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Tropical Depression Twenty-Two Forecast Discussion Number 4
2020-09-18 16:49:10| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Fri Sep 18 2020 000 WTNT42 KNHC 181449 TCDAT2 Tropical Depression Twenty-Two Discussion Number 4 NWS National Hurricane Center Miami FL AL222020 1000 AM CDT Fri Sep 18 2020 Satellite imagery indicates that Tropical Depression Twenty-Two is getting better organized, with gradually increasing convective banding in the northeastern semicircle. Satellite intensity estimates include 35 kt from TAFB, 30 kt from SAB, and 35 kt from CIMSS satellite consensus, which means the depression is close to tropical-storm strength. Given the lack of organization seen in earlier scatterometer data, the intensity will be held at 30 kt pending the data from the next set of scatterometer overpasses. It should be noted that the Air Force Reserve Hurricane Hunter aircraft that was scheduled to investigate the depression had to turn back after getting hit by lightning. The initial motion is a somewhat uncertain 015/6. For the next 24 h or so, the cyclone should move north-northeastward as it is steered by a mid- to upper-level trough over Texas and northeastern Mexico. This trough is then expected to lift out to the northeast, with low- to mid-level ridging building to the north of the cyclone. This should cause a westward turn at a continued slow forward speed. Near the end of the forecast period, a mid-latitude trough over the central United States should cause the ridge to weaken and steer the cyclone northward to northeastward near the Texas coast. While the guidance agrees with this general sense of the motion, there are a lot of differences in the models on the when's and where's of the various turns. Therefore, it is critical that users not focus on the exact forecast track, especially at days 4 and 5 when the average NHC forecast error is about 175 and 200 miles, respectively. The depression is currently in an environment of light to moderate southwesterly shear, and the global models suggest that this will generally continue through the forecast period. This, combined with forecast dry air entrainment near the 72 h point, has resulted in the intensity guidance keeping the system near to below hurricane strength through the forecast period. The new intensity forecast is changed little from the previous one and calls for the cyclone to be at hurricane strength at 60 and 72 h. However, this part of the forecast lies at the upper edge of the intensity guidance envelope. Key Messages: 1. Tropical Depression Twenty-Two is expected to strengthen to a tropical storm, and possibly a hurricane, while moving slowly over the western Gulf of Mexico during the next few days. 2. There is an increasing risk of heavy rainfall and flooding along the Texas coast from Sunday through at least the middle of next week as the system is forecast to move slowly near the Texas coast. For additional information, see products from your local National Weather Service office. 3. While it is too early to determine what areas could see direct wind and storm surge impacts from this system, interests throughout the western Gulf of Mexico should monitor the progress of this system and future updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 23.8N 93.9W 30 KT 35 MPH 12H 19/0000Z 24.8N 93.6W 35 KT 40 MPH 24H 19/1200Z 25.9N 93.4W 45 KT 50 MPH 36H 20/0000Z 26.3N 93.8W 50 KT 60 MPH 48H 20/1200Z 26.5N 94.6W 60 KT 70 MPH 60H 21/0000Z 26.6N 95.6W 65 KT 75 MPH 72H 21/1200Z 26.9N 96.2W 65 KT 75 MPH 96H 22/1200Z 27.5N 96.5W 60 KT 70 MPH 120H 23/1200Z 28.5N 95.5W 55 KT 65 MPH $$ Forecaster Beven
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