Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 333 AM EDT Mon Aug 28 2017 Valid 12Z Mon Aug 28 2017 - 12Z Wed Aug 30 2017 ...Life-threatening flash floods to continue across southeast Texas while expanding into coastal southwestern Louisiana... ...A tornado threat remains from the upper Texas Gulf coast into southern Louisiana... ...Heavy rainfall expected over the coastal Carolinas as a tropical cyclone likely forms... Tropical storm Harvey continues to be a slow mover given the weak steering currents. As a result, very little motion has been evident during the past couple of days as it spins west of Houston, Texas. Spiral bands of convection, both near the center itself as well as on the perimeter, will remain foci for extremely heavy rainfall. On early Sunday morning, three hour rainfall totals exceeded 12 inches over southern Houston. Given such a history, extreme rates as these are possible within any training band of thunderstorms. As an expansive area of southeast Texas has seen 20 to 30 inches of rainfall due to Harvey, the grounds are beyond saturation leading to abundant runoff. Consequently, life-threatening flash floods are possible with any additional heavy rainfall. The threat will continue to expand eastward in time into southwestern Louisiana as Harvey drifts toward the upper Texas coast. Additionally, as is common with any tropical circulation, brief tornadoes may form anywhere from Galveston, Texas eastward to just south of New Orleans, Louisiana. The threat is expected to maximize closer to the coast where some of the better instability will reside. While much of the nation focuses on the impacts from Harvey, a potential tropical cyclone is likely to form over the coastal waters of Georgia. The current forecast track takes the circulation east-northeastward, generally grazing the southern Outer Banks of North Carolina. The close proximity to the coastal Carolinas will lead to heavy rainfall, gusty winds, and rough seas in the Atlantic. During the next couple of days, expected rainfall amounts will range from 3 to 5 inches from Myrtle Beach, South Carolina up to the Outer Banks. Elsewhere in the country, broad ridging extending across the western United States will bring a widespread heat wave to the region. Based on the latest forecast high temperatures, a number of daily records may be broken from the West Coast into the Intermountain West. During the next couple of days, highs between 105 and 110 degrees are likely over the interior central valleys of California with mid to upper 90s into the central Great Basin and eastern Oregon/Washington. Relative to climatology for late August, these readings are anywhere from 10 to 20 degrees above average. This is in stark contrast to temperatures across the Southern Plains/Lower Mississippi Valley and Mid-Atlantic/Carolinas with highs 5 to 10 degrees below climatology. Rubin-Oster Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php