Hilo

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 70 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 79 to 85 near the shore to 65 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy. Showers likely in the evening, then occasional showers after midnight. Lows 63 to 70 near the shore to around 56 at 4000 feet. Light winds. Chance of rain 90 percent.

Kona

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 73 near the shore to 49 to 54 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Friday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 67 near 5000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then mostly clear with isolated showers after midnight. Lows around 73 near the shore to 49 to 54 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 71 near the shore to 54 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 65 to 84. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 56 to 62 near 3000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Kohala

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 71 near the shore to 54 to 61 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 65 to 84. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 56 to 62 near 3000 feet. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

South Big Island

Tonight: Mostly clear. Isolated showers in the evening. Lows around 74 near the shore to around 53 near 5000 feet. East winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Friday: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 84 near the shore to around 67 near 5000 feet. Southeast winds 10 to 15 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 73 near the shore to around 52 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Puna

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 70 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 79 to 85 near the shore to 65 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy. Showers likely in the evening, then occasional showers after midnight. Lows 63 to 70 near the shore to around 56 at 4000 feet. Light winds. Chance of rain 90 percent.

Waikoloa

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to 51 to 56 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Highs 84 to 89 near the shore to 65 to 72 above 4000 feet. Northwest winds 10 to 15 mph shifting to the west in the afternoon.

Friday Night: Partly cloudy. Isolated showers in the evening. Lows around 74 near the shore to 51 to 56 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Light to locally moderate trade winds will are expected through the weekend, bringing a few showers to windward areas. Afternoon sea breezes will bring clouds and showers to leeward and interior areas. A low aloft will destabilize the island atmosphere Saturday night and Sunday, bringing the potential for some locally heavy showers and a chance for thunderstorms. Expect stronger trade winds to return next week.

Discussion

Light to moderate trade winds are being supported by a weakening high pressure cell far NE of the islands. Like last night, satellite and radar images show limited and small patches of low-level moisture approaching most islands from the E, and a relatively dry night is anticipated outside of a few brief windward showers.
The high to the distant NE will diminish Friday and trade winds will ease as the low-level pressure gradient slackens. The light trades will persist through the weekend, allowing land and sea breezes to prevail over sheltered leeward areas. Nighttime land breezes will lead to mostly clear conditions leeward, with just a few windward showers. The afternoon sea breezes will drive cloud and shower formation over leeward and interior areas.
A shortwave trough will dig toward the islands from the NW Friday and Saturday, developing into a closed low that moves close to the islands this weekend. While there remains some uncertainty as to where the core of the low will eventually move, confidence is increasing that the island atmosphere will become destabilized by this feature, especially Saturday night and Sunday. The potential for thunderstorms and/or locally heavy showers has been included in the forecast for portions of the area. PWAT will be somewhat limited, thus widespread coverage of rainfall is not expected, but the showers that do occur will have the potential to become heavy. One of the more likely areas for this to occur would be the Big Island's Kona slopes on Sunday afternoon.
Trade wind speeds will increase early next week as new high pressure to the distant NW builds eastward. Stability will also increase as the low aloft weakens and moves away to the NE.

Aviation

High pressure north of the state will maintain moderate trade winds over the region through Friday evening. Relatively dry and stable conditions are expected. VFR flight conditions will prevail at most locations, but brief MVFR ceilings and visibility will be possible within any showers that pass through.
A weak eddy just southwest of the Big Island will keep the Kona and Kau coasts shrouded in clouds most of the night. Lee-side clearing should occur shortly after sunrise. In the afternoon, cumulus build- ups will redevelop along south and west facing slopes of the Big Island and linger through the evening.

Marine

Moderate to locally fresh trade winds are expected to slowly decline to gentle to moderate speeds on Friday through Saturday, as a series of fronts pass far north of the state. Isolated thunderstorms could be possible Saturday night through Sunday for the windward waters as an upper low moves through the area. Winds should then gradually strengthen Sunday into the first half of next week as high pressure builds north of the state. Winds could potentially reach Small Craft Advisory levels for the windier waters and channels around Maui County and the Big Island by next week Monday.
For north facing shores, a pair of overlapping small, short period north swells should maintain small surf in place along north- facing shores through this weekend. A short lived small, short to medium period northeast swell is expected Saturday night through Sunday. This will also give east facing shores a slight bump on Sunday. Although there is some uncertainty on how strong the event will be, there is the potential for the arrival of a moderate long period north- northwest swell as early as Sunday and likely peaking next Monday, below advisory levels for north facing shores. This swell could linger through the middle of next week as it slowly fades.
The current long period south southwest swell will continue to gradually fade over the next few days. Buoys near Samoa have steadily risen throughout the day and plateaued at moderate levels, and will translate to a moderate, long period south swell that will slowly fill in Saturday, peak Sunday and hold into Monday then gradually decline through the middle of next week. This swell will may boost surf along south facing shores to near advisory levels during its peak.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov