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Potential Tropical Cyclone Three Forecast Discussion Number 5
2021-06-18 22:34:00| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Fri Jun 18 2021 000 WTNT43 KNHC 182033 TCDAT3 Potential Tropical Cyclone Three Discussion Number 5 NWS National Hurricane Center Miami FL AL032021 400 PM CDT Fri Jun 18 2021 A few hours ago, an ASCAT-A pass indicated that maximum winds were about 40 kt well east of the ill-defined center of circulation, and the initial wind speed was increased to that value at the intermediate advisory at 18Z. Recent surface observations just offshore of southeastern Louisiana have been reporting maximum winds between 30 and 40 kt. Based on a combination of these data, and since the structure of the system has not changed much during the past few hours, the initial intensity is held at 40 kt for this advisory. Although the disturbance has wind speeds of tropical storm intensity, it has not been named a tropical storm yet since its center is ill defined and broad as evident in the Air Force Hurricane Hunter data and surface observations. Regardless of its status, heavy rains and tropical-storm-force winds are spreading across portions of the northern Gulf coast, and these conditions will spread inland through tonight. There has not been much change to the track forecast reasoning. The cyclone is moving northward at about 14 kt, and a general north to north-northeast motion is expected through landfall, which is likely to occur overnight or early Saturday morning. After the system moves inland, a turn to the northeast and then east-northeast across the southeast U.S. is predicted when the cyclone becomes embedded in the westerlies on the north side of the subtropical ridge. The models remain in relatively good agreement, and only small changes were made to the previous track forecast. There is some opportunity for a little strengthening during the next 6 to 12 hours before the system makes landfall. However, significant intensification is not expected due to the cyclone's broad and asymmetric structure, and ongoing west-southwesterly vertical wind shear. After landfall, weakening is forecast, and dissipation is still predicted to occur by 72 hours. However, it should be noted that the ECMWF and UKMET models hold onto the vortex for a while longer. 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. Key Messages: 1. The system is expected to produce heavy rainfall and considerable flash, urban and small stream flooding tonight and through the weekend along the Central Gulf coast. Flood impacts will spread northeastward into the Southern Appalachians. 2. Tropical storm conditions have begun along portions of the central Gulf Coast from east of Morgan City, Louisiana, to the Okaloosa/Walton County line, Florida, including New Orleans. These winds will spread inland and continue into Saturday. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 27.9N 91.2W 40 KT 45 MPH...POTENTIAL TROP CYCLONE 12H 19/0600Z 29.5N 90.8W 40 KT 45 MPH...INLAND 24H 19/1800Z 31.4N 89.4W 35 KT 40 MPH...INLAND 36H 20/0600Z 32.8N 87.4W 30 KT 35 MPH...INLAND 48H 20/1800Z 33.8N 84.9W 25 KT 30 MPH...INLAND 60H 21/0600Z 34.7N 81.9W 20 KT 25 MPH...POST-TROP/REMNT LOW 72H 21/1800Z...DISSIPATED $$ Forecaster Cangialosi
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