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Posted at 02:00 PM ET, 05/21/2012

California hurricane odds extremely low, but not zero


(Courtesy of National Hurricane Center)

The May 15-November 30 eastern Pacific hurricane season is well underway with the National Hurricane Center forecasting that Tropical Depression TWO-E should become Tropical Storm Bud later today. The Center says it could hit southwestern Mexico near the resort city of Manzillo as a Category 2 hurricane on Friday.

Aletta, this year’s first eastern Pacific tropical storm formed on May 14 and died on May 19 without ever threatening land.

Prevailing easterly winds usually push most eastern Pacific tropical storms and hurricanes away from North America, which is why these storms usually attract little public attention.

Nevertheless, nearly every year two or three of these storms move to the east to hit Mexico’s Pacific Coast, sometimes as a Category 3 or stronger storm.

For example, on Oct. 12, 2011, Hurricane Jova hit the Mexican states of Colima and Jalisco, where the resort city of Puero Vallarta is located, with 125 mph Category 3 winds that killed eight people and did an estimated $191 million (in U.S. dollars) damage.

Since hurricanes quickly begin to weaken when they move over cool water, the chilly ocean usually protects California from tropical storms and hurricanes, but not always.

On Oct. 2, 1858, a Category 1 hurricane with winds of 74-95 mph hit San Diego. This storm had been forgotten until Michael Chenoweth, a hurricane historian, and Chris Landsea, who is now science and operations officer at the National Hurricane Center, published their study of the storm in the November 2004 issue of the Bulletin of the American Meteorological Society (BAMS).

Their study was based on weather data from the U.S. Army fort in San Diego and newspaper reports. In addition to hurricane winds in San Diego the storm brought 39-73 mph winds to the coast north to Long Beach and dumped flooding rain across inland areas.

On Sept. 25, 1939, a tropical storm came ashore between San Diego and Long Beach with 50 mph winds, killing at least 45 people, mostly on boats and ships. This storm also brought flooding rain to large areas of Southern California.

Finally, for now at least, on September 13, 1997, forecasters using satellite images estimated that Hurricane Linda, which was then centered 800 miles south of San Diego, was a Category 5 storm with winds faster than 155 mph — making it the strongest eastern Pacific storm ever observed. Even more disconcerting, some Hurricane Center forecasting models were indicating that it could hit Southern California as a Category 1 hurricane. (Cold water offshore would weaken it). Even as a weaker storm, waves and heavy rain would cause major damage if the models were correct.

The National Weather Service and broadcast meteorologists began mentioning the possibility of the storm hitting California while urging residents not to panic.

That was good advice. As Bob Sheets (director of the NHC from 1987-1995) and I say in our 2001 book, “Hurricane Watch: Forecasting the Deadliest Storms on Earth,” reports from NOAA’s Gulfstream IV jet, which collects upper air data from far around storms, “convinced the computer models that Linda would turn away far at sea. NO watches or warnings were issued and Linda did turn away from southern California.”

Linda, the 1939 tropical storm, and possibly the 1858 San Diego hurricane occurred during years when El Nino had brought unusually warm water to the U.S. West Coast.

In their 2004 BAMS article Chenoweth and Landsea say the “implication of this current work is that a hurricane has directly impacted southern California in recorded history and, under the right circumstances, will again hit the region.” Hurricane Linda “had the potential to duplicate the track and impact of the 1858 hurricane,” they said. “Today, if a category 1 hurricane made a direct landfall in either San Diego or Los Angeles, damage would likely be on the order of a few to several hundred million dollars.

“The rediscovery of this storm is relevant to climate change issues and the insurance emergency management communities risk assessment of rare and extreme events in the region.”

By Jack Williams  |  02:00 PM ET, 05/21/2012

Categories:  Latest, Tropical Weather, U.S. Weather

 
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