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March 1, 1998

A weekly feature provided by scientists at the Hawaiian Volcano Observatory.

What is El Ni?o, and what is its impact here?

Someone once said, "Climate is what you expect, weather is what you get." The weather of the last week or so has brought a sigh of relief to many east Hawaii residents. The return of the trades has brought much needed moisture, creating the joyful sound of water trickling into depleted water tanks and easing fire danger that had reached critical levels.

Although the weather on the the Big Island, as well as around the globe, varies from year to year, the increasingly familiar El Ni?o events often accompany extreme climate-related problems, such as droughts, floods, and hurricanes. By now, perhaps many of us have been flooded with media reports of El Ni?o, but what actually is El Ni?o, and what are some of the effects observed on the Big Island?

An El Ni?o (EN) occurs when unusually warm water appears at the surface in the central and eastern Pacific Ocean near the equator. The term El Ni?o, is Spanish for "the Christ Child." It was originally used by Peruvian fisherman to describe the annual appearance of warm water along their western coast around Christmas time each year. In the early 1960s, it was discovered that changes in atmospheric pressure across the Pacific Basin (referred to as the southern oscillation, or SO) are also associated with the warming events. These combined changes are referred to as ENSO (El Ni?o-Southern Oscillation) or, more commonly, El Ni?o events.

During "normal" non-El Ni?o conditions, prevailing easterly trade winds blow warm surface water to the Western Pacific, and cool water upwells in the Eastern Pacific. The warm water in the Western Pacific adds moisture to the air, causing greater rainfall relative to the eastern Pacific.

During El Ni?o conditions, the tradewinds blowing from the east relax, and the normal distribution of warm surface water to the west is disrupted. Reduced upwelling of cold water in the eastern Pacific leads to a rise in sea-surface temperature. Rainfall follows the warm water eastward, with associated flooding in places like Peru and California. Droughts can occur in Indonesia, in Australia, and in islands in the Central and Western Pacific.

The magnitude and resulting effects of El Ni?o events vary. During the 1982-83 El Ni?o, the largest recorded thus far, Hurricane Iwa hit Oahu and Kauai, and drought occurred on the Big Island. During the 1991-1992 El Ni?o, which was weaker than both the 1982-83 and current El Ni?o, Hurricane Iniki inundated Kauai. The current El Ni?o, which appears to have peaked sometime around last July, is nearly as strong as the 1982-83 event.

During the current El Ni?o, the disruption of moisture-laden tradewinds has had two main effects here on the Big Island. One effect is the worst drought in recorded history. Additionally, during non-tradewind conditions, poor air quality can affect the entire Big Island, as well as other islands in the Hawaiian chain. East Hawaii, being relatively close to Kilauea and the volcanic gas emission sources, often experiences the worst air quality in the state during non-tradewind conditions. In fact, the lack of tradewinds, combined with a large increase in gas emissions from Kilauea, caused record-breaking levels of vog in Hawaii Volcanoes National Park over the last several months. On several occasions between November and January, the National Park Service closed park facilities at the summit of Kilauea due to poor air quality and sent their employees in search of cleaner air. Near the Park's visitor center, Federal health standards were exceeded eight times.

Some authorities have predicted that the current, particularly strong, El Ni?o could continue through the spring. If this happens, the recent period of tradewinds could cease, and Big Island windward residents could again be watching their water tanks and looking for voggy conditions. In the end, the climate we have come to expect will yield to the weather that we get.

Activity update

During the past week, there was constant effusion of lava from the vent within Puu Oo. Lava continued to flow through a network of tubes down to the seacoast where it entered the ocean at two locations - Wahaula and Kamokuna. The public is reminded that the ocean entry areas are extremely hazardous, with explosions accompanying frequent collapses of the lava delta. The steam cloud is highly acidic and laced with glass particles.

There were no earthquakes reported felt in the past seven days. skip past bottom navigational bar

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Updated: December 11, 2006 (pnf)