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Monsoon forecast: an early, wet southern Arizona season

It will be an early and wet monsoon if a long-range outlook from the federal Climate Prediction Center holds true.

Based on hints in Caribbean and Pacific surface temperatures, the Rocky Mountain snowpack, and Plains states drought and computer models, the agency calls for above average rainfall for southeast Arizona in June, July and August.

University of Arizona monsoon researcher Christopher Castro tentatively agreed.

“Those indicators are pointing to an early and wet monsoon,” Castro said.

Two computer models foresee rapid development of a typical monsoon high pressure zone in May, then a rapid advance northward of the zone, the CPC outlook said.

Each year, this high pressure zone settles over the Four Corners area in northeast Arizona, shifting our prevailing winds from the west to the southeast. This wind shift is the monsoon, and when it happens early we typically get more rain than average.

Of the past 20 monsoons, Tucson got less than average rainfall (6.06 inches) in 13 and more than average in seven, according to the National Weather Service. Last year, the airport, where official tallies are kept, got 5.52 inches, the weather service said.

Tucson typically gets about half of its annual rainfall during the monsoon, June 15-Sept. 30.

Rain is not in this week’s forecast, with temperatures expected to climb into the mid-90s by Friday. Windy, dry conditions prompted a fire danger warning for Tuesday across the southeast quadrant of Arizona.


By the numbers

6.06 inches, normal monsoon rainfall for Tucson

5.52 inches, last year’s total

13.84 inches, wettest monsoon (1964)

1.59 inches, driest monsoon (1924)

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