Hilo

Tonight: Cloudy with numerous showers. Locally heavy rainfall possible. Lows 66 to 73 near the shore to 58 to 63 at 4000 feet. Southeast winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Monday: Cloudy with scattered showers. Locally heavy rainfall possible. Highs 79 to 87 near the shore to around 68 at 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 65 to 72 near the shore to around 59 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kona

Tonight: Partly cloudy with isolated showers. Lows around 76 near the shore to 52 to 57 near 5000 feet. Light winds becoming northeast around 10 mph after midnight. Chance of rain 20 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 86 to 91 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 70 percent.

Monday Night: Partly cloudy. Scattered showers in the evening. Lows around 76 near the shore to 52 to 57 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy with numerous showers. Lows 67 to 74 near the shore to 59 to 66 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 67 to 87. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 66 to 74 near the shore to 58 to 65 near 3000 feet. East winds 10 to 20 mph. Chance of rain 60 percent.

Kohala

Tonight: Mostly cloudy with numerous showers. Lows 67 to 74 near the shore to 59 to 66 near 3000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 67 to 87. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday Night: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows 66 to 74 near the shore to 58 to 65 near 3000 feet. East winds 10 to 20 mph. Chance of rain 60 percent.

South Big Island

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 77 near the shore to around 56 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Locally heavy rainfall possible in the morning. Highs around 87 near the shore to around 70 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy early in the evening then becoming mostly clear. Breezy. Scattered showers in the evening. Lows around 76 near the shore to around 56 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Cloudy with numerous showers. Locally heavy rainfall possible. Lows 66 to 73 near the shore to 58 to 63 at 4000 feet. Southeast winds up to 10 mph shifting to the west after midnight. Chance of rain 70 percent.

Monday: Cloudy with scattered showers. Locally heavy rainfall possible. Highs 79 to 87 near the shore to around 68 at 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy with numerous showers. Lows 65 to 72 near the shore to around 59 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Waikoloa

Tonight: Mostly clear with isolated showers. Lows around 77 near the shore to around 58 above 4000 feet. Light winds becoming east around 10 mph after midnight. Chance of rain 20 percent.

Monday: Partly sunny with scattered showers. Highs 86 to 92 near the shore to 69 to 76 above 4000 feet. Light winds becoming north around 10 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 77 near the shore to around 57 above 4000 feet. Northeast winds around 10 mph. Chance of rain 30 percent.

Detailed Forecast

Synopsis

The general theme this week will be breezy winds and typical showers, with higher rain amounts confined to windward exposures and upper elevations, in a trade wind regime. A slug of higher moisture passing through from the east tonight will increase precipitation areal coverage with possible periodic heavy rainfall primarily over windward Big Island and Maui County.

Discussion

A large area of surface high pressure approximately 1,400 miles from Oahu will remain anchored in place through the week. The pressure gradient downstream of the high will remain tight enough to support areawide breezy to locally gusty easterly winds through terrain gaps the next several days. The high will weaken late this week and the gradient will slacken off just enough to allow trades to slightly fall off. Precipitation will primarily be focused along windward areas with the bulk of the rain falling during the overnight hours. Night time into early morning windward mauka showers will occasionally pass over the ridge tops and wetten leeward slopes or provide sprinkles to leeward communities.
Higher mid-level moisture moving across Big Island tonight (greater than 2 inch precipitable water air mass) is noted on satellite by a wide swath of warmer broken to overcast clouds moving onto Big Island and eastern Maui County this afternoon. This area of deeper moisture and associated mid-level troughing will pass across Big Island and windward Maui County tonight into early Monday morning. The depth of this higher moisture increases the probabilities that various windward Big Island and Maui County communities may experience bouts of brief heavy rainfall tonight. While the increase in moisture over the smaller islands is not expected to be quite as deep, a higher frequency of (predominantly windward) showers is likely. Once mid-level troughing washes out west of the state Tuesday, typical trade wind weather will return. Overall,less mid to late week diurnal rainfall is expected (in both frequency and areal coverage) as a drier air mass advects in. Windward slopes and smaller island higher elevations will still pick up a daily half an inch to an inch of rain during the overnight hours.
The extended forecast going into the final third of the month is looking somewhat wet. Forecast guidance has an upper low moving toward the state from the north northeast a week from now. While rain probabilities will be on the rise, the chances for heavy rain and isolated thunder (as upper levels cool a touch and mildly destabilize the regional atmosphere) are low due to the uncertainty of this low's location or proximity to the islands.

Aviation

High pressure centered far north of the state will maintain moderate to breezy trades over the next few days. Clouds and showers will generally favor windward and mauka areas, though the temperature inversion heights will remain elevated enough to allow occasional showers to pass over island terrain into leeward areas.
Tonight, a plume of deeper moisture will move in from the southeast, affecting primarily east and southeast portions of the Big Island and Maui. MVFR conditions, and possibly isolated IFR, are expected in heavier showers. Elsewhere, VFR conditions are expected to prevail.
With locally breezy trade winds prevailing across the state, AIRMET Tango remains in effect for low-level turbulence over and downwind of terrain. This AIRMET will likely continue through Monday.
AIRMET Sierra will likely be needed by this evening for east and southeast facing slopes of the Big Island and possibly Maui to account for mountain obscuration due to low clouds and showers.

Marine

Moderate to locally strong trade winds will hold through Wednesday, as a strong surface high meanders 1,000 to 1,400 nm north of the islands. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around the Big Island and Maui County through Tuesday night, though the advisory may need to be extended through Wednesday. The high will weaken and move eastward late Wednesday and Thursday, leading to a slight decline in the trades.
Surf across most shores will be below seasonal average through the week. Trade winds will drive short period seas of around 5 to 6 feet at 7 seconds into Wednesday, maintaining moderate east shore surf. A decrease in trade winds will cause east shore surf to decline Thursday and Friday. Moderate surf along south facing shores will slowly decline Monday and Tuesday as the current south swell drops. A small southwest pulse out of the Tasman Sea could produce a slight rise in surf Friday. Aside from trade wind wrap, surf along north facing shores will be minimal through Wednesday, and a tiny northwest swell will be possible Thursday or Friday.
The combination of seasonally high astronomical tides and water levels running around 6 inches higher than predicted will produce localized coastal inundation each afternoon through Tuesday. A Coastal Flood Statement has been issued to highlight these conditions.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov