Hilo

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy with numerous showers. Highs 80 to 86 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Friday Night: Numerous showers in the evening, then occasional showers after midnight. Lows around 70 near the shore to around 56 at 4000 feet. Light winds. Chance of rain near 100 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 68 to 74 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 72 near 5000 feet. Light winds. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 72 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows around 67 near the shore to 54 to 61 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Friday: Partly sunny with scattered showers. Highs around 82 near the shore to 72 to 79 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows around 67 near the shore to 54 to 61 near 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Friday: Partly sunny with scattered showers. Highs around 82 near the shore to 72 to 79 near 3000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Isolated showers after midnight. Lows around 68 near the shore to around 53 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 73 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows around 70 near the shore to around 55 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Puna

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Friday: Mostly cloudy with numerous showers. Highs 80 to 86 near the shore to 67 to 72 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Friday Night: Numerous showers in the evening, then occasional showers after midnight. Lows around 70 near the shore to around 56 at 4000 feet. Light winds. Chance of rain near 100 percent.

Waikoloa

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 69 to 74 near the shore to 50 to 57 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Friday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to 68 to 74 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 73 near the shore to 52 to 59 above 4000 feet. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to locally moderate trade winds will continue through Friday night, supporting mainly modest windward showers and spotty afternoon showers over leeward and interior sections. Increased trade winds and rainfall are expected during the weekend, with heavy showers and thunderstorms possible for mainly windward areas. Breezy and somewhat showery trade wind weather is expected early next week.

Discussion

Somewhat weak trade winds will support modest windward showers through Friday, and localized afternoon sea breezes will generate spotty afternoon showers. With a shallow and dissipating front about 150 miles north of the islands creeping southward, the local surface pressure gradient will remain capable of producing only light to moderate trade winds, which will be overpowered by sea breezes across sheltered leeward areas. Expect minimal windward rainfall through much of tonight, followed by an increase over the Big Island then Maui late tonight and Friday as a batch of low-level moisture moves in on the trades. Sea breezes will produce clouds over sheltered leeward terrain each afternoon. There has not be much leeward rainfall today, but showers chances will increase tomorrow afternoon on the Big Island and Maui as the moisture moves in. A mid-level ridge will erode during this time, but it should remain strong enough to inhibit any heavy showers.
Trade winds and shower activity will increase during the weekend, with some potential for flooding impacts on windward Big Island and east Maui. Trades will slowly strengthen on Saturday into Sunday as the front dissipates and surface high pressure builds far north then northeast of the state. The mid-level ridge over the islands will weaken considerably as an upper-level low develops to the northeast on Saturday, and unstable conditions are expected to develop Saturday night and Sunday as the upper low moves overhead. The above mentioned area of low-level moisture should remain in place over the Big Island and Maui, and perhaps spread as far west as Oahu, resulting in heavy showers and possibly thunderstorms over mainly windward slopes and chances for winter weather on the high summits of the Big Island. Given long duration of shower activity on windward Big Island and possibly Maui, we will have to closely monitor the potential for flooding as soils become saturated. Moisture from the dissipated front could also act as a fuel for increased rainfall on Kauai and Oahu, but confidence in that is lower.
A wet and breezy trade wind weather pattern looks to persist on Monday. As the upper low weakens and drifts south of the state, chances for heavy showers and thunderstorms will diminish, but deep moisture will likely linger over the state and maintain an active pattern of windward showers, while showers periodically pass over leeward sections.
A breezy and increasingly stable trade wind flow is expected Tuesday and Wednesday.

Aviation

Light to moderate trades will prevail through Friday as a cold front north of the state has weakened the pressure gradient across the islands. This moderate background flow is producing some afternoon cloud buildups across leeward areas, though most locations across the state remain dry. Tonight, land breezes will return and clouds should diminish over the islands. The exception will be some windward showers moving in on the moderate trade winds, particularly for windward Big Island and Maui, as a band of moisture moves through.
On Friday, afternoon cloud buildups and showers will be possible again over interior and leeward sections as daytime sea breezes return to sheltered areas.
There are currently no AIRMETs in effect. However, mountain obscuration could become an issue across windward Big Island and possibly Maui later this evening or tonight.

Marine

Relatively low pressure across the central Pacific has allowed the pressure gradient to relax in support of light to moderate trades. Light wind conditions will continue through Saturday. Strengthening high pressure then becomes established north of the islands early next week setting the stage for a return of fresh to strong trades Sunday well into next week. Small Craft Advisories will likely be needed as stronger trade winds return.
High Surf Advisory (HSA) remains in effect through Saturday for the current moderate-to-large medium period NNE (010-030) swell which continues to run solidly above guidance. Another pulse out of the NNE will arrive early Friday causing another boost in surf along east-facing and other exposed shorelines. The swell will then steadily decline through the weekend. 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 NNE swell. Small, mixed medium to long period NE/E swells emanating from the Gulf of Alaska and Hurricane Kristy then arrive early next week maintaining elevated surf along east facing exposures and potentially borderline HSA conditions. Strengthening trades will also cause an increase in short period trade wind swell during this time.
Surf along south facing shores will remain small as the tiny long-period swell from the south-southwest, will hold tonight before declining Thursday. A slightly larger south swell is possible this weekend.

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