Hilo

Tonight: Cloudy with numerous showers. Lows 58 to 66 near the shore to 48 to 55 at 4000 feet. North winds up to 10 mph. Chance of rain 70 percent.

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 81 near the shore to around 64 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. Light winds becoming north up to 10 mph after midnight. Chance of rain 70 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 69 near the shore to 41 to 48 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 83 near the shore to around 65 near 5000 feet. Light winds. Chance of rain 40 percent.

Monday Night: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 69 near the shore to 42 to 48 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 69 near the shore to 52 to 59 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 76 near the shore to 67 to 75 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 59 to 68 near the shore to 51 to 58 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 69 near the shore to 52 to 59 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 76 near the shore to 67 to 75 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with scattered showers. Lows 59 to 68 near the shore to 51 to 58 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Tonight: Mostly cloudy. Isolated showers in the evening. Lows around 71 near the shore to around 49 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Monday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 65 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 70 near the shore to around 48 near 5000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Puna

Tonight: Cloudy with numerous showers. Lows 58 to 66 near the shore to 48 to 55 at 4000 feet. North winds up to 10 mph. Chance of rain 70 percent.

Monday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 76 to 81 near the shore to around 64 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 58 to 66 near the shore to 47 to 54 at 4000 feet. Light winds becoming north up to 10 mph after midnight. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 67 to 72 near the shore to 45 to 51 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the afternoon. Highs 81 to 86 near the shore to 63 to 69 above 4000 feet. Southeast winds up to 10 mph shifting to the north in the afternoon. Gusts up to 30 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Isolated showers in the evening. Lows 67 to 72 near the shore to 45 to 51 above 4000 feet. Light winds becoming east up to 10 mph after midnight. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will prevail through tonight, before trending down through mid-week as a decaying front passes by to the north and a stronger front approaches the area. Showers will mainly focus over windward and mauka areas during this time. A cold front could bring more widespread rainfall Thursday night and Friday, with a slight chance for a few thunderstorms. A more typical trade wind pattern is expected next weekend.

Discussion

Latest satellite and radar imagery still has an upper-level cutoff low to the south of the Big Island helping to provide some instability upstream of the state. This is helping to enhance showers as they develop upstream of the islands and move into windward areas of the islands. Moderate to locally breezy trade winds will remain in the forecast through tonight, before gradually diminishing during the first half of the week due to a weak front passing north of the state, weakening the high to our northeast. Clouds and showers will remain focused along windward and mauka regions. The eastern half of the state will still have a good chance for enhanced tradewind showers as the upper low slowly weakens and shifts northeastward tonight through Monday. Mid-level ridging will build over the state as the upper low exits the area to the east, creating a drier and more stable tradewind weather pattern by Tuesday.
A strong cold front approaching the state midweek will cause the winds to shift out of the southeast and weaken on Wednesday, becoming light and variable Wednesday night through much of Thursday. This will allow for sea and land breezes to develop, with showers favoring island interiors each afternoon. The front is expected to quickly sweep across the state during the second half the next week. Depending on the strength and progression of the cold front through the islands Thursday night and Friday, we could see more widespread rain affect the islands, with some heavier showers and even a few thunderstorms not out of the question. In the wake of the front, we will transition back into a typical trade wind regime through next weekend.

Aviation

Locally breezy trade winds are expected to ease a bit tonight and Monday as an approaching front weakens the ridging north of the islands. Meanwhile, an upper low just southwest of the island chain could continue to produce moderate to isolated severe upper level turbulence this evening and tonight from Maui to the Big Island, though this area will move further east away from the islands by Monday as the upper low weakens and progresses eastward.
Showers embedded within the trades will generally favor north through east sections of the islands throughout the forecast period. Periods of MVFR ceilings and visibilities will be possible for windward locations, with VFR flight conditions prevailing elsewhere.
AIRMET Sierra continues for tempo mountain obscuration along windward sections of the smaller islands this afternoon. Additionally, AIRMET Tango remains in effect for moderate low-level turbulence downwind of island terrain due to the breezy trade winds, but this AIRMET will likely be cancelled later this afternoon or this evening as trades ease. Finally, AIRMET Tango also remains in effect for moderate to isolated severe upper level turbulence from Maui to the Big Island, and will likely be needed until early Monday morning.

Marine

The Small Craft Advisory (SCA) for moderate to locally strong trade winds has been cancelled. Wind speeds have fallen below advisory criteria and will further weaken overnight.
High pressure over the northeast Pacific will continue to weaken. A weak front will pass just north of the state Tuesday night. A second cold front will move into the western waters Thursday night. In response, trade winds will weaken through Wednesday. On Thursday, winds will further weaken and shift to the north. By late Friday, the front should exit the area, and light trade winds return.
The current moderate northwest (330) swell has peaked and will fade overnight. On Monday, a new larger long-period northwest (320) will quickly build in to take its place. This second swell is expected to peak Monday afternoon or evening then gradually decline through midweek. A High Surf Advisory has been issued for north and west facing shores of Niihau, Kauai, Oahu, and Molokai, as well as north facing shores of Maui. The advisory goes into effect early Monday and continues through Tuesday afternoon.
Towards the end of the week, an even larger northwest swell will build. This third and largest swell could bring warning level surf to most north and west facing shores on Friday and Saturday.
Surf along east facing shores will hold relatively steady through tomorrow then lower a bit Tuesday and Wednesday as the trade winds ease. East shore surf looks to become very small Wednesday and Thursday as the trades become disrupted, with a north swell potentially giving surf a boost to exposed shorelines on Friday.
South shore surf will remain very small through the middle of the week. An out of season long-period south swell may move through the islands at the end of the week, bringing a sizable boost to south shore surf.

Fire weather

No critical fire weather conditions expected through the forecast period as low-level moisture remains sufficient, with wind speeds remaining below critical thresholds. In addition, a front could bring a period of more widespread rainfall to the islands around the end of the week.

HFO Watches/Warnings/Advisories

High Surf Advisory from 6 AM Monday to 6 PM HST Tuesday 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.

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Data Courtesy of NOAA.gov