Monsoon could be wetter than normal


Kelly Presnell / Arizona Daily Star 2012
In the aftermath of an evening summer storm, lightning arcs through the night skies over Saguaro National Park West. This photo was taken on Aug. 21, 2012. A good lightning storm is sure to bring out the photographers.

4 hours ago • By Douglas Kreutz


Photos: Monsoon 2013

Why the monsoon matters

Roughly half of Tucson's annual rainfall comes during the monsoon in a normal year — but the city has some catching up to do on moisture this year.
Tucson has received a paltry 0.61 inches of rain since the beginning the year. Normally we've had about 3 inches of rain by this date.

The moisture is vitally important for a variety of reasons: It benefits native vegetation, reduces the need for watering landscape plants, minimizes the impact of wildfires and cools the city at least temporarily.

The monsoon — Tucson’s summer rainy season — begins Sunday, and here’s a splash of good news for our drought-stricken area: Weather experts say we could see more rain than normal.

“A computer model is showing slightly favorable chances for a wetter-than-normal monsoon,” said J.J. Brost, a meteorologist with the National Weather Service. “This is encouraging compared to what it’s been in the last few years,” when the models showed equal chances for a drier-than-normal, normal, or wetter-than-normal season.

Normal rainfall for the monsoon, defined as the period from June 15 through Sept. 30, is 6.08 inches.

Last year, the city got a meager 3.74 inches during that period.

PREDICTIONS ARE COMPLEX

This year’s encouraging model was prepared by the Climate Prediction Center, an arm of the National Weather Service.

“Their climate models are similar to our weather models,” Brost said, noting that prediction factors can include temperature, moisture in the atmosphere, wind speeds and ocean water temperatures. “They look for signals all over the hemisphere and consider what those signals have meant in the past.”

One well-known factor in long-range predictions is known as El Niño.

“We are in an El Niño event when the surface waters in the Pacific Ocean along the equator are warmer than they normally are,” Brost said. “When they are colder than they normally are, that’s a La Niña.”

He said we currently are in an El Niño that is expected to continue through the monsoon — but that might not tell us much about monsoon rainfall.

“If there’s an El Niño in the winter, it usually means more moisture, but that doesn’t hold up in the monsoon,” Brost said. “There’s really not a strong correlation between El Niño and the monsoon in the Southwest.”

STORMS POSE THREATS

As much as rain is needed, the storms that bring it can be violent in nature and potentially dangerous.

“An important takeaway message is that no matter what the overall outlook, we’re going to get some thunderstorms this year,” Brost said.

“With those thunderstorms come threats such as lightning, downburst winds and flash flooding — and these can be life-threatening.”

He said even one thunderstorm “could create significant impacts. If it’s a wetter-than-normal monsoon, it will probably mean more lightning, flash flooding and downburst winds as well.”

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