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Potential Tropical Cyclone Three Forecast Discussion Number 4
2021-06-18 17:10:49| National Hurricane Center (Atlantic)
Issued at 1000 AM CDT Fri Jun 18 2021 000 WTNT43 KNHC 181510 CCA TCDAT3 Potential Tropical Cyclone Three Discussion Number 4...Corrected NWS National Hurricane Center Miami FL AL032021 1000 AM CDT Fri Jun 18 2021 Corrected second Key Message The cyclone is gradually becoming better organized. Deep convection has increased during the past several hours, but it remains confined to the east side of the circulation due to about 20 kt of west-southwesterly wind shear. The Air Force Hurricane Hunters have been investigating the system and they found a surface center a little to the east of where we previously expected it to be, but have otherwise reported generally light winds. Based on surrounding surface observations and the aircraft data, the initial intensity is held at 30 kt for this advisory. The leading edge of the rain is just reaching portions of the northern Gulf coast, and conditions will continue to deteriorate there through tonight. The broad disturbance is moving north-northeastward at about 12 kt into a weakness in the subtropical ridge. This motion should continue during the next 12 to 24 hours, taking the center of the cyclone to the coast of southeastern Louisiana overnight or on Saturday morning. After landfall, a turn to the right across the southeast U.S. is expected when the system becomes embedded in the westerly flow on the north side of the ridge. The models are in good agreement, and the NHC track forecast is a little to the east of the previous one based on the initial position and motion. Although the system will likely become a tropical storm later today or tonight, significant strengthening is not expected due to its broad and asymmetric structure, ongoing west-southwesterly shear, and limited time over the Gulf of Mexico waters. The models are in quite good agreement overall, and the NHC intensity forecast lies near the HCCA and IVCN consensus aids. It should be noted that the cyclone could be a little stronger at landfall than shown below since that is expected to occur between the 12- and 24-h forecast times. 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 today and continuing through the weekend along the Central Gulf coast. Flood impacts will spread northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin later today in areas near and well to the east of the center along portions of the central Gulf Coast from east of Morgan City, Louisiana, to the Okaloosa/Walton County line, Florida, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 18/1500Z 26.5N 91.1W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 19/0000Z 28.2N 90.9W 35 KT 40 MPH...TROPICAL CYCLONE 24H 19/1200Z 30.3N 90.3W 35 KT 40 MPH...INLAND 36H 20/0000Z 32.1N 88.9W 30 KT 35 MPH...INLAND 48H 20/1200Z 33.4N 86.4W 25 KT 30 MPH...INLAND 60H 21/0000Z 34.5N 83.8W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/1200Z...DISSIPATED $$ Forecaster Cangialosi
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