Weather Tidbits: La Nina & Hurricanes

This edition of Weather Tidbits will be explaining La Nina and how it can impact hurricane development in the Pacific and Atlantic. La Nina is a global climate pattern that strengthens the easterly trade winds along the equatorial region. The strengthened trade winds causes the ocean waters along the western coast of South America is upwell. The process of upwelling brings the cooler, denser water lower in the ocean up to it’s surface. This creates an overall mass of cooler than average water in this area. The general atmospheric response to this is for a trough of low pressure with the associated dip in the jet stream to form in the eastern Pacific and a ridge of high pressure to develop in the Atlantic Ocean. The trough increases wind shear, or a change of wind speed and/or direction with height, which the ridge of high pressure decreases wind shear.

This set-up can limit hurricane development in the Pacific while making conditions favorable for more frequent development in the Atlantic. This is especially true if Atlantic water temperatures are running above normal. This is because hurricanes need a calm environment to develop. Wind shear will rip a hurricane apart. So while there are certainly many other factors to consider when monitoring hurricane development, A transition to a La Nina is one of the many clues forecasters can use when projecting the frequency and intensity of hurricane development during the hurricane season.