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Tropical Depression Twenty-two Forecast Discussion Number 2
2020-09-18 04:43:29| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Thu Sep 17 2020 000 WTNT42 KNHC 180243 TCDAT2 Tropical Depression Twenty-Two Discussion Number 2 NWS National Hurricane Center Miami FL AL222020 1000 PM CDT Thu Sep 17 2020 Inspection of flight-level wind data from the earlier Air Force Reserve mission indicates that the depression has a somewhat elongated circulation, but a sufficiently well-defined center and pressure minimum were found just to the west of NOAA buoy 42055. The plane measured maximum surface winds of 30 kt in the deep convection to the southwest of the center using the SFMR instrument, and that remains the initial intensity. As best as I can tell, the depression is moving very slowly northeastward with an initial motion of 035/3 kt. A positively tilted mid- to upper-level trough extends across Texas and northern Mexico, and this feature should cause the depression to move toward the north-northeast during the next 36 hours. The trough is expected to dissolve soon after that time, with a mid-tropospheric high building over the south-central United States. The high should force the cyclone to turn and move very slowly westward on days 3 and 4, and then potentially stall or meander off the lower Texas/ northeastern Mexico coast by day 5. There is lower-than-normal confidence in the official track forecast due to fairly significant spread among the track guidance. However, the models do agree on the general scenario, and they all suggest that the depression is unlikely to move a whole lot for the entire forecast period. This new NHC forecast lies very close to the TVCN multi-model consensus. Unfortunately, there is also significant uncertainty in the intensity forecast. Light-to-moderate southerly to southwesterly shear is expected to affect the depression for the next couple of days while it moves over very warm waters of 30-31 degrees Celsius and in a very moist environment. Things change quickly after 48 hours due to a cold front entering the northern Gulf, and the drier, more stable air mass behind the front could be entrained into the cyclone's circulation from day 3 to day 5. The GFS- and ECMWF-based SHIPS models show the most significant strengthening, bringing the intensity to 75-80 kt in about 3 days, while many of the other intensity models don't even raise it to hurricane intensity. As a compromise between these various solutions, the NHC intensity forecast shows the cyclone just reaching the hurricane threshold in 2-3 days and then gradually weakening thereafter due to the less favorable environment. However, it cannot be stressed enough that this forecast is highly uncertain. 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 18/0300Z 22.0N 94.2W 30 KT 35 MPH 12H 18/1200Z 22.9N 93.8W 35 KT 40 MPH 24H 19/0000Z 23.9N 93.3W 45 KT 50 MPH 36H 19/1200Z 24.8N 92.9W 55 KT 65 MPH 48H 20/0000Z 25.4N 93.2W 60 KT 70 MPH 60H 20/1200Z 25.6N 94.0W 65 KT 75 MPH 72H 21/0000Z 25.7N 94.8W 65 KT 75 MPH 96H 22/0000Z 26.1N 95.9W 60 KT 70 MPH 120H 23/0000Z 26.4N 96.0W 55 KT 65 MPH $$ Forecaster Berg
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