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Big Island Drought Expands; Scientists Say Tradewinds Easing

Posted October 15, 2012, 05:22 PM HST Updated October 16, 2012, 09:34 AM HST
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This map from the National Oceanic and Atmospheric Administration shows the levels of drought in Hawaii. The "S" label shows short-term trends while the "L" signifies droughts lasting more than six months.

Dry weather continues to plague the state, with two more areas on the Big Island officially being affected.

And scientists say the situation could persist as four decades of observation are showing a decrease in moisture-bringing trade winds in Hawaii.

Kevin Kodama, hydrologist for the National Weather Service’s Honolulu office, said areas on the Big Island considered to be under “D3” or extreme drought conditions have expanded from South Kohala and Pohakuloa to North Kona. Because of the ongoing dry weather the Ka`u district has once again been classified as under an extreme drought.

The drought continues to affect farmers and ranchers on the Big Island and elsewhere in the state, Kodama said.

Like much of the US mainland, the US Department of Agriculture has classified the entire state as being under a federal drought disaster declaration.

Quirino Antonio, manager of the county Department of Water Supply, said so far the Big Island’s municipal system, which is fed almost exclusively by deep wells, is holding up under the dry conditions.

“Our sources are keeping up with consumption,” he said.

The only exception is in Waimea where a conservation notice is still in effect because a 50-million-gallon reservoir, one of three in the area, is awaiting repair of damage sustained in the 2006 earthquake.

Kodama said the upcoming wet season, which typically lasts from October through April, is expected to be drier than normal.

Part of the reason is the continuing development of El Nino conditions, a warming of the waters in the Equatorial Pacific which usually result in less rainfall in Hawaii. The El Nino is expected to be a mild one, Kodama said.

Maui County also has extreme drought affecting the leeward slopes of Haleakala and over southwest Lanai.

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Kauai’s southern and eastern lower slopes are classified under severe drought while the leeward slopes of the Waianae mountain range is considered under a moderate drought.

The wet season is expected to bring some drought relief statewide but full recovery will be difficult on the Big Island and on Maui because of the severity and length of dry conditions there.

Parts of the state have been under at least severe drought conditions continuously since June 2008, Kodama said.

Meanwhile, scientists at the University of Hawaii at Manoa have documented a decrease in the frequency of northeast trade winds over the past 40 years.

According to a study published recently in the Journal of Geophysical Research, in the 1970s trade winds occurred an average of 291 days per year at Honolulu’s airport. Today they only occur 210 a year.

That is significant because trade winds drive much of Hawaii’s weather, affecting cloud formation and precipitation, particularly over windward slopes.

“We have seen more frequent drought in the Hawaiian islands over the last 30 years,” UH meteorology professor Pao-Shin Chu noted in a statement issued Thursday.

“Precipitation associated with the moisture-laden northeasterly trades along the windward slopes of the islands contributes much of the overall rainfall in Hawaii.”

The researchers said when trades fail to develop the air can become dormant and unpleasant weather can develop.

Last week provided a classic example of that. The absence of trade winds resulted in volcanic emissions known as vog enveloping much of the state and dry, hot conditions prevailing in the usually balmy and moist windward side of the Big Island.

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