Intense thundershowers knocked out electricity, disabled traffic signals and flooded streets and highways around Oahu on Sunday.
The dynamic weather, a continuation of conditions that first developed late Friday, was attributed to a low aloft that brought heavy showers and thunderstorms to Kauai and Oahu.
Oahu experienced the heaviest rain Sunday.
At 11:41 a.m. radar detected rain falling at rates in excess of 2 inches per hour along Windward Oahu from Hauula to Kaneohe. Water levels in Punaluu and Kahana streams also rose rapidly during that period.
By 2:09 p.m. the weather service issued a flash flood warning as heavy rain moved over Central Oahu, falling at rates exceeding 4 inches per hour.
In the six-hour period ending at 5:45 p.m. Sunday, 3.77 inches of rain fell on the Palisades area. Heavy rain was also recorded at Makaha Stream (3 inches), Waiawa (2.92 inches) and Dillingham (2.75 inches).
The rain kept Hawaiian Electric Co. repair personnel busy through the late afternoon and evening.
A power outage in Mililani left some 2,680 HECO customers without electricity starting at 3:05 p.m. Power was fully restored within an hour.
In Wahiawa, 1,290 customers were without service from 3:20 to 4:50 p.m.
Another 2,310 customers in Makaha lost power around 4:45 p.m.
Honolulu Fire Department spokesman David Jenkins said there were at least four reported emergency incidents that were likely related to the weather, including a vehicle that stalled in high water at a bridge in Wahiawa, a blown roof in Moanalua, a group of overdue hikers in Waiau and flooding at St. Philomena Church in Salt Lake.
At the height of the storm, a lightning strike reportedly disabled traffic signals in Pearl City. Traffic signals were also reported out or malfunctioning in Moanalua, Waimalu and Wahiawa.
The Department of Health issued a brown-water advisory for the island, notably Waimea Bay, and advised the public to avoid floodwaters due to possible contamination from overflowing cesspools, sewers, animals, chemicals and other debris.
Mililani High School postponed its scheduled graduation ceremony at Aloha Stadium due to weather concerns. The ceremony has been rescheduled for 5 p.m. Monday at the stadium.
The 50th State Fair, also staged at Aloha Stadium, closed for the day due to the bad weather.
The stormy weather is expected to move eastward to Maui and Hawaii island Monday.
Meanwhile, Kauai and Oahu are expected to experience a return of tradewinds, which signal a much-anticipated end to hot, muggy conditions that have lingered over the last week.
