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Potential Tropical Cyclone Three Forecast Discussion Number 1
2021-06-17 22:34:35| National Hurricane Center (Atlantic)
Issued at 400 PM CDT Thu Jun 17 2021 880 WTNT43 KNHC 172034 TCDAT3 Potential Tropical Cyclone Three Discussion Number 1 NWS National Hurricane Center Miami FL AL032021 400 PM CDT Thu Jun 17 2021 Visible satellite images show that the cloud pattern associated with the broad area of low pressure located over the southwestern Gulf of Mexico is gradually becoming better organized. Deep convection is beginning to form a broad curved band over the eastern portion of the system, similar to what one might see in a developing subtropical cyclone. Although the upper-level winds are not particularly favorable for development, with lots of westerly shear over the area, the global models do suggest tropical/subtropical cyclogenesis within the next 12 hours or so. Given the proximity of the disturbance to land, which requires tropical storm warnings at this time, advisories are being initiated on this system as a potential tropical cyclone. Earlier scatterometer data suggested that the circulation was still rather broad. An Air Force Hurricane Hunter plane is currently investigating the system and has not yet found a well-defined center. Maximum winds based on surface observations and the scatterometer pass are near 25 kt. Numerical intensity guidance do not indicate a great deal of strengthening before the system reaches the coastline, and the official forecast is at the high end of the guidance. Since the center is not that well-defined at this time, the initial motion estimate, 360/8 is quite uncertain. The system is expected to move northward into a weakness in the subtropical ridge for the next day or so and then, after landfall along the central Gulf Coast, turn toward the northeast on the northwest side of a mid-level anticyclone near Florida. The official track forecast is closest to the GFS and ECMWF predictions. It should be noted, however, that these models suggest some reformation of the center near the Louisiana coast rather than just motion from the southwest Gulf to the expected coastal landfall point. 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 and considerable flash, urban, and small stream flooding beginning Friday and continuing through the weekend along the central Gulf coast and 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 17/2100Z 22.9N 92.4W 25 KT 30 MPH...POTENTIAL TROP CYCLONE 12H 18/0600Z 24.5N 92.5W 25 KT 30 MPH...TROPICAL CYCLONE 24H 18/1800Z 26.5N 92.5W 35 KT 40 MPH 36H 19/0600Z 29.0N 92.0W 40 KT 45 MPH 48H 19/1800Z 31.5N 89.5W 30 KT 35 MPH...INLAND 60H 20/0600Z 34.0N 87.0W 25 KT 30 MPH...INLAND 72H 20/1800Z 35.0N 84.0W 20 KT 25 MPH...INLAND 96H 21/1800Z...DISSIPATED $$ Forecaster Pasch/Brennan
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