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Tropical Storm Gert Forecast Discussion Number 4
2017-08-13 22:32:18| National Hurricane Center (Atlantic)
Issued at 500 PM EDT Sun Aug 13 2017 000 WTNT43 KNHC 132032 TCDAT3 Tropical Storm Gert Discussion Number 4 NWS National Hurricane Center Miami FL AL082017 500 PM EDT Sun Aug 13 2017 Satellite images indicate that the tropical cyclone is gradually strengthening. The banding features have become better established during the last several hours, and the system has become less vertically tilted. The Dvorak classification from TAFB and ADT values from CIMSS at the University of Wisconsin support increasing the initial wind speed to 35 kt, making the system Tropical Storm Gert. Gert is moving north-northwestward at 9 kt on the southwestern periphery of a subtropical ridge. A northward motion is expected tonight and Monday while the system rounds the western side of the ridge, and Gert is expected to be about midway between Bermuda and North Carolina on Monday and Tuesday. After that time, a progressively faster motion to the northeast and east-northeast is forecast as the system moves on the north side of the ridge and becomes embedded in the mid-latitude westerlies until it dissipates in about 5 days. The track guidance remains in very good agreement, and only small changes were made to the previous NHC prediction. This forecast lies near the middle of the tightly clustered guidance envelope. The system is over warm 29 deg C SSTs, and it will remain over these warm waters during the next few days. In addition, the global models indicate that the upper-level pattern should become conducive for strengthening during the next 36 hours or so. The combination of these conditions should allow Gert to strengthen during the next couple of days. Thereafter, a sharp increase in west-southwesterly shear, drier air, and decreasing sea surface temperatures should end the strengthening trend and lead to extratropical transition in a little more than 3 days. The NHC intensity forecast is slightly above the previous one, but remains on the lower side of the guidance. The center of Gert recently passed very near NOAA buoy 41047, and that data has been helpful in estimating the minimum pressure of the system. FORECAST POSITIONS AND MAX WINDS INIT 13/2100Z 28.1N 71.7W 35 KT 40 MPH 12H 14/0600Z 29.3N 72.1W 40 KT 45 MPH 24H 14/1800Z 31.1N 72.1W 50 KT 60 MPH 36H 15/0600Z 32.9N 71.3W 55 KT 65 MPH 48H 15/1800Z 35.1N 68.8W 55 KT 65 MPH 72H 16/1800Z 39.8N 59.1W 50 KT 60 MPH 96H 17/1800Z 45.0N 44.5W 45 KT 50 MPH...POST-TROP/EXTRATROP 120H 18/1800Z...DISSIPATED $$ Forecaster Cangialosi
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