A Cold Front approaching the state is expected to bring widespread rainfall on Hawaii Island and the possibility of more winter weather for the summits of Maunakea and Mauna Loa Wednesday night (February 3rd) and Thursday (February 4th).
Published by: HIRSC - Weather Team
Trade winds will weaken today, then turn to the south tonight as a cold front approaches the islands. A few showers will affect windward areas today and tonight, with showers expected to move over leeward areas on Tuesday as they come in from the south. The front will move over Kauai Tuesday night, Oahu and Maui County on Wednesday, and the Big Island Wednesday night. The front will bring a period of widespread rainfall, locally gusty winds, the potential for thunderstorms, and winter weather to the upper elevations of the Big Island. The front will move east of the islands on Thursday, with post-frontal north to northeast winds delivering a wintry chill that will likely persist into the weekend.
In summary, the strongest cold front of the season will sweep through the island chain Tuesday night through Wednesday night, bringing a period of widespread rainfall, locally gusty SW to W winds, the potential for thunderstorms, and winter weather to the upper elevations of the Big Island. A cool and dry air mass will move over the islands with the gusty N to NE winds that follow the front on Thursday and Friday, with little in the way of rainfall expected. Lighter winds may develop over the weekend, with the cool and dry air mass remaining in place. Light to moderate trade winds are currently being supplied by a 1024 mb high to the distant NNE, with the associated ridge extending SW to about 400 miles N of Kauai. The leading edge of a cold front is about 800 miles NW of Kauai moving SE at 10-15 mph. An E-W oriented area of showery low clouds lies upstream of the smaller islands, and is fueling a few windward showers, with some showers pushing leeward on Oahu. Meanwhile, the Big Island is currently under mostly sunny skies, with visible imagery highlighting the snow-covered peaks of Mauna Kea and Mauna Loa. The ridge will move SE over the next 48 hours as the front approaches, leading to weakening and veering low-level winds, becoming light SE-S on Tuesday. Little overall change is expected in the short term, although the weakening winds may allow afternoon sea breezes to drive some leeward cloudiness to develop, with a few pop- up showers likely along the Kona slopes. The low-level SE to S flow will become weakly convergent tonight and Tuesday, and global models indicate the nearby moisture will fuel a few showers ahead of the approaching front. The front will move over Kauai Tuesday night, Oahu and Maui County on Wednesday, and the Big Island Wednesday night, accompanied by a vigorous trough aloft, which will likely support thunderstorm development with the frontal passage, with winter weather over the Big Island Summits. Locally gusty SW to W winds may develop just ahead of the front, especially where they accelerate downslope, with windward Oahu one of the most likely areas to experience this gustiness. Interestingly, the coldest air (and greatest instability) associated with the trough aloft will likely move over the islands after the frontal moisture has cleared to the E, and a very dry air mass moves over the islands. So while these type of mid-level temperatures (bottoming out near -19C) have historically brought winter weather to the Haleakala Summit, the air mass may be too dry to produce much, if any, precipitation. It does appear that overnight lows will drop below freezing on Haleakala for a couple nights though, with the coldest temperatures of the winter season statewide as dew points plummet into the lower 50s. A strong and gusty N-NE wind flow will bring the cool dry air through Friday, with little in the way of rainfall expected. Lighter winds over the weekend will continue the mostly dry pattern, with the air mass remaining cool.