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Tropical Depression Eta Forecast Discussion Number 21
2020-11-05 21:54:22| National Hurricane Center (Atlantic)
Issued at 300 PM CST Thu Nov 05 2020 000 WTNT44 KNHC 052054 TCDAT4 Tropical Depression Eta Discussion Number 21 NWS National Hurricane Center Miami FL AL292020 300 PM CST Thu Nov 05 2020 The low-level circulation of Eta has become disorganized to the point that the system more resembles a remnant low than a tropical cyclone. However, the system continues to produce convection in an area just north and northwest of the estimated center position, as well as in a cluster well to the northeast. Based on this, and the expectation that the system will start re-developing during the next several hours as it moves back over water, Eta is maintained as a tropical depression for this advisory. The initial intensity is increased to 30 kt based on scatterometer data, with those winds occuring well to the northeast of the center. The center appears to be just south of the northwestern coast of Honduras, and the initial motion is an uncertain 330/7. During the next 24 h, Eta should recurve northeastward in southwesterly flow between a ridge over the central Caribbean and a developing mid- to upper-level trough over the central Gulf of Mexico. This motion should persist through about 72 h. After that, the trough is forecast to become a closed low in the vicinity of western Cuba, with Eta turning to the west-northwest as it interacts or merges with the low. While the models are in good agreement with the synoptic pattern, they are in poor agreement on the details of the track. The forecast tracks show possible landfalls in Cuba anywhere between 77W-83W, and after the turn some of the tracks are as far north as southern Florida while other stay over Cuba. In addition, there is a significant speed difference between the faster GFS/HWRF/HMON and the slower Canadian/ECMWF/UKMET. The low-confidence official forecast compromises between these various extremes and is not changed much from the previous forecast. Little change in strength is expected during the next 12 h or so as Eta starts to re-organized over water. After that, gradual strengthening is expected until the system reaches Cuba in about 72 h, with the main limiting factor being increasing southwesterly shear during that time. From 72-120 h, there is a possibility that Eta will take on subtropical or hybrid characteristics as it interacts with the developing upper-level low. The intensity forecast will be held at 50 kt during that time due to this interaction. The new intensity forecast has only minor tweaks from the previous forecast. However, it lies below the bulk of the intensity guidance for the first 60 h and above the bulk of the guidance from 72-120 h. The new forecast track, intensity, and wind radii require a Tropical Storm Watch for the Cayman Islands at this time. A Tropical Storm Watch will likely be required for portions of Cuba later tonight or on Friday. Key Messages: 1. Through Monday morning, heavy rainfall from Eta will lead to catastrophic, life-threatening flash flooding and river flooding across portions of Central America, along with landslides in areas of higher terrain. Flash and river flooding is also possible across Jamaica, southeast Mexico, the Cayman Islands and western Cuba. 2. Eta is forecast to regain tropical storm strength over the northwestern Caribbean Sea in a day or so. Although the details of the future track and intensity of Eta are uncertain, there is an increasing risk of impacts from wind and rainfall in portions of the Cayman Islands, Cuba, southern Florida and the Florida Keys this weekend and early next week. FORECAST POSITIONS AND MAX WINDS INIT 05/2100Z 15.7N 87.7W 30 KT 35 MPH...INLAND 12H 06/0600Z 16.4N 87.8W 30 KT 35 MPH...OVER WATER 24H 06/1800Z 18.1N 86.3W 35 KT 40 MPH 36H 07/0600Z 19.1N 84.8W 40 KT 45 MPH 48H 07/1800Z 20.1N 83.1W 45 KT 50 MPH 60H 08/0600Z 21.3N 81.5W 45 KT 50 MPH 72H 08/1800Z 22.4N 80.1W 50 KT 60 MPH...INLAND 96H 09/1800Z 23.5N 82.0W 50 KT 60 MPH...OVER WATER 120H 10/1800Z 24.5N 84.5W 55 KT 65 MPH $$ Forecaster Beven
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