Hurricanes typically decrease during an El Niño. Hurricanes, which develop off the coast of Africa, are affected by the jet stream, a wind current 40,000 feet up in the atmosphere. The jet stream strengthens. Winds whip up across Central America to the Atlantic Ocean and onto Africa. The winds shear off the tops of thunderclouds before they can develop into hurricanes.

During a La Niña, the jet stream weakens, and hurricanes often increase in number and intensity. Some bring more than wind and rain. In 1998, Hurricane Joan brought swarms of African locusts to the Caribbean. The 1998 La Niña of the same year triggered extreme wetness in Africa's deserts. Vegetation increased and locust populations swelled. When the rains diminished, locusts migrated west in search of food. Millions rode Hurricane Joan's strong, westerly winds across the Atlantic.