POSTED: 4:34 p.m. HST, May 3, 2011
LAST UPDATED: 5:07 p.m. HST, May 3, 2011
The National Weather Service lifted a flood advisory for the Big Island at about 5 p.m. this afternoon as an unstable weather system that delivered impressive thunder and lightning last night gradually gives way to a return of the tradewinds.
The National Weather Service said early this afternoon that rain was falling at 2 inches an hour along the coast and lower slopes of the Leeward Big Island.
The rain may be the last gasp of the system that lit up the skies of Oahu last night.
The weather service reported hail, waterspouts, road flooding, and heavy thunderstorms. About 60,00 Hawaiian Electric Co. customers on Oahu were without power for a few hours yesterday evening and company officials suspect lightning strikes caused the outage. The outage knocked out many traffic signals, making the evening commute a slow, sloggy mess for East Oahu and Windward motorists.
The weather service said a surface high far northeast of the islands will help weaken the weather system and will produce locally breezy trade winds tonight, and into the weekend.
Earlier flood advisories for Oahu and Kauai were canceled this morning.
"When the stronger tradewinds come in, the thunderstorms aren't going to be able to sit in one place like they did last night," said forecaster Ian Morrison.
If skies remain cloudy this morning, that will also lessen the chance of heavy thunderstorms because surface temperatures will be cooler, Morrison said.
The temperature in the upper atmosphere is at minus 12 degrees, he said, while surface temperatures are in the 80s. The thunderstorms are generated when moist, warm air rises because of ground heating and hits the cold upper atmosphere. The temperature difference causes the warm air to rise faster and releases more energy, Morrison said.
The upper atmosphere temperatures are cold enough for snow on the Big Island summits, where a winter weather advisory is in effect until 9 a.m. Wednesday with "freezing drizzle fog."
The weather service says the tradewind weather should last through Friday, but that unstable weather, similar to yesterday's, could return this weekend.