A cold front brought heavy rain to Kauai and thunderstorms to Oahu on Sunday before heading for Molokai, Lanai and West Maui.
A flash flood watch was in effect for Oahu and Maui County until the early afternoon. Forecasters said only scattered showers remained over Maui County just before 4 p.m..
The front was expected to weaken near the central islands Sunday night and today, with winds remaining light. As the front dissipates Tuesday, light tradewinds will return, with moderate tradewinds and windward showers for the remainder of the week, the National Weather Service said.
The storm cut power to about 3,000 Hawaiian Electric Co. customers in Waialua, a HECO spokesman said.
The outage started around 10:30 a.m. and lasted until a little after 1 p.m., spokesman Darren Pai said.
The origin of the blackout is unknown, but Pai it started in Waialua.
"We believe this was weather-related," Pai said. "There were reports of lightning strikes in the area."
Troubleshooters, however, were unable to pinpoint an exact cause.
A flood watch and warnings for Kauai were dropped Sunday morning as the storm moved east away from the Garden Island.
But Kauai remained under a brown-water advisory as heavy stormwater continued to flow into the ocean at Waimea, Nawiliwili and Hanalei, state Department of Health officials said.
The public was advised to stay out of flood- and stormwater runoff because of possible overflowing cesspools, sewers, pesticides, animal fecal matter, dead animals, pathogens, chemicals and debris.
Storm runoff was blamed for a discharge of up to 300,000 gallons of treated effluent from the Waimea Waste Water Treatment Plant into Kikiaola Harbor along the western sea wall.
Effluent is normally discharged into an irrigation ditch, but officials said it had to be released from the reservoir to prevent flooding from heavy rain. Officials said the Kikiaola irrigation ditch was opened on purpose Sunday morning to prevent flooding from occurring in Waimea.
Warning signs will be posted and water samples collected in the area, the Health Department said, and the public was advised to stay out of harbor waters until bacteria levels return to normal.
Wastewater officials also reported an overflowing manhole Sunday morning at the intersection of Kaumualii Highway and Eleele Road. About 2,000 gallons of sewage and stormwater spilled from the manhole into Hanapepe Valley from about 7:25 to 7:45 a.m., officials said. Officials said they notified the Health Department about the incident.
In the 24-hour period ending at 2 p.m., the storm dropped 5.4 inches on Makaha Ridge on Kauai, and more than 4 inches fell on Waimea Heights and Mana. Nearly 4 inches was recorded at Kokee.
On Oahu, 4.2 inches fell at the Pacific Tsunami Warning Center in Ewa Beach. About 2.8 inches fell in Poamoho and Palisades, and about 2.7 inches was recorded in Waiawa and Waipio.