Areas covered by watches due to what the weather service's Las Vegas office calls "abundant tropical moisture from Hurricane Rosa" include southern Nevada, southeastern California, southwestern and central Utah and the western two-thirds of Arizona.
The best chance for rain in Mohave County is late Sunday night into early Monday morning.
Hurricane Rosa, in the eastern Pacific, on Thursday night was upgraded to a major category 4 hurricane with 125 miles per hour sustained winds.
The storm had maximum sustained winds of 120 mph and was located 625 miles southwest of the southern tip of Baja California as of Friday evening.
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Hurricane Rosa is a major hurricane in the Pacific that will impact Baja California next week with heavy rain and possible flooding for the Desert southwest. The storm is expected to drop 3-to-6 inches of rain, with isolated spots of 10 inches of rain in the next few days, the weather service said.
Rosa is expected to make landfall Monday as a tropical storm then continue moving northeast, soaking the southwestern US.
"Heavy rainfall associated with Rosa or its remnants is expected to affect parts of the southwest United States by early next week, which could cause flooding in this region", the National Hurricane Center said. Forecasters say up to 4 inches could fall in some areas through Wednesday, including Flagstaff, Payson, Prescott and the Grand Canyon's South Rim.