There a few factors driving the danger. The most immediate is the heavy rain, which is falling thanks to a storm system that stalled over the region. Extremely warm sea surface temperatures are partially behind the rainfall. The surface of the Gulf of Mexico is about 90°F — 4°F above average for this time of year — and that’s helping provide a constant source of moisture to the storm system. In New Orleans, atmospheric moisture on Friday was among the top 5 ever recorded in August and on par with past hurricane measures according to Capital Weather Gang.
Warmer ocean temperatures are also one of the hallmarks of global warming as most of the heat the planet is accumulating is ending up in ocean.
Heavy downpours are also on the rise across the U.S. due in part to climate change. Louisiana has seen a 15 percent increase in since 1950, but some cities in the region have seen even more notable increases. Baton Rouge has had seen 120 percent increase in days with heavy rainfall according to a Climate Central analysis.
The current bout heavy rain is only part of the story. The region has had a steady dose of precipitation all week, soaking soil to the point where it can’t hold anymore water. That’s helping drive flooding. Reports indicate that 500-year floodplains are already underwater and more rain could push floodwaters to even higher ground.
Even after the heaviest rain has past, flooding will continue to be a threat as all the water works its way down rivers. A number of rivers in southeast Louisiana are forecast to reach record flood levels and remain there for days. That’s why even after the flash flood warnings expire on Saturday morning, flood warnings will remain in place until at least Monday