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Tropical Depression Nine Forecast Discussion Number 3
2018-09-08 10:55:34| National Hurricane Center (Atlantic)
Issued at 500 AM AST Sat Sep 08 2018 357 WTNT44 KNHC 080855 TCDAT4 Tropical Depression Nine Discussion Number 3 NWS National Hurricane Center Miami FL AL092018 500 AM AST Sat Sep 08 2018 The depression continues to be affected by moderate to strong east to southeasterly vertical wind shear, which has resulted in the bulk of the deep convection being displaced to the west of the low-level center. The initial intensity has been held at 30 kt based on Dvorak satellite intensity estimate of T2.0/30 kt from both TAFB and SAB. The depression has been meandering in the same general area for the past 12-18 h due to being caught in a weakness in the subtropical ridge. However, recent microwave satellite data suggest that the cyclone is now moving slowly northwestward. A turn toward the west is expected to occur later today as a shortwave trough to the north that has weakened the ridge lifts out, allowing the ridge to fill back in and build westward to the north of the Lesser Antilles. The latest NHC model guidance suite remains tightly packed, and the official forecast track lies down the middle of the envelope near a blend of the consensus aids TCVA, HCCA, FSSE. Although the wind shear is forecast to gradually weaken and become less than 5 kt by 36-48 h, which would favor rapid strengthening, the airmass that the cyclone is embedded is fairly dry. Since mid-level humidity values are forecast to decrease from the current 60-percent range down to around 50 percent by 48 hours and beyond, only modest strengthening is expected during the next 4 days. By day 5, vertical wind shear from the southwest is forecast to increase to 20-25 kt, serving to cap the intensification process. The NHC intensity forecast is based on a blend of the IVCN and the HCCA consensus models, and continues to remain below the stronger HWRF model at days 4 and 5, which makes the cyclone a major hurricane in 78 h. FORECAST POSITIONS AND MAX WINDS INIT 08/0900Z 14.3N 35.4W 30 KT 35 MPH 12H 08/1800Z 14.4N 36.1W 35 KT 40 MPH 24H 09/0600Z 14.5N 37.5W 40 KT 45 MPH 36H 09/1800Z 14.7N 39.5W 45 KT 50 MPH 48H 10/0600Z 14.6N 42.0W 55 KT 65 MPH 72H 11/0600Z 14.5N 47.3W 75 KT 85 MPH 96H 12/0600Z 14.6N 52.7W 80 KT 90 MPH 120H 13/0600Z 14.9N 57.2W 80 KT 90 MPH $$ Forecaster Stewart
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