Flash-flood risks to rise as downpours drench much of Southeast through next week

A push of cool and dry air has slashed humidity in the Midwest and Northeast, but it has stirred the atmosphere up in the Southeast, where rounds of showers and thunderstorms will continue to erupt and drench some communities through much of next week, AccuWeather meteorologists say.

The uptick in shower and thunderstorm activity and extensive clouds will help limit temperatures in the Southeast. Widespread highs in the 80s F are in store, a few degrees below the historical average for the latter half of July, when some areas experience low to mid-90s.

Most areas in the Southeast will remain quite humid in the pattern as the dry air widespread in the Midwest and Northeast will only slightly nose into parts of the Tennessee Valley, southern Appalachians and lower mid-Atlantic coast this weekend.

By next week, the general flow of air over the Southeast states will be from the Gulf of Mexico and the southwestern Atlantic, which will boost humidity levels further and provide more opportunities for showers and thunderstorms to bring torrential downpours.

Any downpour that erupts will have the potential to dump 1-2 inches of rain in an hour, which can easily trigger flash urban flooding of streets and underpasses.

From 2 to 4 inches of rain will fall over much of the Southeast states through the end of next week. This rainfall will work wonders for areas that are abnormally dry or experiencing drought and will help revitalize withering crops and browning lawns.

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For example, Chattanooga, Tennessee, typically receives about 5 inches of rain during July, but so far this month, through Thursday night, only about 0.10 of an inch has fallen. Jackson, Mississippi, has fared only slightly better, with rainfall of 0.77 of an inch compared to a historical average of nearly 5 inches.

There will be a zone where downpours may occur more regularly and result in high cumulative rainfall totals. That zone is likely to extend from the Louisiana and upper portion of the Texas coast northeastward to the southern Appalachians and then to the coasts of North Carolina and Virginia. Some locations in this swath may pick up 4-8 inches of rain, which can lead to rises in small streams and area rivers.

Those with camping plans along small streams in hilly terrain should exercise caution when downpours are in the vicinity or upstream.

Any disturbance in the jet stream or weak area of low pressure can lead to an uptick in thunderstorms. A small percentage of the thunderstorms may become severe with damaging wind gusts. One such zone will extend from eastern Alabama to Georgia, the Carolinas and southern Virginia on Saturday.

For those with a beach vacation in the coming days, as a general rule for daily thunderstorm activity, most storms tend to hold off on the beach until the evening or nighttime hours as the sea breeze fades. However, there can be exceptions to this, especially when the weather pattern is as busy as it will be through next week.

Always seek immediate shelter at the first rumble of thunder or distant lightning, as a deadly strike could occur at a moment's notice.

Meanwhile, AccuWeather meteorologists are tracking a tropical wave of low pressure that will reach Florida later this weekend.

Florida, especially the Peninsula, typically receives a daily dose of pop-up thunderstorms. The storms first occur near the beach during the morning or midday hours, wander inland during the afternoon and fall apart during the evening.

"As the tropical wave approaches and moves northwestward across the state from Sunday to Tuesday, an uptick in the showers and thunderstorms will occur with the potential for some to bring flooding downpours, strong wind gusts and even waterspouts near the beaches," AccuWeather Lead Hurricane Expert Alex DaSilva said.

The tropical wave is not forecast to develop into a tropical depression or a named tropical storm.

Because a significant amount of dust from the Sahara Desert is nearby, rain from late this weekend to next week may appear muddy and leave a residue on exposed surfaces in southern and central Florida.

Overall, the Atlantic basin will remain quiet through next week due to vast areas of Saharan dust and dry air limiting the potential for tropical waves to organize, DaSilva added.