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What was once Hurricane Miriam has weakened into a tropical storm in the Pacific Ocean, and the reduction in the storm's strength will also mean less rain in Southern Arizona than earlier forecasts projected.

There's now about a 10 percent chance of rain in the Tucson metropolitan area, said Ken Drozd, warning coordination meteorologist at the National Weather Service in Tucson.

The higher elevations may have about a 30 percent chance of rain in the coming days, he said.

This change results from circumstances that often weaken tropical storms and hurricanes as they head north from the warmer parts of the Pacific, Drozd said.

“Quite a bit of cold water is encountered, because the flow generally in the Pacific along the west coast of the United States is from north to south, so there’s cooler air always infiltrating from the northern Pacific, so that’s why when you go along the California coast it’s usually pretty cool water," he said.

"That’s why you don’t usually hear about San Diego or Los Angeles getting just smacked with a large hurricane, they just can’t sustain that far northward with any intensity," he said.

That's different from the conditions in the Atlantic and Gulf of Mexico, Drozd said.

“In the Atlantic, as you move north, you encounter very warm waters in the Gulf of Mexico which allow hurricanes to continue their intensity and strengthen as they enter the Gulf," he said.