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Tropical Storm Laura Forecast Discussion Number 12
2020-08-22 22:52:19| National Hurricane Center (Atlantic)
Issued at 500 PM AST Sat Aug 22 2020 000 WTNT43 KNHC 222052 TCDAT3 Tropical Storm Laura Discussion Number 12 NWS National Hurricane Center Miami FL AL132020 500 PM AST Sat Aug 22 2020 A couple of hours ago an observing site on the southeast coast of Puerto Rico, Las Mareas, reported sustained winds of 52 kt. These winds were apparently associated with a mesocyclone embedded within the larger-scale circulation and not representative of the intensity of the tropical storm. Scatterometer data and WSR-88D Doppler velocities from San Juan support an intensity of 45 kt. Since the center should be moving over land for the next 48 hours or so, no additional intensification is anticipated until Monday night when the center moves over the southeastern Gulf of Mexico. Over warm waters, with anticipated weak vertical shear, and anticyclonic flow aloft, Laura will likely strengthen into a hurricane before it reaches the northern Gulf of Mexico coast. The NHC intensity forecast is close to the multi-model consensus, but given the possibility of a favorable upper-air environment over the Gulf, this forecast could be conservative. At this time it does not seem likely that Marco, which is forecast to make landfall on the north-central Gulf coast a day or two earlier than Laura, should have much of an influence on the latter system. Center locations from earlier scatterometer data, low-cloud motions, and Dvorak fixes from both TAFB and SAB, give a motion of about 280/16 kt. Laura should move west-northwestward along the southern side of a mid-tropospheric anticyclone centered near the southeastern U.S. coast through 72 hours. Then, the cyclone is expected to turn northwestward to northward on the western side of the high. The official track forecast is on the right side of the track guidance suite. Given the predicted track and wind radii, a Tropical Storm Watch has been issued for the Florida Keys and the Dry Tortugas. Key Messages: 1. Tropical storm conditions are expected to continue across portions of the U.S. Virgin Islands and Puerto Rico through this evening. Tropical storm conditions are also expected across portions of the Dominican Republic and Haiti, the Turks and Caicos, the southeastern Bahamas, and central and eastern Cuba through Sunday. Heavy rainfall is likely across these areas and could cause mudslides and flash and urban flooding through Sunday, with widespread river flooding possible in Puerto Rico. 2. Tropical storm conditions are possible over portions of the central Bahamas and Andros Island Sunday night and Monday, and in the Florida Keys on Monday. 3. The details of the long-range track and intensity forecasts remain uncertain since Laura is forecast to move near or over portions of the Greater Antilles through Monday. However, Laura is forecast to strengthen over the Gulf of Mexico and could bring storm surge, rainfall, and wind impacts to portions of the U.S. Gulf Coast by the middle of next week. This could result in a prolonged period of hazardous weather for areas that are likely to be affected by Tropical Storm Marco earlier in the week. Interests there should monitor the progress of Laura and Marco and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/2100Z 18.0N 68.1W 45 KT 50 MPH 12H 23/0600Z 18.9N 70.6W 45 KT 50 MPH...INLAND 24H 23/1800Z 20.1N 74.3W 45 KT 50 MPH...INLAND 36H 24/0600Z 21.6N 78.1W 45 KT 50 MPH...INLAND 48H 24/1800Z 23.0N 81.6W 45 KT 50 MPH...INLAND 60H 25/0600Z 24.3N 84.5W 55 KT 65 MPH...OVER WATER 72H 25/1800Z 25.7N 87.3W 65 KT 75 MPH 96H 26/1800Z 29.0N 90.7W 75 KT 85 MPH 120H 27/1800Z 33.0N 91.0W 30 KT 35 MPH...INLAND $$ Forecaster Pasch
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