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ZCZC MIATCDAT4 ALL TTAA00 KNHC DDHHMM Hurricane Harvey Special Discussion Number 17 NWS National Hurricane Center Miami FL AL092017 100 PM CDT Thu Aug 24 2017 This special advisory is being issued to update Harvey's initial and forecast intensities through the 48-hour period. The storm surge values in the public advisory have also been updated based on the new intensity forecast. Recent data from Air Force Reserve and NOAA Hurricane Hunter aircraft indicate that Harvey's maximum sustained winds have increased to 75 kt. The Air Force plane measured maximum 850-mb flight-level winds of 88 kt and reliable SFMR winds around 75 kt. Based on the hurricane's current rate of intensification, the forecast intensities at 12 and 24 h have been raised by 15 kt, with a 10-kt increase at 36 h. There are no changes to the track or wind radii forecast with this special advisory. It is critical that users not focus on the exact forecast track of Harvey, since cycle-to-cycle adjustment are likely. All locations within the hurricane and storm surge warning areas should be preparing for the possibility of major hurricane-force winds and life-threatening storm surge. Note that this special advisory takes the place of the scheduled 100 PM CDT (1800 UTC) intermediate advisory. Key Messages: 1. Harvey has intensified rapidly, and is forecast to be a major hurricane at landfall, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast. Preparations to protect life and property should be completed by tonight, as tropical-storm-force winds will first arrive in the hurricane and storm surge warning areas on Friday. 2. A Storm Surge Warning is in effect for much of the Texas coast. Life-threatening storm surge flooding could reach heights of 6 to 12 feet above ground level at the coast between the north entrance of the Padre Island National Seashore and Sargent. For a depiction of areas at risk, see the Storm Surge Watch/Warning Graphic at hurricanes.gov. 3. Life-threatening flooding is expected across much of the Texas coast from heavy rainfall of 12 to 20 inches, with isolated amounts as high as 30 inches, from Friday through early next week. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. 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. This map best represents the flooding potential in those locations within the watch and warning areas. FORECAST POSITIONS AND MAX WINDS INIT 24/1800Z 24.4N 93.6W 75 KT 85 MPH 12H 25/0000Z 24.9N 94.2W 85 KT 100 MPH 24H 25/1200Z 26.0N 95.3W 105 KT 120 MPH 36H 26/0000Z 27.3N 96.3W 110 KT 125 MPH 48H 26/1200Z 28.3N 97.0W 100 KT 115 MPH...INLAND 72H 27/1200Z 29.0N 97.7W 40 KT 45 MPH...INLAND 96H 28/1200Z 28.5N 97.5W 35 KT 40 MPH...INLAND 120H 29/1200Z 28.5N 96.5W 30 KT 35 MPH...INLAND $$ Forecaster Berg NNNN