Hilo

Today: Partly sunny with scattered showers. Highs around 85 near the shore to 68 to 74 at 4000 feet. Northwest winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 71 near the shore to around 57 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Showers likely in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to 66 to 73 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kona

Today: Partly sunny in the morning, then cloudy with scattered showers in the afternoon. Highs 83 to 89 near the shore to around 70 near 5000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows 70 to 75 near the shore to around 54 near 5000 feet. North winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Tuesday: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 82 to 88 near the shore to around 69 near 5000 feet. West winds around 10 mph. Chance of rain 50 percent.

Waimea

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 72 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 65 to 70 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Showers likely in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to 71 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Kohala

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 82 near the shore to 72 to 81 near 3000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 65 to 70 near the shore to 56 to 63 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Breezy. Showers likely in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to 71 to 80 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

South Big Island

Today: Breezy. Partly sunny in the morning, then cloudy with scattered showers in the afternoon. Highs around 86 near the shore to around 72 near 5000 feet. Northeast winds up to 25 mph shifting to the east 10 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly clear. Breezy. Lows around 72 near the shore to around 53 near 5000 feet. Northeast winds 10 to 25 mph.

Tuesday: Breezy. Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 85 near the shore to around 71 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Puna

Today: Partly sunny with scattered showers. Highs around 85 near the shore to 68 to 74 at 4000 feet. Northwest winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 71 near the shore to around 57 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Showers likely in the morning, then isolated showers in the afternoon. Highs around 84 near the shore to 66 to 73 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Partly sunny. Isolated showers in the afternoon. Highs around 87 near the shore to 70 to 75 above 4000 feet. Southeast winds 10 to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear with isolated showers. Lows around 73 near the shore to 52 to 58 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Sunny in the morning then becoming partly sunny. Isolated showers. Highs around 86 near the shore to 68 to 74 above 4000 feet. North winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trade winds will remain gentle to moderate this week, delivering a few showers to windward areas. Winds will be light enough to allow afternoon sea breezes to bring some clouds and showers to leeward areas as well. Shower coverage and intensity may increase from Wednesday into Friday as moisture increases and the atmosphere becomes unstable. Light to moderate east to southeast winds are expected next weekend.

Discussion

Mid-level troughing NW of Kauai and a mid-level ridge extending over the Big Island from the E will prevail for the next couple of days, keeping modest instability over the W end of the islands chain. The trough will move SE over the islands as the ridge weakens from Wednesday through Friday, potentially leading to increased shower coverage and intensity. Trade winds will be gentle to moderate as weak low pressure systems far to the N will lie between the islands and relatively weak high pressure cells. While daily land/sea breezes can be expected over most leeward areas in this wind regime, there remains some uncertainty as to the amount of cloud and shower coverage the afternoon sea breeze circulation will generate the next couple of days.
Satellite shows few to scattered showery clouds moving W around 15 mph near the islands, while broken mid- and high-level clouds moving over Maui and the Big Island from the SW are gradually diminishing. Radar loop shows scattered showers, with a few heavy rain cores highlighting the modest atmospheric instability, also seen in the 12Z PHLI sounding. With the instabililty and very light winds over land this morning, leeward PoPs have been nudged upward for this afternoon. With surface pressure rises of 3-4 mb over the past 24 hours, the forecast expects the coverage and intensity of showers to be less than that of the last 2-3 days.
An increase in low-level moisture is forecast to arrive on the trade wind flow tonight and Tuesday, primarily affecting windward portions of Maui and Big Island with some increase in shower coverage. Latest guidance indicates this moisture will remain primarily limited to the lowest 10-12 thousand feet as the mid-level ridge builds. This modest moisture increase is currently seen between 150W and 153W, lending some credence to the model guidance. This moisture will also likely supply the other islands see a few windward showers.
From Wednesday into Friday, the mid-level trough NW of Kauai will move slowly SE over the islands, while low-level moisture gradually pools in the area as a low-level trough develops nearby. This combination of moisture and instability will increase chances for some locally heavy downpours, and potentially thunderstorms. Afternoon leeward sea breezes could be the strongest forcing for heavy shower development as trade winds weaken again, but some windward downpours appear possible as well. Light to moderate E-SE winds are projected for next weekend, with some decrease in shower coverage and intensity.

Aviation

An upper level trough just west of Hawaii will keep the air mass over the state moderately unstable. Weak trade wind flow in the lower levels will allow local sea breezes to predominate by day and land breezes at night.
As of 2 AM Monday, satellite and radar imagery indicated isolated to scattered light showers dotted across the smaller islands and windward Big Island. By late afternoon, showers will have increased in intensity and become focused over island interiors. VFR conditions will nevertheless prevail through at least early evening except for isolated MVFR CIG or VIS in showers.
The next significant band of trade wind showers is not expected to arrive until late this evening. Mountain obscuration could be an issue for windward Big Island late tonight or Tuesday morning.

Marine

The north to south pressure gradient down upon the islands will remain slack as surface high pressure does not establish itself to the north of the state until next weekend. This will result in several days of gentle to moderate trade winds with localized coastal daily sea breezes and weak overnight land breezes taking over.
A small, medium to long period south southwest swell will continue to build in through the day. This swell, in tandem with the arrival of a low, medium period southeast swell, has a High Surf Advisory in effect through 6 AM HST Tuesday. A small, medium period easterly swell from former Tropical Cyclone Kay will also move around the chain through Tuesday. The combination of these three swells will keep surf elevated along many southeast and east-facing shorelines into the middle of the week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Tuesday for south facing shores of all islands.

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Data Courtesy of NOAA.gov