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Hurricane Harvey Forecast Discussion Number 20
2017-08-25 10:47:15| National Hurricane Center (Atlantic)
Issued at 400 AM CDT Fri Aug 25 2017 000 WTNT44 KNHC 250847 TCDAT4 Hurricane Harvey Discussion Number 20 NWS National Hurricane Center Miami FL AL092017 400 AM CDT Fri Aug 25 2017 The satellite presentation has improved during the past several hours with an intermittent eye feature surrounded by a ring of very deep convection. There are various cyclonically curved convective bands primarily to the north of the eye and the outflow is fair. NOAA and Air Force Hurricane Hunter planes penetrated the eye various times during the past several hours, and the most significant data were a flight-level peak wind of 103 knots, and a peak SFMR surface wind of 88 kt. The central pressure dropped to 967 mb. Based on these data, the initial intensity was adjusted upward to 90 kt. Another reconnaissance plane will be in the eye of Harvey shortly. Since Harvey is embedded within light shear and moving over warm waters, additional strengthening is anticipated before landfall in about 24 hours. Thereafter, gradual weakening is forecast but since a good portion of the circulation will remain over water, the weakening process could be slower than normal. Radar and reconnaissance fixes indicate that Harvey is moving toward the northwest or 320 degrees at 8 kt. The hurricane is on the western edge of a persistent area of high pressure over the eastern Gulf of Mexico, and this pattern will maintain the current hurricane motion until landfall. Once Harvey is inland over Texas, the steering currents are forecast to collapse and the cyclone should begin to meander, prolonging the flooding conditions for several days. The track guidance between now and landfall is very consistent and there is high confidence in the track forecast. After landfall, the track models show large variability and the confidence is low. In any case, NHC forecast depicts a slow moving tropical cyclone near or over Texas for the next five days. Once again, it is very critical that users not focus on the exact forecast track of Harvey, since cycle-to-cycle adjustments 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. Key Messages: 1. Harvey is expected 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 this morning, as tropical-storm-force winds will first arrive in the hurricane and storm surge warning areas later today. 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. Devastating and life-threatening flooding is expected across the middle and upper Texas coast from heavy rainfall of 15 to 25 inches, with isolated amounts as high as 35 inches, from today through next 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. 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 25/0900Z 25.9N 95.4W 90 KT 105 MPH 12H 25/1800Z 26.9N 96.3W 105 KT 120 MPH 24H 26/0600Z 28.0N 97.1W 105 KT 120 MPH 36H 26/1800Z 28.5N 97.4W 65 KT 75 MPH...INLAND 48H 27/0600Z 28.5N 97.5W 60 KT 70 MPH...INLAND 72H 28/0600Z 28.3N 97.0W 35 KT 40 MPH...INLAND 96H 29/0600Z 28.5N 96.0W 35 KT 40 MPH...OVER WATER 120H 30/0600Z 29.5N 95.0W 35 KT 40 MPH...INLAND $$ Forecaster Avila
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