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Tropical Storm Laura Forecast Discussion Number 9
2020-08-22 04:54:37| National Hurricane Center (Atlantic)
Issued at 1100 PM AST Fri Aug 21 2020 000 WTNT43 KNHC 220254 TCDAT3 Tropical Storm Laura Discussion Number 9 NWS National Hurricane Center Miami FL AL132020 1100 PM AST Fri Aug 21 2020 Laura remains quite disorganized this evening. Although satellite and radar images show a fair amount of deep convection over and to the east of the northern Leeward Islands, NOAA Hurricane Hunter data and surface observations indicate that the low-level center is located well to the west of the main area of deep convection. This asymmetric structure indicates that Laura is still not vertically aligned due to at least moderate wind shear. The initial intensity is held at a possibly generous 40 kt, and most of the strongest winds are well north and east of the center. The steering pattern for Laura appears to be very well established. A subtropical ridge over the central and western Atlantic is expected to expand westward, and that should cause Laura to move west-northwestward at a fairly quick pace during the next few days. This should take the storm across Puerto Rico on Saturday, near Hispaniola Saturday night, and close to or over Cuba on Sunday and Monday. By early next week, Laura should approach the western end of the ridge and that should cause the storm to slow down and turn toward the northwest over the eastern and central Gulf of Mexico. Even though the steering pattern is well established, there are still chances of center reformations, which could cause small but important track changes. The NHC track forecast has been adjusted a little to the south of the previous one to account for the more southern initial position and westward motion. Near the end of the period, Laura's track could also be influenced by Tropical Storm Marco, which is also forecast to be over the Gulf of Mexico, however the details of that interaction are highly uncertain at this time. Although the storm's structure is quite ragged at the moment, some of the models do show Laura becoming better organized this weekend and early next week due to a decrease in wind shear and very warm waters. However, there is significant uncertainty on how much the circulation will interact with the rugged islands of Hispaniola and Cuba. If the storm is able to stay north of those islands, some notable strengthening is possible as depicted by the HWRF and HMON models. However, if the storm moves over the islands, it might not strengthen at all until it passes through that area. The bottom line is the intensity forecast is very track dependent, which makes it more uncertain than normal. Given that the new track shows more land interaction, this forecast shows less strengthening in the short term, but is largely unchanged at the longer forecast times. Key Messages: 1. Tropical storm conditions are expected across portions of the northern Leeward Islands, the Virgin Islands, and Puerto Rico through Saturday. Tropical storm conditions are also expected along the northern coasts of the Dominican Republic and Haiti, and the Turks and Caicos and southeastern Bahamas Saturday into Sunday. Heavy rainfall is likely across these areas beginning and could cause mudslides and flash and urban flooding through Sunday. 2. Tropical storm conditions are possible over portions of the central Bahamas Sunday night. 3. The details of the long-range track and intensity forecasts remain more uncertain than usual since Laura is forecast to move near or over portions of the Greater Antilles through Monday. However, Laura could bring storm surge, rainfall, and wind impacts to portions of Cuba, the Bahamas, and Florida early next week and the northern U.S. Gulf Coast by the middle of next week. Interests there should monitor the progress of Laura and updates to the forecast during the next few days. FORECAST POSITIONS AND MAX WINDS INIT 22/0300Z 17.0N 63.5W 40 KT 45 MPH 12H 22/1200Z 17.6N 65.9W 40 KT 45 MPH 24H 23/0000Z 18.4N 69.3W 40 KT 45 MPH...INLAND 36H 23/1200Z 19.5N 72.8W 40 KT 45 MPH...INLAND 48H 24/0000Z 20.8N 76.4W 45 KT 50 MPH...INLAND 60H 24/1200Z 22.1N 80.1W 45 KT 50 MPH...INLAND 72H 25/0000Z 23.8N 83.3W 55 KT 65 MPH...OVER WATER 96H 26/0000Z 26.5N 87.7W 65 KT 75 MPH...OVER WATER 120H 27/0000Z 29.2N 90.2W 65 KT 75 MPH...OVER WATER $$ Forecaster Cangialosi
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