Hilo

Tonight: Partly cloudy with scattered showers. Lows 58 to 66 near the shore to 47 to 53 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 81 near the shore to 61 to 66 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. Light winds. Chance of rain 20 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to 42 to 49 near 5000 feet. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 79 to 84 near the shore to around 63 near 5000 feet. Light winds. Chance of rain 30 percent.

Thursday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 70 near the shore to 40 to 47 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Partly cloudy with isolated showers. Lows 59 to 68 near the shore to 51 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 58 to 67 near the shore to 50 to 58 near 3000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

Kohala

Tonight: Partly cloudy with isolated showers. Lows 59 to 68 near the shore to 51 to 58 near 3000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 10 mph. Chance of rain 40 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 58 to 67 near the shore to 50 to 58 near 3000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

South Big Island

Tonight: Partly cloudy. Lows around 70 near the shore to around 48 near 5000 feet. Northeast winds up to 15 mph.

Thursday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 81 near the shore to around 63 near 5000 feet. East winds up to 15 mph. Chance of rain 30 percent.

Thursday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 69 near the shore to around 47 near 5000 feet. Light winds. Chance of rain 20 percent.

Puna

Tonight: Partly cloudy with scattered showers. Lows 58 to 66 near the shore to 47 to 53 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 76 to 81 near the shore to 61 to 66 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 40 percent.

Thursday Night: Partly cloudy with isolated showers. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. Light winds. Chance of rain 20 percent.

Waikoloa

Tonight: Partly cloudy. Lows 67 to 72 near the shore to 46 to 52 above 4000 feet. Light winds.

Thursday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 80 to 85 near the shore to 61 to 68 above 4000 feet. Southwest winds up to 10 mph shifting to the west in the afternoon. Chance of rain 30 percent.

Thursday Night: Mostly cloudy with scattered showers. Lows 66 to 71 near the shore to 44 to 50 above 4000 feet. Light winds. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Moderate trades briefly weaken on Thursday then transition to cool and dry northeasterly trades for the weekend.

Discussion

The islands reside at the inflection point between expansive deep ridging to the west and upper troughing to the east at press time. Stable, moderate trades prevail beneath this pattern, though the inversion does slope upward from 6kft at Lihue to 8kft at Hilo owing to the latter's closer proximity to upper troughing. In this area, showers are somewhat deeper and more numerous relative to the western end of the state, but overall a very typical stable trade wind pattern remains established through today.
Existing upper trough then serves as a conduit for additional mid- latitude energy to dig southward, the associated surface pressure falls eradicating the pressure gradient by tomorrow. Consequently, a land and sea breeze pattern with pockets of interior afternoon showers is expected for Thursday. Friday into Saturday represents a transition period to noticeably cooler weather as additional upper energy digs southward over the islands. Meaningful forcing remains largely north and east of the area during this time as ridging remains firmly in control. This wave will, however, force a shallow cold front through the area late Friday through Saturday. The inversion remains stout for the duration of the frontal passage limiting rainfall potential. The exception may be the high elevations of the Big Island and potentially Maui where a brief window for thunderstorms will exist Friday into Friday night. The front itself will hit with a brief round of shallow showers followed by winds veering to the northwest Friday night and eventually transitioning to breezy NEly trades by late Saturday.
This weekend will be characterized by dry weather and dewpoints falling through the 60s into the 50s bringing a seasonable chill to air. Trades persist through this time with strong post-frontal ridging bringing very high stability and significantly reducing shower coverage and intensity.
Strong consensus exists among the extended guidance that another upper wave will dig toward the islands during the middle of next week causing trades to weaken once more. This likely precedes another cold front pushing into the forecast area.

Aviation

Moderate trades will gradually weaken through tomorrow as a cold front approaches from the northwest. Clouds and showers will generally favor windward and mauka areas, especially overnight into the early morning hours. However, sea breezes will become more pronounced tomorrow as the trades weaken, bringing clouds and few showers to leeward interiors in the afternoon and land breezes will likely help to clear out leeward areas overnight. Brief MVFR conditions will be possible in showers. Otherwise, VFR should prevail.
No AIRMETs are in effect.

Marine

Trade winds will ease through tonight then become gentle and variable on Thursday as a cold front approaches. The front, currently about 500 nm northwest of Kauai, will push the subtropical ridge toward the islands tonight, causing moderate trade winds to drop substantially. A weak prefrontal trough could develop near Maui on Thursday and serve as the boundary between gentle west to northwest winds over most islands and gentle southerlies around the Big Island. The shallow front will reach Kauai on Thursday night, then bring gentle to moderate northwest winds as it moves down the island chain Friday and Friday night. Thunderstorms will be possible near Maui along the trough Thursday night, with chances spreading to Big Island waters Friday. High pressure will build north of the region during the weekend, leading to increased fresh to strong northeast winds. A Small Craft Advisory (SCA) will likely be needed for some waters Saturday night and Sunday, with winds easing on Monday.
The current northwest swell will decline slightly through Thursday, followed by a large swell Friday. PacIOOS nearshore buoys are showing the slowly declining northwest swell at around 5 feet at 12 to 13 seconds this afternoon, and a slight drop is expected tomorrow. A deep, slow-moving, northwest Pacific storm has been generating a large swell that will pass through the area into the weekend. Long period forerunners will arrive Thursday night, and the swell will produce High Surf Warning conditions across most north and west facing shores during the peak Friday into early Saturday. A SCA will be needed for waters exposed to this swell. The swell will gradually decline late Saturday into Monday, followed by a slightly smaller northwest swell next Wednesday.
An out of season period of south-southwest swell is due Thursday through the weekend. An increase in small inconsistent swell is expected Thursday, followed by a larger pulse arriving Friday. South shore surf is expected to be at or slightly above summertime average during the peak of the swell Friday and Saturday, but we will need to monitor the local buoys late Thursday and Friday in case the swell produces larger surf. The swell will gradually decline Sunday and Monday.
East shore surf is already below seasonal average and will decline on Friday as trade winds become disrupted. Rough east shore surf will rebuild Saturday night and Sunday as northeasterly trade winds strengthen, then decline again early next week as winds ease. Due to significant differences between forecast models for local winds during the middle of next week, the locally generated wind wave forecast is uncertain.

Fire weather

Relative humidity is forecast to fall well into the 40s each afternoon from Saturday through at least Monday as drier air pushes into the area. However, winds are forecast to remain well below criteria for critical fire conditions.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov