Hilo

Tonight: Mostly cloudy. Occasional showers in the evening, then showers likely after midnight. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. North winds up to 10 mph. Chance of rain 90 percent.

Wednesday: Partly sunny with scattered showers. Highs 76 to 82 near the shore to 62 to 68 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 71 near the shore to 44 to 51 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy in the evening then becoming mostly clear. Isolated showers. Lows around 71 near the shore to 46 to 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers. Highs 62 to 81. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny with scattered showers. Highs 62 to 81. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows 61 to 70 near the shore to 53 to 60 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 72 near the shore to around 50 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 83 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy in the evening then becoming mostly clear. Lows around 72 near the shore to around 51 near 5000 feet. Northeast winds 10 to 15 mph.

Puna

Tonight: Mostly cloudy. Occasional showers in the evening, then showers likely after midnight. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. North winds up to 10 mph. Chance of rain 90 percent.

Wednesday: Partly sunny with scattered showers. Highs 76 to 82 near the shore to 62 to 68 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Isolated showers in the evening. Lows 69 to 74 near the shore to 48 to 53 above 4000 feet. Northeast winds up to 10 mph shifting to the southeast after midnight. Chance of rain 20 percent.

Wednesday: Sunny. Isolated showers in the afternoon. Highs 81 to 87 near the shore to 64 to 70 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly clear. Lows around 71 near the shore to 49 to 54 above 4000 feet. Light winds.

Detailed Forecast

Synopsis

Trade winds will continue to gradually diminish, becoming light and variable by Friday. The trade winds will deliver clouds and a few showers to windward areas of all islands through tonight, with a drying trend thereafter, except for continued passing showers on windward Big Island. Light winds and mostly dry weather will continue on Saturday, but a weak cold front will bring a wind shift to the northwest, and a chance of showers on Sunday. Northeasterly trade winds and mostly dry weather are expected early next week.

Discussion

A 1024 mb high centered about 600 miles N of the islands is supporting locally breezy trade winds that are much weaker than the past several days. A low aloft over the area is gradually weakening and drifting E, and the island atmosphere is stabilizing, with afternoon overnight soundings indicating a subsidence inversion near 8000'. Satellite imagery shows scattered to broken stable and showery low clouds moving W near 20 mph.
A modest increase in windward showers is expected this evening as a area of increased PWAT moves W over the islands, with a general drying trend thereafter. Global and regional forecast guidance is consistent in indicating significant drying in the low-levels tomorrow as a strengthening mid-level ridge brings significant warming and a lowering subsidence inversion. The exception is windward Big Island, where lingering moisture may fuel scattered showers.
The high to the N will weaken and move S Wednesday and Thursday, as several areas of low pressure pass N of the islands, allowing trade winds to trend even lighter. As the high dissipates on Friday, a ridge will extend over the area from the E, with light and variable winds and mostly dry weather prevailing as the mid-level ridge persists. This regime will continue Saturday, with ensemble guidance indicating that the most probable outcome is that a weak/ dissipating front will move over the islands from the NW on Sunday, bringing a chance of showers, but little total rainfall. Ensemble consensus indicates high pressure will build N of the islands early next week, with Sunday's post-frontal NW winds veering to the NE Monday and Tuesday. A mid-level ridge building over the area will support a mostly dry regime.

Aviation

Trade winds will diminish gradually through Wednesday. An increase of showers this afternoon and evening should produce brief MVFR ceilings and visibilities across windward and mauka areas. A few of these showers could reach leeward areas at times. Otherwise, VFR conditions should prevail.
AIRMET Sierra will be possible this evening into tonight as a batch of showers move in. Drier weather should return on Wednesday with the exception of windward Big Island, where showery conditions are likely to persist into Wednesday. No other AIRMET's are expected.

Marine

Fresh to locally strong trade winds will decline over the next couple of days as high pressure to the north weakens and drifts southward. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around the Big Island and Maui County through tonight. The SCA will likely be dropped by Wednesday morning, and once down, SCA conditions are not expected through at least the weekend. A surface ridge will sit near or possibly move over the northern end of the island chain Friday and Saturday, producing gentle to locally moderate trade winds around the Big Island and light to gentle trades over remaining waters. Light winds are favored for Sunday as a weak front approaches Kauai.
No significant swells are expected through Wednesday, with slowly declining trade wind seas dominating. Windward PacIOOS buoys continue to show the well-developed trade wind swell at 5 to 8 feet at 9 to 10 seconds, which will maintain rough east shore surf above seasonal average tonight. The trade wind swell will decline to about 4 ft at 8 seconds by Thursday and drop further through the weekend.
Swells from the north-northeast and the northwest are due Thursday into early next week, with swells from both directions peaking on Sunday. A medium period north-northeast swell will build on Thursday and persist at around 3 to 5 feet through early next week. A tiny northwest swell is due on Thursday through Friday. This will be followed by a medium period 3 to 6 foot northwest swell Saturday night and Sunday, and a smaller reinforcing pulse of swell is due Monday and Tuesday. None of these swells is expected to produce advisory level surf on north, west, or east shores.
Surf along south facing shores will remain small through the week.

Fire weather

KBDI values remain high, yet the potential for critical fire weather conditions the next several days is extremely limited due to diminishing wind speeds. On Wednesday, afternoon RH will likely approach critical values of 45% for a brief period, but sustained winds will not reach criterion.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov