Published Tuesday, June 3, 2003 in the San Jose Mercury News

Weather Corner

Experts expecting more active hurricane season in Atlantic

Hurricane season is here -- and forecasts say it will be a blustery one.

Monday marked the official beginning of the hurricane season in the Atlantic and Caribbean, and already there has been one named storm. This was tropical storm Ana, which lasted April 22 through April 24 and is the first such recorded storm known to have formed as early as April.

But given the unusually cool and wet April weather pattern over California, it is not entirely surprising to see other unusual weather events occurring. The forecast for the 2003 Atlantic hurricane season says this will be a slightly more active year. Forecasters predict there will be 12 Atlantic tropical storms, compared with the average of 10, and that eight of these will reach hurricane strength, compared with the normal six.

Such Atlantic hurricanes won't be the only big storms of the season. The eastern Pacific hurricane season that runs from May 15 to Nov. 30 has also gotten under way with Tropical Storm Andres.

In the Indian Ocean, where tropical storms are called cyclones, the season is from April through December with a peak in activity in May and another peak in November. In the western Pacific, where such tropical storms are called typhoons, there is no specific season -- storms occur all year long.

The primary characteristic for all of these storms is that they form and are fueled by warm tropical waters. The necessary ocean temperature for these storms to grow is at least 80 degrees, which explains why we never see hurricanes over the 50- and 60-degree water along the California coast.

As these storms develop, they are called tropical depressions when their sustained winds are less than 39 mph. The name changes to tropical storms from 39 to 73 mph. A storm hits the hurricane (or typhoon or cyclone) level when its speed reaches 74 mph or more.

Once a storm reaches hurricane strength, it is ranked by category on the Saffir-Simpson scale. A category 1 hurricane has winds of 74 to 95 mph, category 2 of 96 to 110 mph, category 3 of 111 to 130 mph, category 4 of 131 to 155 mph and category 5 of more than 155 mph.

Hurricanes are thought of primarily as devastating wind storms, but only about 12 percent of U.S. hurricane deaths result from the wind. Instead, freshwater flooding from heavy rainfall accounts for most of the deaths -- about 59 percent. Surf and offshore accidents, hurricane-induced tornadoes and storm surges account for the rest.

More information about the current hurricane season and background information on hurricanes can be found at hurricane.htm.

Q In San Jose, which season has the most dew? Lauren Mitchell, second grade - San Jose

A Winter in the Bay Area will typically have the most dew because of the lower temperatures and higher humidities. The cool temperatures allow the air to condense moisture in the air into tiny droplets.

The conditions most likely to produce dew are clear, calm nights when the ground is wet due to recent rains.

Q How is it that, despite similar latitudes, the northern coast of California doesn't get snow and the coast of lower Massachusetts does? As a native Californian, it's a strange thing to go to Massachusetts and see snow on the beach!  Christy Somers - Santa Rosa

A It's all a matter of air masses. The weather systems that pass through Northern California develop over the North Pacific Ocean and are classed as ``maritime polar'' -- while they are wet, they are relatively mild and usually only produce rain at sea level. Conversely, the air masses that bring storms to New England originate over the Arctic and northern Canada, are much colder and can cause there to be both sand and snow on the beaches of New England.

Q Does our wet spring mean we may have a milder-than-usual summer? I believe the last time we had a spring with ``unspringlike'' weather, the summer temperatures were below average.  Sal Murillo - Gilroy

A It would be nice if there were some good correlation from one season to the next. But, alas, from all the data that I have looked at, there is not a good correlation from the conditions of one season to those of future seasons.

Q Tornadoes are an incredible force, but can I assume that they do not occur when mountains get in their way? For a tornado to originate, doesn't this phenomenon require enough flat ground to generate the power to destroy anything in its path? Were it not for the Appalachians, would Tornado Alley extend beyond Ohio? Tom Dryg - Los Gatos

A One of the more persistent myths about tornadoes is that they do not occur in mountainous areas. While they usually are not as intense as those over the Plains and the Midwest, there are tornadoes in mountain regions. The reason they aren't as strong is that the wind shear needed for their formation is often disrupted by the turbulent flow of air over and around the mountains.

Jan Null, founder of Golden Gate Weather Services, is a retired lead forecaster with the National Weather Service. Send questions to him c/o Weather Corner, San Jose Mercury News, 750 Ridder Park Drive, San Jose, Calif. 95190. You also can telephone questions at (510) 657-2246, fax them to (510) 315-3015 or e-mail them to or fill out a form online at