A historic plume of atmospheric moisture from Hurricane Polo is moving northward through the Southwest with rainfall rates up to two inches per hour, creating flash flood conditions rarely seen this far north. The amount of moisture is expected to be near or above record levels for late September across parts of Arizona, New Mexico, Texas, and Oklahoma, according to The Weather Channel.
The flooding poses a major threat to millions across the region. Over 150 million people in 30+ states face dangerous flood risks this week, according to FOX Weather. A Level 3 out of 4 flash flood risk covers more than 230,000 square miles across southern and eastern Arizona, much of New Mexico, southern Colorado, the Texas and Oklahoma Panhandles, and southwestern Nebraska—an area larger than any U.S. state except Alaska and Texas.
Poло made its second landfall near Guaymas on Mexico's Pacific coast on Tuesday as a Category 1 hurricane with maximum sustained winds around 120 km/h, according to CBC. The storm had previously battered Baja California as a Category 2 storm. While no lives were lost in Baja California Sur, the U.S. National Hurricane Center warned that Polo's moisture-laden remnants could trigger a deluge across the American Southwest and Plains. In the U.S., a box truck was already swept away by floodwaters north of Phoenix on Tuesday, though the driver escaped safely. Flooding overwhelmed roads and sections of Interstate 10 between Tucson and Phoenix, and washes in New Mexico are running high.
The flooding threat will spread eastward Wednesday and Thursday as moisture from Tropical Storm Rachel combines with the larger storm system, bringing the danger across the Plains and into the Midwest.