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Tropical Storm Fred Forecast Discussion Number 27

2021-08-16 10:50:38| National Hurricane Center (Atlantic)

Issued at 400 AM CDT Mon Aug 16 2021 000 WTNT41 KNHC 160850 TCDAT1 Tropical Storm Fred Discussion Number 27 NWS National Hurricane Center Miami FL AL062021 400 AM CDT Mon Aug 16 2021 Earlier reconnaissance aircraft data and satellite imagery indicated that Fred's low-level circulation center briefly emerged out from underneath the southwestern edge of the convective cloud shield between 0200-0400 UTC. The circulation center, however, has recently moved back underneath the edge of the main region of convection, with a new bust of thunderstorms having developed over or near the low-level center. Having said that, Fred still remains a sheared tropical cyclone, with Tallahassee NOAA Doppler radar data indicating that the upper-level circulation at around 30,000 ft is tilted about 40 nmi northeast of the low-level center. The last reports from the Air Force Reserve reconnaissance aircraft indicated that the central pressure had risen from 999 mb to 1004 mb during the time the low-level center was fully exposed southwest of the deep convection. However, the pressure has likely fallen again now the center is back underneath the convection. An intensity of 45 kt is being maintained for this advisory based on the last reliable reconnaissance SFMR data of about 45 kt, which corresponds well with a T3.0/45 kt Dvorak satellite shear-pattern intensity estimate. Fred is moving northward now, or 355/08 kt. The latest NHC model guidance remains in excellent agreement that Fred will continue moving in a general northward motion today as the cyclone moves through a break in the subtropical ridge that is oriented east-to-west across northern Florida. Landfall is expected in the western Florida Panhandle region by late afternoon or evening today. The track guidance has shifted slightly to the east of the previous advisory track, and the new official forecast track has been nudged in that direction, but not as far east as the tightly packed consensus models owing to the strength of the ridge noted in 16/0000 UTC upper-air data. Fred is forecast to remain in moderate vertical wind shear conditions throughout the 48-h forecast period. However, the shear vector is expected to gradually back around from the current southwesterly direction to more of a south-southwesterly component right up until landfall occurs, which will align more with Fred's track direction. This reduction in the effective shear across the cyclone should allow for some additional strengthening until landfall occurs, with the distinct possibility that Fred could reach a peak intensity of 55 kt in 18 hours. After landfall, the combination of land interaction and the vertical shear increasing to more than 20 kt should result in rapid weakening, with Fred forecast to dissipate by 60 hours over the southern Appalachian Mountains. The official intensity forecast closely follows a blend of the HCCA and IVCN intensity consensus models. Users are reminded not to focus on the exact forecast track of Fred, since rainfall, storm surge, and wind hazards will extend over an area well east of the center. KEY MESSAGES: 1. Through Tuesday, heavy rainfall may lead to flash, urban, small stream, and isolated river flooding impacts across the Southeast. By the middle of the week as Fred lifts northward and inland, heavy rainfall and flooding will impact the southern and central Appalachians, the Piedmont of the Southeast, and the Mid-Atlantic. 2. Dangerous storm surge inundation is possible along portions of the coast of the Florida Panhandle and the Florida Big Bend region, and a Storm Surge Warning is in effect for this area. Interests in these areas should follow any advice given by local officials. 3. Tropical storm conditions are expected in the tropical storm warning area beginning later this morning. FORECAST POSITIONS AND MAX WINDS INIT 16/0900Z 27.9N 86.0W 45 KT 50 MPH 12H 16/1800Z 29.1N 86.1W 50 KT 60 MPH 24H 17/0600Z 31.0N 85.7W 40 KT 45 MPH...INLAND 36H 17/1800Z 33.1N 85.2W 25 KT 30 MPH...INLAND 48H 18/0600Z 35.6N 84.2W 20 KT 25 MPH...POST-TROP/INLAND 60H 18/1800Z...DISSIPATED $$ Forecaster Stewart

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