Heavy Rains, Flash Floods Predicted for Greater Phoenix

Heavy Rains, Flash Floods Predicted for Greater Phoenix
Bo Insogna/Flickr

The National Weather Service has issued a flash-flood watch for much of Arizona — including Maricopa County — because of a northward-moving storm system that’s predicted to unleash heavy rains today and Tuesday.

The tropical cyclone is making its way across northern Mexico and is expected to hit the Valley this afternoon. The heaviest downpours will begin late in the day and last through the night as the center of the system moves north toward the Mogollon Rim.

Between tonight and Tuesday morning, 1 to 2 inches of rain are predicted to fall over most of southwest and central Arizona, while areas to the northeast could get at least 2 to 3 inches. 

Radar image of the cyclone as of early Monday morning.
Radar image of the cyclone as of early Monday morning.
NOAA

An NWS forecast states that this type of rain activity is “capable of producing dangerous flash floods” in areas near creeks or other drainage areas so “residents and motorists living or traveling in flood prone areas should concern themselves with this flood potential . . . and be prepared to take immediate action should heavy rain and flooding occur or a flash flood warning be issued.”

A flash-flood watch means conditions are favorable for flash flooding while a flash flood warning means the activity is imminent, explains NWS meteorologist Valerie Myers.

As of Monday morning, rain already is falling in the Yuma area, and Myers says, “It’s just a matter of time before rain and heavy showers increase across the area and become more widespread.”

A tropical cyclone, despite its ominous name, is the generic term for a low-pressure system with thunderstorm activity and heightened winds over tropical or sub-tropical waters. The system making its way toward Phoenix is technically a tropical depression, which means its one step up from a tropical disturbance but not quite a tropical storm. (Tropical storms must have sustained wind speeds of at least 39 miles per hour, and those associated with this system are coming in at about 35 mph.)

But this is not to say that individual thunderstorms won’t produce stronger gusts, Myers says, meaning that if this storm is anything like the ones we’ve experienced in the last few weeks, it’s probably best to keep a flashlight handy. 

Image of water vapor associated with the cyclone early Monday morning.
Image of water vapor associated with the cyclone early Monday morning.
NOAA

***A flash flood watch is in place for the following areas:
-The lower Colorado River Valley
-Northwest and southwest Maricopa County
-Northwest and north central Pinal County
-Southern Gila County/Tonto National Forest Foothills
-The area near Yuma/Martinez Lake


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