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Tropical Depression Four Forecast Discussion Number 1
2021-06-28 16:51:59| National Hurricane Center (Atlantic)
Issued at 1100 AM EDT Mon Jun 28 2021 000 WTNT44 KNHC 281451 TCDAT4 Tropical Depression Four Discussion Number 1 NWS National Hurricane Center Miami FL AL042021 1100 AM EDT Mon Jun 28 2021 The area of disturbed weather and associated low pressure system that the NHC has been tracking the past couple of days has developed into a tropical depression off the coast of South Carolina this morning. The inner-core cloud structure noted in high-resolution visible satellite imagery has continued to tighten up and deep convection with cloud top temperatures of -60 deg C have persisted northwest through southwest of the center, yielding a Dvorak shear pattern intensity estimate of 30 kt. This intensity estimate is consistent with overnight scatterometer surface wind data of 31-32 kt just north of the well-defined center. The initial motion estimate is 300/14 kt. The small tropical cyclone is expected to maintain a west-northwestward to northwestward motion for the next couple of days, resulting in landfall along the south-central coast of South Carolina later this evening. The small cyclone is expected to dissipate by 48 hours, if not sooner, when the system will be located over the southern Appalachian Mountains. The NHC track forecast lies close to the tightly packed GFS- and ECMWF-based Beta-Advection models due to the lack of any significant inner-core convection, which is allowing the cyclone to be steered more by the low-level flow rather than the deep-layer flow as depicted by the global and regional models. There is a narrow window of opportunity this afternoon for the depression to strengthen into a tropical storm before landfall occurs. During the next few hours, the small cyclone will be passing over the warmer Gulf Stream where sea-surface temperatures are around 28 deg C. In addition, as the outer wind field begins to interact with land, low-level frictional convergence along and just offshore should help to generate deep convection just prior to landfall, helping to spin up the wind field. The NHC forecast shows the system becoming a tropical storm before landfall, and as a result a tropical storm warning has been issued for a portion of the South Carolina coast. An Air Force Reserve Unit reconnaissance aircraft will investigate the system this afternoon beginning around 1800 UTC, providing more detailed information on the cyclone's intensity. Key Messages: 1. Heavy rainfall is possible from coastal southern South Carolina and Georgia, inland across the Piedmont of Georgia into northeast Alabama. Isolated flooding is possible across urban areas of the southern South Carolina and Georgia coasts. 2. Tropical-storm-force winds are expected across portions of the South Carolina coast late this afternoon and tonight where a Tropical Storm Warning is in effect. 3. Swells generated by the depression are expected to affect portions of the South Carolina coast this afternoon and tonight. These swells could cause life-threatening surf and rip currents. FORECAST POSITIONS AND MAX WINDS INIT 28/1500Z 31.9N 78.3W 30 KT 35 MPH 12H 29/0000Z 32.8N 80.6W 35 KT 40 MPH...INLAND 24H 29/1200Z 34.2N 83.3W 20 KT 25 MPH...POST-TROP/INLAND 36H 30/0000Z 35.2N 85.6W 15 KT 15 MPH...POST-TROP/INLAND 48H 30/1200Z...DISSIPATED INLAND $$ Forecaster Stewart
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Category:Transportation and Logistics
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