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Potential Tropical Cyclone Three Forecast Discussion Number 3
2021-06-18 10:55:14| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Fri Jun 18 2021 000 WTNT43 KNHC 180855 TCDAT3 Potential Tropical Cyclone Three Discussion Number 3 NWS National Hurricane Center Miami FL AL032021 400 AM CDT Fri Jun 18 2021 The system became a little better organized overnight at the northern end of its associated broad surface trough over the central Gulf of Mexico. Satellite images show increasing deep convection along with more curvature to the low clouds, suggesting that the ill-defined center of this system is trying to re-form farther to the north. Since it still lacks a well-defined center, the system remains a potential tropical cyclone. Recent scatterometer data indicate that winds have increased to at least 30 kt and have grown over a larger area on the east side of the circulation. The initial motion is a highly uncertain 360/12. There is fair agreement that this northward motion, with some re-formation of the center, will continue as the system remains steered by a subtropical ridge to the southeast. The low should then turn northeastward and move across the southeastern U.S. No significant changes were made to the previous track forecast and the guidance is in fairly good agreement. It should also be noted that model "spaghetti" plots are not doing a good job tracking the center of this system, and could give a very misleading impression on the forecast track if used by themselves. There is still a lot of shear over the Gulf of Mexico and that should continue through landfall. However, the system is somewhat hybrid in nature and the shear shouldn't prevent its intensification to a tropical storm later today (possibly with subtropical characteristics). Model guidance is consistent with slow strengthening until landfall, and the new forecast is close to the previous one. After landfall, most of the global models show a strong band of heavy rain and tropical-storm-force winds persisting on the southeastern side. The expected large distance from the center necessitates extending the Tropical Storm Warning into the northwestern Florida panhandle. The system will likely dissipate in about 3 days over the southeastern United States. 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 with flood impacts spreading northeastward into the Southern Appalachians. 2. Tropical storm conditions are expected to begin today in areas near and well to the east of the center along portions of the central Gulf Coast from Intracoastal City, Louisiana, to the Okaloosa/Walton County line, Florida, including New Orleans. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 25.2N 91.5W 30 KT 35 MPH...POTENTIAL TROP CYCLONE 12H 18/1800Z 27.0N 91.5W 35 KT 40 MPH...TROPICAL CYCLONE 24H 19/0600Z 29.2N 91.2W 40 KT 45 MPH 36H 19/1800Z 31.0N 89.5W 35 KT 40 MPH...INLAND 48H 20/0600Z 32.6N 87.6W 25 KT 30 MPH...INLAND 60H 20/1800Z 34.5N 85.0W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/0600Z...DISSIPATED $$ Forecaster Blake
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