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| #898500 (Received by flhurricane at: 4:44 PM 15.Aug.2017) TCDAT3 Hurricane Gert Discussion Number 12 NWS National Hurricane Center Miami FL AL082017 500 PM EDT Tue Aug 15 2017 Gert has exhibited hints of an eye in visible satellite imagery during the day, but that feature has not appeared in infrared images. Still, the satellite presentation has improved since the last advisory, and the initial intensity is set at 70 kt based on a blend of final-T Dvorak numbers of T4.0 from TAFB and SAB and T4.7 from the UW-CIMSS ADT. Vertical shear is expected to be relatively low--less than 20 kt--for the next 24 hours or so, which should allow Gert to strengthen a little more over the warm waters south of the northern wall of the Gulf Stream. The NHC forecast has been increased slightly through 36 hours to account for the latest intensity guidance, although it is still not as high as what is shown by models such as HWRF and the HFIP Corrected Consensus. Southwesterly shear increases substantially after 48 hours, which should cause Gert to weaken, and the cyclone is also expected to become extratropical by 72 hours. There is a lot of uncertainty on the ultimate fate of the extratropical low, but most of the global models keep Gert as a separate entity at least through day 4. Gert`s trajectory continues to veer as it rounds the western edge of the subtropical ridge, and the initial motion is 020/10 kt. Gert will soon become embedded in the mid-latitude westerlies, sandwiched between a mid-oceanic high and a large cut-off low over eastern Canada. This pattern will cause Gert to turn northeastward and accelerate over the northwestern Atlantic during the next 48-72 hours. The cyclone will then likely slow down and turn more northward by day 4 as it interacts with the aforementioned cut-off low. There is very little cross-track spread among the track models, but the latest suite of guidance has slowed down slightly from previous runs. As a result, the new NHC forecast is just a little slower than the previous one, near the various multi-model consensus aids. Swells from Gert should spread northward along the mid-Atlantic coast of the United States during the next few days, with the first impacts expected to occur tonight. These swells are likely to produce dangerous surf and rip current conditions. Please consult products from your local National Weather Service office. FORECAST POSITIONS AND MAX WINDS INIT 15/2100Z 33.7N 71.2W 70 KT 80 MPH 12H 16/0600Z 35.3N 69.4W 75 KT 85 MPH 24H 16/1800Z 37.4N 64.9W 80 KT 90 MPH 36H 17/0600Z 39.7N 58.4W 80 KT 90 MPH 48H 17/1800Z 42.9N 50.2W 70 KT 80 MPH 72H 18/1800Z 51.5N 37.1W 50 KT 60 MPH...POST-TROP/EXTRATROP 96H 19/1800Z 55.5N 33.0W 40 KT 45 MPH...POST-TROP/EXTRATROP 120H 20/1800Z...DISSIPATED $$ Forecaster Berg |
