West Kaua’i

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 71 near the shore to around 61 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tuesday: Mostly sunny. Highs 84 to 90 near the shore to around 76 above 3000 feet. East winds up to 15 mph.

Tuesday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows around 71 near the shore to around 61 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight.

South Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 72. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 80 to 89. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday Night: Mostly cloudy with isolated showers. Lows around 72. Northeast winds around 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs 75 to 82 in the valleys to around 66 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday Night: Breezy. Mostly cloudy with scattered showers. Lows 63 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 20 mph. Chance of rain 40 percent.

North Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 73. East winds up to 15 mph. Chance of rain 40 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 86. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 30 percent.

Tuesday Night: Mostly cloudy with isolated showers. Lows 65 to 73. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 65 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 85. East winds 10 to 15 mph. Chance of rain 40 percent.

Tuesday Night: Mostly cloudy with isolated showers. Lows 65 to 75. East winds 10 to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A stable trade wind flow established over the Big Island and Maui County will spread westward across Oahu and Kauai tonight as high clouds diminish. Aside from a few lingering showers around Kauai and leeward Oahu this evening, expect somewhat dry and locally breezy trade winds to focus modest showers on windward slopes through Wednesday. A slight increase in shower activity will be possible Thursday and Friday as trade winds decrease. Light to moderate winds are expected for the weekend.

Discussion

A humid east-southeast flow with increased shower activity remains in place near Kauai and Oahu this afternoon, while drier and more stable trade winds prevail over Maui County and the Big Island. The flow is veered across the western end of the state due to an upper-level low and its associated surface trough a couple hundred miles west of Kauai. Dew points have held in the lower 70s on much of Kauai and Oahu, leading to a humid feel and supporting sporadic bands of showers over both windward and leeward areas of Kauai and to a lesser degree on Oahu this afternoon. Over Maui County and the Big Island, strong surface high pressure far to the northeast is driving locally breezy trade winds. Mid-level ridging is producing a low and strong inversion over these islands, and a drier air mass with dew points in the mid to upper 60s is generating modest rainfall over windward areas and sheltered leeward terrain. The upper low to the west continues to send areas of high clouds over the entire island chain, but these clouds are thinning.
A somewhat dry stable and breezy trade wind flow with diminished high clouds will spread to Oahu and Kauai tonight as the upper- level low and associated surface trough drift westward. Dew points should fall into the mid 60s, reducing humidity, and precipitable water will be near or slightly below seasonal average. As a result, showers on all islands will be limited and focused over windward areas, and aside from scattered afternoon showers on the Kona slopes of the Big Island, leeward areas will be mostly dry.
Some changes are expected Thursday and Friday. A weakened version of the above mentioned upper-level low will swing overhead late Thursday and Friday. This will likely bring another bout of thicker high clouds and may produce an increase in shower activity, mainly windward. Trades will remain locally breezy Thursday but drop a notch Friday as the surface ridge is weakened.
For the weekend, light to moderate trade winds with stable and somewhat dry conditions are favored.

Aviation

This evening and tonight, the moderate to breezy southeasterly background flow that the state has experienced over the last few days will back to become more easterly. Meanwhile, drier air will advect into the region as high pressure far northeast of the islands expands westward. Therefore, from tonight into Tuesday, expect a return of more typical, and drier, easterly trade wind weather across the island chain. VFR flight conditions are expected to prevail for most locations, though brief MVFR ceilings and visibilities will remain possible within any showers that pass through. Showers and low clouds will generally favor north through east sections of the islands. In addition, afternoon cloud buildups will be possible again along the Kona slopes of the Big Island Tuesday afternoon. Expect a decrease in high clouds as well as troughing to our west moves farther away from the state.
AIRMET Tango remains in effect for moderate low-level turbulence downwind of island terrain. This AIRMET will likely be needed through at least Tuesday night.

Marine

Moderate to fresh east southeast winds will gradually turn to more of a usual easterly/northeasterly direction tonight through tomorrow as a trough to the west of the islands moves west. Winds will also decrease in strength slightly tonight through the week into the moderate to locally fresh range as high pressure northeast of the state weakens slightly. Winds could then weaken further Friday into the weekend. Small craft Advisory (SCA) conditions are in effect for winds over the typical windy waters in addition to the windward Maui waters through tonight. The SCA will then shrink in coverage and be in effect only for the typically windy waters surrounding Maui and Big Island tonight through Wednesday afternoon.
Small northwest swell will linger through tomorrow, keeping surf slightly elevated above flat today and tomorrow with north and west- facing shore surf dropping to near June averages by Wednesday. Surf along south-facing shores will continue to see a mix of small background swell today and tomorrow, followed by small southwest swells late Tuesday and Wednesday. A larger, longer period south southwest swell will build in Friday and peak over the weekend. This should produce near advisory level (10 foot) surf along south facing shores.
East-facing shore surf will remain choppy for the next few days due to the moderate trade winds and could see a moderate medium period swell around the second half of the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Maui County Windward Waters, Big Island Windward Waters.
Small Craft Advisory until 8 PM HST Wednesday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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