Hilo

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 65 to 72 near the shore to 52 to 59 at 4000 feet. Southeast winds up to 10 mph shifting to the west around 10 mph after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 80 to 88 near the shore to 66 to 71 at 4000 feet. South winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 52 to 58 at 4000 feet. East winds up to 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 74 near the shore to 50 to 55 near 5000 feet. Light winds. Chance of rain 40 percent.

Friday: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 87 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday Night: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 71 to 76 near the shore to around 53 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 66 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs 66 to 86. East winds 10 to 20 mph. Chance of rain 20 percent.

Friday Night: Partly cloudy with isolated showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

South Big Island

Tonight: Partly cloudy. Lows around 75 near the shore to around 56 near 5000 feet. Northeast winds 10 to 15 mph.

Friday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 85 to 90 near the shore to around 71 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy in the evening then becoming mostly clear. Lows around 75 near the shore to around 57 near 5000 feet. East winds 10 to 15 mph.

Puna

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 65 to 72 near the shore to 52 to 59 at 4000 feet. Southeast winds up to 10 mph shifting to the west around 10 mph after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 80 to 88 near the shore to 66 to 71 at 4000 feet. South winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 52 to 58 at 4000 feet. East winds up to 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Waikoloa

Tonight: Partly cloudy. Lows around 74 near the shore to 51 to 57 above 4000 feet. East winds up to 15 mph.

Friday: Sunny. Highs 85 to 90 near the shore to 67 to 75 above 4000 feet. East winds up to 15 mph shifting to the north in the afternoon.

Friday Night: Mostly clear. Lows around 74 near the shore to 52 to 57 above 4000 feet. East winds up to 10 mph.

Detailed Forecast

Synopsis

High pressure north of the islands will maintain moderate to locally breezy trade winds through the weekend, followed by a slight decrease in winds early next week. Stable summertime conditions will bring periods of mainly windward and mauka showers, while most leeward areas remain rather dry.

Discussion

A stable and rather dry trade wind flow remains in place. Broad surface high pressure far north of the state is not particularly strong by August standards, but the ITCZ is displaced north of 10N, leading to a somewhat tight pressure gradient that is driving locally breezy trade winds over the islands. A mid-level ridge is maintaining stable conditions with an inversion based between 5,000 and 7.000 ft, and no organized moisture is noted in the trade wind flow. As a result, windward rainfall has been minimal since mid morning, and leeward areas have been dry, even across the Kona slopes of the Big Island where afternoon showers are usually active in August.
Little change is expected to the relatively dry and stable trade wind weather pattern through Sunday. Trades may ease a notch and shift out of a more easterly direction for Monday and Tuesday as the surface ridge to the north is briefly weakened. The mid-level ridge should remain strong enough to maintain stable conditions, and an area of tropical moisture may clip the Big Island on Monday or Tuesday, though odds favor the moisture passing to the south. Longer term guidance suggests moderate trades and continued modest shower activity for the second part of next week.

Aviation

Moderate to breezy trade winds will continue through the next several days as high pressure remains to the northeast and stable conditions prevail. Clouds and showers will focus primarily over the windward and mountain areas, particularly overnight and into the morning hours. MVFR conditions will be possible in showers, otherwise VFR will likely prevail.
No AIRMETs are currently in effect.

Marine

A high pressure ridge north of the Hawaiian Islands will maintain fresh to locally strong trade winds through early next week. The Small Craft Advisory (SCA) remains in effect for the windier waters and channels near Maui County and the Big Island through Saturday. This SCA will likely continue for these windier waters into early next week.
A series of small overlapping medium and long period south (170-190 degree) swells will continue for the rest of this week, with surf heights near the summertime average through Friday along south facing shores. Surf heights should decrease to background levels early next week as the swell energy fades. Another small, long period south swell will arrive by midweek next week.
Choppy conditions will continue for east facing shores through the forecast period due to the persistent fresh trades. Surf along north facing shores will remain nearly flat through next week.
Peak high tides associated with the lunar cycle will lead to minor coastal flooding along shorelines and low lying coastal areas during the afternoon high tides through Friday afternoon. A Coastal Flood Statement remains in effect for minor coastal flooding.

Fire weather

Trade winds will remain in the moderate to locally breezy range into Sunday, while a ridge aloft maintains an inversion between 5,000 and 7,000 ft. Under this stable and rather dry weather pattern, relative humidity will drop into the low to mid 40s percent range each afternoon, bringing near critical fire weather conditions. We do not anticipate fire weather headlines through the weekend, but fire weather concerns will be elevated.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov