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| #895760 (Received by flhurricane at: 4:39 AM 18.Jul.2017) TCDAT5 Tropical Storm Don Discussion Number 3 NWS National Hurricane Center Miami FL AL052017 500 AM AST Tue Jul 18 2017 Don`s convective pattern has continued to improve overnight and early this morning, including the development of a pronounced central dense overcast (CDO) feature. There have also been periodic bursts of deep convection very near the center, accompanied by significant clusters of lightning activity, which is indicative of strong updrafts in or near the radius of maximum winds. The last recon data around 0000Z indicated peak SFMR surface winds of 41 kt. Given the marked increase in convective organization since that time, the initial intensity has been increased to 45 kt. The initial motion estimate remains 280/16 kt. There is no change to the previous track forecast or reasoning. Although the models continue to differ some on Don`s forward speed, there is very little cross-track difference. The models are in good agreement that the broad Bermuda-Azores ridge to north of the cyclone will remain strong and move little for the next several days, which should act to keep Don moving briskly westward until dissipation occurs at around 72 hours. The new NHC forecast track is essentially just an extension of the previous advisory track, and is slightly north of the multi-model consensus TVCN. Don is expected to remain embedded within a narrow east-west zone of low vertical wind shear for another 24-36 hours, which should allow for some additional strengthening. Since Don is a compact tropical cyclone, significant changes in intensity -- both up and down -- can occur due to small fluctuations in wind shear and/or interaction with the mountainous Windward Islands. By 36 hours, increasing westerly shear is expected to cause Don to weaken while it moves across the southeastern Caribbean Sea, and degeneration into an open wave is forecast to occur by 72 hours. The NHC intensity forecast is similar to the previous advisory and remains below the consensus models ICON and IVCN. However, the intensity guidance continues to vary widely between only showing an open wave (most of the global models) to Don achieving hurricane strength (HWRF, ECMWF, and some of the statistical models). As a result, confidence in the intensity forecast remains low. FORECAST POSITIONS AND MAX WINDS INIT 18/0900Z 11.5N 56.2W 45 KT 50 MPH 12H 18/1800Z 11.8N 59.1W 50 KT 60 MPH 24H 19/0600Z 12.1N 63.2W 50 KT 60 MPH 36H 19/1800Z 12.4N 67.4W 50 KT 60 MPH 48H 20/0600Z 12.7N 71.6W 40 KT 45 MPH 72H 21/0600Z...DISSIPATED $$ Forecaster Stewart |
