Hilo

Tonight: Mostly cloudy. Haze through the night. Isolated showers after midnight. Lows 59 to 67 near the shore to 48 to 54 at 4000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Haze. Highs 77 to 82 near the shore to 64 to 71 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 59 to 67 near the shore to 48 to 56 at 4000 feet. Light winds becoming northwest up to 10 mph after midnight. Chance of rain 80 percent.

Kona

Tonight: Mostly cloudy. Haze through the night. Isolated showers after midnight. Lows around 69 near the shore to 42 to 48 near 5000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 83 near the shore to around 67 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 30 percent.

Wednesday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 70 near the shore to 43 to 49 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows 60 to 68 near the shore to 51 to 59 near 3000 feet. Light winds.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Haze. Highs around 77 near the shore to 68 to 75 near 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 60 to 68 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Haze. Lows 60 to 68 near the shore to 51 to 59 near 3000 feet. Light winds.

Wednesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Haze. Highs around 77 near the shore to 68 to 75 near 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 60 to 68 near the shore to 52 to 59 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy. Haze through the night. Isolated showers after midnight. Lows around 69 near the shore to around 49 near 5000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs around 83 near the shore to around 67 near 5000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 30 percent.

Wednesday Night: Partly cloudy. Isolated showers in the evening. Lows around 71 near the shore to around 50 near 5000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Haze through the night. Isolated showers after midnight. Lows 59 to 67 near the shore to 48 to 54 at 4000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Haze. Highs 77 to 82 near the shore to 64 to 71 at 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 59 to 67 near the shore to 48 to 56 at 4000 feet. Light winds becoming northwest up to 10 mph after midnight. Chance of rain 80 percent.

Waikoloa

Tonight: Mostly cloudy. Haze through the night. Isolated showers after midnight. Lows 66 to 72 near the shore to 46 to 52 above 4000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 80 to 85 near the shore to 64 to 70 above 4000 feet. North winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 30 percent.

Wednesday Night: Partly cloudy. Isolated showers in the evening. Lows 67 to 72 near the shore to 47 to 52 above 4000 feet. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A cold front will continue to approach the islands this evening, bringing moist southerly winds and increasing rainfall chances. The front will reach Kauai later this evening, then stall and diminish around Oahu and Molokai Wednesday through Thursday. Lingering residual moisture combined with an upper disturbance over the region will keep rainfall chances around through the second half of the week. As trade winds gradually return, the focus of rainfall will shift to windward and mauka areas later in the week through early next week.

Discussion

Current radar and satellite imagery show isolated to scattered showers streaming into leeward areas on the south-southwesterly winds this afternoon, with a line of showers moving northeast along a frontal boundary about 100 miles to the northwest of Lihue as of 2 PM HST. These breezy south-southwesterly winds will persist through this evening before the cold front moves into Kauai. Moisture caught up in this flow will continue to deliver periodic showers to south- and west-facing slopes through the evening for Kauai and into tomorrow for the rest of the island chain. With VAD wind profiles showing 25 to 30 knots in a layer from 2,000 to 8,000 feet above the surface over Kauai and Molokai this afternoon under stable conditions, strong downsloping winds may impact windward areas through this evening.
Short-term model guidance remains in decent agreement on the timing and progression of the cold front currently on Kauai's doorstep. This front, driven by a shortwave trough diving southeast and sweeping across the Central Pacific, is forecast to move into Kauai later this evening before stalling near Oahu and Molokai tomorrow night into Thursday. Breezy west-northwesterly winds will fill in behind the front this evening, then veer out of the northeast by tomorrow night as the front gradually progresses down the island chain. While most of the dynamics and deeper moisture are expected to remain north of the state, increasing lift and pooling low- level moisture along the boundary will enhance the potential for some much needed rainfall across the islands, particularly over the dry leeward areas.
Moderate to breezy east-northeasterly trades will return Thursday through the weekend as high pressure builds north of the state, helping to focus clouds and showers over windward and mauka areas. However, as a short-wave trough dives southeast across the island chain Thursday night into Friday and forms a cutoff low over the state this weekend, instability associated with this feature along with ample upstream moisture will help to enhance showers across the area. Instability from the cold pool aloft may lead to a few heavier showers or even isolated thunderstorms, particularly from Oahu to the Big Island later this week as the upper trough moves into the area and begins to close off. For the Big Island summits, this setup could support periods of wintry precipitation from late Thursday through early Saturday.
Heading into next week, the upper level low will get caught up in the westerly flow aloft and move east of the state, bringing a return to more typical trade wind weather.

Aviation

A front will move over Kauai this evening, while the rest of the state remains under a deep south to southwest flow. Due to stable conditions ahead of the front, AIRMET Tango is in place for low level turbulence over and downwind of terrain on Kauai and Oahu. This turbulence should diminish quickly during the evening as the strongest winds aloft driving the front lift away from the area. The front will bring MVFR conditions to Kauai after sundown, and AIRMET Sierra will likely be needed for mountain obscuration along south through northwest slopes of Kauai until around midnight. Shallow moisture ahead of the front will support mainly light showers over southern slopes from Oahu to Maui tonight, though VFR is expected to prevail. The front will stall on Oahu and likely generate mountain obscuration through much of the day on Wednesday.

Marine

Overlapping large to extra large long-period swells will maintain warning level surf along most north and west facing shores through Thursday. Wave heights have increased throughout the day at buoys 51001 and 51101 northwest of Kauai, though the Hanalei and Waimea buoys have held relatively steady thus far with swell heights around 10-11 feet and 9 feet 15 seconds, respectively. Thus, surf along north and west facing shores has also remained steady near or just above High Surf Warning criteria.
As we head into this evening and tonight, however, expect that surf along north and west facing shores will trend up even further to extra-large heights as a significant NW swell builds. This swell will peak on Wednesday, producing large and dangerous surf well above High Surf Warning criteria for exposed shorelines. As some of the swell is being generated by an extensive fetch of west to northwest winds passing just north of the islands, a wide range of wave periods is expected. See the latest High Surf Warning (CFWHFO) and Surf Zone Forecast for Hawaii (SRFHFO) for details. Northwest swell will then gradually diminish from Thursday into Saturday, with surf falling below High Surf Warning levels Thursday night and falling below High Surf Advisory heights by Saturday. A new, moderate northwest swell is possible Sunday.
Locally strong southwest winds will bring choppy wind waves to south and west facing shores (especially on Kauai and Oahu) through tonight before diminishing. Surf along east facing shores will remain small throughout the next few days.
Combined seas 10 feet or greater have resulted in a Small Craft Advisory for all Hawaiian coastal waters (except Maalaea Bay) through Thursday. Additionally, the latest advanced scatterometer pass shows that southwest winds have become strong over waters near Kauai and Oahu as an approaching front tightens the pressure gradient between it and a ridge near the eastern end of the state. The front is expected to moves over Kauai and Oahu tonight into Wednesday, with moderate north to northeast winds developing behind the front. Meanwhile, winds over Big Island and Maui waters will remain light and variable.
Moisture along the front will combine with a developing low aloft to bring the potential for some locally heavy downpours and isolated thunderstorms as the island atmosphere becomes increasingly unstable from late Wednesday into the weekend. High pressure building north of the islands will support moderate to locally strong northeast to easterly trade winds from Wednesday night into Friday. Long term guidance favors a continued trade wind flow through next weekend.

Fire weather

No critical fire weather conditions are expected through the week due to increasing moisture and rain chances associated with a front forecast to move into the area this evening and stall across the central part of the state Wednesday night into Thursday. Enhanced tradewind showers with the potential for isolated thunderstorms will be possible through the rest of the week into the weekend.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Thursday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kona, Kohala, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island South.
Small Craft Advisory until 6 PM HST Thursday for all Hawaiian waters except Maalaea Bay,

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Data Courtesy of NOAA.gov