Light trade winds will prevail across the state today through the weekend and into early next week. Seabreezes will develop across many interior and leeward sections each afternoon, producing cloud buildups and some showers, while land breezes bring clearing at night. Stronger trades may return to the state around the middle of next week.
Radar loops depict scattered showers along the windward coasts of the Big Island and east Maui, with just isolated small showers dotting the waters elsewhere around the state. Rain gauge data indicate light accumulations at a few windward stations during the past six hours, with most places remaining dry. Early morning visible satellite imagery reveals a small low cloud swirl, apparently marking a weak low level trough, centered about 250 miles east-northeast of Hilo and moving slowly to the southwest. Regional surface analysis depicts an east-west high pressure ridge far to our north along 40°N, with a weak remnant low from former east Pacific tropical cyclone Lowell near 30°N 148°W, and a much larger remnant low from former east Pacific tropical cyclone Marie near 29°N 133°W. The 12Z soundings and more recent 88D VWP data indicate weakening trades over the state, with near normal pwats of 1.3 to 1.4 inches, and higher than normal inversions based around 10k feet. Stable conditions remain in place aloft, with 500 mb temps around -2C, and a mid/upper level ridge centered a few hundred miles southwest of the Big Island.
In the near term, with the trades weakening, expect seabreezes to develop across many interior and leeward sections this afternoon. This should encourage cloud buildups along with scattered showers in these areas. Isolated heavier downpours will be possible with slow moving showers. Otherwise, showers may continue to be enhanced along the windward coasts of Maui and the Big Island, as an area of enhanced moisture associated with the approaching low level trough impacts those areas. May need to nudge shower coverage up for those windward areas, otherwise the existing forecast appears to be on track.
Through the holiday weekend, the northeast Pacific high will remain rather weak and far to the north, due to a combination of the former tropical cyclone remnant lows moving slowly westward along 30°N and a weak cold front moving slowly eastward from the international dateline. This synoptic regime will allow for light trade winds to continue across the state, with a convective seabreeze pattern and associated clouds/showers likely to develop across interior and leeward areas each afternoon. Some clouds and passing showers will linger over windward areas as well, most likely occurring during the nights and early mornings. Land breezes should clear out the remainder of the smaller islands during the nighttime hours. Nearby mid/upper level ridging should maintain a fairly stable regime over Hawaii, but there will be a couple of areas of somewhat higher moisture (pwats around 1.5 inches) moving through the state during the weekend. Isolated heavier downpours will be possible each afternoon, when slow moving showers will be most likely to develop along the seabreezes.
The light trade wind pattern seems likely to continue through about next Tuesday, as the east Pacific ridge remains relatively weak and far to the north. Would expect a continued seabreeze/land breeze pattern across leeward/interior sections, with some clouds and passing showers persisting windward. Most of the guidance indicates trades increasing back to moderate levels during the middle and later part of next week, which would bring a return to typical trade wind weather across the state.
A light trade wind pattern may allow for the development of seabreezes this afternoon, interior cloud build ups are likely with this occurring. A region of lower clouds just NE of Maui and the Big Island this morning has become increasingly isolated. However, passing clouds and showers, mainly along windward Big Island and Maui, can be expected. Otherwise, VFR conditions will prevail. No airmets are expected at this time.
The anticipated long period easterly swell arrived at the cdip near shore buoys north of Oahu and Maui during the predawn hours. Barbers point cdip buoy shows south swell continuing as well. Expect marginal advisory level surf on both east and south facing shores today into tonight. Strong currents will develop in some areas due the interaction between the long period east and south swells. The surf from both swells will slowly decline during the weekend.
Small craft advisory criteria winds of 25 kt or greater are not expected through the holiday weekend. However, the long period easterly and southerly swell mentioned above could bring confused seas to areas exposed to both swells.
High surf advisory until 6 am HST Saturday for Niihau, Kauai windward, Kauai leeward, Oahu south shore, Waianae coast, Oahu Koolau, olomana, Molokai, Lanai makai, Kahoolawe, Maui windward west, Maui leeward west, Maui central valley, windward Haleakala, leeward Haleakala, Kona, south Big Island, Big Island north and east.