Western Hemisphere Warm Pool

The Western Hemisphere Warm Pool (WHWP) is a region of sea surface temperatures (SST) warmer than 28.5 °C that develops west of Central America in the spring, then expands to the tropical waters to the east.

A dipole pattern off Central America appears due to surges of cooler, drier air through the gap at the Isthmus of Tehuantepec.

A large (or small) AWP reduces (or increases) the tropospheric vertical wind shear in the main development region for Atlantic hurricanes and increases (or decreases) the moist static instability of the troposphere, both of which favor (or do not favor)[clarification needed] the intensification of tropical storms into major hurricanes.

An El Niño weakens the Amazonian cell, the anticyclone and the easterly tradewinds, causing the tropical North Atlantic to warm more than usual in the spring.

About half of El Niño events persist sufficiently into the spring months for the warm pool to become unusually large by summer.