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Tropical Depression Twenty-Two Forecast Discussion Number 3
2020-09-18 10:39:30| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Fri Sep 18 2020 000 WTNT42 KNHC 180839 TCDAT2 Tropical Depression Twenty-Two Discussion Number 3 NWS National Hurricane Center Miami FL AL222020 400 AM CDT Fri Sep 18 2020 The depression is still not very well organized. It's surface wind circulation appears to be elongated from southwest to northeast and deep convection is mostly limited to the northeast quadrant of the cyclone. Overnight ASCAT data and the latest TAFB Dvorak estimate both support an intensity of 30 kt. An Air Force Reserve Hurricane Hunter aircraft is scheduled to investigate the system later this morning and should provide more information about the structure of the cyclone. Confidence in the details of the track forecast remain low at this time. Due to the slow forward speed of the cyclone expected into next week, small fluctuations in the depression's heading or speed could have very large implications on any hazards experienced along the Mexico or Texas coasts. 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. My long-term motion estimate is 025/5 kt, but in reality the depression's movement has been unsteady since it formed yesterday. There is still good general agreement that the system will move slowly north-northeastward for about 36 h, and then turn westward as a ridge builds over the southeast United States. The cyclone will then likely inch closer to the northern Mexico or southern Texas coasts. The details of this evolution vary greatly from model to model and the track guidance spread is higher than usual. The most certain aspect of the forecast is that the depression will not be moving anywhere very quickly well into next week. Although the depression is located within an environment supportive of intensification, only slow strengthening is likely until it gets better organized. Beyond 72 h, the cyclone will begin to interact with a cold front and the drier, more stable air behind it. This should at the very least end any intensification and could lead to weakening. Interaction with land could also cause the system to weaken. The latest statistical intensity guidance is less aggressive, but those models still show the system becoming a hurricane within a couple of days, while the dynamical hurricane models (HWRF, HMON, COAMPS-TC) do not strengthen it quite that much. For now the NHC intensity forecast is largely unchanged and is at the top end of the 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. While it is too early to determine what areas could see direct wind, storm surge, and rainfall 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 18/0900Z 22.9N 94.1W 30 KT 35 MPH 12H 18/1800Z 23.7N 93.7W 35 KT 40 MPH 24H 19/0600Z 24.9N 93.2W 45 KT 50 MPH 36H 19/1800Z 25.7N 93.2W 50 KT 60 MPH 48H 20/0600Z 25.9N 93.8W 60 KT 70 MPH 60H 20/1800Z 26.0N 94.6W 65 KT 75 MPH 72H 21/0600Z 26.3N 95.6W 65 KT 75 MPH 96H 22/0600Z 26.7N 96.3W 60 KT 70 MPH 120H 23/0600Z 27.5N 96.0W 55 KT 65 MPH $$ Forecaster Zelinsky
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