Hilo

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs 75 to 81 near the shore to 61 to 67 at 4000 feet. Northwest winds up to 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy with scattered showers. Haze. Lows 57 to 66 near the shore to 46 to 53 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Kona

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 68 near the shore to 41 to 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with scattered showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs 79 to 84 near the shore to around 63 near 5000 feet. Northwest winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 68 near the shore to 40 to 47 near 5000 feet. North winds up to 15 mph. Chance of rain 30 percent.

Waimea

Tonight: Mostly cloudy with scattered showers. Haze. Lows 58 to 68 near the shore to 52 to 58 near 3000 feet. Southwest winds up to 15 mph. Chance of rain 40 percent.

Friday: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy with scattered showers. Lows 57 to 67 near the shore to 50 to 57 near 3000 feet. Southwest winds up to 10 mph shifting to the northeast after midnight. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy with scattered showers. Haze. Lows 58 to 68 near the shore to 52 to 58 near 3000 feet. Southwest winds up to 15 mph. Chance of rain 40 percent.

Friday: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs around 77 near the shore to 67 to 74 near 3000 feet. West winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy with scattered showers. Lows 57 to 67 near the shore to 50 to 57 near 3000 feet. Southwest winds up to 10 mph shifting to the northeast after midnight. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows around 69 near the shore to around 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs around 80 near the shore to around 64 near 5000 feet. West winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows around 69 near the shore to around 47 near 5000 feet. North winds up to 20 mph shifting to the southeast up to 10 mph after midnight. Chance of rain 30 percent.

Puna

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 58 to 67 near the shore to 47 to 54 at 4000 feet. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs 75 to 81 near the shore to 61 to 67 at 4000 feet. Northwest winds up to 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Friday Night: Partly cloudy with scattered showers. Haze. Lows 57 to 66 near the shore to 46 to 53 at 4000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Tonight: Mostly cloudy with scattered showers. Haze. Lows 66 to 72 near the shore to 45 to 50 above 4000 feet. Light winds becoming south up to 10 mph after midnight. Chance of rain 40 percent.

Friday: Mostly sunny with scattered showers in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Haze through the day. Highs around 82 near the shore to 61 to 67 above 4000 feet. West winds up to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 71 near the shore to 44 to 49 above 4000 feet. South winds up to 10 mph shifting to the east after midnight. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A brief round of showers can be expected along a passing cold front tonight followed by developing northerly winds Friday into Saturday. Cool and dry weather anticipated for the weekend.

Discussion

A stout trade wind inversion slopes upward from around 5kft at Lihue to nearly 8kft at Hilo at press time. Surface pressure falls in advance of a digging shortwave trough have largely eradicated the surface pressure gradient leading to variable winds which have given way to sea breeze in select sheltered locales this afternoon. Shower activity on radar is sparse, slow-moving and generally directed offshore as mostly dry conditions prevail. Aloft, the islands are positioned at the inflection point between expansive deep ridging to the west and upper troughing to the east. As the aforementioned wave digs south, it will bring a wave of strong forcing for ascent north and east of the islands where heavy showers and thunderstorms will be possible. Locally, this feature will usher a shallow cold front through the area bringing little more than a transient period of clouds and showers tonight into Friday, particularly along north-facing slopes as moderate northerlies develop coincident with the approach of the front. Just a slight chance of an afternoon t-storm or two over the terrain of the Big Island and/or Maui on Friday afternoon as the front advances into the eastern end of the state.
Moderate to locally breezy northerlies then advect much drier air into the forecast area Friday night into Saturday guaranteed to bring a chill to the air as dewpoints fall well into the 50s. At the same time, expansive mid-level ridging anchored west of the area will build over the state in the wake of the departing trough. Strong subsidence will force the trade wind inversion below 5kft areawide for the balance of the weekend. This stability combined with stout dry advection in the boundary layer brings assurance of a dry pattern for several days following the cold frontal passage with little more than an isolated light shower possible windward and mauka.
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

Winds will remain light across the state through this evening as a front approaches from the northwest, allowing for sea breezes to persist through the afternoon and bring clouds and a few showers to leeward and interior areas. Then heading into the evening, land breezes will help to clear out island interior cloud cover ahead of the front. The cold front will move down the island chain late tonight through tomorrow, bringing showers along its boundary and northerly winds that will usher in drier air in its wake. VFR conditions will generally prevail, but MVFR will be possible in showers.
No AIRMETs are in effect. However, AIRMET Sierra might be needed late tonight into tomorrow for portions of the island chain due to incoming clouds and showers with the frontal boundary.

Marine

A cold front will steadily move down the island chain through Friday night and will bring some unsettled weather. The most likely area for thunderstorms should be around the waters of Maui and the Big Island on Friday. The front will reach Kauai by tonight and will produce moderate to fresh northwest to north winds as it moves down the island chain. High pressure will build in behind the front this weekend and will bring the return of locally strong trade winds.
A new long-period west-northwest to northwest swell (300 degree to 320 degree) should steadily fill in tonight into Friday and will produce warning level surf across most north and west facing shores on Friday and likely through at least the first half of Saturday. This swell is expected to peak Friday afternoon through the evening. Seas will also get above the 10 ft threshold and a Small Craft Advisory will be issued for waters exposed to this swell. The swell will gradually decline from late Saturday into Monday, followed by a slightly smaller northwest swell by next Wednesday.
An out of season south swell continues to slowly fill in this afternoon and will continue to fill in throughout the day Friday. South shore surf will rise slightly above summertime average levels during the peak of the swell from Friday afternoon to early Saturday. This swell will gradually decline over the weekend.
East shore surf will remain small 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 trade winds ease. Select surf spots should see some wrap from the large northwest swell building on Friday.

Fire weather

Critical fire weather conditions are not anticipated during the forecast period. However, Saturday and Sunday will be worth monitoring as they feature the lowest post-frontal relative humidities and a relative peak in N to NE winds. While not anticipated at this time, the highest probability to reach critical thresholds will be Sunday afternoon.

HFO Watches/Warnings/Advisories

High Surf Warning from midnight tonight to 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
High Surf Warning from 10 AM Friday to 6 AM HST Saturday for Kona, Kohala, Big Island South.
Small Craft Advisory from 6 AM Friday to 6 AM HST Saturday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov