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Tropical Storm Elsa Forecast Discussion Number 13
2021-07-03 17:01:49| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Sat Jul 03 2021 000 WTNT45 KNHC 031501 TCDAT5 Tropical Storm Elsa Discussion Number 13 NWS National Hurricane Center Miami FL AL052021 1100 AM EDT Sat Jul 03 2021 Reports from an Air Force Reserve Hurricane Hunter aircraft and satellite imagery indicate that Elsa has weakened some since the last advisory. The aircraft reported maximum 700-mb flight-level winds of 64 kt well to the northeast of the center, and maximum surface winds estimates from the SFMR of about 55 kt. The aircraft-reported central pressure is near 999 mb and gradually rising, In addition, the center was exposed for a few hours, although it is now located at the northwestern edge of a new convective burst. Based on the aircraft data, the initial intensity is reduced to 60 kt. The initial motion is now 295/25. Elsa is approaching a weakness in the subtropical ridge caused by a large baroclinic trough over the eastern United States. The global models forecast this trough to move eastward into the Atlantic, but the southern portion is likely to split off and become an upper-level low pressure area over the western Gulf of Mexico, with the subtropical ridge over the Atlantic situated to the east of the this low. This evolution should cause Elsa to slow its current breakneck forward speed during the next day or so, then turn northwestward between 36-60 h, followed by a general northward motion from 72-96 h and recurvature into the westerlies after that time. The track guidance is in much better agreement than this time yesterday, and Elsa is expected to pass near or over southwestern Haiti, Cuba, and the eastern Gulf of Mexico or the Florida Peninsula during the next 3 days or so. After that, the system is likely to cross portions of the southeastern United States on its way into the Atlantic. The new NHC forecast track has only minor adjustments from the previous one, and it lies near the various consensus models. Elsa continues to be affected by northwesterly shear that is at least partly due to the fast forward motion. While the forward speed is forecast to decrease over the next few days, continued westerly shear and land interaction are expected to cause additional weakening. Indeed, by 60 h, the GFS, UKMET, and ECMWF show Elsa as a weak system with some separation between the low- and mid-level centers. While some shear is likely to continue when the storm is near or over the eastern Gulf of Mexico, upper-level divergence associated with the aforementioned upper-level low could allow for some re-intensification. The new NHC intensity forecast calls for more weakening in the first 48 h than previously forecast and then shows re-intensification over the Gulf of Mexico. Through the first 72 h, the forecast is at the upper edge of the intensity guidance. Although Elsa is now a tropical storm, hurricane warnings remain in effect for portions of the Dominican Republic and Haiti at this time, as conditions have not yet reached their worst there and the possibility that a short-lived re-intensification might occur due to a convective burst. Given that there is still uncertainty in the track forecast and the degree of land interaction with Hispaniola and Cuba, users are urged to factor in some of this uncertainty. For reference, average NHC track errors at days 3 and 4 are 125 miles and 150 miles, respectively. The average NHC intensity errors are around 15 mph for both days 3 and 4. Key Messages: 1. A hurricane warning remains in effect for portions of Haiti and the Dominican Republic, where near-hurricane conditions and dangerous storm surge are expected through this evening. 2. Widespread heavy rain will move across southern Hispaniola and Jamaica today into Sunday where isolated to scattered flash flooding and mudslides will be possible. Heavy rain will impact the Cayman Islands and Cuba Sunday into Monday, resulting in significant flooding and mudslides over Cuba. As Elsa approaches the Florida Keys and southern Florida early next week, isolated flash flooding and minor river flooding will be possible. 3. Tropical storm conditions and dangerous storm surge are expected with hurricane conditions possible in portions of eastern Cuba beginning early Sunday, with tropical storm conditions possible in central Cuba Sunday night and Monday. 4. There is an increasing risk of tropical storm conditions, storm surge, and rainfall impacts beginning Monday in the Florida Keys and the southern Florida Peninsula. This risk will spread northward along the Florida Peninsula through Wednesday and reach the coasts of Georgia and the Carolinas Wednesday and Thursday, however uncertainty in the forecast remains larger than usual due to Elsa's potential interaction with the islands of Hispaniola and Cuba. Interests in Florida and along the southeast U.S. coast should monitor Elsa's progress and updates to the forecast. FORECAST POSITIONS AND MAX WINDS INIT 03/1500Z 17.0N 71.6W 60 KT 70 MPH 12H 04/0000Z 18.1N 74.0W 60 KT 70 MPH 24H 04/1200Z 19.6N 76.7W 60 KT 70 MPH 36H 05/0000Z 21.2N 78.9W 55 KT 65 MPH 48H 05/1200Z 22.7N 80.5W 45 KT 50 MPH...INLAND 60H 06/0000Z 24.0N 81.8W 50 KT 60 MPH...OVER WATER 72H 06/1200Z 25.9N 82.5W 55 KT 65 MPH 96H 07/1200Z 30.0N 82.5W 50 KT 60 MPH...INLAND 120H 08/1200Z 35.0N 78.0W 35 KT 40 MPH...INLAND $$ Forecaster Beven
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