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| #899584 (Received by flhurricane at: 4:59 PM 25.Aug.2017) TCDAT4 Hurricane Harvey Discussion Number 22 NWS National Hurricane Center Miami FL AL092017 400 PM CDT Fri Aug 25 2017 Despite its concentric eyewall structure, Harvey's winds have increased during the day. NOAA and Air Force Reserve Hurricane Hunter planes have measured maximum flight-level winds of 129 kt and SFMR winds to 102 kt. Based on these data, Harvey's maximum surface winds are estimated to be 110 kt. Harvey's central pressure has also continued to fall, and the latest estimate based on dropsonde data is 941 mb. Harvey still has not slowed down, and the initial estimate is 325/9 kt. Based on the forecast track, Harvey is expected to make landfall along the middle Texas coast tonight. After that, the track models insist that the hurricane will slow down considerably during the next 24 hours, and it is likely to move very little between 36 and 120 hours. In fact, there has been a somewhat notable change in the guidance, with very few of the models showing Harvey lifting out toward the northeast by the end of the 5-day forecast period. As a result, the NHC track forecast has been pulled back a bit and keeps Harvey near or just inland of the Texas coast through the middle of next week. This slow motion only exacerbates the heavy rainfall and flooding threat across southern and southeastern Texas. Harvey may continue to strengthen during the 6-12 hours it has before landfall, but regardless it is expected to make landfall at major hurricane strength. Gradual weakening is anticipated after the center moves inland, but Harvey's slow motion will keep a significant portion of its circulation over water, which may slow the weakening rate. As a result, the NHC intensity forecast leans closer to the global model guidance instead of the statistical- dynamical guidance, which seems to weaken Harvey too fast. Harvey could maintain tropical storm strength for the entire 5-day forecast period due to its proximity to the northwestern Gulf of Mexico. Key Messages: 1. Harvey will make landfall tonight, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast. Tropical-storm-force winds have moved onshore in portions of the warning areas and conditions will continue to deteriorate as the eye of Harvey approaches the middle Texas coast tonight. 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. Due to the slow motion of Harvey and a prolonged period of onshore flow, water levels will remain elevated for several days. 3. Catastrophic and life-threatening flooding is expected across the middle and upper Texas coast from heavy rainfall of 15 to 30 inches, with isolated amounts as high as 40 inches, through Wednesday. Please refer to products from your local National Weather Service office and the NOAA Weather Prediction Center for more information on the flooding hazard. FORECAST POSITIONS AND MAX WINDS INIT 25/2100Z 27.5N 96.5W 110 KT 125 MPH 12H 26/0600Z 28.2N 97.0W 100 KT 115 MPH...INLAND 24H 26/1800Z 28.8N 97.5W 75 KT 85 MPH...INLAND 36H 27/0600Z 28.9N 97.8W 60 KT 70 MPH...INLAND 48H 27/1800Z 28.6N 97.8W 50 KT 60 MPH...INLAND 72H 28/1800Z 28.1N 96.9W 40 KT 45 MPH...INLAND 96H 29/1800Z 28.5N 96.0W 40 KT 45 MPH...OVER WATER 120H 30/1800Z 29.5N 95.5W 35 KT 40 MPH...INLAND $$ Forecaster Berg |
