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Tropical Storm Vicente Forecast Discussion Number 6

2018-10-20 22:32:32| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Sat Oct 20 2018 000 WTPZ43 KNHC 202032 TCDEP3 Tropical Storm Vicente Discussion Number 6 NWS National Hurricane Center Miami FL EP232018 400 PM CDT Sat Oct 20 2018 The cloud pattern associated with Vicente is quite peculiar. In addition on being unusually small, it has an intermittent eye feature surrounded by moderate to shallow convection. A very useful ASCAT pass a few hours ago showed that Vicente has a very tight circulation with maximum winds of 40 to 45 kt, and the tropical-storm-force winds extend only 20 n mi from the center. On this basis, and an average of Dvorak estimates from TAFB and SAB, the initial intensity has been adjusted upward to 45 kt. Now that the circulation is farther from land, the chances of some slight strengthening have increased in the next 24 to 36 hours before Vicente encounters the larger circulation of Willa. In fact, most of the global models advertise that in about 3 days or so Vicente will dissipate, and so does the official forecast. Satellite fixes indicate that Vicente is moving toward the west or 265 degrees at 8 kt. The nose of a strong subtropical ridge is forecast to amplify and expand westward. This flow pattern should force Vicente to move on a west or even west-southwest track for the next 24 to 36 hours. Then as the cyclone reaches the southwestern end of the ridge and encounters the eastern portion of Willa's circulation, Vicente should turn toward the northwest and north. Vicente should become absorbed by the larger Willa and dissipation could occur earlier than indicated in the forecast at this time given the solution of the global models. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 14.6N 94.3W 45 KT 50 MPH 12H 21/0600Z 14.0N 95.5W 45 KT 50 MPH 24H 21/1800Z 13.7N 97.2W 50 KT 60 MPH 36H 22/0600Z 14.0N 99.0W 40 KT 45 MPH 48H 22/1800Z 15.0N 101.0W 40 KT 45 MPH 72H 23/1800Z 17.5N 103.5W 30 KT 35 MPH 96H 24/1800Z...DISSIPATED $$ Forecaster Avila

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Tropical Storm Willa Forecast Discussion Number 3

2018-10-20 22:32:07| National Hurricane Center (East Pacific)

Issued at 400 PM CDT Sat Oct 20 2018 000 WTPZ44 KNHC 202032 TCDEP4 Tropical Storm Willa Discussion Number 3 NWS National Hurricane Center Miami FL EP242018 400 PM CDT Sat Oct 20 2018 Willa appears to be wrapping up quickly, and the low-level center is now embedded beneath a ragged central dense overcast. ASCAT data from several hours ago indicated winds were as high as 40 kt, but more recent satellite estimates support an intensity between 45-55 kt, and the maximum winds are set at 50 kt for this advisory. Willa has turned west-northwestward and slowed down, and the initial motion is estimated to be 295/5 kt. The cyclone is forecast to recurve around the western edge of a mid-level ridge that lies over Mexico during the next few days, and then accelerate northeastward into mainland Mexico by days 4 and 5 ahead of a broad mid-latitude trough. Compared to previous model runs, the new track guidance has sped up significantly and also now shows a sharper recurvature, both of which suggest that Willa's hazards could reach the coast of Mexico sooner than originally thought. The GFS and ECMWF remain the fastest of the models, and although the updated NHC track forecast trends in their direction, it hangs back a bit to give some weight to the HWRF, HCCA, and Florida State Superensemble. Even with that consideration, the new forecast does bring Willa to the coast sooner than before. The satellite signature suggests that the storm is organizing quickly and is probably in the beginning stages of rapid intensification (RI). The RI indices are even higher this afternoon than they were this morning, and incredibly, the HWRF, SHIPS, HCCA, and Florida State Superensemble all bring Willa near or at major hurricane intensity in 36 hours. The NHC forecast follows those models' lead and indicates significant strengthening over the next couple of days. A peak in intensity is likely to occur between 48-72 hours, followed by some weakening due to lower oceanic heat content and increasing vertical shear. Despite the expected weakening, Willa is expected to reach the coast of west-central mainland Mexico as a hurricane in about 4 days. FORECAST POSITIONS AND MAX WINDS INIT 20/2100Z 15.2N 105.8W 50 KT 60 MPH 12H 21/0600Z 15.5N 106.3W 65 KT 75 MPH 24H 21/1800Z 16.1N 106.9W 85 KT 100 MPH 36H 22/0600Z 16.8N 107.4W 105 KT 120 MPH 48H 22/1800Z 17.6N 107.8W 110 KT 125 MPH 72H 23/1800Z 19.1N 108.1W 100 KT 115 MPH 96H 24/1800Z 22.0N 106.5W 80 KT 90 MPH 120H 25/1800Z 24.5N 103.5W 40 KT 45 MPH...INLAND $$ Forecaster Berg

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Tropical Storm Willa Forecast Discussion Number 2

2018-10-20 16:46:36| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Sat Oct 20 2018 000 WTPZ44 KNHC 201446 TCDEP4 Tropical Storm Willa Discussion Number 2 NWS National Hurricane Center Miami FL EP242018 1000 AM CDT Sat Oct 20 2018 A GMI microwave pass over the depression at 0916 UTC revealed that a tight inner core has developed, with a cyan and pink ring noted in the low-level 37-GHz channel. Outer convective banding has also been increasing, and a consensus of the latest subjective and objective satellite intensity estimates supports raising the maximum winds to 35 kt and designating the cyclone as Tropical Storm Willa. On an historical note, this is the first time that at least 21 named storms have formed within the eastern Pacific basin since the 1992 season. The microwave data suggest that Willa's center is a little farther south than previously estimated, and the initial motion is calculated to be westward, or 270/8 kt. The storm is already located near the western periphery of a mid-level ridge which extends across northern and central Mexico, and Willa is expected to slowly recurve around the ridge axis during the next 4 days. By the end of the forecast period, a mid-latitude trough located over the western U.S. is likely to cause Willa to accelerate toward the northeast in the direction of mainland Mexico. All of the track models agree on this general scenario, but there are some differences on how wide a turn Willa makes while it recurves. There are also some speed differences that appear to be related to how strong Willa will be when the mid-latitude trough becomes the main steering driver. The NHC forecast is very close to the previous forecast during the first 48 hours. After that time, the forecast has been nudged eastward since the GFS and ECMWF models are both near or east of the multi-model consensus aids. With a low-level ring already observed in microwave imagery, and Willa located in an environment of low shear and over very warm ocean water, the cyclone appears poised to go through a period of rapid intensification (RI). Several of the various RI indices are over 50 percent, and thus the NHC forecast favors the high end of the intensity guidance and explicitly shows rapid strengthening over the next 48 hours. Willa is expected to be moving more slowly by days 3 and 4 (about 3 kt), and upwelling of colder water could induce some weakening by that time. An increase in shear is likely to cause more significant weakening by the end of the forecast period. The new NHC intensity forecast is a bit higher than the previous forecast to account for the possibility of rapid intensification, and it shifts Willa's expected peak intensity about a day earlier. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 14.8N 105.7W 35 KT 40 MPH 12H 21/0000Z 15.0N 106.5W 50 KT 60 MPH 24H 21/1200Z 15.3N 107.3W 65 KT 75 MPH 36H 22/0000Z 15.8N 107.9W 80 KT 90 MPH 48H 22/1200Z 16.6N 108.5W 95 KT 110 MPH 72H 23/1200Z 17.7N 109.0W 100 KT 115 MPH 96H 24/1200Z 19.0N 109.0W 90 KT 105 MPH 120H 25/1200Z 22.0N 107.5W 75 KT 85 MPH $$ Forecaster Berg

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Tropical Storm Vicente Forecast Discussion Number 5

2018-10-20 16:44:34| National Hurricane Center (East Pacific)

Issued at 1000 AM CDT Sat Oct 20 2018 000 WTPZ43 KNHC 201444 TCDEP3 Tropical Storm Vicente Discussion Number 5 NWS National Hurricane Center Miami FL EP232018 1000 AM CDT Sat Oct 20 2018 Conventional satellite imagery and microwave data continue to reveal that Vicente is an unusually small tropical cyclone. Data show a ring of convection defining the center with most of the thunderstorm activity on the southwestern portion of the circulation. Dvorak estimates from TAFB and SAB yield an initial intensity of 35 kt. The cyclone is not in the best environment for intensification given that the circulation has been interacting with land, however the shear is not high, and the cyclone is over 29 degree Celsius water. Once the circulation separates from land, some slight strengthening is then forecast. After that time, Vicente will be approaching the much larger circulation of strengthening Tropical Cyclone Willa, and the most likely scenario is that at least by 96 hours, Vicente will become absorbed within an outer band of Willa. This is the same scenario which occurred with Hurricane John and Tropical Storm Ileana back in August this year. Vicente is moving toward the west or 270 degrees at 6 kt. The nose of a strong subtropical ridge is forecast to amplify and expand westward. This flow pattern should force Vicente to move on a west to west-southwest track for about 36 hours. Then as the cyclone reaches the southwestern end of the ridge and encounters the eastern portion of Willa's circulation, Vicente should turn toward the northwest until it becomes absorbed. It is interesting to note that unanimously, the track guidance forces Vicente to acquire a west-southwesterly component due to the expansion of the ridge, increasing the confidence in the the track forecast during the next 2 to 3 days. FORECAST POSITIONS AND MAX WINDS INIT 20/1500Z 14.3N 93.6W 35 KT 40 MPH 12H 21/0000Z 14.2N 94.5W 35 KT 40 MPH 24H 21/1200Z 13.5N 96.3W 40 KT 45 MPH 36H 22/0000Z 13.3N 98.0W 40 KT 45 MPH 48H 22/1200Z 13.8N 100.0W 40 KT 45 MPH 72H 23/1200Z 16.5N 103.5W 35 KT 40 MPH 96H 24/1200Z 19.0N 106.0W 25 KT 30 MPH 120H 25/1200Z...ABSORBED BY WILLA $$ Forecaster Avila

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Tropical Depression Twenty-Four-E Forecast Discussion Number 1

2018-10-20 11:06:03| National Hurricane Center (East Pacific)

Issued at 400 AM CDT Sat Oct 20 2018 000 WTPZ44 KNHC 200905 CCA TCDEP4 Tropical Depression Twenty-Four-E Discussion Number 1...Corrected NWS National Hurricane Center Miami FL EP242018 400 AM CDT Sat Oct 20 2018 Corrected advisory number from 2 to 1 Various satellite data indicate that the area of low pressure that NHC has been monitoring off the coast of southern Mexico for thew past few days has acquired enough convective organization to be designated as a tropical depression, the twenty-fourth one of the very busy 2018 eastern North Pacific hurricane season. Although the depression is a sheared system, some banding features have recently developed south of the center, while overshooting cloud tops just west of the center are quite cold -85 to -91 deg C). The initial intensity is set to 30 kt based on a satellite intensity estimate of T2.0/30 kt from both TAFB and SAB. The initial motion estimate is 280/08 kt, based primarily on passive microwave fixes and GOES-16 nighttime imagery. A gradual turn toward the west-northwest is expected by this afternoon, followed by a slower northwestward motion on Sunday as the system moves along the southwestern periphery of a weakening mid-level ridge. A slow northwestward motion is expected to continue into early next week while the ridge to the north changes little. On days 4 and 5, however, a series of weak shortwave troughs are forecast to move through the larger scale southwesterly flow locked in over the southwestern U.S. and northern Mexico, causing an erosion of the western portion of the ridge, which should allow the cyclone to gradually recurve northward and north-northeastward. The NHC model guidance is in good agreement overall on this developing track scenario, and the official forecast track lies between the HCCA and TVCE track consensus aids. The depression is expected to steadily strengthen during the next 96 hours due to very favorable environmental conditions consisting of low vertical wind shear (less than 10 kt), high amounts of mid-level moisture, and warm 28-30 deg C SSTs. As a result, the cyclone is expected to become a tropical storm later this morning, a hurricane by Sunday night, and be near major hurricane strength by Wednesday. Given the very favorable conditions expected on Sunday and Monday, there is a fair chance of rapid intensification occurring similar to that depicted by the COAMPS-TC and HMON models, which bring the cyclone to category-4 status around 72 hours. The NHC official intensity forecast near the HCCA and IVCN consensus models through 96 hours, and then a little above the guidance at 120 hours despite an increase in the shear expected at that time. FORECAST POSITIONS AND MAX WINDS INIT 20/0900Z 15.1N 104.9W 30 KT 35 MPH 12H 20/1800Z 15.5N 105.7W 40 KT 45 MPH 24H 21/0600Z 15.9N 106.6W 50 KT 60 MPH 36H 21/1800Z 16.5N 107.4W 60 KT 70 MPH 48H 22/0600Z 17.1N 108.0W 75 KT 85 MPH 72H 23/0600Z 18.0N 109.0W 90 KT 105 MPH 96H 24/0600Z 19.2N 109.4W 100 KT 115 MPH 120H 25/0600Z 21.7N 108.5W 95 KT 110 MPH $$ Forecaster Stewart

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