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Tropical Storm Elsa Forecast Discussion Number 4
2021-07-01 16:53:09| National Hurricane Center (Atlantic)
Issued at 1100 AM AST Thu Jul 01 2021 000 WTNT45 KNHC 011453 TCDAT5 Tropical Storm Elsa Discussion Number 4 NWS National Hurricane Center Miami FL AL052021 1100 AM AST Thu Jul 01 2021 Just-received scatterometer data showed 35-40 kt winds to the northeast of the center, so the initial intensity is increased to 40 kt. Some slight revisions were also made to the initial and forecast wind radii. Over all, the organization of the storm has changed little during the past several hours, with the low-level center partly exposed to the north and northwest of the primary convective band. Elsa continues to move a little faster with the initial motion now 280/24. 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 ECMWF ensemble mean forecast a turn toward the north while the GFS and UKMET are forecasting a west-northwestward to northwestward motion. The latter part of the new NHC forecast track will lean more toward the GFS/UKMET solutions at this time, but the large spread in both the deterministic models and the ensembles make this part of the forecast of low confidence. The new official forecast track has only minor adjustments from the previous forecast. Some additional 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 some decoupling of the lower and upper parts of the storm, and this could limit strengthening. The latter part of the intensity forecast also has high uncertainty due to the possibility of land interaction and disagreements among the global models on how favorable the upper-level winds will be. 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. 2. Heavy rainfall from Elsa will move quickly across the Windward and southern Leeward Islands, including Barbados, on Friday, with outer rain bands impacting Puerto Rico Friday into Saturday. Isolated flash flooding and mudslides are possible. 3. There is a risk of wind and rainfall impacts in portions of Hispaniola, Cuba, 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 southern 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 01/1500Z 10.1N 51.4W 40 KT 45 MPH 12H 02/0000Z 11.2N 54.9W 45 KT 50 MPH 24H 02/1200Z 12.6N 59.9W 50 KT 60 MPH 36H 03/0000Z 14.1N 64.9W 50 KT 60 MPH 48H 03/1200Z 15.9N 69.8W 50 KT 60 MPH 60H 04/0000Z 17.6N 73.6W 50 KT 60 MPH 72H 04/1200Z 19.3N 76.5W 45 KT 50 MPH 96H 05/1200Z 22.0N 80.5W 50 KT 60 MPH 120H 06/1200Z 25.6N 82.5W 50 KT 60 MPH $$ Forecaster Beven
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