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Tropical Depression Fred Forecast Discussion Number 14
2021-08-13 04:52:38| National Hurricane Center (Atlantic)
Issued at 1100 PM EDT Thu Aug 12 2021 464 WTNT41 KNHC 130252 TCDAT1 Tropical Depression Fred Discussion Number 14 NWS National Hurricane Center Miami FL AL062021 1100 PM EDT Thu Aug 12 2021 Data from an Air Force Reserve reconnaissance aircraft this indicate that Fred's inner-core wind field Fred remains poorly organized. Also, data from a NOAA reconnaissance aircraft suggests that the 650-mb mid-level circulation center is titled at least 40 nmi to the east of the low-level center. The maximum 925-mb flight-level wind measured thus far has been 43 kt and the highest reliable SFMR surface wind speed sampled has been 33 kt. A blend of these data support maintaining a solid 30-kt intensity for this advisory, but Fred is right on the cusp of regaining tropical storm status. Fred has slowed down some more, with the initial motion estimate an uncertain 295/08 kt. The uncertainty in Fred's forward motion is related to the speed due to the low-level center jumping around every time a small convective tower develops within the larger cloud mass. However, the general motion of the wind field and the associated pressure envelope is toward the west-northwest or 295 degrees. Otherwise, there is no significant changes to the previous track forecast or reasoning. Fred is expected to continue moving west-northwestward along the southwestern periphery of a deep-layer for the next 36 hours or so, followed by a northwestward motion near or just offshore the Florida west coast in the 48-to-72-hour period. On days 4 and 5, a slower northward motion is forecast as Fred moves into a developing weakness in the ridge. The latest track guidance has become more divergent, with the GFS model dissipating and then redeveloping Fred over south Florida in about 48 hours, with the other models taking a weakening cyclone more westward. The exception is the westward-trending ECMWF model, which moves Fred along the Florida west coast. The new NHC track forecast was nudged slightly to the east or right of the previous advisory track after 24 hours, but lies to the left of the ECMWF model and between the NOAA-HCCA and TVCA consensus track models. Fred is forecast to remain under the influence of westerly to southwesterly vertical wind shear for the next 72 hours. It is the magnitude of the shear that is in question. The GFS maintains 15-20 kt of shear for the next three days, whereas the ECMWF model decreases the shear to around 10 kt in the 24-to-60-hour period, with the latter scenario favoring some strengthening if Fred doesn't interact too much with the Florida peninsula. Due to the uncertainty in the amount of shear and land interaction that will be encountered, latest official intensity forecast remains similar to the previous advisory and a blend of the HCCA and TVCA consensus model intensity forecasts. KEY MESSAGES: 1. From Friday into Monday, heavy rainfall could lead to areal, urban, small stream, and exacerbated river flooding, across southern and central Florida, and into the Big Bend of Florida. By early next week, heavy rain and flood impacts could extend into other portions of the Southeast and into the southern and central Appalachians and Piedmont. 2. Tropical storm conditions are possible beginning Friday night and Saturday in the Florida Keys and portions of southern Florida, where a Tropical Storm Watch is in effect. The risk of tropical storm conditions will spread northward along portions of the Florida west coast and to the Florida Panhandle Saturday night through Monday. FORECAST POSITIONS AND MAX WINDS INIT 13/0300Z 21.5N 75.6W 30 KT 35 MPH 12H 13/1200Z 22.2N 77.1W 35 KT 40 MPH 24H 14/0000Z 23.0N 79.0W 35 KT 40 MPH 36H 14/1200Z 24.2N 80.6W 40 KT 45 MPH 48H 15/0000Z 25.5N 82.1W 40 KT 45 MPH 60H 15/1200Z 27.2N 83.1W 45 KT 50 MPH 72H 16/0000Z 29.1N 84.2W 45 KT 50 MPH 96H 17/0000Z 31.8N 85.6W 35 KT 40 MPH...INLAND 120H 18/0000Z 34.4N 85.5W 25 KT 30 MPH...INLAND $$ Forecaster Stewart
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