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Tropical Storm Elsa Forecast Discussion Number 15
2021-07-04 05:00:03| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Sat Jul 03 2021 000 WTNT45 KNHC 040259 TCDAT5 Tropical Storm Elsa Discussion Number 15 NWS National Hurricane Center Miami FL AL052021 1100 PM EDT Sat Jul 03 2021 Elsa is undergoing a convective bursting pattern the past few hours, with some cold overshooting tops of -90 deg C east and northeast of the center. However, data from an Air Force Reserve reconnaissance aircraft indicate that this convective increase has not translated into an intensity increase. To the contrary, 5000-ft flight-level and SFMR surface winds have decreased while the central pressure has increased to 1004 mb. Based on the latest recon data, the intensity has been lowered to 55 kt. The aircraft has now climbed to 10,000 ft for safety reasons and will be penetrating the area of intense convection to check for stronger winds there. The initial motion estimate is now 295/15 kt. Elsa is forecast to gradually move around the western periphery of a deep-layer subtropical ridge over the next 96 hours, accompanied by an additional decrease in forward speed. The latest model guidance has continued to converge along the previous advisory track, with the corrected-consensus models HCCA and FSSE nearly on top of each other. The TCVA simple consensus model is also similar to the HCCA and FSSE models. However, out of respect for the slightly more westward GFS and GFS-ensemble models, which have performed admirably thus far with Elsa, the new official forecast lies a tad west of the aforementioned consensus models and lies nearly on top of the previous advisory track. After interacting with the mountainous terrain of southwestern Haiti, which could have caused some disruption in the low-level field despite the center remaining offshore, little change in intensity is expected tonight. However, some slight restrengthening could occur by Sunday afternoon as Elsa approaches the south-central coast of Cuba where the sea-surface temperatures are quite warm at more than 30 deg C and the water is deep. Weakening is expected after the cyclone moves across west-central Cuba, followed again by some slight restrengthening after Elsa emerges over the warm Gulf Stream in the Straits of Florida. Westerly vertical wind shear increasing to near 20 kt by 96 hours should prevent any significant strengthening from occurring. Elsa should become a very asymmetrical tropical cyclone late on day 3 and on day 4 with most of the heavy rain and strongest winds displaced along and to the east of the forecast track. The initial intensity is similar to the previous advisory and closely follows the simple and corrected consensus models. Given the remaining 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. Widespread heavy rain will move across southern Haiti and Jamaica tonight into Sunday where isolated to scattered flash flooding and mudslides will be possible. Heavy rain will then impact the Cayman Islands and Cuba Sunday into Monday resulting in significant flooding and mudslides over Cuba. As Elsa approaches the Florida Keys and Florida Peninsula early next week, isolated flash flooding and minor river flooding will be possible. 2. 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 and western Cuba Sunday night and Monday. 3. 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, and a Tropical Storm Watch is now in effect for portions of the Florida Keys. 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 elsewhere 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 04/0300Z 17.9N 75.3W 55 KT 65 MPH 12H 04/1200Z 19.2N 77.3W 55 KT 65 MPH 24H 05/0000Z 20.9N 79.4W 60 KT 70 MPH 36H 05/1200Z 22.5N 81.0W 50 KT 60 MPH...INLAND 48H 06/0000Z 24.1N 82.2W 45 KT 50 MPH...OVER WATER 60H 06/1200Z 26.0N 82.8W 50 KT 60 MPH 72H 07/0000Z 28.0N 83.0W 50 KT 60 MPH 96H 08/0000Z 32.7N 81.0W 45 KT 50 MPH...INLAND 120H 09/0000Z 37.7N 74.9W 35 KT 40 MPH...OVER WATER $$ Forecaster Stewart/Papin
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