Monsoon Storms Could Bring Flash Flooding, Hail To Tucson Monday

TUCSON, AZ — Southern Arizona faces an elevated monsoon threat Monday, with afternoon and evening thunderstorms capable of producing flash flooding, severe winds and hail, according to the National Weather Service in Tucson.

A Flood Watch is in effect from 2 to 10 p.m. Monday for areas from Tucson westward, including western Pima County and the Tohono O'odham Nation, according to the forecast discussion issued at 9:06 a.m. Monday.

Conditions are in place for thunderstorms to develop, with the best chances centered from Tucson west, forecasters said. Monday is expected to be a transition day, meaning storms could bring both a severe wind threat and a flash flooding threat.

The forecast discussion gives a 10% probability of 50-knot winds within a 40-kilometer area. Those winds could loft blowing dust. Thunderstorms may also become longer-lived because of 20 to 30 knots of wind shear.

Any storm that develops could produce 1 to 3 inches of rainfall, according to the weather service. That amount of rain could lead to running washes, flooded low-water crossings and flooded roadways.

Hail up to one inch in diameter is also possible.

When Storms Could Develop

Storms could begin developing around 1 or 2 p.m. in Santa Cruz County and the White Mountains, according to the forecast.

Storm coverage is expected to increase around 3 or 4 p.m. before storms move northwest and begin exiting the area around 10 or 11 p.m.

Overnight activity could continue along the international border in Santa Cruz County and over the Tohono O'odham Nation, the weather service said.

Monday and Wednesday are expected to be the most active days of the week, according to the weather service synopsis.

Daily chances for showers and thunderstorms are expected through at least Thursday before a drier southwest flow aloft reduces storm coverage Friday into the weekend.

Southeastern Arizona remains under a slight chance of excessive rainfall from Monday through Thursday. Precipitable water values between 1.20 inches and 1.70 inches are expected to support the potential for heavy rain.

Temperatures are expected to remain near normal Monday and Tuesday before falling about 3 to 6 degrees below normal Wednesday and Thursday. Temperatures are expected to warm again into the weekend.

Outside of thunderstorms, winds are expected to remain terrain driven at around 10 mph, with occasional afternoon gusts reaching 20 mph.