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Tropical Storm Laura Forecast Discussion Number 20
2020-08-24 22:45:19| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Aug 24 2020 000 WTNT43 KNHC 242045 TCDAT3 Tropical Storm Laura Discussion Number 20 NWS National Hurricane Center Miami FL AL132020 500 PM EDT Mon Aug 24 2020 The satellite presentation of the tropical storm has improved somewhat with deep convection remaining over the center, and an increase in banding over the southeastern portion of the circulation. Earlier aircraft and scatterometer data, however, indicated that there has been little change in strength today, and the initial intensity remains 50 kt. These observations have shown the the stronger winds are located in the convective band well east and southeast of the center, and that the system currently lacks an inner core. This is likely the reason that Laura has not been able to strengthen while it has moved over water today. The aircraft also reported a fairly stable minimum pressure of 1001-1003 mb during its mission this morning and early afternoon. The intensity forecast philosophy remains the same as the previous advisory. Once Laura moves over the southeastern Gulf of Mexico tonight, a combination of warm sea surface temperatures and low vertical wind shear should allow for steady strengthening. The latest iterations of the global and regional hurricane models continue to show significant deepening while Laura traverses the Gulf of Mexico, and a period or rapid strengthening is possible once an inner core is able to organize. The statistical guidance is again on the lower side of the intensity forecast envelope while the HWRF and CTCI models bringing Laura to major hurricane strength. The NHC intensity forecast is again between these solutions and is close to the consensus aids. The initial motion estimate is 290/16 kt. A deep-layer ridge over the western Atlantic is expected to build westward during the next day or so. By early Wednesday, a mid- to upper-level trough over the south-central United States is forecast to erode the western portion of the ridge, which should cause Laura to turn northwestward and then northward toward the northwestern Gulf coast. After landfall, Laura or its remnants are expected to become embedded in the mid-latitude westerlies and recurve over the eastern U.S. on days 4 and 5. The latest runs of the dynamical models are in a little better agreement, but the 1200 UTC ECMWF ensemble mean is located considerably left of its deterministic run, indicating that uncertainty regarding the track forecast remains. Users are again reminded to not to focus on the exact details of the track or intensity forecasts as the average NHC track error at 60 h is around 90 miles and the average intensity error is close to 15 mph. In addition, wind, storm surge, and rainfall hazards will extend far from the center. The new NHC forecast necessitates the issuance of storm surge and hurricane watches for portions of the U.S. Gulf Coast. Key Messages: 1. Laura is forecast to reach the northwestern Gulf Coast as a hurricane late Wednesday and early Thursday. Do not focus on the details of the official forecast given the typical uncertainty in NHC's 2 to 3 day track and intensity predictions. In addition, storm surge, wind, and rainfall hazards will extend well away from Laura's center along the Gulf Coast. 2. There is a risk of life-threatening storm surge from San Luis Pass, Texas, to Ocean Springs, Mississippi, within the next 48 hours, and a storm surge watch has been issued for these areas outside of the southeast Louisiana Hurricane and Storm Damage Risk Reduction System. Residents in these areas should follow any advice given by local officials. 3. Hurricane conditions are possible by late Wednesday from Port Bolivar, Texas, to west of Morgan City, Louisiana, with tropical storm conditions possible by Wednesday afternoon, and a hurricane watch has been issued. Additional hurricane watches may be needed farther south along the Texas coast if the track forecast shifts toward the south and west tonight and Tuesday. 4. Tropical storm conditions and heavy rainfall are expected across central and western Cuba through tonight. These rains could cause mudslides and life-threatening flash and urban flooding. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 21.7N 82.2W 50 KT 60 MPH 12H 25/0600Z 22.7N 84.5W 50 KT 60 MPH 24H 25/1800Z 24.2N 87.4W 60 KT 70 MPH 36H 26/0600Z 25.7N 90.0W 75 KT 85 MPH 48H 26/1800Z 27.5N 92.0W 85 KT 100 MPH 60H 27/0600Z 29.8N 93.1W 90 KT 105 MPH 72H 27/1800Z 32.5N 93.0W 45 KT 50 MPH...INLAND 96H 28/1800Z 36.1N 90.0W 25 KT 30 MPH...INLAND 120H 29/1800Z 36.5N 80.5W 25 KT 30 MPH...POST-TROP/REMNT LOW $$ Forecaster Brown
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