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Potential Tropical Cyclone Three Forecast Discussion Number 2
2021-06-18 04:38:42| National Hurricane Center (Atlantic)
Issued at 1000 PM CDT Thu Jun 17 2021 000 WTNT43 KNHC 180238 TCDAT3 Potential Tropical Cyclone Three Discussion Number 2 NWS National Hurricane Center Miami FL AL032021 1000 PM CDT Thu Jun 17 2021 Satellite imagery and data from an Air Force Reserve Hurricane Hunter aircraft indicate that the low pressure area over the southwestern Gulf of Mexico has changed little in organization during the past several hours, and the associated convection lies well to the east of the broad and poorly defined center. The initial intensity will be held at 25 kt based partially on ship reports from the northeastern and northern parts of the system. Due to the poorly defined center, the initial motion is a highly uncertain 360/8. The system should move generally northward for the next 24-36 h to a position near the coast of Louisiana, followed by a motion toward the northeast across the southeastern United States as it moves through a weakness in the subtropical ridge caused by an upper-level trough over Texas, northern Mexico, and the adjacent Gulf of Mexico. The forecast track is basically an update of the previous forecast. It should be noted that the latest GFS run continues to forecast a re-formation of the center to the north sometime on Friday, and the forecast forward motion tries to account for this possibility. The aforementioned upper-level trough is causing shear over the system, and present indications are that some shear will persist through landfall and hinder development. The intensity forecast calls for the low to become a tropical cyclone in about 12 h, followed by some modest strengthening to tropical storm strength at 24-36 h. This would be followed by weakening over land, with the system dissipating over the southeastern United States between 72- 96 h. There is a chance that, due to the interaction with the upper-level trough, the system may take on subtropical cyclone characteristics instead of tropical cyclone characteristics. The new intensity forecast is similar to the previous forecast, and it lies at the upper edge of the intensity guidance envelope. Given the current and anticipated structure of this system, users should not focus on the exact track of the center, as rainfall and wind hazards are likely to extend well east of the center and arrive well in advance of landfall. Key Messages: 1. The system is expected to produce heavy rainfall, considerable flash, urban and small stream flooding beginning Friday and continuing through the weekend along the Central Gulf coast, spreading northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin Friday in areas near and well to the east of the center along portions of the central Gulf Coast from Intracoastal City, Louisiana, to the Alabama/Florida border, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 18/0300Z 23.5N 92.2W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 18/1200Z 25.0N 92.4W 30 KT 35 MPH...TROPICAL CYCLONE 24H 19/0000Z 27.2N 92.4W 35 KT 40 MPH 36H 19/1200Z 29.8N 91.1W 40 KT 45 MPH...INLAND 48H 20/0000Z 32.0N 88.8W 30 KT 35 MPH...INLAND 60H 20/1200Z 34.1N 86.1W 25 KT 30 MPH...POST-TROP/INLAND 72H 21/0000Z 35.6N 83.0W 20 KT 25 MPH...POST-TROP/INLAND 96H 22/0000Z...DISSIPATED $$ Forecaster Beven
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