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| #898912 (Received by flhurricane at: 4:35 PM 19.Aug.2017) TCDAT4 Tropical Depression Harvey Discussion Number 10 NWS National Hurricane Center Miami FL AL092017 500 PM EDT Sat Aug 19 2017 The cloud pattern of Harvey has continued to decay during the day, at least in part due to 15-20 kt of northerly shear. The convective area near the center is neither very concentrated or curved, and overall the pattern more resembles that of an open wave than a tropical cyclone. Based on the decay and data from the aircraft mission this morning, the cyclone is downgraded to a tropical depression. Another Air Force Reserve Hurricane Hunter aircraft will investigate the system this evening to see if the circulation still exists. The intensity forecast is problematic. The current shear should subside over the next 24 h, and the statistical guidance responds to this by forecasting significant strengthening. On the other hand, the structure of the cyclone has decayed to the point where it may not be able to take advantage of the better environment, as suggested by the ECMWF and GFS. The intensity forecast follows the trend of the previous forecast, albeit with lower intensities, in showing gradual strengthening until landfall in Belize or Yucatan. However, an alternative forecast scenario is that the system degenerates to an open wave and is unable to regenerate during the next 72 h. The initial motion remains 275/19. There is no change in the forecast philosophy from the previous advisory, and there are only minor tweaks to the forecast track. A low- to mid-level ridge extending across the western Atlantic should keep Harvey, or its remnants, on a fast westward course across the Caribbean Sea for the next 36 h. Thereafter, there should be a weakness in the ridge north of Harvey caused by a strong mid/upper-level low currently seen in water vapor imagery over the Gulf of Mexico. This pattern should cause a turn toward the west-northwest and a decrease in forward speed. The track guidance remains in good agreement that Harvey should pass near or just north of northeastern Honduras, and then cross Belize and/or the Yucatan Peninsula into the Bay of Campeche. A Tropical Storm Watch could be required for portions of the northern coast of Honduras and northeastern Nicaragua tonight. At the present time, there is enough uncertainty about whether Harvey will actually be a tropical storm in 48 h that a watch is not warranted. FORECAST POSITIONS AND MAX WINDS INIT 19/2100Z 14.1N 70.0W 30 KT 35 MPH 12H 20/0600Z 14.3N 73.0W 30 KT 35 MPH 24H 20/1800Z 14.6N 77.0W 35 KT 40 MPH 36H 21/0600Z 15.2N 80.5W 40 KT 45 MPH 48H 21/1800Z 16.0N 83.8W 45 KT 50 MPH 72H 22/1800Z 18.0N 89.0W 45 KT 50 MPH...INLAND 96H 23/1800Z 19.0N 92.0W 30 KT 35 MPH...OVER WATER 120H 24/1800Z 19.5N 94.0W 40 KT 45 MPH $$ Forecaster Beven |
