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Tropical Depression Eta Forecast Discussion Number 25
2020-11-06 21:59:38| National Hurricane Center (Atlantic)
Issued at 300 PM CST Fri Nov 06 2020 000 WTNT44 KNHC 062059 TCDAT4 Tropical Depression Eta Discussion Number 25 NWS National Hurricane Center Miami FL AL292020 300 PM CST Fri Nov 06 2020 Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that the center of Eta is elongated east-to-west with multiple vorticity centers present. The central pressure is near 1002 mb, and the maximum flight-level winds were 30-35 kt at 1500 ft. There were a few spot reports of 35-45 kt winds from the Stepped Frequency Microwave Radiometer, but these were in areas of heavy rain and their reliability is suspect. Based on these data, the initial intensity is kept at 30 kt. The aircraft data shows that the center is farther south than previously thought, and the initial motion is an uncertain 040/6 kt. There is no change to the previous track forecast philosophy. A developing mid- to upper-level trough over the Gulf of Mexico is expected to steer Eta northeastward for the next 48 h or so with an increase in forward speed. Between 48-72 h, the trough is forecast to become a closed low near south Florida and western Cuba, causing Eta to turn northwestward around and into the low. After 72 h, the merged system is likely to move slowly westward to northwestward. While the guidance is in good agreement on the synoptic evolution, there remain differences in the track forecast details in terms of both the heading and the forward speed, with the GFS-based guidance tending to be to the east and north of the UKMET/ECMWF/Canadian. In addition, the HWRF/HMON/Canadian are faster than the other guidance. The new forecast track overall is a little slower than the previous track, and due to the initial position the first 36 h have been shifted southward. Eta will move over the warm waters of the northwestern Caribbean during the next 48 h or so, and the upper-level divergence is forecast to be quite strong. This should allow some strengthening, although this is likely to be slowed by 20-30 kt of southwesterly vertical wind shear. The intensity forecast for this part of the cyclone's life is again similar to the previous forecast and lies near the bulk of the intensity guidance. Between 48-72 h , Eta may take on at least some subtropical cyclone characteristics as it merges with the mid- to upper-level low. The HWRF and HMON models still suggest the possibility that a tight inner wind core may develop, however, the guidance has trended weaker since this morning, and the new intensity forecast is above the bulk of the guidance. After 72 h, dry air entrainment is expected to cause the cyclone to weaken. The wind field of Eta is expected to increase in size during the next few days, and the cyclone will likely produce a large area of tropical-storm-force winds on its north side when it is near Cuba, the Florida Keys, and southern Florida. The new forecast track requires a Tropical Storm Warning for portions of Cuba at this time. Watches may be required for portions of south Florida and the Florida Keys tonight. Key Messages: 1. Heavy rainfall is diminishing across portions of Central America, although the threat of life-threatening flooding may continue, along with landslides in areas of higher terrain. Heavy rainfall from Eta will move into the Cayman islands and portions of Cuba, resulting in significant, life-threatening flash flooding and river flooding. Flash flooding and urban flooding is also possible for Jamaica and southeast Mexico. 2. Tropical storm conditions are expected this weekend in portions of the Cayman Islands and Cuba, where a Tropical Storm Warning is in effect. 3. There is an increasing risk of impacts from wind and flash and urban flooding due to heavy rainfall in portions of southern Florida, the Florida Keys, and portions of the Bahamas this weekend and early next week. Tropical Storm or Hurricane Watches will likely be issued for a portion of this area tonight. FORECAST POSITIONS AND MAX WINDS INIT 06/2100Z 17.3N 86.5W 30 KT 35 MPH 12H 07/0600Z 18.2N 84.8W 35 KT 40 MPH 24H 07/1800Z 19.4N 82.5W 40 KT 45 MPH 36H 08/0600Z 20.8N 80.7W 45 KT 50 MPH 48H 08/1800Z 22.5N 80.0W 50 KT 60 MPH...INLAND 60H 09/0600Z 24.2N 80.6W 55 KT 65 MPH...OVER WATER 72H 09/1800Z 24.9N 81.8W 55 KT 65 MPH 96H 10/1800Z 25.0N 84.0W 50 KT 60 MPH 120H 11/1800Z 26.5N 85.5W 50 KT 60 MPH $$ Forecaster Beven
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