Honolulu residents can expect a noticeable shift in weather as we head into the weekend. The National Weather Service in Honolulu has reported a weakening of the trade winds today, with a cold front set to sweep across the islands from Saturday night through Monday. This transition is likely to result in rainfall primarily on the windward slopes, followed by strong trade winds that are expected to persist into the next week. The front, moving from north to south, will bring mostly windward showers, but some might spill over to leeward areas of the smaller islands, as per the forecast.
Regarding current conditions, the National Weather Service describes satellite imagery that shows "the ridge axis anchored north- northeast of the state with little upper level troughing." Despite the weakening winds, showers are still on the cards, especially in typical windward and mauka locations. The advisory suggests that with the reduced wind activity, we are likely to see a sea/land breeze regime develop, potentially ushering in isolated showers across leeward and interior locales by Friday into Saturday. However, with the front approaching, those planning outdoor activities should prepare for potential changes in weather patterns.
Aviation-wise, there have been no AIRMETs in effect, as moderate trades are expected to ease and veer east-southeast throughout the day. While there may be a few windward and mauka showers that could create marginal VFR conditions, overall VFR conditions are predicted to prevail. The aviation community should nonetheless remain vigilant as the aforementioned front approaches the region.
In the marine environment, while the north-northwest swell has failed to meet predicted heights, leaving surf just below High Surf Advisory thresholds, a new swell is on the horizon. Expected from late this weekend, a large north-northeast swell could exceed advisory thresholds and cause heavy surging, especially in north-facing harbors like Kahului and Hilo. According to the NWS, "The highest swell energy with the current north-northwest (340-350 degree) swell continues to pass just northeast of the Hawaiian Islands." South shore surf heights will also see a modest uptick due to a small long-period south-southwest swell later this week, with a larger out-of-season south swell possible by early next week.
Lastly, for fire weather concerns, the National Weather Service anticipates stable trades shifting east-southeast with relative humidity values staying below critical fire weather thresholds into the weekend. The temperature inversion layer is forecast to be situated between 5,000 and 6,000 feet today, a factor that can influence the spread and behavior of wildfire should they ignite.
