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Tropical Storm HARVEY
ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM Tropical Storm Harvey Discussion Number 15 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Thu Aug 24 2017 NOAA and Air Force Hurricane Hunter planes have been sampling Harvey during the past few hours. Both aircraft indicate that Harvey is becoming better organized and the central pressure is falling. An average of the flight-level winds and the SFMR yield an initial intensity of 40 kt. There are some unconfirmed reports of stronger winds at flight-level to the northeast of the center, but I am waiting for the plane to go back to that area for confirmation. It appears that the environment has finally become favorable and all of the guidance calls for intensification. In fact, the Rapid Intensification Index is up to 45 percent. The current NHC forecast is a little lower than the model consensus to maintain continuity from the previous advisory. If the current intensity trend continues, the winds will have to be adjusted upward in the next advisory. The initial motion is toward the north or 360 degrees at 9 kt. However, this is a combination of motion and reformation under the convection. Harvey is already on the western edge of the subtropical ridge extending from the Atlantic westward across the Gulf of Mexico. This pattern will steer the cyclone on a general northwest to north-northwest track for the next 2 to 3 days. Once Harvey makes landfall in Texas, most of the global models predict that the steering currents will collapse and Harvey will begin to meander over Texas and perhaps will move back into the northwestern Gulf of Mexico. Key Messages: 1. Harvey is likely to bring multiple hazards, including heavy rainfall, storm surge, and possible hurricane conditions to portions of the Texas coast beginning on Friday. 2. Heavy rainfall is likely to spread across portions of eastern Texas, Louisiana, and the lower Mississippi Valley from Friday through early next week and could cause life-threatening flooding. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 3. A Storm Surge Warning is now effect from Port Mansfield to San Luis Pass, Texas, indicating the possibility of life-threatening inundation from rising water moving inland from the coast during the next 36 hours. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 4. The Potential Storm Surge Flooding Map is available on the NHC website. This product depicts a reasonable worst-case scenario - the amount of inundation that has a 10 percent chance of being exceeded at each individual location. Because the Flooding Map is based on inputs that extend out only to about 72 hours, it best represents the flooding potential in those locations within the watch area. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 23.2N 92.8W 40 KT 45 MPH 12H 24/1800Z 24.0N 93.6W 50 KT 60 MPH 24H 25/0600Z 25.1N 94.8W 60 KT 70 MPH 36H 25/1800Z 26.3N 95.8W 70 KT 80 MPH 48H 26/0600Z 27.5N 97.0W 75 KT 85 MPH 72H 27/0600Z 28.5N 97.8W 40 KT 45 MPH...INLAND 96H 28/0600Z 28.5N 97.8W 35 KT 40 MPH...INLAND 120H 29/0600Z 27.6N 97.0W 35 KT 40 MPH...INLAND $$ Forecaster Avila NNNN