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Tropical Storm HARVEY
ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM Tropical Storm Harvey Discussion Number 8 NWS National Hurricane Center Miami FL AL092017 500 AM AST Sat Aug 19 2017 GOES-16 shortwave infrared imagery shows the partially exposed center of Harvey on the eastern edge of a large area of deep convection. While the center is closer to the convection than a few hours ago, cirrus clouds be clearly seen moving from northeast to southwest across the system; an indication of the persistent shear. Satellite estimates suggest the maximum winds of Harvey remain 35 kt. The storm has picked up some forward speed with a recent motion estimate of 275/18. A low- to mid-level ridge extending across the western Atlantic should keep Harvey on a fast westward course across the Caribbean Sea for the next 48 hours. Thereafter, the ridge weakens across the Gulf of Mexico due to a strong mid/upper-level low currently seen there on water vapor images. This steering flow change should cause Harvey to slow down and turn a little more to the west-northwest in the northwestern Caribbean Sea, with an even slower motion forecast for Harvey in the Bay of Campeche. Model guidance is in fairly good agreement on this scenario, and no significant changes were made to the previous forecast. Harvey should be moving into a more conducive environment for strengthening early next week since the strong northeasterly shear that has been affecting the cyclone is forecast by almost all of the guidance to weaken within about 24 hours. In a few days, most of the global models show a favorable upper-level environment for intensification, and Harvey could be near hurricane strength between the 72 hour forecast period and landfall. There has been little change to the guidance so the new intensity forecast is similar to the previous one, close to the model consensus. However, with a weak storm moving so quickly across the central Caribbean, one always has to be careful of the system opening up into a wave. This is a plausible alternative scenario still suggested by the GFS and ECMWF models. FORECAST POSITIONS AND MAX WINDS INIT 19/0900Z 13.8N 65.9W 35 KT 40 MPH 12H 19/1800Z 14.0N 68.7W 35 KT 40 MPH 24H 20/0600Z 14.3N 72.7W 40 KT 45 MPH 36H 20/1800Z 14.6N 76.7W 45 KT 50 MPH 48H 21/0600Z 15.2N 80.1W 50 KT 60 MPH 72H 22/0600Z 17.0N 86.5W 55 KT 65 MPH 96H 23/0600Z 18.3N 90.5W 35 KT 40 MPH...INLAND 120H 24/0600Z 19.3N 93.0W 40 KT 45 MPH...OVER WATER $$ Forecaster Blake NNNN