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Tropical Depression Twenty Forecast Discussion Number 5
2020-09-13 22:34:19| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sun Sep 13 2020 000 WTNT45 KNHC 132034 TCDAT5 Tropical Depression Twenty Discussion Number 5 NWS National Hurricane Center Miami FL AL202020 500 PM AST Sun Sep 13 2020 The depression's center is a little closer to the deep convection compared to this morning, but the overall structure has not changed significantly. Based on this morning's ASCAT pass, and recent Dvorak estimates of T2.0 from TAFB and SAB, the initial intensity remains 30 kt. The northerly shear over the system has been analyzed to have decreased since this morning (now around 10 kt), which is probably why the center is closer to the convection. The shear is forecast to decrease further, and once the depression becomes more detached from the ITCZ/monsoon trough, it is expected to go through a significant phase of strengthening as it heads west toward higher oceanic heat content and a more unstable atmosphere. As discussed this morning, the GFS-based SHIPS guidance indicates that there is a 50-50 chance that the depression will strengthen by at least 65 kt during the next 3 days, which is 10 times higher than the climatological mean. And, all three regional hurricane models (HWRF, HMON, and COAMPS-TC), as well as the HCCA aid, show the cyclone becoming a major hurricane by the end of the forecast period. As a result, the NHC intensity forecast has been adjusted upward and now explicitly shows major hurricane strength on days 4 and 5. The motion remains west-northwestward (290/10 kt), with the depression located south of a large mid-level high centered over the central Atlantic. This feature should continue driving the system westward or west-northwestward for the next 2 days. After that time, the ridge is expected to shift northward, causing the potentially strengthening hurricane to move a little slower toward the northwest. Most of the track models are clustered close together, although the HWRF remains a southern outlier and the ECMWF model is a little slower and on the right side of the envelope. The new NHC track forecast has not moved much from the previous prediction and now lies closest to the HFIP Corrected Consensus. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 12.7N 37.6W 30 KT 35 MPH 12H 14/0600Z 13.2N 39.5W 35 KT 40 MPH 24H 14/1800Z 13.6N 42.1W 45 KT 50 MPH 36H 15/0600Z 14.1N 44.4W 60 KT 70 MPH 48H 15/1800Z 14.7N 46.3W 70 KT 80 MPH 60H 16/0600Z 15.6N 47.7W 80 KT 90 MPH 72H 16/1800Z 16.8N 49.0W 90 KT 105 MPH 96H 17/1800Z 19.5N 51.5W 100 KT 115 MPH 120H 18/1800Z 22.5N 54.0W 100 KT 115 MPH $$ Forecaster Berg
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