Scientist predicting weak El Nino
By Jan TenBruggencate
Advertiser Science Writer
The Pacific appears to be drifting into a weak El Nino phase, the first in several years, and it is likely to push Hawai'i winter weather toward drier conditions with fewer winter storms.
That bodes ill for a state that has been struggling with dry conditions for much of the past few years. Although this summer has seen some improvement in rainfall, water wells across the state remain at low levels, prompting warnings from water departments and increased brush fire activity.
University of Hawai'i oceanographer Roger Lukas, who studies climate phenomena such as the El Nino and La Ni–a cycles, predicted a drier-than-normal winter, but not drought.
Winter rainfall in the Islands is linked to Pacific-wide climate events such as El Nino.
Lukas said he agrees with the National Weather Service predictions that call for an El Nino of limited strength, beginning to be felt by the end of this year. The weather service's Climate Prediction Center, in its most recent statement on the situation, said that based on sea surface temperatures, patterns and winds in the Pacific, "it seems most likely that the intensity of warming will be weak to moderate."
An El Nino event occurs when tradewinds weaken in the Western Pacific and an associated pool of warm water that moves along the equator from west to east. Its arrival along the coast of Central America in the winter was linked with Christmas, and it was named El Nino, Spanish for the Christ child. Because of the pool of warm water, El Nino is also sometimes called a warm event.
During strong El Ninos, there can be drought in the Hawaiian Islands and other parts of the Pacific, rainstorms and flooding in the Americas, a sharp drop in certain fisheries near Central America, and increased hurricane activity between the Mainland and Hawai'i.
Another related climate event is La Ni–a, which occurs when waters of the Eastern Pacific are cooler than normal. It can be associated with a range of other unusual weather events around the region.
The Pacific earlier this year came out of an extended La Ni–a weather event, and oceanic conditions now appear to be close to normal for this time of the year, meaning it is neither El Nino nor La Ni–a.
"There are different definitions for El Ninos, but we probably wouldn't be in one until the early spring" of 2002, Lukas said.
But as early as December, the effects of the coming warm episode should begin to make themselves felt. By itself, the El Nino will be weak enough not to have much of an impact, but it will be superimposed over a larger-scale Pacific climate event, the Pacific Decadal Oscillation — an ocean-atmosphere circulation pattern that cycles over five to 20 years.
Lukas said the overlapping of the El Nino and the larger-scale event is likely to increase the classic El Nino effect.
Generally, by late December, it means the Islands will have a higher likelihood of dry conditions and light and variable winds, with high-pressure conditions prevalent over the state much of the time.
The winter storms that tend to drench the Islands, providing much of our winter rainfall, will tend to be deflected away.
"It won't be bone dry," but drier than in normal winters, he said.
Reach Jan TenBruggencate at jant@honoluluadvertiser.com or (808)245-3074.
