Significant heavy rain/flash flooding threat with gusty winds wellahead of Potential T.C. One expected to impact southern Texas onWednesday......Severe Thunderstorms and Excessive Rainfall possible over portions ofthe Great Plains and Upper/Middle Mississippi Valley tonight......A heat wave will persist over the Great Lakes, Ohio Valley and theNortheast through midweek...Potential T.C. One will likely strengthen while it slowly approachesMexico's northeast coast tonight. This system carries with it; coastalflooding, wind impacts, and a significant plume of tropical moisture,which it is poised to transport into the central Gulf Coast down tonortheastern Mexico over the next couple of days. There's a Moderate Risk(at least 40%) of Excessive Rainfall leading to Flash Flooding from theLouisiana-Texas coast down to just north of Corpus Christi, Texas wherethe heaviest axis of precipitation is likely to occur tonight. A broaderSlight Risk (at least 15%) of Excessive Rainfall is also in place from thecentral Louisiana Gulf Coast down to southern Texas. PTC One is thenforecast to strengthen into a Tropical Storm Wednesday afternoon beforemaking landfall over northeastern Mexico that evening. Tropical moisturewill likely continue to flow into southern Texas and the Rio Grande Valleywhere yet another Moderate Risk of Excessive Rainfall is in effect. T.S.One will quickly weaken upon landfall Wednesday night before eventuallydiminishing Thursday evening. Additional heavy rainfall may certainlycontinue over the Rio Grande Valley and south Texas on Thursday beforerainfall rates drop and conditions improve. All in all, Potential TropicalCyclone One is currently forecast to produce rainfall totals of 5 to 10inches from northeast Mexico to south Texas, with maximum totals of 15inches possible.A line of thunderstorms will develop out ahead of a cold front sweepingacross the Plains this afternoon. The Storm Prediction Center issued aSlight Risk of Severe Thunderstorms from parts of the Upper MississippiValley into the Mid Missouri Valley/Central Plains and Southern HighPlains where scattered to severe storms are expected to produce large hailand severe/damaging winds. A few tornadoes may also occur. Rainfall rateswithin some of these storms to support Excessive Rainfall, which is whythere is currently a Slight Risk in effect from the Upper Midwest down tothe Central Plains.Meanwhile, a heat wave continues to impact much of the Ohio Valley, GreatLakes, Northeast and Mid-Atlantic this week. Widespread daily records arelikely for afternoon high temperatures and warm overnight lows, with somemonthly records possible. Heat index readings are expected to peak from100 to 105 degrees in many locations. Those without access to reliable airconditioning are urged to find a way to cool down. Record warm overnighttemperatures will prevent natural cooling and allow the heat danger tobuild over time indoors without air conditioning. Conditions improveslightly this weekend.