WISHE – Wind-Induced Surface Heat Exchange

The main energy source for tropical cyclones is warm ocean water. The warmth of the sea water in the ocean is calculated by the observed sea surface temperatures, which often give an indication whether conditions are favorable for tropical cyclone development. Research has shown that sea surface temperatures need to be at least 26 degrees Celsius (79 degrees Fahrenheit) in order to support the existence of tropical cyclones. The inward spiraling winds along the surface within a tropical cyclone are warmed by the higher sea surface temperatures, which makes that air more unstable. Because of this buildup of warm, moist air near the surface, convection becomes more likely, especially around the center of the tropical cyclone within the eyewall.

Stronger convection within the eyewall causes more rising motion, which promotes stronger surface winds spiraling in toward the center of the tropical cyclone. Those stronger surface winds bring more warmth from the higher sea surface temperatures in toward the eyewall creating more instability. This creates a positive feedback loop where stronger convection within the eyewall leads to more instability, which further strengthens the convection.

This process of the warm ocean waters heating up the air just above the surface within tropical cyclones is known as Wind-Induced Surface Heat Exchange, or WISHE. This is the predominant theory of how tropical cyclones strengthen or intensify.