Tropical Storm Harvey: SE Texas Impacts 10 AM CDT UPDATE Thursday, August 24, 2017 Prepared by: Dan Reilly, Brian Kyle PLEASE MUTE YOUR LINES AND DON T PUT ON HOLD!
Situation Overview Tropical Storm Harvey Intensifying, now forecast to be a category 3 hurricane at landfall Landfall, middle Texas coast Friday night Storm surge inundation 6 to 10 feet above ground level for Matagorda County up to Sargeant, 4 to 7 feet AGL Sargeant to San Luis Pass, 2 to 4 feet Galveston Bay Steering flow weakens considerably after landfall; slow movement means heavy rainfall & potentially life threatening flooding especially coastal counties Satellite Image of Harvey, Thursday morning
Watches and Warnings Hurricane Warning in effect from Port Mansfield to Matagorda Tropical Storm Warning in effect from Matagorda to High Island Storm Surge Warning is in effect from Port Mansfield to San Luis Pass Storm Surge Watch is in effect from San Luis Pass to High Island
Watches and Warnings (continued) Flash Flood Watch in effect for Matagorda, Jackson, Wharton, Colorado Counties on west Watches will likely be extended eastward later today or tonight
Forecast Cone Forecast to make landfall on the Texas coast (most likely mid-coast) Friday night then stall Track of center within cone 2/3 of the time based on past errors. Note the considerable uncertainty once inland (large hatched cone after landfall)
Wind Probabilities
Most Likely Time of Arrival TS Winds
Rainfall, Flood Threat Landfall then a slow track over the area would mean periods of heavy rain from late Friday into next week. Possibility of 10 to 20 inches with local amounts 20+ possible generally south of I-10; less further inland. There may be a tight gradient on northern edge of the rainfall pattern. Details of track still uncertain; timing and location of heaviest rainfall could still change! Flash Flood Watches have been posted for southwest portions of the area. Will likely be expanded to include more of southeast Texas to account for the weekend and early week heavy rainfall. Keep in mind that the greatest threat probably will not be realized for several days! Do not let your guard down. 7 Day Average Rainfall 15+
Rainfall, Flood Threat Timing of onset and end of heavier rains uncertain Most likely start Matagorda, Jackson Counties, closest to the hurricane, Friday/Friday night continuing Bands east of the center to set up into areas farther east Saturday and Sunday Could be sharp gradient north to south with coastal counties seeing most rain over the multiday period 2 to 3 in 3 to 4 in 15+ 4 to 6 in 6 to 8 in 8 to 10 in 10 to 15 inches 15+ inches
Rainfall, Flood Threat Rivers River modelling based on forecast rainfall If this were to occur could be looking at moderate or major flooding along Lavaca/Navidad, Colorado and San Bernard basins 2 to 3 in 3 to 4 in 15+ 4 to 6 in 6 to 8 in 8 to 10 in 10 to 15 inches 15+ inches
Storm Surge Flooding Threat Storm Surge Warning in effect for immediate coastal areas facing the Gulf of Mexico southwest of San Luis Pass and Matagorda Bay. Storm Surge Watch east of San Luis Pass to High Island including Galveston Bay. Expecting 6 to 10 feet above ground level closer to landfall area and in and around Matagorda Bay 4 to 7 feet Matagorda Bay to San Luis Pass, 2 to 4 feet closer to the Galveston area and Galveston Bay. Water levels will begin to rise Thursday night into Friday morning with coastal flooding possible starting Friday.
Potential Storm Surge Flooding Reasonable worst case scenario for storm surge flooding; Depth above ground level; this map is updated every 6 hours about 1 hour after advisory released https://nowcoast.noaa.gov/
Potential Storm Surge Flooding Reasonable worst case scenario for storm surge flooding; Depth above ground level; will update every 6 hours about 1 hour after advisory released
Potential Storm Surge Flooding Plots show spread of possibilities relative to MLLW; NHC forecasting surge flooding 6 to 9 feet above ground level this area
Potential Storm Surge Flooding Plots show spread of possibilities relative to MLLW; 2 to 4 feet above ground level possible in this area
Marine, Coastal Issues Potential hazard timing along the Texas coast Seas Higher period swell begins showing today. Seas build through the day. Onset of seas > 7 feet within 20 NM (higher offshore): Tonight. Winds Onset of sustained tropical storm / gale force winds within 20 NM: Friday Onset of hurricane force winds within 20 NM: Friday night Wave Heights Fri Night Coastal flooding, surge & tides Onset of coastal flooding risk due to tide, surge & surf: Friday Reasonable worst case storm surge (based on current forecast): 6-10 foot inundation near landfall, tapering to 2-4 feet extreme north and south. Port Status WHISKEY. Normally set when gale force winds are expected to arrive at the port within 72 hours. Port Status X-RAY. Normally set when gale force winds are expected to arrive at the port within 48 hours. Port Status Yankee. Normally set when gale force winds are expected to arrive at the port within 24 hours. Port Status ZULU. Normally set when gale force winds are expected to arrive at the port within 12 hours.
Summary of Marine Impacts Deteriorating marine conditions as early as Thursday. Potential tropical storm or hurricane affecting the Texas coastline Friday. Increasing Winds and Winds/Seas Large surf & strong rip currents Coastal Flooding TS force winds approaching the TX coast Friday. Seas with 20 NM of shore increasing to > 7ft tonight. Large surf. Strong rip currents. Beach erosion. Coastal flood risk as early as Friday. 6-10 feet inundation near landfall. 2-4 feet inundation extreme north/south Periods of rain/storms. Tornadoes possible in spiral bands mainly on the right side of the track Prolonged heavy/flooding rain a good possibility. Spans several days. Potential river flooding and elevated water levels into early next week. Precipitation
Questions? Questions? Dan Reilly Next briefing 4:15 pm Dan.reilly@noaa.gov