By The Chronicle Staff

Meteorologists around the world are closely watching the Pacific Ocean as a rapidly strengthening El Niño event is expected to influence weather patterns across much of the globe during the coming months.

The World Meteorological Organization (WMO) says El Niño has officially developed and is likely to intensify between July and September. Forecasters believe the event has the potential to become a "strong" El Niño, increasing the likelihood of extreme weather in many regions.

What Is El Niño?

El Niño is a naturally occurring climate pattern caused by warmer-than-average sea surface temperatures in the central and eastern tropical Pacific Ocean. Those warmer waters alter atmospheric circulation, affecting weather thousands of miles away.

The phenomenon typically develops every two to seven years and can last anywhere from nine months to more than a year. While El Niño is a natural part of Earth's climate cycle, scientists note that its effects can be amplified by an already warming global climate.

What It Could Mean for the United States

Although every El Niño is different, forecasters have identified several weather trends that often accompany the climate pattern.

For much of the southern United States, El Niño frequently brings a wetter-than-normal and cooler winter. Meanwhile, northern states often experience warmer and drier conditions during the winter months.

The Atlantic hurricane season may also become less active because El Niño increases upper-level wind shear over the Atlantic Ocean, making it more difficult for tropical storms and hurricanes to organize and strengthen. That doesn't eliminate the threat of hurricanes, but it can reduce the overall number of storms.

Heat Still a Major Concern

Despite the possibility of cooler winter conditions in some areas later this year, forecasters warn that El Niño often contributes to higher global temperatures.

As warm ocean waters release additional heat into the atmosphere, the combination of El Niño and long-term climate warming can increase the chances of record-breaking temperatures worldwide.

Climate experts caution that periods of intense heat, heavy rainfall, flooding and drought may all become more likely in different parts of the world as the event strengthens.

Global Impacts

Outside the United States, El Niño can dramatically alter weather patterns.

Some regions of South America and East Africa often experience increased rainfall and flooding, while parts of Australia, Indonesia and southern Africa may face drier conditions and an elevated risk of drought and wildfires. Agricultural production, water supplies and fisheries can also be affected depending on the severity of the event.

What Comes Next?

Scientists emphasize that El Niño is only one factor influencing weather, and local conditions will still depend on many other atmospheric patterns. However, because this event appears to be strengthening quickly, forecasters will continue monitoring ocean temperatures and atmospheric conditions throughout the summer and into the fall.

For residents, the developing El Niño serves as a reminder that seasonal weather forecasts may shift in the months ahead, making it important to stay informed about local forecasts and be prepared for changing weather conditions. ■