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Tropical Depression Fifteen Forecast Discussion Number 1
2020-08-31 22:44:31| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Mon Aug 31 2020 000 WTNT45 KNHC 312044 TCDAT5 Tropical Depression Fifteen Discussion Number 1 NWS National Hurricane Center Miami FL AL152020 500 PM EDT Mon Aug 31 2020 Satellite images indicate that the area of low pressure offshore of the Carolinas has had convection organized in bands since before dawn, and scatterometer plus an Air Force Reserve Hurricane Hunter mission data confirm that the circulation is closed. Thus, this is now a tropical depression, and the initial wind speed is set to 30 kt in accordance with 25-30 kt ASCAT-A data plus buoy 42001 readings which earlier had an adjusted 10-m peak of 30 kt. The depression is moving northeastward at about 10 kt. The system should gradually turn toward the east-northeast by Wednesday due to it moving around the northwest side of the subtropical ridge, then move eastward in a few days around the flat ridge. By late week, the cyclone could slow and eventually turn back toward the northeast around a rather strong mid-latitude high pressure system over the northeast Atlantic. There is considerable spread in the guidance, which really seems to depend upon whether the system stays coherent, like the official forecast, or would become a shallow low-level swirl by 120h and end up slower and south of forecast track. This forecast is near the corrected-consensus guidance, leaning toward the ECMWF-based models, and it should be considered of low confidence. Gradual strengthening is expected over the next day or so while the depression remains in a low-to-moderate shear environment. Although the depression is expected to be traversing the warm Gulf Stream for the next several days, wind shear is expected to greatly increase by Wednesday, which should limit intensification. In fact there's some chance the system could decay and lose any deep convection in rather strong shear in a few days. However, since it likely will be moving near the Gulf Stream, I suspect it will continue to pulse thunderstorm activity and stay alive throughout the period. The NHC intensity forecast is near or just above the model consensus on that reasoning, closest to the HWRF model. The cyclone could become extratropical (or a remnant low) by the end of the forecast, but this is very uncertain. FORECAST POSITIONS AND MAX WINDS INIT 31/2100Z 32.6N 76.5W 30 KT 35 MPH 12H 01/0600Z 33.8N 75.0W 35 KT 40 MPH 24H 01/1800Z 34.9N 72.4W 40 KT 45 MPH 36H 02/0600Z 35.8N 69.7W 40 KT 45 MPH 48H 02/1800Z 36.7N 67.0W 40 KT 45 MPH 60H 03/0600Z 37.6N 63.7W 35 KT 40 MPH 72H 03/1800Z 38.2N 60.5W 35 KT 40 MPH 96H 04/1800Z 39.0N 55.0W 35 KT 40 MPH 120H 05/1800Z 41.5N 49.5W 35 KT 40 MPH...POST-TROP/EXTRATROP $$ Forecaster Blake
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