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Tropical Depression Eta Forecast Discussion Number 27
2020-11-07 09:56:14| National Hurricane Center (Atlantic)
Issued at 400 AM EST Sat Nov 07 2020 593 WTNT44 KNHC 070856 TCDAT4 Tropical Depression Eta Discussion Number 27 NWS National Hurricane Center Miami FL AL292020 400 AM EST Sat Nov 07 2020 Satellite images show a large area of deep convection associated with Eta, but there is not much organization to the thunderstorm activity. An ASCAT-A pass from several hours ago showed that the circulation of Eta has become a little better defined, and the center was located a fair distance to the west-southwest of what was previously analyzed. The pass also showed that Eta has not strengthened to a tropical storm yet, with the maximum winds in the 25-30 kt range. Based on that data, and a blend of the latest Dvorak classifications, the initial intensity is held at 30 kt. After adjusting the initial position, the estimated motion is a little slower to the east-northeast than before, 060/9 kt. It should be noted that some of the models show the center re-forming to the northeast later today, which is possible given the depression's convective asymmetry. Regardless of these details, the large scale track forecast reasoning is unchanged. A continued east-northeast to northeast motion is expected during the next day or two as Eta moves in the flow on the east side of a mid- to upper-level trough over the Gulf of Mexico. This motion should take Eta near or to the west of the Cayman Islands later today and over central Cuba tonight and Sunday. After that time, the mid- to upper-level low is expected to cut off over the eastern Gulf of Mexico or the Florida Straits. As a result, Eta will pivot around the low, which should cause a slow down and a turn to the north and then the northwest toward the Florida Keys and south Florida Sunday night and Monday. As Eta merges with the upper low, a slower motion to the northwest or north is forecast across the eastern Gulf of Mexico by the middle of next week. The NHC track forecast lies between the GFS and ECMWF models, and is quite similar to the previous one. Eta is expected to gradually strengthen on its approach to Cuba as it remains over warm waters and in an region of upper-level diffluence. However, by the time Eta reaches Cuba, the models show an increase in southwesterly wind shear and drier air being drawn into the circulation. These factors should cause Eta to level off in strength, and likely become asymmetric. When Eta interacts and merges with the upper low, it will likely take on a subtropical appearance and develop a large wind field near southern Florida. The storm is forecast to slowly weaken when it passes to the west of Florida as it moves in a drier environment. The NHC intensity forecast is largely an update of the previous one and lies near the high end of the model guidance. Based on the new forecast, the government of the Bahamas has issued a Tropical Storm Warning for the northwestern Bahamas. In addition, the Tropical Storm Watch along the east coast of Florida has been extended northward. 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 continue across the Cayman Islands and portions of Cuba, resulting in significant, life-threatening flash flooding and river flooding in Cuba. Flash and urban flooding will also be possible for the Cayman Islands, Jamaica, the Bahamas and southern Florida. 2. Tropical storm conditions are expected later today and Sunday in portions of the Cayman Islands, Cuba, and the northwestern Bahamas, where a Tropical Storm Warning is in effect. 3. Tropical storm conditions are possible in the Florida Keys and portions of south and central Florida beginning late Sunday, where a Tropical Storm Watch is in effect. Tropical Storm Warnings could be required for these areas later today. FORECAST POSITIONS AND MAX WINDS INIT 07/0900Z 18.3N 84.9W 30 KT 35 MPH 12H 07/1800Z 19.3N 82.9W 40 KT 45 MPH 24H 08/0600Z 20.7N 80.9W 45 KT 50 MPH 36H 08/1800Z 22.6N 80.2W 50 KT 60 MPH...INLAND 48H 09/0600Z 23.8N 80.2W 55 KT 65 MPH...OVER WATER 60H 09/1800Z 24.9N 81.2W 55 KT 65 MPH 72H 10/0600Z 25.5N 83.7W 50 KT 60 MPH 96H 11/0600Z 26.0N 84.7W 45 KT 50 MPH 120H 12/0600Z 27.3N 85.0W 40 KT 45 MPH $$ Forecaster Cangialosi
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