How do meteorologists measure the speed at which a hurricane is traveling?

Hurricanes are a breed of tropical cyclone.

These savage storms are called typhoons in the Pacific, where they occur most frequently; hurricanes in the Atlantic; and cyclones in the Indian Ocean and Australia. They arise near (but not on) the equator, at points at which the surface temperature of the water has been warmed to at least 78 degrees Fahrenheit.

As the earth spins, the sloping of the earth to the north and south of the equator may grip and organize potential cloud clusters into an eddy. Suction from winds in the upper air creates an updraft in the center of a wall of clouds, some 35,000 to 40,000 feet high. Moist air spirals in toward this vortex, rises within the wall, and escapes over the top.

The storm is driven primarily by heat released by condensing water vapor, a major source being the warm sea surface. The initial speed of the whole storm is about 15 miles per hour, but it may increase to 60 or more miles per hour as the hurricane moves farther from the equator.

Most hurricanes rage for five to ten days, covering about 50 to 125 miles with gusting winds that may fluctuate rapidly from 20 or 30 to 100 miles per hour within minutes. The strongest winds surround the eye of the storm, spiraling inward in a clockwise direction in the Southern Hemisphere, counterclockwise in the Northern Hemisphere.

Although winds of hurricane force (65 miles per hour) can be found at nearly any time somewhere in the world, it is the whirling shape of the storm with its distinctive central eye that constitutes a hurricane or cyclone. It is by tracking the eye that forecasters can determine the speed at which the hurricane is moving. Satellites take pictures of the storm every half hour and plot the clearly identifiable eye on a map over a period of hours or days. Viewed from the height of a satellite, the hurricane resembles a majestic spiral galaxy.

If the storm is near a coastline, radar is used to trace the center of the storm, take pictures, and plot the positions on a map. The National Weather Service has a buffer line of overlapping weather radar installations from Texas to New England which can continuously track a hurricane’s movement.

During World War II, when a U.S. Navy fleet was battered by a hurricane, the government decided to use reconnaissance aircraft as an early warning system. Today the U.S. Air Force and the National Oceanic and Atmospheric Administration use planes equipped with radar to estimate the position of a storm.

For more detailed information, they actually send planes right into the eye of a hurricane to chart its path and measure winds and pressure fields, a task for daredevils, it would seem, but the National Hurricane Center in Miami says this is no more hazardous than driving on the expressway at rush hour.

None of these methods is totally accurate, however. The eye of a storm might be 10 or more miles across, making it difficult to plot precisely. Other errors may arise from navigational difficulties in the plane, for the measurements are accurate only to the extent the pilot knows where he is.

Sophisticated navigational systems, including Doppler radar, are used to guide the plane, but the farther from shore the aircraft flies, the harder it is to track it.