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Tropical Storm GASTON Forecast Discussion Number 4
2016-08-23 16:35:52| National Hurricane Center (Atlantic)
Issued at 1100 AM AST TUE AUG 23 2016 000 WTNT42 KNHC 231435 TCDAT2 TROPICAL STORM GASTON DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 AM AST TUE AUG 23 2016 Gaston continues to intensify. The cyclone's cloud pattern has been gradually transitioning from a curved-band pattern to a central dense overcast (CDO). Within the formative CDO, a ragged eye-type feature has occasionally been evident during the last few hours. A satellite classification of T3.5 is used to increase in the initial intensity estimate to 55 kt, in agreement with the latest UW-CIMSS ADT values. Only light vertical wind shear is forecast to affect Gaston during the next 24 to 36 hours while the cyclone moves over marginally warm waters and through a generally moist environment. These factors suggest that further intensification is likely during this period of time. By 48 hours, Gaston should encounter increasing southwesterly to westerly flow at upper-levels associated with a potent trough over the east-central Atlantic. In the very least, the forecast shear and a drier atmosphere associated with this feature should result in an arrested development phase, if not weakening. Late in the forecast period, global models indicate a reduction of the shear while Gaston is over warmer waters of 29 deg C, which could allow for some re-strengthening. Through 36 hours, the NHC intensity forecast is a bit above the multi-model consensus and closest to the FSU Superensemble output and the LGEM. After that time, the forecast trends toward the multi-model consensus. The initial motion estimate is 285/18. Gaston is being steered quickly toward the west-northwest around the western extension of a mid-level subtropical ridge extending westward from North Africa. The ridge's orientation begins to change as Gaston approaches a significant break in the subtropical ridge in the central Atlantic, which results in a northwestward heading and a reduction in forward speed during the next few days. A northward turn with an even greater decrease in forward speed is expected by 120 hours once Gaston enters the weakness over the central Atlantic. The latest NHC track forecast is largely similar to the previous one and close to the model consensus aids. FORECAST POSITIONS AND MAX WINDS INIT 23/1500Z 13.8N 34.6W 55 KT 65 MPH 12H 24/0000Z 14.6N 36.9W 65 KT 75 MPH 24H 24/1200Z 16.1N 39.9W 75 KT 85 MPH 36H 25/0000Z 17.8N 42.4W 85 KT 100 MPH 48H 25/1200Z 19.8N 44.6W 80 KT 90 MPH 72H 26/1200Z 24.2N 48.9W 75 KT 85 MPH 96H 27/1200Z 27.7N 52.5W 75 KT 85 MPH 120H 28/1200Z 30.7N 53.5W 80 KT 90 MPH $$ Forecaster Kimberlain
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