Hurricane 101

The technical terms and path projections swirling around the storm aren't that hard to master.

Evacuation Zones

Evacuation zones are created according to the expected threat of a storm surge along the coast.

Winds from a tropical storm or hurricane push water against the shoreline, causing it to rise far above normal tide levels.

A small hurricane's storm surge can flood houses along the Gulf coast and the shore of Tampa Bay with 5 feet or more of water.

A powerful hurricane can cause a storm surge high enough to submerge houses to their rafters.

Evacuations are ordered to move residents away from expected flooding.

On evacuation maps, each zone is given a different color for ease of understanding.

Most counties use five zones labeled A through E. The A zone is vulnerable to even weak storms; the E zone would flood during only a very powerful storm. Orders to evacuate are given by zone, and not all zones may be affected.

Check an evacuation map for your county to learn whether you live in a zone and which one. If you're in E, and only A and B must evacuate, you can stay home.

That is, unless you live in a mobile home or believe your house would not withstand the hurricane's winds. All mobile home dwellers must evacuate.

Evacuations are ordered by zones based on the strength of the storm as it threatens to make landfall.

Time To Evacuate

Whether to order an evacuation is one of the most ticklish and important of the decisions forecasters and emergency management officials must make.

It can take days to clear heavily populated areas.

During these clearance times, the storm could change course.

Because forecasts can be uncertain, it is impractical to order an evacuation much more than 24 hours in advance.

Also, long before the center of the storm makes landfall, weather will become too dangerous to drive. That also must be considered in the evacuation call. Evacuation orders are usually issued in time to give people 12 to 15 hours of good weather.

Causeways and bridges over the Bay close when wind speeds reach 40 mph.

Safety may not be far away. Most counties have substantial areas that are not in evacuation zones.

A Long Season

For the East Coast of the United States, hurricane season occupies half the year, from June 1 through Nov. 30.

The dates were selected because 97 percent of all tropical storms and hurricanes form during those six months.

The most active months are August, September and October, with the first two weeks of September being the peak of the season. During those three months, the ocean is warmest and winds high in the atmosphere are the most favorable for hurricanes.

Storms generally start in the eastern Atlantic Ocean and move westward. So many form near the Cape Verde Islands just off the coast of Africa that they are often called Cape Verde storms.

This doesn't mean hurricanes won't form in the western Caribbean Sea or the Gulf of Mexico, but the Atlantic Ocean is the main breeding ground during the most active parts of the season.

In June and July, storms tend to develop in the Gulf or Caribbean and head toward the Texas and Mexico coastlines.

In late October through November, the number of Cape Verde storms drops, but the western Caribbean and Gulf storms become more dangerous.

Late-season storms tend to curve eastward, toward the west coast of Florida.

The Thin Line

Although forecasts improve each year, predictions of a hurricane's path will never be perfect.

The National Hurricane Center issues hurricane forecasts every six hours, predicting where the storm will be up to five days in the future.

Last year, the hurricane center's map of a storm's projected path showing a swath with a thin black line down the center dominated television screens and newspaper graphics.

The line shows the forecaster's best prediction of a storm's track. The swath, called the cone of probability, shows possible errors in the forecast.

The storm could be any place in that cone.

People tend to focus on the line. That is what happened during Hurricane Charley last year, when the black line showed the storm making landfall near Tampa.

Instead, Charley hit in Punta Gorda, about 100 miles south. That was within the average error of a forecast and inside the cone of probability on forecast maps, but some people were unprepared.

Hurricane center experts considered eliminating the line in forecasts for this year but decided to keep it.

When making a forecast, meteorologists at the center examine more than 20 computer models of hurricane behavior.

The models often give diverging plots of the storm's path because each model has certain biases and strengths. Part of the forecast develops from knowing how each model behaves.

The forecast is a combination of model data, observations from aircraft inside and around the storm, satellite analysis and radar, blended with the opinions and experience of the meteorologists making the prediction.

Some television stations use software such as VIPIR that combines radar images and computer models to give a three-dimensional view of the atmosphere.

Faster computers and more data are improving the forecasts about 2 percent a year. Still, that leaves room for error.

The average error for a 24- hour forecast is 67 miles in any direction.

The error for three days is 174 miles.

Watches, Warnings And Other Terms

When a hurricane is approaching land, the National Hurricane Center will begin issuing watches and warnings.

A hurricane watch means hurricane-force winds of more than 73 mph are possible within 36 hours.

A hurricane warning is issued when those winds are possible within 24 hours.

Watches and warnings also are issued for tropical-storm- strength winds of 39 to 73 mph.

Because of uncertainty in forecasting a storm's path and strength, watches and warnings cover large areas of coastline.

Those alerts mean anyone in a watch or warning area could be hit by the storm.

A tropical storm generates winds from 39 to 74 mph. Tropical storms become hurricanes when winds top 74 mph.

Taking Shelter

Emergency management officials open shelters based on the strength of the storm.

To get a list of open shelters, check local news sources, the Internet, government access television channels or call the county's emergency management citizen information phone lines.

Each county designates special-needs shelters for evacuees who need medical attention such as oxygen or nursing care but are not ill enough for hospitalization.

County health departments provide volunteer doctors and nurses for the shelters.

Anyone who requires a special-needs shelter should call county emergency management now to register and be assigned a shelter. Early registration lets officials determine staffing needs.

Women within six weeks of delivery or in labor, people with acute infections or those with an emergency condition should not evacuate to special needs-shelters. These evacuees should go to a hospital.