“Precipitation totals of 6 to 8 inches are possible,” said the NWS Weather Prediction Center (WPC).
Five million people in parts of Southern Louisiana, Mississippi and Alabama will be under lightning-fast flooding until Thursday.
Life-threatening floods can occur in the next 48 hours from Louisiana in southern Mississippi to lower Alabama. Precipitation rates of nearly 1.5 inches per hour have already dropped with a few storms.
The main ingredient for the heavy rainfall potential is the moisture in the Gulf of Mexico. The old adage “It’s not the heat; it’s the humidity” applies here. Relative humidity is usually only displayed as a number on a daily weather forecast. When the number is 100%, you know the air is stuffy – there may even be fog.
That number you are seeing is only a measurement of the Earth’s surface, but when the relative humidity is 100% up to 12,000 meters above the ground – which will happen today through Thursday along the Gulf Coast – the flooding potential increases from the intense rainfall of that available moisture.
This very humid air pattern will remain in place for the next 48 hours in Louisiana, Mississippi and Alabama.
Urban and minor power floods will be significant with the stronger storms. Even larger rivers can experience major floods.
Given the recent heavy rainfall that has already taken place, some rivers are now in the inundation phase and may continue to rise, the NWS’s Michael Mugrage said in Mobile.