Weather watchers are warning of a strong upper-level low-pressure front forecast to move eastward across the island chain, potentially bringing severe thunderstorms and flash flooding to the Big Island as early as this afternoon.
The National Weather Service in Honolulu on Thursday issued a flash flood watch for the entire state effective until 6 a.m. Saturday. In addition, both NWS and the commercial forecasting service AccuWeather issued special weather statements on Thursday.
NWS’s statement called the front “an usually strong upper level disturbance.”
“The latest guidance indicates an increasing potential for strong to severe thunderstorms, which could produce damaging winds and large hail, as well as the possibility for localized intense rainfall and flash flooding.”
NWS said there was a potential for impacts on the western end of the state, Kauai and Niihau Thursday night with “a transition to more of a widespread potential (today) through Saturday.”
The flash flood watch cautioned that rainfall rates during the heaviest of downpours could be “in excess of three inches per hour.”
“The threat for flash flooding is expected to be the greatest (today) through (this) evening,” the document stated. “Conditions should steadily improve from west to east late Friday into Saturday.”
A statement from AccuWeather Senior Meteorologist John Feerick said that during the day today, “the greatest risk for downpours and flooding problems is expected to be across Oahu, potentially impacting Honolulu.”
“During the day Friday, the upper level storm’s progress to the east will slow down as we head into the weekend, which very well could mean a longer threat for heavy rain and thunderstorms for Maui and the Big Island from (this) afternoon through the weekend. The greatest concern will be heavy rain producing flash flooding, but storms could also produce isolated damaging wind gusts and small hail. As is often the case, there is even likely to be heavy snow on top of Mauna Loa over the weekend with blizzard conditions a possibility.
“The islands should return to a more of a standard trade wind pattern again early next week.”
Talmadge Magno, Hawaii County Civil Defense Administrator, said Thursday mid-afternoon that his agency and Civil Defense at the other three counties, plus Hawaii Emergency Management Agency had all been briefed by NWS.
“The county is doing enhanced monitoring at this time. The departments have been briefed and we will take actions based upon what we see,” Magno said.”We request that people be prepared to take caution. Because even though (forecasters) say the effects will be scattered, we don’t know what areas are going to be hit or where these thunderstorms are going to sit over. So if you’re in a flood-prone area, take proper precautions. If your home or facility is (vulnerable) to wind impacts, take those precautions.
“Everybody should be prepared for severe thunderstorms with heavy rain, high winds and lightning.”
Email John Burnett at jburnett@hawaiitribune-herald.com.