Remnants of hurricane to bring 'long steady drenching' to Arizona

Rosa takes aim at Arizona, bringing a great change in weather

From 105-degree heat to downpour in three days, forecasters and an ASU professor say remnants from Hurricane Rosa will usher in a big change in the weather this week. 

Previously a powerful Category 4 hurricane with sustained winds of 140 mph, Rosa weakened over the weekend and is expected to bring potentially heavy rain, blustery winds and thunderstorms to the Valley from Sunday through Tuesday, forecasters said. 

Difficult driving conditions may begin Sunday afternoon as tropical moisture ahead of the storm washes into the state. One to three inches of rain could fall in Phoenix and Tempe, according to a flash flood watch issued by the National Weather Service in Phoenix. 

Rosa was creeping northeast Sunday morning as a Category 1 hurricane, with sustained winds of 75 mph, according to the National Hurricane Center. 

The storm is forecast to weaken and arrive as a tropical depression. 

The storm will be unlike Arizona’s typical summer thunderstorms, said Randall Cerveny, an ASU professor at the School of Geographical Sciences and Urban Planning

“We are going to have a whole bunch of rain and it’s ... not the kind of thunderstorm rain that (is) associated with the monsoon (season),” Cerveny said. “It’s going to be a long steady drenching that’s probably going to last for 24 to 48 hours.” 

The heaviest rain will fall on Tuesday as the forecast predicts the center of the remnant hurricane could pass close to Phoenix, but Matthew Hirsch, a meteorologist at the NWS in Phoenix, said heavy rain will be widespread regardless of where the center ends up. 

"Just be prepared for some heavy rain ... allowing some extra time for your drive Tuesday morning," Hirsch said. 

Cerveny said it’s rare for tropical cyclones to hit Arizona and that they can be “drought busters.” 

“We can get enough rain here to make a significant dent in some of our water supplies,” Cerveny said. “In some ways, these things are really, really good. In other ways they can be bad because we’re going to get a lot of water and we could have the risk of flooding or flash flooding.”

 Reach the reporter at or follow @monsoonchaser on Twitter. 

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