Hilo

Tonight: Mostly cloudy with showers likely. Lows 63 to 70 near the shore to around 57 at 4000 feet. North winds up to 10 mph shifting to the northwest after midnight. Chance of rain 60 percent.

Sunday: Partly sunny. Chance of showers in the morning, then slight chance of showers in the afternoon. Highs 78 to 86 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Sunday Night: Partly cloudy with a 20 percent chance of showers. Lows 64 to 70 near the shore to around 57 at 4000 feet. Light winds.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. A 20 percent chance of showers. Lows around 73 near the shore to around 52 near 5000 feet. Light winds.

Sunday: Sunny in the morning, then mostly cloudy with a 20 percent chance of showers in the afternoon. Highs 82 to 88 near the shore to around 68 near 5000 feet. Light winds.

Sunday Night: Mostly cloudy in the evening then becoming mostly clear. A 20 percent chance of showers. Lows around 73 near the shore to 50 to 55 near 5000 feet. Light winds.

Waimea

Tonight: Mostly cloudy with a 50 percent chance of showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph.

Sunday: Mostly sunny in the morning then becoming partly sunny. A 20 percent chance of showers. Highs 65 to 84. East winds up to 10 mph.

Sunday Night: Partly cloudy with a 20 percent chance of showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds around 10 mph in the evening becoming light.

Kohala

Tonight: Mostly cloudy with a 50 percent chance of showers. Lows 63 to 71 near the shore to 55 to 62 near 3000 feet. East winds 10 to 15 mph.

Sunday: Mostly sunny in the morning then becoming partly sunny. A 20 percent chance of showers. Highs 65 to 84. East winds up to 10 mph.

Sunday Night: Partly cloudy with a 20 percent chance of showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds around 10 mph in the evening becoming light.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. A 20 percent chance of showers. Lows around 74 near the shore to around 54 near 5000 feet. East winds 10 to 15 mph shifting to the northeast after midnight.

Sunday: Sunny in the morning, then mostly cloudy with a 20 percent chance of showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds up to 15 mph.

Sunday Night: Mostly cloudy with a 20 percent chance of showers early in the evening, then partly cloudy in the late evening and overnight. Lows around 73 near the shore to around 54 near 5000 feet. East winds around 10 mph in the evening becoming light.

Puna

Tonight: Mostly cloudy with showers likely. Lows 63 to 70 near the shore to around 57 at 4000 feet. North winds up to 10 mph shifting to the northwest after midnight. Chance of rain 60 percent.

Sunday: Partly sunny. Chance of showers in the morning, then slight chance of showers in the afternoon. Highs 78 to 86 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Sunday Night: Partly cloudy with a 20 percent chance of showers. Lows 64 to 70 near the shore to around 57 at 4000 feet. Light winds.

Waikoloa

Tonight: Partly cloudy with a 20 percent chance of showers. Lows around 74 near the shore to around 55 above 4000 feet. East winds up to 15 mph.

Sunday: Sunny in the morning, then mostly cloudy with a 20 percent chance of showers in the afternoon. Highs around 86 near the shore to 66 to 74 above 4000 feet. Northeast winds up to 10 mph shifting to the northwest in the afternoon.

Sunday Night: Partly cloudy with a 20 percent chance of showers. Lows around 74 near the shore to around 55 above 4000 feet. Northwest winds up to 10 mph in the evening becoming light.

Detailed Forecast

Synopsis

Light to moderate trade winds will bring a few brief showers, mainly to windward areas, before gradually diminishing on Sunday. Light and variable winds thereafter will result in mostly clear nights and mornings, and warm and muggy afternoons and evenings through Wednesday. Showers will be limited, and most areas will be dry. Cooling trade winds will return by Thursday, and remain breezy into next weekend.

Discussion

After one more day of trade winds delivering a few windward showers, light winds and mostly dry weather will prevail well into next week.
High pressure cells centered far NE and NW of the islands are supporting the current light to moderate trade wind flow, with wind speeds up slightly from yesterday. A strong shortwave aloft digging sharply southward along ~152W to the distant NNE of the islands will develop into a strong cutoff low as it stalls near 32N 150W (about 900 miles NNE of the islands) by Monday. This will incite the development of a surface low, with the vertically-stacked cutoff low then tracking slowly W along ~32N and slowly weakening through the end of the week.
In response to this deep-layer low passing N of the islands, the local pressure gradient will become quite slack, and winds will be light and variable from Sunday night through Tuesday night. As the low slowly dissipates and begins to move N later in the week, high pressure building far NE of the area will promote a light SE flow on Wednesday, and a strengthening trade wind flow by Thursday. Breezy trade winds are expected for next weekend as the low completely dissipates.
A strong mid-level ridge will bring anomalously warm 500 mb temperatures the next couple of days while PWAT will be near to below normal, thus any rainfall that occurs will produce little in the way of accumulation. In the short term, best chance of showers will be windward as trades persist. The light winds will result in mostly clear nights and mornings as overnight land breezes develop. This will be followed by warm and muggy afternoons and evenings, with sea breezes driving the formation of interior clouds and isolated showers. There could be a bit more cloud and shower coverage across Kauai as a dissipating frontal boundary brings increased moisture as it nears on Tuesday. In the shorter term, a low cloud band now about 200 miles N of Kauai will likely dissipate as it nears Kauai on Sunday, but could still bring a modest moisture increase.

Aviation

Light to moderate trade winds will decrease tonight into tomorrow allowing local land and sea breezes to form. Showers will focus primarily over windward and mountain areas.
No AIRMETs in effect and none are expected.

Marine

Moderate to fresh northeast to east trades will continue through tonight over the windier channels and waters around Maui County and the Big Island, while light to moderate breezes continue elsewhere. Winds will trend down Sunday through early next week as a diminishing frontal boundary drifts southward into the area and stalls near the state around Tuesday. Winds are expected become light and variable on Monday and continue through Tuesday. As the frontal boundary dissipates, a ridge of high pressure will gradually build north of the area and we should see breezy trades return by the end of next week.
Surf along north-facing shores will steadily lower through Monday as a north swell that peaked early Friday fades. Guidance continues to show a gale developing to our north this weekend along an old frontal boundary, with a decent sized area of strong-to gale-force northerly winds focused at the islands around 700 nautical miles away. This will generate a larger, short- to medium-period north to north-northeast swell that will arrive Monday night, then peak Tuesday night.
Surf along east-facing shores should see some moderate surf from the north-northeast swell, which should peak Tuesday night. Otherwise the lack of fresh to strong breezes upstream of the state will continue to produce minimal windswell through the middle of next week.
A small south-southeast swell that peaked Friday should continue to produce some small surf along south facing shores through Sunday. Mainly background swells are expected for the upcoming week with mainly a combination of short-period southeast and background medium- to long-period south-southwest swells. Guidance does show a storm- force low passing south of New Zealand today, with seas peaking around 30 ft east-southeast of New Zealand. Although the bulk of this energy is focused at Central America, we should see a small, long-period south- southwest swell from this source next weekend (9/14-15).

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov