| Floater: http://www.ssd.noaa.gov/PS/TROP/floaters/09L/09L_floater.html Track: http://www.nhc.noaa.gov/refresh/graphics_at4+shtml/?cone#contents Hurricane Harvey Discussion Number 19 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Thu Aug 24 2017 Harvey's rapid intensification seems to have slowed for the moment, as an eye seen earlier in satellite imagery has lost definition during the past few hours. In addition, reports from an Air Force Reserve Hurricane Hunter aircraft show that 700-mb flight level winds are in the 75-80 kt range, with reliable surface wind estimates from the Stepped Frequency Microwave Radiometer remaining near 75 kt. The aircraft also reported that the central pressure has slowly fallen to 973 mb inside the 16 n mi wide eye. Based on these data, the initial intensity remains 75 kt, and this could be a little conservative. Harvey has turned a little to the left since the last advisory with the initial motion now 315/9. A mid-level anticyclone over the eastern Gulf of Mexico is expected to steer Harvey generally northwestward with a decreasing forward speed for the next 36-48 h, with the center now forecast to make landfall on the middle Texas coast in about 36 h. This part of the new forecast track has been nudged a little to the left based mainly on the initial position and motion. After landfall, the cyclone is likely to get stuck between the Gulf anticyclone and a stronger anticyclone over the western United States, with little motion likely from 48-96 h. A slow eastward motion appears likely by 120 h due to the influence of a trough in the westerlies digging into the eastern United States. There is some spread in the guidance at that time, with the GFS showing Harvey drifting slowly eastward and the ECMWF showing a faster motion. The new forecast track splits this difference of 5-day forecasts and lies near the consensus models. It is unclear why the intensification has slowed, although it is possibly due to some dry air seen earlier wrapping around the north side of the core convection. Otherwise, Harvey remains in an favorable environment for further strengthening with low vertical shear and high oceanic heat content. The intensity forecast will use the scenario that rapid intensification will resume tonight, with Harvey becoming a major hurricane before landfall in Texas. After landfall, the intensity forecast is based on the scenario that Harvey will weaken over land, but it will remain close enough to the coast so that the weakening will be slower than normal. Thus, the forecast keeps Harvey as a tropical storm from 72-120 h. It is 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 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. 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 Friday 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 25/0300Z 25.2N 94.6W 75 KT 85 MPH 12H 25/1200Z 26.1N 95.6W 95 KT 110 MPH 24H 26/0000Z 27.2N 96.5W 110 KT 125 MPH 36H 26/1200Z 28.1N 97.1W 100 KT 115 MPH...INLAND 48H 27/0000Z 28.6N 97.3W 70 KT 80 MPH...INLAND 72H 28/0000Z 28.5N 97.5W 35 KT 40 MPH...INLAND 96H 29/0000Z 28.5N 97.0W 35 KT 40 MPH...INLAND 120H 30/0000Z 29.5N 95.0W 35 KT 40 MPH...INLAND $$ Forecaster Beven Hurricane Harvey Advisory Number 19 NWS National Hurricane Center Miami FL AL092017 1000 PM CDT Thu Aug 24 2017 ...HARVEY EXPECTED TO STRENGTHEN AS IT MOVES TOWARDS THE TEXAS COAST... ...LIFE-THREATENING AND DEVASTATING FLOODING EXPECTED NEAR THE COAST DUE TO HEAVY RAINFALL AND STORM SURGE... SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION ----------------------------------------------- LOCATION...25.2N 94.6W ABOUT 250 MI...400 KM SE OF CORPUS CHRISTI TEXAS ABOUT 245 MI...400 KM SSE OF PORT OCONNOR TEXAS MAXIMUM SUSTAINED WINDS...85 MPH...140 KM/H PRESENT MOVEMENT...NW OR 315 DEGREES AT 10 MPH...17 KM/H MINIMUM CENTRAL PRESSURE...973 MB...28.74 INCHES WATCHES AND WARNINGS -------------------- CHANGES WITH THIS ADVISORY: None. SUMMARY OF WATCHES AND WARNINGS IN EFFECT: A Storm Surge Warning is in effect for... * Port Mansfield to High Island Texas A Storm Surge Watch is in effect for... * South of Port Mansfield Texas to the Mouth of the Rio Grande A Hurricane Warning is in effect for... * Port Mansfield to Sargent Texas A Tropical Storm Warning is in effect for... * North of Sargent to High Island Texas * South of Port Mansfield Texas to the Mouth of the Rio Grande A Hurricane Watch is in effect for... * South of Port Mansfield Texas to the Mouth of the Rio Grande A Tropical Storm Watch is in effect for... * South of the Mouth of the Rio Grande to Boca de Catan Mexico A Storm Surge Warning means there is a danger of life-threatening inundation, from rising water moving inland from the coastline, during the next 36 hours in the indicated locations. For a depiction of areas at risk, please see the National Weather Service Storm Surge Watch/Warning Graphic, available at hurricanes.gov. This is a life-threatening situation. Persons located within these areas should take all necessary actions to protect life and property from rising water and the potential for other dangerous conditions. Promptly follow evacuation and other instructions from local officials. A Hurricane Warning means that hurricane conditions are expected somewhere within the warning area. A warning is typically issued 36 hours before the anticipated first occurrence of tropical-storm- force winds, conditions that make outside preparations difficult or dangerous. Preparations to protect life and property should be rushed to completion. A Storm Surge Watch means there is a possibility of life- threatening inundation, from rising water moving inland from the coastline, in the indicated locations during the next 48 hours. A Hurricane Watch means that hurricane conditions are possible within the watch area. In addition, interests in southwestern Louisiana should continue to monitor the progress of this system. For storm information specific to your area in the United States, including possible inland watches and warnings, please monitor products issued by your local National Weather Service forecast office. For storm information specific to your area outside the United States, please monitor products issued by your national meteorological service. DISCUSSION AND 48-HOUR OUTLOOK ------------------------------ At 1000 PM CDT (0300 UTC), the center of Hurricane Harvey was located near latitude 25.2 North, longitude 94.6 West. Harvey is moving toward the northwest near 10 mph (17 km/h). This general motion is expected to continue with a decrease in forward speed during the next couple of days. On the forecast track, Harvey will approach the middle Texas coast on Friday and make landfall Friday night or early Saturday. Harvey is then likely to stall near or just inland of the middle Texas coast through the weekend. Reports from an Air Force Reserve Hurricane Hunter aircraft indicate that maximum sustained winds remain near 85 mph (140 km/h) with higher gusts. While Harvey has changed little in strength over the past several hours, strengthening is expected to resume later tonight, and Harvey is expected to become a major hurricane by Friday before it reaches the middle Texas coast. Hurricane-force winds extend outward up to 25 miles (35 km) from the center and tropical-storm-force winds extend outward up to 105 miles (165 km). The latest minimum central pressure reported by the Hurricane Hunter aircraft is 973 mb (28.74 inches). HAZARDS AFFECTING LAND ---------------------- RAINFALL: Harvey is expected to produce total rain accumulations of 15 to 25 inches and isolated maximum amounts of 35 inches over the middle and upper Texas coast through next Wednesday. During the same time period Harvey is expected to produce total rain accumulations of 7 to 15 inches in far south Texas and the Texas Hill Country eastward through central and southwest Louisiana, with accumulations of up to 7 inches extending into other parts of Texas and the lower Mississippi Valley. Rainfall from Harvey will cause devastating and life-threatening flooding. STORM SURGE: The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline. The water is expected to reach the following heights above ground if the peak surge occurs at the time of high tide... N Entrance Padre Island Natl Seashore to Sargent...6 to 12 ft Sargent to Jamaica Beach...5 to 8 ft Port Mansfield to N Entrance Padre Island Natl Seashore...5 to 7 ft Jamaica Beach to High Island...2 to 4 ft Mouth of the Rio Grande to Port Mansfield...2 to 4 ft High Island to Morgan City...1 to 3 ft The deepest water will occur along the immediate coast near and to the northeast of the landfall location, where the surge will be accompanied by large and destructive waves. Surge-related flooding depends on the relative timing of the surge and the tidal cycle, and can vary greatly over short distances. For information specific to your area, please see products issued by your local National Weather Service forecast office. WIND: Hurricane conditions are likely within the hurricane warning area late Friday and Friday night, with tropical storm conditions expected to first reach the coast in the hurricane warning area Friday. These conditions are likely to persist into Saturday in portions of the hurricane and tropical storm warning area. SURF: Swells generated by Harvey are likely to affect the Texas, Louisiana, and northeast Mexico coasts by Friday. These swells are likely to cause life-threatening surf and rip current conditions. Please consult products from your local weather office. TORNADOES: Isolated tornadoes are possible across portions of the middle and upper Texas coast on Friday. NEXT ADVISORY ------------- Next intermediate advisories at 1200 AM CDT and 200 AM CDT. Next complete advisory at 400 AM CDT. $$ Forecaster Beven |