Southwest Louisiana faces a "high risk" of flash flooding from Tropical Depression Nicholas on Wednesday morning, the National Weather Service warned.

Why it matters: Such "high risk" outlooks are rarely issued anywhere in the U.S. There's also a medium risk of flash-flooding in New Orleans, which is still reeling from Hurricane Ida striking the state last month.

• "Life-threatening" flash floods are also expected for other parts of the Deep South, per the National Hurricane Center.

Our thought bubble: The alert is due to the former hurricane slowing down its forward movement. As the bands of rain work east, they're moving into ground more saturated in the wake of Ida — which raises the risk of flash flooding in the rest of Louisiana as well as parts of Mississippi.

Threat level: Rain from the slow-moving storm was expected to produce 5 to 10 inches of rainfall across parts of southern and central Louisiana, southern Mississippi, far southern Alabama, and the western Florida Panhandle through early Friday, the NHC said late Tuesday.

• Isolated storm totals of 20 inches were possible from southern Louisiana to the far western Florida Panhandle.
• "Life-threatening flash flooding impacts, especially in urban areas, are possible across these regions," the NHC warned.

By the numbers: More than 125,000 customers were without power in Texas and over 75,000 others in Louisiana had no electricity on Wednesday morning, according to the utility tracking site poweroutage.us.

The big picture: Nicholas made landfall near Sargent Beach, Texas, as a Category 1 hurricane early on Tuesday.

• It later weakened to a tropical depression, but continued to dump heavy rains on the Houston metro area as it slowly moved its way over southeastern Texas and southwestern Louisiana.

Line of heavy rain slowly moving NE could produce 3 to 5 inches of rain over many locations from now through 7am pic.twitter.com/U7Icd76jCW

— NWS New Orleans (@NWSNewOrleans) September 15, 2021