 27 degrees C later tonight, Walaka will likely experience a more rapid weakening trend through early Thursday morning. We continue to weaken it below major hurricane status within 12 hours. By late Thursday, the guidance continues to suggest the vertical wind shear may relax somewhat. However, water temperatures and ocean heat content will become limiting factors, since SST would likely cool to 24-25 degrees C. As was mentioned above, we are still not certain how the interaction with the cold core low will affect Walaka. Assuming it survives intact, we continue to maintain it as a tropical storm between 36 and 48 hours. After that, extratropical transition will likely occur, so that Walaka will likely be an extratropical low by day 3. Note that the latest intensity forecast was adjusted slightly up from the previous package during the 36 to 72 hour time periods. This is more in line with the latest GFS and ECMWF output.

FORECAST POSITIONS AND MAX WINDS
 
INIT  04/0900Z 24.8N 166.7W  110 KT 125 MPH - Category 3 (ENE Johnson Atoll)
 12H  04/1800Z 27.5N 166.5W   90 KT 105 MPH - Category 2 (ESE Midway Atoll)
 24H  05/0600Z 30.3N 167.2W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)
 36H  05/1800Z 32.5N 166.6W   60 KT  70 MPH - Tropical Storm (ENE Midway Atoll)
 48H  06/0600Z 35.4N 164.2W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 72H  07/0600Z 46.0N 156.0W   45 KT  50 MPH - Tropical Storm (ESE Astoria, OR)
 96H  08/0600Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 200 PM HST Wed Oct 03 2018

DISCUSSION AND OUTLOOK

At 200 PM HST (0000 UTC), the eye of Hurricane Walaka  was located near latitude 22.2 North, longitude 168.0 West. Walaka is moving toward the north-northeast near 23 mph (37 km/h) and this motion is expected to continue through tonight. Walaka is forecast to turn toward the north with a slower forward speed Thursday and Thursday night. On this forecast track, the center of Walaka will cross the Papahanaumokuakea Marine National Monument between French Frigate Shoals and Gardner Pinnacles tonight.

Maximum sustained winds are near 130 mph (210 km/h) with higher gusts. Walaka is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. A continued weakening trend is forecast tonight and expected to continue through Friday. However, Walaka will remain a powerful and life-threatening hurricane as it crosses the Papahanaumokuakea Marine National Monument tonight.

Hurricane-force winds extend outward up to 70 miles (110 km) from the center and tropical-storm-force winds extend outward up to 220 miles (355 km).

The estimated minimum central pressure is 946 mb (27.94 inches).Hurricane Walaka Distances 1400 Hours October 3 2018

HAZARDS AFFECTING LAND

WIND: Tropical storm force winds are starting to spread across the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef this afternoon, with hurricane conditions expected over portions of the area between French Frigate Shoals and Maro Reef tonight.

SURF: Large surf associated with Walaka will continue to affect Johnston Atoll through this afternoon. Large surf will impact the Papahanaumokuakea Marine National Monument through early Thursday morning. These large waves will likely inundate some of the low-lying atolls, especially from French Frigate Shoals to Maro Reef.

RAINFALL: Torrential rainfall will continue to spread across the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef through tonight.

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Wed Oct 03 2018

Hurricane Walaka’s Satellite imagery shows Walaka apparently feeling the effects of increasing vertical wind shear. The deep convection on the west and southwestern eyewall has narrowed, and the upper level cirrus outflow is being eroded to the southwest and elongating off to the northeast. The current intensity is held at 120 kt for this advisory based on a blend of the latest subjective Dvorak estimates and the ADT from UW-CIMSS. These range from 5.5/102 kt from SAB to 7.0/140 kt from JTWC to 6.6/130 kt from the ADT.

Walaka has continued accelerating toward the north-northeast this morning, and the initial motion for this advisory is 020/19 kt. Walaka is expected to continue accelerating a bit more toward the north-northeast into tonight as it remains under the influence of steering flow around a deep low pressure system to the north. Once the hurricane gets closer to this extratropical low pressure feature, it is expected to slow considerably. There is good agreement in this scenario, with only minor northward changes in the track through Friday, due to faster motion in the short term. Beyond Friday, Walaka gets picked up by a trough moving along in the westerlies and accelerates off to the northeast, becoming extratropical by Sunday.

Rapid weakening is forecast tonight and Thursday as continued vertical wind shear values of up to 35 kt combine with SST dropping below 27 degrees C. Later on Thursday, the vertical wind shear relaxes, but continued weakening is expected due to cooler SSTs. As Walaka gets picked up in the westerlies, a slow weakening is forecast as it transitions to extratropical status. The intensity forecast is near the stronger statistical guidance, SHIPS, and higher resolution dynamical guidance, HWRF/HMON, and represents a compromise between the stronger GFS/ECMWF and much weaker HCCA and LGEM.

FORECAST POSITIONS AND MAX WINDS
 
INIT  03/2100Z 21.4N 168.5W  120 KT 140 MPH - Category 4 (ENE Johnson Atoll)
 12H  04/0600Z 24.2N 167.4W  110 KT 125 MPH - Category 3 (ENE Johnson Atoll)
 24H  04/1800Z 27.9N 167.0W   85 KT 100 MPH - Category 2 (ENE Midway Atoll)
 36H  05/0600Z 30.5N 167.3W   70 KT  80 MPH - Category 1 (ENE Midway Atoll)
 48H  05/1800Z 32.4N 166.7W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 72H  06/1800Z 40.0N 160.6W   45 KT  50 MPH - Tropical Storm (ESE Portland, Oregon)
 96H  07/1800Z 51.5N 149.0W   35 KT  40 MPH - Tropical Storm (ESE Moresby Island, BC Canada)
120H  08/1800Z...DISSIPATED

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Wed Oct 03 2018

Hurricane Walaka’s  eye became much more distinct overnight. In addition, the cloud tops cooled significantly in the eyewall. Note that in the last couple of hours, the northwestern eyewall is beginning to show some signs of becoming more narrow. This may be due to increasing vertical wind shear, as well interaction with an upper-level trough located to the northwest of Walaka. Prior to this, some of the satellite fix agencies showed intensification occurred early this morning. The most recent subjective Dvorak current intensity estimates were 6.5/127 kt from JTWC, 6.0/115 kt from PHFO, and 5.5/102 kt from SAB. The latest UW-CIMSS ADT estimate was 7.0/140 kt. Based on a blend of these estimates, we have increased Walaka’s initial intensity to 120 kt for this advisory.

Walaka has been accelerating toward the north-northeast overnight, and the initial motion for this advisory is 015/15 kt. The primary steering mechanism is the circulation around a vertically-stacked low pressure area near 32N 170W. Therefore, Walaka is expected to continue accelerating toward the north-northeast into tonight. Once the hurricane gets closer to this extratropical feature, the track guidance indicates its forward motion will slow during the 24 to 48 hour time period. The latest track forecast continues to show a brief bend in the track toward the north-northwest, followed by rapid acceleration toward the northeast between 48 and 96 hours. The track guidance remains in remarkably good agreement considering the rather complex interaction between Walaka and the extratropical low. This latest track forecast is very close to the previous advisory package through 36 hours, except for some minor increase in forward motion. The track was adjusted to the left around 48 hours to more closely follow the consensus guidance, which appears to be in general agreement in regards to the interaction with the low. There was little change in the track from the previous advisory during the 72 to 120 hour time periods.

As the vertical wind shear near Walaka becomes increasingly hostile during the next 24 to 36 hours, steady weakening is forecast. Although the shear diminishes somewhat by 36 hours, the tropical cyclone will begin moving over increasingly cool sea surface temperatures and reduced ocean heat content. There is some uncertainty about how Walaka’s interaction with the extratropical low will affect its intensity. The global models seem to be in good agreement that some semblance of a warm core system will remain after Walaka interaction with the extratropical low. Therefore, the current forecast maintains Walaka as a tropical cyclone through 72 hours. However, it would not be surprising if the system becomes extratropical sooner. The latest intensity forecast shows a slower rate of weakening than most of the dynamical models. It is in best agreement with the ECMWF and GFS output. The current intensity forecast is showing a somewhat faster weakening trend beyond 36 hours compared with the previous advisory package.

FORECAST POSITIONS AND MAX WINDS
 
INIT  03/1500Z 19.6N 169.4W  120 KT 140 MPH - Category 4 (ENE Johnson Atoll)
 12H  04/0000Z 22.2N 168.4W  110 KT 125 MPH - Category 3 (ENE Johnson Atoll)
 24H  04/1200Z 25.9N 167.3W  100 KT 115 MPH - Category 3 (ESE Midway Atoll)
 36H  05/0000Z 29.0N 167.4W   85 KT 100 MPH - Category 2 (ENE Midway Atoll)
 48H  05/1200Z 30.7N 167.5W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)
 72H  06/1200Z 35.0N 163.5W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
 96H  07/1200Z 44.5N 155.5W   45 KT  50 MPH - Tropical Storm (ESE Portland, Oregon)
120H  08/1200Z 53.0N 143.0W   30 KT  35 MPH - Tropical Storm (ESE Queen Charlott, BC Canada)

NWS Central Pacific Hurricane Center Honolulu HI 1100 AM HST Tue Oct 02 2018

Hurricane Walaka – Morning visible and infrared satellite imagery trends showing Walaka has degraded somewhat over the past several hours. The eye has become less distinct with a clouds apparently partially covering the eye. Cloud tops have warmed in the eyewall and surrounding convective ring, and Dvorak intensity estimates started to follow this weakening trend which began overnight. Current intensities range from 6.0 at SAB to 6.5 at PHFO and JTWC. Have conservatively lowered the initial intensity to 130 kt for this forecast cycle as Satcon estimates as of 1528 UTC were at 132 knots, with a very slow weakening in the short term as Walaka appears to be completing an eyewall replacement cycle based on earlier composite microwave data overnight. A solid ASCAT pass from 0816 UTC was useful to make minor adjustments to the wind radii, and an altimeter pass aided in adjusting the 12 foot seas radii.

The initial motion was set at 355/09 knots, as Walaka continues to be drawn northward by the deep low pressure system to the north. This motion is expected to continue over the next day or two with some acceleration as the influence of this low pressure over the Walaka steering currents increases. By Thursday and Friday, Walaka slows as it interacts with the mid latitude trough which remains cutoff from the mid latitude westerlies aloft. By early Saturday, another sharp upper trough picks the tropical cyclone up and shifts it off to the northeast through the weekend, resulting in accelerating northeastward motion. Overall, the track guidance envelope remains fairly tightly clustered through Friday, with some variations on how quickly Walaka gets picked up by the westerlies over the weekend. The official forecast stays very close to the previous advisory and is only slightly nudged towards HCCA and ECMWF beyond Friday.

Although experiencing a weakening trend since last night, the environment surrounding Walaka remains somewhat conducive for intensification during the next 12 to 18 hours. The tropical cyclone will remain within a deep moist airmass with low vertical wind shear, high ocean heat content and sea surface temperatures near 29 or 30 degrees C. The forecast shows continued weakening in the short term, due to current trends, then steady intensity tonight through early Wednesday, as this period has the potential for another round of intensity fluctuations within aforementioned conducive conditions. Between 24 and 48 hours, vertical wind shear increases dramatically due to interaction with the upper level jet around the deep low to the north, resulting in steady and rapid weakening of Walaka especially Thursday and Friday. Weakening trend relaxes Saturday and Sunday as Walaka accelerates to the northeast and transitions to an extratropical cyclone. The official forecast follows the SHIPS and dynamical intensity consensus through the 5 day forecast, except holds the intensity up through the first 24 hours owing to potential fluctuations.

The forecast track will take Walaka near Johnston Island later today, with hurricane conditions expected this afternoon and this evening. Therefore a Hurricane Warning remains in effect for this location. The forecast track also takes the hurricane across the Papahanaumokuakea Marine National Monument between French Frigate Shoals and Maro Reef late Wednesday, therefore, a Hurricane Warning has been issued for this area. A Tropical Storm Warning has been issued east of French Frigate Shoals to Nihoa as tropical storm conditions are expected to reach that area late Wednesday.

FORECAST POSITIONS AND MAX WINDS
 
INIT  02/2100Z 15.6N 170.1W  130 KT 150 MPH - Category 4 (WSW Johnson Atoll)
 12H  03/0600Z 17.4N 169.9W  125 KT 145 MPH - Category 4 (ENE Johnson Atoll)
 24H  03/1800Z 20.5N 169.1W  125 KT 145 MPH - Category 4 (ENE Johnson Atoll)
 36H  04/0600Z 23.9N 167.8W  110 KT 125 MPH - Category 3 (ESE Midway Atoll)
 48H  04/1800Z 27.0N 167.3W   85 KT 100 MPH - Category 2 (ESE Midway Atoll)
 72H  05/1800Z 31.0N 167.2W   65 KT  75 MPH - Category 1 (ENE Midway Atoll)
 96H  06/1800Z 35.3N 162.7W   55 KT  65 MPH - Tropical Storm (ENE Midway Atoll)
120H  07/1800Z 44.6N 154.2W   45 KT  50 MPH - Tropical Storm (WSW Portland, Oregon)

NWS Central Pacific Hurricane Center Honolulu HI 800 AM HST Tue Oct 02 2018

Hurricane Walaka  SUMMARY OF WATCHES AND WARNINGS IN EFFECT:

A Hurricane Warning is in effect for… * Johnston Atoll A Hurricane Watch is in effect for… * Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef A Hurricane Warning means that hurricane conditions are expected in the warning area within 36 hours. A Hurricane Watch means that hurricane conditions are possible within the watch area within 48 hours.

DISCUSSION AND OUTLOOK

At 800 AM HST (1800 UTC), the center of Hurricane Walaka was located near latitude 15.1 North, longitude 170.1 West. Walaka is moving toward the north near 10 mph (17 km/h). This general motion is expected to continue through Wednesday night with a steady increase in forward speed. On the forecast track, the center of Walaka is expected to pass just to the west of Johnston later today. Maximum sustained winds are near 150 mph (240 km/h) with higher gusts. Walaka is a category 4 hurricane on the Saffir-Simpson Hurricane Wind Scale. Little change in intensity is expected through tonight, with rapid weakening expected Wednesday and Wednesday night.

Hurricane-force winds extend outward up to 40 miles (65 km) from the center and tropical-storm-force winds extend outward up to 185 miles (295 km).

The estimated minimum central pressure is 932 mb (27.52 inches).

HAZARDS AFFECTING LAND

WIND: Tropical storm force winds are already occurring across Johnston Island, with hurricane conditions expected to begin this afternoon and last through this evening. Tropical storm force winds are possible across the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef beginning late Wednesday, with hurricane conditions possible Wednesday night.

SURF: Large surf associated with Walaka will continue to affect the Johnston Island reefs and shorelines through Wednesday. Large surf will affect the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef beginning early Wednesday.

RAINFALL: Heavy rainfall associated with Walaka will continue across Johnston Island through early Wednesday, and may reach rainfall may reach the Papahanaumokuakea Marine National Monument from Nihoa to French Frigate Shoals to Maro Reef late tonight or Wednesday.

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Tue Oct 02 2018

Hurricane Walaka The satellite presentation of Walaka which was being degraded by an eye wall replacement cycle overnight, has just begun to improve with a ring of deep convection beginning to once again encircle the well defined eye, which could be a sign that the eyewall replacement cycle is getting ready to complete. The latest intensity estimates from PHFO, SAB, JTWC were 6.5 (127 knots) while the ADT held at 6.6 (130 knots). Based on constraints likely holding the intensity of Walaka too low Monday afternoon, have only reduced the initial intensity slightly with this advisory to 135 knots. The initial motion was set at 350/09 knots.

A deep north Pacific upper level low in the vicinity of 30N 170W will draw Walaka northward over the next several days, before another sharp upper trough shifting across the north Pacific picks the tropical cyclone up and shifts it off to the northeast Friday night and Saturday. Overall the guidance envelope remains fairly tightly clustered through the forecast period. The official forecast remains very close to that of the previous advisory and is fairly well aligned with the latest GFEX, TVCN, HCCA consensus guidance.

The environment surrounding Walaka remains conducive for additional intensification during the next 24 hours. The tropical cyclone will remain within a deep moist airmass with low vertical wind shear, high ocean heat content and sea surface temperatures between 84 to 86 Fahrenheit. Eyewall replacement cycles could lead to some fluctuations in intensity through this time frame, so the intensity forecast shows little intensity change through 24 hours. Beyond 24 hours, the combination of increasing vertical wind shear, drier mid-level air entraining into the cyclone, sea surface temperatures becoming marginal and even unfavorable, along with interaction with the deep upper level low should result in steady and even rapid weakening of Walaka. As a result, the intensity forecast calls for Walaka to begin weakening on Wednesday, with rapid weakening then continuing through the end of the forecast period. The official intensity forecast was adjusted downward slightly, but remains above all guidance through 36 hours before trending closer to a blend of the statistical and dynamical models thereafter. Walaka is expected to become an post-tropical/extra-tropical low by 120 hours.

The forecast track will take Walaka near Johnston Island later today, with hurricane conditions expected this afternoon and this evening. Therefore a Hurricane Warning remains in effect for this location. The forecast track also takes the hurricane across the Papahanaumokuakea Marine National Monument between French Frigate Shoals and Laysan Island late Wednesday. Therefore, a Hurricane Watch remains in effect for the region from Nihoa to Maro Reef.

FORECAST POSITIONS AND MAX WINDS
 
INIT  02/1500Z 14.7N 170.0W  135 KT 155 MPH - Category 4 (WSW Johnson Atoll)
 12H  03/0000Z 16.2N 170.2W  135 KT 155 MPH - Category 4 (WSW Johnson Atoll)
 24H  03/1200Z 18.9N 169.7W  135 KT 155 MPH - Category 4 (WNW Johnson Atoll)
 36H  04/0000Z 22.3N 168.4W  120 KT 140 MPH - Category 4 (ENE Johnson Atoll)
 48H  04/1200Z 26.2N 167.4W  100 KT 115 MPH - Category 3 (ESE Midway Atoll)
 72H  05/1200Z 30.5N 168.0W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)
 96H  06/1200Z 33.0N 164.0W   60 KT  70 MPH - Tropical Storm (ENE Midway Atoll)
120H  07/1200Z 41.0N 157.5W   50 KT  60 MPH - Tropical Storm (WSW Brookings, Oregon)

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Mon Oct 01 2018

Hurricane Walaka –  The satellite presentation of Walaka has improved significantly overnight as the cyclone continues to rapidly intensify. The well defined eye is surrounded by a large ring of -70 to -85C cloud tops, and continues to show excellent outflow in all quadrants as evident in geostationary satellite animations. Additionally, large deep convective banding features are present on both the east and west side of Walaka early this morning. The latest intensity estimates came in at 5.5 (102 knots) from PHFO, SAB, and JTWC, while the UW-CIMSS ADT was 5.4 (100 knots). As of 01/14Z, raw DT numbers are as high as 7.0 (140 knots), but need to be held down due to intensification constraints. Based on this data along with the continued improvement in the appearance and organization, the initial intensity of Walaka for this advisory was increased to 110 knots, making it 5 knots short of category 4 status. The initial motion was set at 295/09 knots.

Walaka is beginning to round the southwest periphery of a large subtropical ridge this morning and is currently moving toward the west-northwest. A turn toward the northwest is expected later today as a deep north Pacific upper trough digs southward in the vicinity of 30N 170W and further erodes the western end of the subtropical ridge. A turn toward the north is then expected on Tuesday, with Walaka continuing on this course through Tuesday night with an increase in forward speed. The tropical cyclone should then make a turn toward the north-northeast Wednesday and Wednesday night as it begins to feel the influence of the deep upper level trough. The track guidance then suggests a shift back toward the north with a decrease in forward speed Thursday through Friday as Walaka interacts with the deep upper level trough, with a turn back toward the northeast expected Friday night. The official track forecast was changed very little from the previous advisory and remains in close proximity to the tightly clustered HCCA, TVCN, and GFEX consensus guidance.

The environment surrounding Walaka remains very conducive for additional intensification during the next 36 hours and possibly even a bit longer. Today through Tuesday, the tropical cyclone will remain within a deep moist airmass, with vertical wind shear forecast to remain around 10 knots, and sea surface temperatures holding in the 84 to 86 Fahrenheit range. As a result, additional rapid intensification is expected today into tonight, with the cyclone then forecast to level off late tonight through Tuesday night. Given the environment surrounding the system, the intensity forecast brings Walaka up to category 5 intensity tonight, and is slightly above the intensity guidance which doesn’t explicitly indicate Walaka will reach category 5 intensity. There is the potential that Walaka could intensify even more than currently forecast, but due to eyewall replacement cycles likely leading to some fluctuation in intensity, the forecast was held nearly steady from late tonight through Tuesday night. Vertical wind shear is expected to steadily increase Wednesday and Wednesday night as Walaka approaches and begins to interact with the deep upper level trough over the north-central Pacific, with sea surface temperatures dropping off during this time as well. The intensity forecast calls for rapid weakening beginning beyond 48 hours, with this weakening trend expected to continue through the end of the forecast period. The official intensity forecast has been increased from the previous advisory and is slightly higher than all intensity guidance through 36 hours, then falls more closely in line with a blend of the statistical and dynamical guidance for forecast hour 72 through 120.

FORECAST POSITIONS AND MAX WINDS
 
INIT  01/1500Z 12.3N 168.3W  110 KT 125 MPH - Category 3 (ESE Johnson Atoll)
 12H  02/0000Z 13.1N 169.4W  130 KT 150 MPH - Category 4 (WSW Johnson Atoll)
 24H  02/1200Z 14.5N 170.4W  140 KT 160 MPH - Category 5 (WSW Johnson Atoll)
 36H  03/0000Z 16.4N 170.7W  140 KT 160 MPH - Category 5 (WSW Johnson Atoll)
 48H  03/1200Z 18.9N 170.1W  135 KT 155 MPH - Category 4 (ENE Johnson Atoll)
 72H  04/1200Z 25.0N 167.5W  100 KT 115 MPH - Category 3 (ESE Midway Atoll)
 96H  05/1200Z 29.5N 167.0W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)
120H  06/1200Z 33.0N 164.0W   60 KT  70 MPH - Tropical Storm (ENE Midway Atoll)

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Sun Sep 30 2018

Hurricane Walaka is undergoing rapid intensification this evening, which is clearly evident given the large ring of -70 to -85C cloud tops surrounding the the well defined eye. Additionally, recent microwave passes indicate that the organization of the system has improved significantly, while geostationary satellite animations show well defined outflow channels in all quadrants. The latest intensity estimates came in at 5.0 (90 knots) from PHFO and SAB, 4.5 (77 knots) from JTWC, while the UW-CIMSS ADT was 4.2 (70 knots). Based on the significant improvement in appearance and organization of Walaka, the initial intensity for this advisory was increased to 90 knots. The initial motion was set at 280/10 knots.

Walaka continues to be steered westward this evening by a subtropical ridge to the north of the system, and this motion is expected to continue tonight. A turn toward the northwest is expected on Monday as a deep north Pacific upper trough digs southward in the vicinity of 30N 170W. A turn toward the north is then expected on Tuesday, with Walaka continuing on this course through Tuesday night with an increase in forward speed. The tropical cyclone should then make a turn toward the north-northeast Wednesday and Wednesday night as it begins to feel the influence of the deep upper level trough. The track guidance then suggests a shift back toward the north with a decrease in forward speed Thursday through Friday as Walaka interacts with the deep upper level trough. The official forecast was nudged slightly to the left through 48 hours, then slightly to the right beyond 48 hours, and is very close to the HCCA, TVCN, and GFEX consensus guidance.

The environment surrounding Walaka remains very conducive for additional intensification through 48 hours. The tropical cyclone will remain within a deep moist airmass, with vertical wind shear forecast to remain around 10 knots or less through 48 hours, and sea surface temperatures holding in the 84 to 86 Fahrenheit range during this time. As a result, additional rapid intensification is expected tonight and Monday, with the cyclone then forecast to level off just below category 5 status Tuesday and Tuesday night. Given the environment surrounding the system, intensification to a category 5 storm is not out of the question, although none of the intensity guidance explicitly indicate this at this time. Additionally, Walaka will likely undergo eyewall replacement cycles which will lead to some fluctuation in intensity. Beyond 48 hours, vertical wind shear will steadily increase as Walaka approaches and begins to interact with the deep upper level trough over the north-central Pacific, with sea surface temperatures dropping off as well. The intensity forecast shows a gradual weakening by 72 hours, with rapid weakening then expected beyond 72 hours through the end of the forecast period. The official intensity forecast has been increased from the previous advisory and is in line with the high end of the intensity guidance.Tropical Storm Walaka Distances 0200 Hours October 1 2018

FORECAST POSITIONS AND MAX WINDS
 
INIT  01/0900Z 11.9N 167.5W   90 KT 105 MPH - Category 2 (ESE Johnson Atoll)
 12H  01/1800Z 12.5N 168.7W  115 KT 130 MPH - Category 4 (ESE Johnson Atoll)
 24H  02/0600Z 13.5N 169.9W  130 KT 150 MPH - Category 4 (WSW Johnson Atoll)
 36H  02/1800Z 15.1N 170.5W  135 KT 155 MPH - Category 4 (WSW Johnson Atoll)
 48H  03/0600Z 17.2N 170.5W  135 KT 155 MPH - Category 4 (WSW Johnson Atoll)
 72H  04/0600Z 23.3N 168.1W  115 KT 130 MPH - Category 4 (ESE Midway Atoll)
 96H  05/0600Z 28.5N 167.5W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)
120H  06/0600Z 31.0N 166.0W   60 KT  70 MPH - Tropical Storm (ENE Midway Atoll)

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sun Sep 30 2018

Tropical Storm Walaka is undergoing rapid intensification this evening, which is clearly evident given the large ring of -70 to -85C cloud tops surrounding the the well defined eye. Additionally, recent microwave passes indicate that the organization of the system has improved significantly, while geostationary satellite animations show well defined outflow channels in all quadrants.

The latest intensity estimates came in at 5.0 (90 knots) from PHFO and SAB, 4.5 (77 knots) from JTWC, while the UW-CIMSS ADT was 4.2 (70 knots). Based on the significant improvement in appearance and organization of Walaka, the initial intensity for this advisory was increased to 90 knots. The initial motion was set at 280/10 knots. Walaka continues to be steered westward this evening by a subtropical ridge to the north of the system, and this motion is expected to continue tonight. A turn toward the northwest is expected on Monday as a deep north Pacific upper trough digs southward in the vicinity of 30N 170W. A turn toward the north is then expected on Tuesday, with Walaka continuing on this course through Tuesday night with an increase in forward speed. The tropical cyclone should then make a turn toward the north-northeast Wednesday and Wednesday night as it begins to feel the influence of the deep upper level trough.

The track guidance then suggests a shift back toward the north with a decrease in forward speed Thursday through Friday as Walaka interacts with the deep upper level trough. The official forecast was nudged slightly to the left through 48 hours, then slightly to the right beyond 48 hours, and is very close to the HCCA, TVCN, and GFEX consensus guidance. The environment surrounding Walaka remains very conducive for additional intensification through 48 hours. The tropical cyclone will remain within a deep moist airmass, with vertical wind shear forecast to remain around 10 knots or less through 48 hours, and sea surface temperatures holding in the 84 to 86 Fahrenheit range during this time. As a result, additional rapid intensification is expected tonight and Monday, with the cyclone then forecast to level off just below category 5 status Tuesday and Tuesday night.

Given the environment surrounding the system, intensification to a category 5 storm is not out of the question, although none of the intensity guidance explicitly indicate this at this time. Additionally, Walaka will likely undergo eyewall replacement cycles which will lead to some fluctuation in intensity. Beyond 48 hours, vertical wind shear will steadily increase as Walaka approaches and begins to interact with the deep upper level trough over the north-central Pacific, with sea surface temperatures dropping off as well. The intensity forecast shows a gradual weakening by 72 hours, with rapid weakening then expected beyond 72 hours through the end of the forecast period. The official intensity forecast has been increased from the previous advisory and is in line with the high end of the intensity guidance.

NWS Central Pacific Hurricane Center Honolulu HI 500 AM HST Sun Sep 30 2018

Tropical Storm Walaka  – The satellite presentation of Walaka has improved significantly overnight, with a large area of deep convection featuring -80 to -90C cloud tops over the difficult to locate low level circulation center.

Due to the lack of any recent microwave imagery to assist in confidently determining the center location, the initial position was based on extrapolation from earlier microwave passes and current geostationary satellite animations. The latest satellite intensity estimates from PHFO and SAB were 3.0 (45 knots), and 2.5 (35 knots) from JTWC. Meanwhile, the ADT value from UW-CIMSS continues to appear unrealistically high at 4.1 (67 knots). Given the improvement in organization and appearance of Walaka since the 12Z satellite intensity estimates, the initial intensity for this advisory has been increased to 50 knots. The initial motion has been set at 275/14 knots.

Walaka is expected to track nearly due west along the south side of a subtropical ridge today and tonight, with a gradual decrease in forward speed. A deep north Pacific upper trough will erode the subtropical ridge to the north of Walaka on Monday and steer the tropical cyclone northwestward, with a turn toward the north expected on Tuesday along with an increase in forward speed. The system should then slow down and be pulled back to the north- northwest on Thursday as it begins to interact with the upper trough.

The guidance is fairly tightly clustered through entire forecast cycle, with a bit more spread noted by forecast hour 120. The official forecast closely follows the GFEX, TVCN, and HCCA consensus guidance, and is very closely aligned with the forecast track from the previous advisory. With the official forecast track bringing the center of Walaka very near Johnston Atoll on Tuesday, a Hurricane Watch has been issued for this location.

The environmental conditions surrounding Walaka will remain very conducive for intensification over the next several days, with high sea surface temperatures of 84 to 86 Fahrenheit, 10 knots or less of vertical wind shear, high ocean heat content, and plenty of deep moisture. As a result, the forecast calls for rapid intensification today through Monday night, with Walaka expected to become a major hurricane on Monday. The intensity should level off a bit Tuesday into Tuesday night following the period of rapid intensification and accounting for the potential for eyewall replacement cycles. Vertical wind shear should then begin to impact the tropical cyclone beginning late Tuesday night or Wednesday as it interacts with a deep upper level trough, and as a result, the intensity forecast calls for steady weakening by forecast hours 96 and 120. The intensity forecast has been increased slightly from the previous advisory and is on the high end of most of the intensity guidance.

Tropical Storm Walaka Distances 0800 Hours September 30 2018

FORECAST POSITIONS AND MAX WINDS
 
INIT  30/1500Z 11.7N 163.9W   50 KT  60 MPH - Tropical Storm (ESE Johnson Atoll)
 12H  01/0000Z 11.9N 165.6W   65 KT  75 MPH - Category 1 (ESE Johnson Atoll)
 24H  01/1200Z 12.3N 167.5W   85 KT 100 MPH - Category 2 (ESE Johnson Atoll)
 36H  02/0000Z 13.3N 168.9W  110 KT 125 MPH - Category 3 (ESE Johnson Atoll)
 48H  02/1200Z 14.9N 169.8W  120 KT 140 MPH - Category 4 (WSW Johnson Atoll)
 72H  03/1200Z 19.8N 169.2W  120 KT 140 MPH - Category 4 (ENE Johnson Atoll)
 96H  04/1200Z 27.0N 167.5W   90 KT 105 MPH - Category 2 (ESE Midway Atoll)
120H  05/1200Z 30.0N 168.5W   65 KT  75 MPH - Category 1 (ENE Midway Atoll)

NWS Central Pacific Hurricane Center Honolulu HI 1100 PM HST Sat Sep 29 2018

Tropical Storm Walaka – The satellite presentation of Walaka has improved this evening, with an increase in deep convection around the low level circulation center. Several microwave passes were helpful in determining the center location, but also indicated that the tropical storm lacks good organization at the moment.

The latest satellite intensity estimates from PHFO, SAB and JTWC all came in at 2.5 (35 knots) with the ADT value from UW-CIMSS appearing unrealistically high at 3.6 (57 knots). As a result, the initial intensity for this advisory will be held at 35 knots. The initial motion based on interpolating between microwave passes along with geostationary satellite animations will be set at 270/14 knots.

Walaka is expected to track nearly due west along the south side of a subtropical ridge through Sunday night, with a gradual decrease in forward speed. A deep north Pacific upper trough will erode the subtropical ridge to the north of Walaka on Monday and steer the tropical cyclone northwestward, with a turn toward the north and northeast along with an increase in forward speed forecast beyond 72 hours. The guidance is fairly tightly clustered through 48 hours with increasing model spread from forecast hour 72 onward. The official forecast closely follows the GFEX and TVCN consensus models through 48 hours, and lies nearly on top of the track from the previous advisory. Beyond 48 hours, the official forecast track was nudged to the right to better align with the latest consensus guidance. Of note, the forecast track currently brings the center of Walaka very near Johnston Atoll, late Monday night or early Tuesday, and watches will likely be needed on Sunday.Tropical Storm Walaka Distances 2300 Hours September 29 2018

The environmental conditions surrounding Walaka will remain very conducive for intensification over the next several days, with high sea surface temperatures of 84 to 86 Fahrenheit, 10 knots or less of vertical wind shear, high ocean heat content, and plenty of deep moisture. As a result, the forecast calls for steady intensification over the next 24 hours as the system becomes better organized, with rapid intensification expected between forecast hour 24 and forecast hour 48, with Walaka expected to become a major hurricane by Monday night. Wind shear should begin to impact the system as it interacts with a deep upper level trough beyond 72 hours, and the forecast calls for steady weakening by forecast hours 96 and 120. The official intensity forecast is generally a blend between the statistical and dynamical models, with the dynamical models showing even a faster rate of intensification than the official forecast.

FORECAST POSITIONS AND MAX WINDS
 
INIT  30/0900Z 11.6N 162.1W   35 KT  40 MPH - Tropical Storm (ESE Johnson Atoll)
 12H  30/1800Z 11.8N 164.2W   50 KT  60 MPH - Tropical Storm (ESE Johnson Atoll)
 24H  01/0600Z 12.1N 166.6W   65 KT  75 MPH - Category 1 (ESE Johnson Atoll)
 36H  01/1800Z 12.8N 168.3W   90 KT 105 MPH - Category 2 (ESE Johnson Atoll)
 48H  02/0600Z 14.0N 169.4W  110 KT 125 MPH - Category 3 (ESE Johnson Atoll)
 72H  03/0600Z 17.9N 169.7W  110 KT 125 MPH - Category 3 (WNW Johnson Atoll)
 96H  04/0600Z 24.5N 167.5W   95 KT 110 MPH - Category 2 (WNW Puʻuwai, Hawaii)
120H  05/0600Z 30.5N 167.5W   75 KT  85 MPH - Category 1 (ENE Midway Atoll)

Article Resources:

Related Articles:

Recent Tropical Storms

Video: Weather update on Tropical Storm Walaka with Kamaka Pili (9/29 at 11 p.m.)
Please follow and like us: