000 WTNT44 KNHC 260301 TCDAT4 Hurricane Harvey Discussion Number 23 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Fri Aug 25 2017 Harvey has continued to slowly strengthen since the last advisory. Air Force Reserve Hurricane Hunter aircraft data earlier indicated 700-mb flight-level winds near 130 kt, and there have been multiple estimates from the Stepped Frequency Microwave Radiometer of winds of 110-115 kt. In addition, there have been winds of 135-150 kt observed at 2500-3000 ft in the north eyewall by the Corpus Christi WSR-88D. Based on these, Harvey is making landfall at this time as a category 4 hurricane with winds near 115 kt. The initial motion is 325/6, a little slower than before. The eye of Harvey should continue this general motion for the next several hours, which would bring it inland over southeastern Texas. After 12 h or so, the hurricane should become embedded in an area of weak steering currents and become nearly stationary. The track guidance is in good agreement that Harvey will move slowly through at least 72 h, and the new forecast track shows a slow cyclonic loop during that time. After 72 h, an equally slow motion toward the north or northeast appears likely. It is unclear at this time whether the center of Harvey will emerge over the Gulf of Mexico, as the guidance is in poor agreement on that. It is clear, though, that Harvey will remain over southeastern Texas or the adjacent waters through the forecast period, thus producing a major rainfall and flooding threat. Gradual weakening is now anticipated as Harvey moves farther inland. However, a large amount of the circulation should remain over the Gulf of Mexico, and the weakening is likely to be slower than normal. The new intensity forecast is slightly changed from the previous forecast, but it still calls for Harvey to remain a hurricane through 24 h and remain a tropical storm through the forecast period. The forecast is based on the premise that the center will remain over land, and the intensities could be higher if the center emerges over the Gulf of Mexico. Key Messages: 1. Harvey is making landfall at this time, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast. Hurricane conditions have been reported in the landfall area. 2. A Storm Surge Warning is in effect for much of the Texas coast. Life-threatening storm surge flooding could reach heights of 9 to 13 feet above ground level at the coast between Port Aransas and Port O'Connor. 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 26/0300Z 28.0N 97.0W 115 KT 130 MPH...ON COAST 12H 26/1200Z 28.6N 97.3W 95 KT 110 MPH...INLAND 24H 27/0000Z 29.0N 97.7W 65 KT 75 MPH...INLAND 36H 27/1200Z 29.0N 97.9W 50 KT 60 MPH...INLAND 48H 28/0000Z 28.7N 97.8W 45 KT 50 MPH...INLAND 72H 29/0000Z 28.0N 97.5W 40 KT 45 MPH...INLAND 96H 30/0000Z 28.5N 96.5W 40 KT 45 MPH...INLAND 120H 31/0000Z 29.5N 96.0W 35 KT 40 MPH...INLAND $$ Forecaster Beven