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Tropical Depression Thirty-One Forecast Discussion Number 1
2020-11-13 16:05:07| National Hurricane Center (Atlantic)
Issued at 1000 AM EST Fri Nov 13 2020 000 WTNT41 KNHC 131504 CCA TCDAT1 Tropical Depression Thirty-One Discussion Number 1...Corrected NWS National Hurricane Center Miami FL AL312020 1000 AM EST Fri Nov 13 2020 Corrected the time from EDT to EST Deep convection associated with the area of low pressure over the central Caribbean Sea has increased and become more concentrated since yesterday. One-minute GOES-16 visible satellite imagery shows that the circulation has also become better defined, with a westerly component seen in the low-cloud motion near the southwestern edge of the primary convective mass. Subjective Dvorak intensity estimates from both TAFB and SAB are T2.0, indicating that the convection has become sufficiently organized for the system to be classified as a tropical depression. The initial wind speed is set at 30 kt, in line with the Dvorak classifications. Environmental conditions of low vertical wind shear, warm sea surface temperatures, and a moist atmosphere favor intensification over the next few days. Given the current broad and sprawling structure of the system, strengthening may begin as gradual today, but once an inner core organizes, steady-to-rapid strengthening appears likely. While the SHIPS rapid intensification index does not show very high chances of rapid strengthening for any one 24-h period over the next few days, it does indicate a 50/50 chance (nearly 10 times the climatological mean) of a 65-kt increase in wind speed over the next 72 hours. As a result, the NHC forecast calls for significant strengthening during the 24 to 72 hour time period, and the system could approach the coast of Central America as a major hurricane in a few days. The NHC track forecast at days 4 and 5 shows the system weakening over land, however some of the track guidance keeps the system just off the coast on Honduras at that time. If a more northern track occurs, the system could be stronger at 96 and 120 h if it remains over water. The depression is moving west-southwestward at about 6 kt. A strong mid-level ridge that lies over Florida and the western Atlantic should steer the cyclone west-southwestward during the next 12 to 24 hours. After that time, the ridge is forecast to begin sliding eastward, and a westward to west-northwestward motion should begin. On the foreast track, the cyclone is expected to approach the coast of Central America in 60-72 h. The track guidance is in good agreement through the first couple of days, but there is increasing cross-track spread after that time. The HMON, HWRF, and GFS show a track near or north of the coast of Honduras after 72 hours, while the ECMWF and UKMET are farther south. For now, the NHC track is near the middle of the guidance envelope between the HFIP corrected consensus model and the TCVA multi-model consensus. Key Messages: 1. The depression is expected to strengthen to a hurricane while it approaches the coast of Central America, and there is a risk of dangerous wind, storm surge, and rainfall impacts across portions of Nicaragua and Honduras beginning Sunday night. Hurricane Watches will likely be issued for a portion of this area tonight. 2. Through Wednesday morning, heavy rainfall from Tropical Depression Thirty-One may lead to life-threatening flash flooding and river flooding across portions of Haiti, Jamaica and Central America. Flooding and landslides from heavy rainfall could be significant across Central America given recovery efforts underway after Hurricane Eta. FORECAST POSITIONS AND MAX WINDS INIT 13/1500Z 14.2N 74.3W 30 KT 35 MPH 12H 14/0000Z 14.0N 75.0W 35 KT 40 MPH 24H 14/1200Z 13.8N 76.0W 45 KT 50 MPH 36H 15/0000Z 13.9N 77.3W 60 KT 70 MPH 48H 15/1200Z 14.1N 79.0W 70 KT 80 MPH 60H 16/0000Z 14.5N 80.9W 85 KT 100 MPH 72H 16/1200Z 14.9N 82.7W 95 KT 110 MPH 96H 17/1200Z 15.2N 85.7W 50 KT 60 MPH...INLAND 120H 18/1200Z 14.7N 88.3W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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