A rare Level 4 of 4 excessive-rain risk was widened deeper into Louisiana, Mississippi and Alabama as life-threatening flash flood emergencies spread across the central Gulf Coast.
Radar and short-range models showed backbuilding storm bands already dropping 9 to 11 inches in parts of Louisiana and Mississippi, with another 5 to 8 inches likely as Arthur's remnants tap record tropical moisture and a 45-to-58 mph low-level jet.
Stone County, Mississippi, faced 6 to 10 inches of rain with 3 to 6 inches more forecast, while Pearl River County's emergency shut Interstate 59 near Picayune in both directions and Avoyelles Parish, Louisiana, reported submerged towns and water rescues.
The threat is also expanding east and north into Georgia and the southern Appalachians, while southern Mississippi and Alabama face spin-up tornado risk from Arthur's feeder bands.
Arthur is no longer a named tropical storm, but forecasters say its remnants will keep an atmospheric firehose over the Southeast through Friday, sustaining catastrophic flood danger.