Hilo

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to 53 to 58 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 78 to 84 near the shore to 63 to 68 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Wednesday Night: Showers. Lows 64 to 70 near the shore to 54 to 60 at 4000 feet. Northeast winds up to 15 mph. Chance of rain near 100 percent.

Kona

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 73 near the shore to 48 to 54 near 5000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 68 near 5000 feet. Light winds. Chance of rain 40 percent.

Wednesday Night: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows around 74 near the shore to 49 to 54 near 5000 feet. East winds up to 10 mph shifting to the north after midnight. Chance of rain 50 percent.

Waimea

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 72 near the shore to 55 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 65 to 84. East winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with numerous showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Kohala

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 63 to 72 near the shore to 55 to 62 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 65 to 84. East winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday Night: Breezy. Mostly cloudy with numerous showers. Lows 64 to 72 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

South Big Island

Tonight: Partly cloudy. Lows around 74 near the shore to around 52 near 5000 feet. Northeast winds 10 to 15 mph.

Wednesday: Breezy. 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.

Wednesday Night: Partly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 75 near the shore to around 53 near 5000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Puna

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 70 near the shore to 53 to 58 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Highs 78 to 84 near the shore to 63 to 68 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Wednesday Night: Showers. Lows 64 to 70 near the shore to 54 to 60 at 4000 feet. Northeast winds up to 15 mph. Chance of rain near 100 percent.

Waikoloa

Tonight: Mostly clear. Breezy. Lows around 74 near the shore to 51 to 56 above 4000 feet. East winds up to 20 mph.

Wednesday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 83 to 90 near the shore to 66 to 72 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Wednesday Night: Mostly clear. Lows around 75 near the shore to 52 to 57 above 4000 feet. East winds up to 10 mph.

Detailed Forecast

Synopsis

Breezy and stable trade winds will prevail through Wednesday as high pressure strengthens north of the state and a low aloft to the southwest weakens. Low clouds and modest showers will be focused across windward slopes, with a few afternoon and evening showers on leeward Big Island. An increase in trade wind showers is expected Wednesday night into Friday, followed by weaker trades this weekend.

Discussion

Shower intensity is decreasing as stability returns to the breezy trade wind flow. The mid- to upper-level level low that produced unsettled conditions for the past few days is filling just southwest of the islands. As a result, high clouds have thinned and thunderstorms just north and west of Kauai have moved away from the area. The afternoon Hilo sound revealed an inversion near 8,000 ft and drier aloft that has been ushered in by a strengthening mid-level ridge. These stable conditions were not yet evident on the Lihue sounding, though a developing inversion was noted around 10,000 ft. Rainfall totals were mostly less than a half inch across windward areas, and strengthening high pressure north of the state is driving breezy trade winds.
A breezy and stable trade wind flow will produce typical trade wind weather tonight and Wednesday, followed by an increase in mainly windward shower activity Wednesday night into Friday. The fuel for the increased showers will be enhanced low-level moisture from former Hurricane Kristy. Guidance shows a mid-level ridge maintaining somewhat stable conditions that will minimize any flood threat, but since moisture is expected to be 10,000 to 12,000 feet deep with precipitable water well in excess of 1.5 inches, a few heavy showers cannot be ruled out. The bulk of the moisture should be concentrated on windward Big Island and Maui County, but we will fine tune the forecast as the moisture moves closer.
Weaker trade winds are favored for the weekend as a north Pacific front erodes the high to our north, and winds may even veer out of the east-southeast over some areas on Sunday and Monday. The GFS and ECMWF suggest that an upper-level trough could dig west of the state, but generally, a stable trade wind flow is likely as a mid-level ridge holds over most islands. Look for typical trade wind weather with an increase in rainfall possible around the Big Island Monday.

Aviation

Breezy to locally strong trades will focus clouds and showers over windward and mauka areas through the forecast period. A brief period of showers ongoing this afternoon will be followed by another band of showers late tonight into early Wednesday. This will ensure periods of MVFR windward, especially over the western half of the state.
AIRMET Sierra for mountain obscuration is in effect for Molokai through Kauai. Sierra may be needed again late tonight into early Wednesday.
AIRMET Tango for lee turb remains in effect.

Marine

A strong ridge to the north will maintain fresh to locally strong easterly trades through Friday. The ridge is expected to weaken over the weekend as a couple of front pass north of the state. Expect the strongest winds and roughest conditions over the windier waters and channels from Oahu to the Big Island through tonight and then scale back to the typical windy waters around Maui County and the Big Island. Latest satellite and radar imagery shows heavy showers and isolated thunderstorm or two is still lingering around Kauai waters, however conditions are expected to improve as we head into the evening hours.
Surf along north facing shores will gradually ease through midweek as a north-northeast swell fades through Wednesday. An upward trend is possible this coming weekend due to a storm-force low centered over the far northwest Pacific near Kamchatka. Guidance shows small, long-period forerunners arriving out of the north-northwest from this system by the end of the day Friday, then peaking near advisory level (15 feet) Saturday.
A combination of a small, medium-period easterly swell and elevated, rough trade wind swell is producing borderline High Surf Advisory (HSA) conditions along east facing shores. Current observations throughout today remain around 6 to 8 feet, in-line with the current forecast. We will continue to monitor all observations and guidance to see if a HSA (10 foot surf heights) is needed for east facing shores as strong trades locally and upstream persists and the small, medium period easterly swell fades.
Surf along south facing shores will gradually lower a notch Wednesday as a small, south-southwest swell moves out and mix of short- period southeast and background, long-period south swell energy maintains small surf through the rest of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Wednesday for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.
Small Craft Advisory until 6 AM HST Thursday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov