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Tropical Depression Twenty-Eight Forecast Discussion Number 2
2020-10-25 03:49:25| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat Oct 24 2020 774 WTNT43 KNHC 250248 CCA TCDAT3 Tropical Depression Twenty-Eight Discussion Number 2...Corrected NWS National Hurricane Center Miami FL AL282020 1100 PM EDT Sat Oct 24 2020 Corrected timing in Key Message number 3 Deep convection has increased during the past few hours south of the estimated low-level position based on aircraft data from just after the release of the previous advisory. In fact, geostationary imagery suggests that the low-level center could be trying to reform closer to the deep convection. The initial intensity is set to 30 kt based on the latest Dvorak estimate from SAB. Another NOAA Hurricane Hunter aircraft will investigate the system overnight and provide additional data on the cyclone's structure and intensity. As noted above, the depression hasn't moved much, and the system currently appears to be stationary. Satellite imagery and upper-air data show a shortwave trough moving through the southeastern United States, which has weakened the steering flow around the cyclone. As the shortwave moves eastward, the subtropical ridge will expand westward to the north of the tropical cyclone by Monday, which should result in a steadier west-northeastward motion. After that time, a powerful mid/upper-level low is forecast to eject out of the southwestern U.S., which will weaken the ridge and cause the tropical cyclone to turn northward and northeastward as it approaches the northern Gulf Coast. The global models are not in good agreement on the details of the timing of the eastward movement of the upper-low. While this isn't unusual, it results in significant differences in when and where the tropical cyclone turns and exactly where it crosses the Gulf Coast next week, with model solutions ranging from Louisiana to the Florida Panhandle. The new NHC track forecast lies near the middle of the guidance envelope between the HCCA and the TVCA multi-model consensus. However, given the current lack of motion of the system and the large model spread late in the period, the details of the track forecast are more uncertain than usual. If the cyclone's low- and mid-level circulations can become better aligned, the environment for the next 2 to 3 days appears conducive for steady intensification, with low shear and SSTs of near 30C in the northwestern Caribbean and above 28C in the southern Gulf. After 72 hours, the shear is expected to increase while the cyclone moves over cooler SSTs near the northern Gulf Coast, which should result in weakening before the center moves inland. The new NHC intensity forecast is a bit higher than the previous one through about 60 hours, and is a blend of the latest intensity consensus aids and HCCA. While the current NHC forecast indicates that the system should weaken below hurricane strength before landfall, users are reminded that strong tropical storms can still produce significant storm surge, rainfall, and wind impacts along the northern Gulf Coast. The cyclone should be absorbed into a frontal system by the end of the forecast period. KEY MESSAGES: 1. The depression is forecast to strengthen to a tropical storm by Sunday and tropical storm conditions are expected in extreme western Cuba on Monday. Tropical storm conditions are possible in the northern Yucatan Peninsula of Mexico Monday night and early Tuesday. 2. Through Wednesday, heavy rainfall is expected across portions of central and western Cuba, the Cayman Islands, Jamaica, the northeast Yucatan peninsula of Mexico, southern Florida and the Florida Keys. This rainfall may lead to flash flooding in urban areas. 3. The system is forecast to approach the northern Gulf Coast as a tropical storm Tuesday night and Wednesday, and could bring storm surge, rainfall, and wind impacts to areas from Louisiana to the Florida Panhandle. Residents in these areas should monitor the progress of the depression and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 25/0300Z 18.9N 83.1W 30 KT 35 MPH 12H 25/1200Z 19.2N 83.3W 35 KT 40 MPH 24H 26/0000Z 20.0N 83.7W 40 KT 45 MPH 36H 26/1200Z 20.7N 84.9W 50 KT 60 MPH 48H 27/0000Z 21.7N 86.6W 55 KT 65 MPH 60H 27/1200Z 23.2N 88.6W 65 KT 75 MPH 72H 28/0000Z 25.4N 90.3W 65 KT 75 MPH 96H 29/0000Z 31.5N 89.5W 40 KT 45 MPH...INLAND 120H 30/0000Z...ABSORBED $$ Forecaster Brennan
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