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The Honolulu Advertiser
Posted on: Thursday, May 13, 2010

Wet season was a dry one

By David Waite
Advertiser Staff Writer

The just-concluded rainy season in Hawai'i was one of the driest in the past 55 years, according to newly released information from the National Weather Service forecast office in Honolulu.

The wet season runs from October through April, and most rain gauges across the state showed below-normal totals for that seven-month period, the weather service said.

Only the wet seasons in 1997-1998, 1977-1978 and 1972-1973 had "comparable rainfall deficits," according to the weather service.

A map that accompanies the report shows that only a weather recording station on O'ahu in an area identified as Oahu Forest, in the Ko'olau mountains above Kualoa Ranch, received more than the normal wet-season rainfall. A total of 131.48 inches of rain fell there during the past seven months, 104 percent of the normal amount, according to the report.

Fifteen of the 37 rainfall recording sites on O'ahu received less than 50 percent of the normal wet season rainfall.

The area between Downtown Honolulu and Wai'anae was especially dry, with many of the gauges recording only about one-third of the normal rainfall, and two them only about one-quarter of normal.

Federal, state and county officials have already expressed concerns about what the dry winter will mean in terms of the potential for wildfires this summer. They have scheduled a news conference today to talk about the threat and impact of wildfires on O'ahu.


Honolulu Board of Water Supply spokesman Kurt Tsue said the agency is not on alert status yet, but is monitoring water supply and demand closely, as it does every year, as O'ahu heads into the traditionally drier and hotter summer months.

El Niņo conditions "of at least moderate intensity" (warmer than normal ocean surface temperatures) were largely responsible for the drier-than-normal winter, the weather service report said.

Kevin Kodama, a hydrologist with the weather office in Honolulu, said El Niņo conditions appear to be tapering out in the Pacific.

"We don't know how that relates exactly in terms of expected rainfall as we head into the dry season, but it is likely to be somewhat lower," Kodama said.

And while a storm system dropped heavy rains on portions of Kaua'i and O'ahu in early April , leeward areas of the Big Island and Maui County remained in desperate need of rain, with the leeward Kohala section of the Big Island listed by federal officials under the "exceptional drought" category.


A low-pressure system northwest of Kaua'i from April 6 through April 9 produced an unstable air mass over the state, causing trade winds to be displaced by winds out of the southeast, the weather service said

Heavy rains over the Ko'olau range on O'ahu during that time resulted in 10- to 15-inch totals in a 12-hour period the night of April 6 and flash flooding in streams draining down both windward and leeward slopes, the weather service said.

"That storm dumped a lot of rain over the upper Ko'olaus and on Kaua'i," Kodama said. But a lot of it was lost to runoff, and O'ahu and Kaua'i did not enjoy the same benefits as with longer-term, soaking rains, Kodama said.

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