Hilo

Tonight: Showers and isolated thunderstorms. Lows 65 to 71 near the shore to 55 to 60 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain near 100 percent.

Saturday: Showers and isolated thunderstorms. Highs 78 to 84 near the shore to around 67 at 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

Saturday Night: Showers and isolated thunderstorms. Lows 64 to 70 near the shore to 54 to 60 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain near 100 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows around 75 near the shore to 49 to 55 near 5000 feet. Light winds.

Saturday: Partly sunny. Scattered showers and isolated thunderstorms in the afternoon. Highs 84 to 89 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Lows 72 to 77 near the shore to 49 to 55 near 5000 feet. Light winds.

Waimea

Tonight: Mostly cloudy with numerous showers and isolated thunderstorms. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 65 to 84. East winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Showers and isolated thunderstorms. Lows 64 to 72 near the shore to 57 to 64 near 3000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

Kohala

Tonight: Mostly cloudy with numerous showers and isolated thunderstorms. Lows 65 to 73 near the shore to 57 to 64 near 3000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 65 to 84. East winds up to 15 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Showers and isolated thunderstorms. Lows 64 to 72 near the shore to 57 to 64 near 3000 feet. East winds up to 20 mph. Chance of rain near 100 percent.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers and isolated thunderstorms. Lows around 75 near the shore to around 53 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers and isolated thunderstorms. Highs around 86 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy. Windy. Lows around 74 near the shore to around 52 near 5000 feet. East winds up to 30 mph shifting to the northeast 10 to 30 mph after midnight.

Puna

Tonight: Showers and isolated thunderstorms. Lows 65 to 71 near the shore to 55 to 60 at 4000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain near 100 percent.

Saturday: Showers and isolated thunderstorms. Highs 78 to 84 near the shore to around 67 at 4000 feet. East winds up to 10 mph. Chance of rain near 100 percent.

Saturday Night: Showers and isolated thunderstorms. Lows 64 to 70 near the shore to 54 to 60 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain near 100 percent.

Waikoloa

Tonight: Partly cloudy with scattered showers and isolated thunderstorms. Lows around 75 near the shore to around 55 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday: Partly sunny. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 84 to 90 near the shore to 66 to 72 above 4000 feet. North winds up to 10 mph. Chance of rain 70 percent.

Saturday Night: Breezy. Mostly cloudy with isolated showers and thunderstorms. Lows around 75 near the shore to 52 to 57 above 4000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light to moderate trades continue into Sunday. Periods of moderate to locally heavy rainfall will spread across the Big Island and portions of Leeward Maui today followed by leeward portions of the remaining islands on Saturday. Isolated thunderstorms are possible over the eastern end of the state by late Saturday. Breezy trades return to begin next week.

Discussion

Moderate ESE trades remain in place at the surface while more veered flow at 850mb steers moisture northwestward into the Big Island this afternoon. Visible satellite confirms development of a hybrid sea breeze pattern over the western end of the state with increased leeward convergence enhancing clouds and showers over Leeward Molokai and portions of Leeward Oahu. High clouds have short-circuited the process over Kauai where skies are mostly clear in the lowest 15kft. Thunderstorms have been noted immediately upstream of the Big Island as incoming moisture has proven deep enough to access the unstable layer aloft even in the absence of meaningful forcing. Therefore suspect coverage of rain rates of 1+”/hr will increase as this moisture is forced upslope this evening and becomes more favorably superposed with short- lived left exit jet dynamics between now and midnight. Moderate to locally heavy rain will persist mainly over the Puna and Hilo Districts for the remainder of the night as moisture spreads toward Windward Maui by early morning.
By Saturday, considerably stronger jet forcing will be in place as the shortwave presently north of the islands near 30N digs southward and deepens. The northwestward spread of moisture occurring coincident with deepening cyclonic flow aloft and favorable but modest upper dynamics will set the stage for deep convection in areas of strong low-level convergence. Given that the strength of the trades will undergo little change during the next 24 hours, expect a repeat of today's convergence patterns except with greater intensity on Saturday, particularly over the western half of Kauai and Oahu. Slow-moving heavy showers have the potential to cause nuisance type flooding on any of the islands on Saturday afternoon. The primary uncertainty comes from the continued infiltration of high clouds from the northwest which may limit sea breeze convergence and subsequent shower development especially over the smaller islands.
Moderate to locally breezy trades become established during Sunday coincident with the upper low positioning directly overhead. This will result in continued enhancement of showers, but strengthening trades will tend to limit low-level convergence for all but the most sheltered locales. As a result, focus returns to Leeward Haleakala and interior/Leeward Big Island for Sunday while remaining areas transition back to a more typical trade wind pattern, though perhaps touch wetter than normal.
Monday through Thursday will be characterized by breezy trades and diminishing moisture depth as moisture is ushered west of the area and the resident upper low is gradually reabsorbed into the westerlies.

Aviation

Light to moderate trades will continue through the weekend as a front just north of the state weakens the pressure gradient over the islands. Lighter winds across the western half of the state will allow for afternoon sea breezes to continue, with isolated interior clouds and showers possible over Oahu and Kauai. Winds will continue to be slightly stronger over the eastern half of the state. This will keep clouds and showers over mainly windward and mauka areas. An area of deep tropical moisture will continue to move across the Big Island today and into portions of Maui county tonight. This will bring an uptick in clouds and showers, with periods of MVFR likely over windward Big Island. MVFR is also possible over windward Maui tonight. Otherwise, expect mainly VFR across the rest of the state.
AIRMET Sierra for tempo mountain obscuration remains in effect over windward Big Island and my become necessary over windward Maui tonight.

Marine

A disturbance just north of the state will continue to keep the trades at moderate speeds with localized land and sea breezes possible near the coast through Saturday. This disturbance will also bring the threat of isolated thunderstorms for the windward waters around Maui and the Big Island through Saturday night. Moderate to locally strong trade winds should return Saturday night in to Sunday as high pressure builds north of the area. Trade winds should continue to strengthen into the first half of next week with widespread strong trades possible next week. Small Craft Advisories for the typical windy waters around Maui County and the Big Island are possible as early as Saturday but likely by Sunday.
Nearshore buoys saw a quick rise during the day today due to the reinforcing NNE swell and is now starting to level off with deep water swell of around 6 to 8 feet. This swell is likely peaking now through this evening and should slowly decline later tonight into Saturday. A High Surf Advisory (HSA) remains in effect for east facing shores through Saturday. A Marine Weather Statement has also been issued to highlight the risk of harbor surges in Kahului and Hilo Harbors as a result of this north-northeast swell.
A new long-period south swell will continue to fill in tonight and peak on Saturday then slowly decline through early next week. Surf along east facing shores will continue to remain at advisory thresholds through Saturday. Surf will likely drop below advisory thresholds by Saturday night, but the combination of strengthening trades and a small long-period east swell from Tropical Cyclone Kristy should continue to produce rough and elevated surf along east facing shores throughout next week. After a few days of strong trades, surf could build to advisory thresholds of 10 feet along east facing shores by the middle of next week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Saturday for Olomana, Maui Windward West, Kauai East, Koolau Windward, Molokai Southeast, Windward Haleakala, Big Island East, Big Island North.

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Data Courtesy of NOAA.gov