Size Forecast Interpretation

Extent of the Hurricane Wind Field

Diagram of concentric circles with arrows indicating counterclockwise wind flow

Adapted from E. Holweg, TAFB/TPC, "Mariner's Guide..."

If a hurricane is its wind field, the series of concentric circles of winds flowing around its center of low pressure (the calm eye of the storm), then the size of a storm is the size of its wind field as measured from center, specifically, the radius of that wind field. The outer edge of the storm is the outermost distance from center at which its winds still form a closed circle. If the storm is roughly a circle, then the size of the storm is understood in terms of the radius of the circle. The wind field of a large storm can extend out more than 200 miles out from center in every direction.

A hurricane's size is not related to its intensity or category on the Saffir-Simpson scale. Intensity is a measure of the speed (miles per hour) of the storm's fastest winds, located in the inner concentric circle of the eyewall, whereas size is the spatial extent of its entire wind field, or all the concentric circles taken together. Wind speeds gradually decrease the farther the distance from the storm's fastest winds, which are found just beyond the eye of the storm.

As size is not related to intensity, there are large high-category storms and small ones, large low-category storms and small ones, and storms of significantly different intensities that are approximately the same size. The two Category-5 storms to have made landfall in the United States during the last half-century or so - Camille (1969) and Andrew (1992) - were both small, tightly-wound storms with small wind fields. Despite their small sizes, the wind fields of both storms wreaked swaths of tremendous damage in their respective areas where they made landfall. The physics of why some storms become smaller or larger than others in terms of the sizes of their respective wind fields is not completely understood.

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