Hilo

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to around 57 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 79 to 86 near the shore to 66 to 72 at 4000 feet. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with numerous showers. Lows 63 to 72 near the shore to 54 to 59 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 70 percent.

Kona

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 74 near the shore to 50 to 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 83 to 89 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 71 to 76 near the shore to 49 to 55 near 5000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 20 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 10 to 20 mph. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 64 to 72 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Tonight: Partly cloudy. Breezy. Lows around 74 near the shore to around 55 near 5000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph after midnight.

Friday: Breezy. Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 86 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows around 74 near the shore to around 55 near 5000 feet. Northeast winds up to 20 mph.

Puna

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to around 57 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers. Highs 79 to 86 near the shore to 66 to 72 at 4000 feet. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Friday Night: Mostly cloudy with numerous showers. Lows 63 to 72 near the shore to 54 to 59 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Partly cloudy. Lows around 75 near the shore to around 56 above 4000 feet. Southeast winds up to 15 mph.

Friday: Mostly sunny. Scattered showers in the afternoon. Highs 84 to 89 near the shore to 66 to 74 above 4000 feet. North winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy. Lows around 75 near the shore to around 55 above 4000 feet. East winds up to 15 mph.

Detailed Forecast

Synopsis

Light to moderate trade winds will prevail through the weekend, before becoming light and variable with land and sea breezes dominant early next week. Showers will initially favor windward slopes and coasts, but will shift to interior and leeward areas early next week. Trade winds will bring the shower focus back to windward areas Wednesday through late next week.

Discussion

Currently at the surface, a 1025 mb high is centered around 1700 miles northeast of Honolulu and a stationary front is located around 400 miles north of Kauai. The resulting gradient is producing light to moderate trade winds across the island chain this evening. Infrared satellite imagery shows partly to mostly cloudy conditions across the state, while radar imagery shows a few light showers moving into windward slopes and coasts. Main short term focus revolves around trade wind trends and rain chances during the next few days.
A front north of the islands will remain nearly stationary through Friday, then begin to shift southward toward the islands over the weekend. Light to moderate trades will prevail through the period, with sea breezes developing in sheltered leeward areas each afternoon. The front will fizzle out near or just north of Kauai Sunday night and Monday, with another front following behind it weakening near Kauai late Monday through Tuesday. This will bring a period of light winds to the islands, with sea and land breezes dominant. The front will weaken into a trough and begin shifting westward Wednesday and next Thursday, allowing the trade winds to return and gradually strengthen across the island chain.
As for the remaining weather details, rather dry trade wind weather will prevail through the weekend. Light showers will favor windward and mauka areas, with localized sea breezes allowing for a few interior and leeward showers to develop each afternoon. Early next week a land and sea breeze pattern will keep showers focused over interior areas each afternoon and over the coastal waters at night. There could be a bit more shower coverage across Kauai in the vicinity of a couple decaying fronts, while shower coverage remains limited across the remainder of the state. The trades will begin to return Wednesday and next Thursday, allowing showers to begin focusing back over windward areas, although rather dry conditions look to persist.

Aviation

Light to moderate trades should bring some SHRA and low cigs to windward and mauka locations. Brief MVFR conds are possible in SHRA but VFR should prevail.
No AIRMETs in effect.

Marine

Moderate to fresh easterly trades will persist through Friday over the windier channels and waters around Maui County and the Big Island, while light to moderate breezes continue elsewhere. A brief return of fresh to strong trades is anticipated early this weekend, before trending lighter Sunday through early next week as the tail-end of a frontal boundary drifts southward into the area.
Surf along north-facing shores will peak tonight, then slowly ease late Friday through the weekend. This swell is holding steady at the offshore buoys this evening, with the peak energy in the 10 to 12 second bands. Looking ahead, guidance suggests a tightening pressure gradient between low pressure developing within the aforementioned stalled trough to the north and the building high pressure south of the Aleutians over the weekend. Fresh to strong northerly breezes focused at the islands around 700 nautical miles away between these features could send a similar, if not slightly larger, short- to medium-period north swell through the area from next Monday night through midweek.
Surf along south-facing shores will remain small through early next week, with mainly a combination of short-period southeast and background medium- to long-period south-southwest swells moving through. Guidance does show a potent storm/hurricane-force low passing south of New Zealand from Friday through Saturday, with seas peaking around 30 ft east-southeast of New Zealand on Saturday. If this materializes, we could see a small, long- period south-southwest swell next weekend (09/14-09/15).
Surf along east-facing shores will remain small and choppy through early next week due to the lack of fresh or strong breezes upstream of the state over the eastern Pacific.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov