Key Idea This Key Idea has an illustration and text describing El Nino and La Nina patterns from a Micronesia point of view. Click "View Source" on the right to see the illustration and read the detailed description.

Under normal conditions, strong equatorial winds blowing east to west keep warm water piled up in the west. This warm pool of water leads to the routine development of thunderstorms and typhoons in the western Pacific.

Sometimes the strong east-to-west surface winds weaken or even become west to east. Warm ocean water and its associated heat move eastward in this El Nino condition. This movement results in thunderstorms and typhoons moving eastward from Pohnpei to the Marshall Islands in a March through June wet phase of the El Nino. After this wet phase, Micronesia is typically drier during El Nino. From the following January through April, conditions can be very dry in Micronesia. Drought, intrusion of seawater into the freshwater lens, fires, and severe coral bleaching can occur. Multiple year El Ninos are rare.

Stronger than usual east-to-west surface winds usher in a La Nina period. Thunderstorm and typhoon development shifts west of normal locations. Higher La Nina sea levels coupled with high surf events, especially near new and full moon periods, can cause episodes of coastal inundation and flooding. Multiple-year La Ninas (2 or 3 in a row) are fairly common.

It is unclear how climate change will impact El Nino and La Nina events, and if they will become more or less frequent and severe.

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