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Tropical storm blows through Southwest

Patrick McCartney

Linda was a bust, but Nora was naughty.

For the fourth time this century, a tropical cyclone struck the Southwest United States with the strength of a tropical storm.

Tropical Storm Nora drenched Arizona and portions of Southern California, and triggered showers as far north as Lake Tahoe. Tropical showers brought rain to Los Angeles after a record 218 days with no precipitation.

By contrast, Hurricane Linda several weeks ago was the strongest hurricane ever observed in the Eastern Pacific, but instead of clobbering Southern California, it took a left turn and ran out of steam over the open ocean.

And, yes, this year’s El Nino condition probably played a part in steering Nora into the Southwest, say climatologists who have studied the history of Southwest storms.

“This is definitely a classic type of situation for El Nino with tropical cyclones,” said Kelly Redmond, regional climatologist with the Western Regional Climate Center in Stead, Nev. “The run-of-the-mill September is usually uninteresting, but this year will be way out on the end of the spectrum.”

According to records compiled by Bob Webb of the U.S. Geological Survey in Tucson, Ariz., a strong link exists between El Nino conditions and tropical cyclones that plow into California and Arizona. In seven years this century, more than one remnant of a tropical cyclone has struck the Southwest, and an El Nino condition existed in six of those years.

El Nino is the popular name given to the cyclic fluctuation of ocean temperatures in the tropical Pacific Ocean. Every five to 10 years, warm water migrates to the Eastern Pacific, causing the trade winds to weaken or die off, changing rainfall patterns around the world.

Redmond said El Nino conditions increase the chance that a tropical storm will strike the U.S. mainland.

“The number of tropical cyclones appear the same, but there’s a higher probability of them curving back into the continent,” Redmond said. “Tropical storms like warm water. With an El Nino, they can get closer to the United States before getting killed off.”

Before Nora struck Arizona Thursday with winds up to 60 mph, only three other times this century did tropical cyclones strike the Western United States as tropical storms, with winds above 40 mph.

Two of the tropical storms – Joanne in 1972 and Kathleen in 1976 – struck Arizona, while just one tropical storm, in September 1939, has hit California. The 1939 storm crossed the coast at Long Beach with sustained winds of 50 mph and dropped more than 5 inches of rain in Los Angeles on Sept. 25.

Despite the early brush with this year’s El Nino, the Tahoe Basin is not guaranteed a wet winter, say climatologists. The condition increases rainfall in the Southwest and decreases in the Northwest, with Central California having only a slightly better-than-average chance of a wetter winter.


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