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Tropical Storm Elsa Forecast Discussion Number 5
2021-07-01 22:47:12| National Hurricane Center (Atlantic)
Issued at 500 PM AST Thu Jul 01 2021 000 WTNT45 KNHC 012047 TCDAT5 Tropical Storm Elsa Discussion Number 5 NWS National Hurricane Center Miami FL AL052021 500 PM AST Thu Jul 01 2021 The structure of Elsa has changed little since the last advisory, with the low-level center partly exposed to the northwest of the somewhat-ragged primary convective band. Various subjective and objective satellite intensity estimates have changed little during the last 6 h, so the initial intensity is held at 40 kt. The initial motion is now 285/25. There is little change to the track forecast philosophy from the previous advisory. A rapid west-northwestward motion is likely for the next 48 h or so as Elsa is steered by the strong subtropical ridge to the north. After that time, the storm is expected to approach a weakness in the ridge caused by a mid-latitude trough over the eastern United states. The guidance becomes rather divergent as this happens, as the ECWMF and the ECMWF ensembles forecast a turn toward the north while the GFS and UKMET are forecasting a continued west- northwestward to northwestward motion. In addition, the GFS ensemble members are spread from a continued west-northwestward motion toward the Yucatan Peninsula on one side to a northward motion east of the northern Bahamas on the other. The latter part of the new NHC forecast track will still lean more toward the deterministic GFS/UKMET solutions, but the confidence remains low. The new official forecast track again has only minor adjustments from the previous forecast. The intensity forecast and its high uncertainty are also little changed from the last advisory. Some strengthening is expected during the next day or so as Elsa is expected to be in an environment of warm sea-surface temperatures, light vertical wind shear, and high mid-level relative humidity. However, as mentioned earlier, the fast forward motion could result in the upper and lower parts of the storm being unable to stay together, and this could limit strengthening. The latter part of the intensity forecast also has the issues of possible land interaction and disagreements among the global models on how favorable the upper-level winds will be, although the latest model runs trended toward less favorable conditions north of about 22N. This uncertainty is highlighted by the UKMET forecasting Elsa to weaken to a trough near western Cuba while the GFS forecasts it to be a hurricane in the same area and time. Based on these factors, the NHC intensity forecast continues to be on the lower end of the intensity guidance suite. Key Messages: 1. Tropical storm conditions are expected beginning early Friday in portions of the Windward and southern Leeward Islands, and are possible over portions of southern Hispaniola on Saturday. 2. Heavy rainfall from Elsa will move quickly across the Windward and southern Leeward Islands, including Barbados, on Friday. Outer rain bands will impact Puerto Rico on Friday and southern Hispaniola by early Saturday. Flooding and mudslides are possible. 3. There is a risk of wind and rainfall impacts in portions of Cuba, Jamaica, the Turks and Caicos, and the Bahamas through early next week. Interests in these areas should monitor Elsa's progress and updates to the forecast. 4. There is a risk of storm surge, wind, and rainfall impacts in the Florida Keys and portions of the Florida Peninsula early next week. However, the forecast uncertainty remains larger than usual due to Elsa's potential interaction with the Greater Antilles this weekend. Interests in Florida should monitor Elsa's progress and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 01/2100Z 11.2N 53.8W 40 KT 45 MPH 12H 02/0600Z 12.1N 57.5W 45 KT 50 MPH 24H 02/1800Z 13.5N 62.4W 50 KT 60 MPH 36H 03/0600Z 15.1N 67.3W 50 KT 60 MPH 48H 03/1800Z 16.7N 71.6W 50 KT 60 MPH 60H 04/0600Z 18.3N 75.0W 50 KT 60 MPH 72H 04/1800Z 19.8N 77.9W 50 KT 60 MPH 96H 05/1800Z 22.5N 82.0W 50 KT 60 MPH 120H 06/1800Z 26.5N 83.5W 50 KT 60 MPH $$ Forecaster Beven
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