While the worst of the high winds are over, scattered showers and thunderstorms are expected to persist as the vigorous storm system continues to pass across the state.

A lingering area of low pressure just north of the Islands drove a cold front across O'ahu early yesterday, with intense thunderstorms and high winds that downed power lines, uprooted trees and closed dozens of schools.

The system should begin to weaken in the next day or two, said Kevin Kodama, a hydrologist with the National Weather Service. "Things should begin to clear a little bit," he said.

But looking out toward the weekend, another low-pressure system may begin to develop.

"It won't be bad like this one. Just something that will keep things unsettled for a little bit longer through Sunday," Kodama said.

Cold fronts, such as the one that caused gusts of up to 70 mph on O'ahu yesterday, are not uncommon during Hawai'i's wet season, Kodama said.

"The reason that it came through so hard was because it had a lot of forward motion to it," he said. "The low-pressure system up to the northwest was fairly strong for something this close to the Islands."

The combination of the low-pressure system and the cold front made for the strong winds out of the southwest and intense thunderstorms, he said.

Forecasters point out that this is a typical storm for Hawai'i's winter season.

"I don't want people to get the idea that this is some once-in-a-decade event or once-in-20-years event. This isn't what we're looking at. We get kona-type weather or kona-type storms like this each year," said Robert Ballard, a National Weather Service forecaster in Honolulu.

Ballard said that most low-pressure areas tend to weaken when they approach the Islands. But in this case, the system actually strengthened. "It had some upper-level energy to help invigorate it as it came toward the Islands," he said.

The winds and heavy rains pummeled O'ahu starting at about 3 a.m. yesterday. The National Weather Service said the Honolulu Airport, Wai'anae Valley and Kahuku saw winds in excess of 40 mph yesterday morning. Schofield recorded the highest gust, at 70 mph.

Forecasters yesterday noted that the cold front continued to move east, toward the Big Island, and said it was expected to stall at some point. Kodama said it was likely to linger east of the Big Island.

That will keep both Maui and the Big Island under continued threat of heavy rain, with a flash-flood risk on the Big Island.