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Tropical Storm HARVEY
ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM Tropical Storm Harvey Discussion Number 6 NWS National Hurricane Center Miami FL AL092017 500 PM AST Fri Aug 18 2017 Again, there has been little change in the structure of Harvey, with the low-level center near the eastern edge of a strong, but poorly organized, convective area. Earlier reports from an Air Force Reserve Hurricane Hunter aircraft included winds suggesting an increased intensity. However, due to uncertainties in how representative these measurements were, no appreciable change in the central pressure, and no improvement in the structure, the initial intensity is held at 35 kt. The initial motion is 275/18. A strong low- to mid-level ridge north of the cyclone should keep Harvey on this general motion for the next 3 days or so, with the system moving from the eastern to the western Caribbean Sea during this time. After 72 h, a west-northwestward motion with a decrease in forward speed is expected when Harvey passes near or over portions of Central America, the Yucatan Peninsula, and eastern Mexico. The new forecast track is a little faster then the previous track, but there were only minor changes in the direction. It should be noted that there is considerable uncertainty about how far north Harvey might get over the Bay of Campeche, with several of the large-scale models not bringing the center back over the water on the latest runs. The current shear should persist for about the next 48 h, and thus the intensity forecast continues the trend of slow strengthening during this time. However, the GFS and ECMWF again forecast Harvey to degenerate to an open wave during this time, and the rest of the intensity guidance has trended toward a weaker cyclone. This lowers the confidence in intensification. After 48 h, conditions appear more favorable for strengthening, with the main uncertainty being how much land Harvey will encounter. The intensity forecast will again call for a peak intensity of 60 kt in 72 h, followed by weakening due to land interaction. FORECAST POSITIONS AND MAX WINDS INIT 18/2100Z 13.4N 62.9W 35 KT 40 MPH 12H 19/0600Z 13.6N 65.7W 35 KT 40 MPH 24H 19/1800Z 13.9N 69.3W 40 KT 45 MPH 36H 20/0600Z 14.2N 73.0W 40 KT 45 MPH 48H 20/1800Z 14.5N 76.7W 45 KT 50 MPH 72H 21/1800Z 15.5N 83.5W 60 KT 70 MPH 96H 22/1800Z 17.5N 88.5W 50 KT 60 MPH...INLAND 120H 23/1800Z 19.0N 92.0W 30 KT 35 MPH...OVER WATER $$ Forecaster Beven NNNN