The National Weather Service is advising the state to prepare for inclement and potentially harmful weather starting tonight.
According to a special weather statement, “an unusually strong low pressure system” will develop northwest of the state tonight, passing a couple hundred miles north of Kauai on Thursday, and “then drag a could front eastward through the islands Thursday night and Friday.”
The weather service also posted a statewide flood watch until noon Friday and a high wind watch until 4 a.m. Friday.
Tom Birchard, a forecaster for NWS in Honolulu, said what this means for the Big Island is “increasing southerly winds.”
“When we get those south winds, it tends to accelerate around the western tips and the eastern tips of the islands,” Birchard said Tuesday. “So, in portions of the Puna and Hilo districts, we’ll see increased winds and also in portions of the Kona district.
“We’re also looking for increasing rainfall potential and definitely expecting some of those showers to be heavy. Thunderstorms are possible. And some of those can bring strong wind gusts.”
The five-day weather forecast on the NWS website places the highest potential for heavy rain on Thursday night and Friday for both Hilo and Kona. For Hilo, the precipitation probability is listed at 70% Thursday night and 60% on Friday. For Kona, the chances for heavy rain are listed at 90% for Thursday night and Friday, with the precipitation probability decreasing to 30% Friday night in Hilo and 20% in Kona.
“The winds will be strong and out of the south on Thursday, and rainfall potential remains high all the way into Friday,” Birchard said. “This will also bring the potential for winter weather for the summits and upper slopes of Maunakea and Mauna Loa.”
The special weather statement warns of “heavy rain capable of producing flash flooding … during this time.”
“Intense rainfall rates are likely, especially over the typically drier south and southwest facing slopes, where the greatest rainfall totals are expected,” the dispatch states.
“The potential for flooding is quite high,” Birchard said. “And when winds are from the south like this, the flooding potential tends to affect the Ka‘u and Puna districts. But islandwide, we could see heavy rain.”
Birchard said computer models are predicting less likelihood of damaging winds on the Big Island than are forecast for Kauai and Oahu, but he added a caveat.
“You could get some localized power outage reports from the Puna and Hilo districts, especially in Puna, with albizia trees falling on power lines,” he cautioned. “Whether we get the damaging wind gusts — and our definition of that is 60 mph — is sort of in question. But we know it doesn’t necessarily take 60 mph wind gusts to have impacts on the Big Island, especially when the wind’s turned south like this.”
Hawaiian Electric also issued a statement Tuesday, urging customers “to check their emergency preparations and prepare for the possibility of power outages.”
“The company urges customers to review family and business emergency plans, ensure they have supplies they need on hand, and keep close watch on the development of the storm. Preparation and safety tips are available at hawaiianelectric.com/stormcenter.
Readiness measures suggested by the power utility include: checking emergency equipment such as flashlights, emergency generators, battery-operated radios, light sticks and lanterns to be sure they are operational, and buying extra batteries.
Email John Burnett at jburnett@hawaiitribune-herald.com.
