Phoenix, Arizona — A dangerous stretch of heavy rain and flooding is developing across the Southwest as tropical moisture associated with Tropical Storms Polo and Rachel pushes north from Mexico, threatening Arizona, New Mexico and Colorado with several days of wet and potentially hazardous weather.
The biggest concern is expected Tuesday, when a surge of tropical moisture will spread across the region. Rainfall totals of 1 to 2 inches are possible across parts of Arizona, New Mexico and Colorado, while some locations in the Texas and Oklahoma Panhandles could receive more than 2 inches.
Forecasters are particularly concerned about flooding in New Mexico, where already-saturated areas could struggle to handle additional rainfall.
New Mexico Faces the Greatest Flood Threat
Tuesday’s weather setup could bring life-threatening flooding to portions of New Mexico, with a Level 3 out of 4 flood threat in place across parts of New Mexico, Arizona and Colorado.
The threat is being fueled by a large surge of tropical moisture moving northward from Mexico.
As the remnants of Hurricane Polo move into the Southwest late Tuesday evening, persistent rainfall is expected to spread farther north. Some areas in Mexico have already been experiencing rainfall rates of 1 to 2 inches per hour, providing a substantial amount of moisture for the developing storm system.
Heavy rain falling over a short period can quickly overwhelm drainage systems, streams and low-lying areas.
Tropical Moisture Could Keep Rain Falling
The Southwest is not expected to dry out immediately after Tuesday.
Instead, repeated rounds of rainfall could continue through Thursday, increasing the potential for additional flooding as the ground becomes increasingly saturated.
The overall rainfall total could reach 2 to 3 inches in parts of the region by the end of the event, although amounts will vary significantly depending on the location and movement of the heaviest rain.
The prolonged nature of the rainfall is one of the biggest concerns. Even if individual rounds of rain are not severe, repeated precipitation can create increasingly dangerous conditions.
Phoenix and Las Vegas Could See More Rain
Major Southwest cities are also being watched as the tropical moisture spreads north.
Prediction markets cited in the original forecast are pricing in a 99% chance of rainfall in Phoenix and Las Vegas, highlighting the broad reach of the moisture surge.
For Phoenix, the threat comes after a period in which intense tropical moisture can produce sudden changes in rainfall conditions. Heavy downpours could create localized flooding, difficult travel and dangerous conditions around normally dry washes and low-lying areas.
Las Vegas could also see thunderstorms and periods of rain as the moisture moves through the region. The National Weather Service has an active flood watch for Phoenix through Tuesday night, with thunderstorms also possible.
Trees and Power Lines Could Become a Problem
Flooding is not the only concern associated with the storm system.
Strong thunderstorms and persistent moisture could contribute to falling trees and power lines, particularly where stronger winds accompany the heaviest rainfall.
Thunderstorms can also produce brief bursts of intense rain that make road conditions deteriorate quickly.
Drivers across Arizona, New Mexico and Colorado should be prepared for rapidly changing conditions, particularly Tuesday and Wednesday when the tropical moisture is expected to be most influential.
Hurricane Polo’s Moisture Could Trigger Major Flooding Across Texas and the Southwest This Week
Wet Weather Could Last Through Thursday
The Southwest’s weather pattern is expected to remain unsettled through the end of the week.
Rainfall could continue in repeated waves through Thursday, with additional precipitation adding to the flood risk in vulnerable areas.
The combination of moisture from the tropics, persistent rainfall and thunderstorms creates a setup that could produce significant flooding even outside areas that receive the highest individual rainfall totals.
Residents under flood watches should continue monitoring local weather alerts and avoid driving through flooded roads or moving water.
The most serious conditions are expected to develop Tuesday, but the threat could remain elevated as additional rain moves across the region.
Is your city expecting heavy rain from this tropical moisture surge? Share your city and state in the comments and let us know whether you’re already seeing flooding, thunderstorms or other impacts.
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