West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 88 near the shore to around 77 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 73 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph after midnight. Chance of rain 20 percent.

Monday: Mostly sunny with isolated showers. Highs 85 to 91 near the shore to around 77 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 90. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows around 74. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 82 to 90. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 70 in the valleys to around 60 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 77 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 77 to 88. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 65 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure will maintain moderate to locally breezy trades through this morning, then gradually ease through Wednesday. Shower activity will be focused predominately across windward and mauka areas, though a brief shower or two may pass over leeward areas. Only exception would be the Kona slopes of the Big Island, where heavier showers and a brief thunderstorm remains possible during the afternoon and early evening hours. Trades are expected to strengthen on Thursday and Friday.

Discussion

Broad, building high pressure well north of the Hawaiian Islands will help maintain moderate to locally breezy trades under slightly unstable conditions throughout the day. Trades begin to ease shortly thereafter through midweek as the aforementioned high meanders eastward.
Instability associated with a passing upper-level low and associated trough, propagating southward along the east side of the islands, maintaining just enough instability to combine within the wet trade flow regime to bring heavier shower activity to windward areas. While current models are not projecting any particularly organized areas of moisture, as acknowledged late last week, there is indication of some pockets of likely enhanced shower activity favoring windward areas of Maui and Big Island early in the week. Elsewhere, including leeward areas on all islands, may experience a brief passing shower or two, but will ultimately miss out otherwise. The only exception would be the Kona slopes on the Big Island, where spotty shower activity may develop in the afternoon and evening hours. A passing thunderstorm in the vicinity cannot be ruled out either.
Toward the latter end of the week, latest model guidance remains in relatively good agreement, portraying trades strengthening as early as Thursday and Friday, with robust mid-level ridging increasing stability across the state. Shower activity associated with these trades will be less intense and limited to predominately windward and mauka areas for all islands, prevailing through the remainder of the outlook period.

Aviation

Moderate to locally breezy trades will persist through this morning, gradually easing shortly thereafter. Instability associated with a passing low to the east of the islands will allow pockets of enhanced shower activity to pass over predominately windward and mauka areas. Expect MVFR conditions in heavier showers, briefly reducing visibility and/or ceilings. Otherwise, VFR conditions prevail.
AIRMET Tango is in effect across the island chain for tempo moderate turbulence below 9,000 ft on the leeward areas of terrain.

Marine

Moderate to locally strong trades will gradually weaken today across the Hawaiian coastal waters as a surface high shifts further northeast. Moderate to locally fresh trades will develop tonight into Monday and persist through mid week as the surface high lingers far northeast of the state and another high develops far northwest. A Small Craft Advisory (SCA) remains in effect over the windier waters and channels surrounding Maui County and the Big Island through the day today. The SCA may need to be extended later this afternoon if the trade winds speeds continue to hold within locally strong range a little longer than expected.
Surf along north and west facing shores will continue to slowly trend down today as two moderate, long-period northwest and north- northwest swells fade. A series of small to moderate, long period northwest to north-northwest swells (320-340 degrees) will fill in throughout the week, keeping surf elevated. The first of these swells (320-330 degree) is expected to fill in tonight, before peaking Monday, producing above average surf. A slightly smaller size swell (330-340 degree) will peak late Tuesday before fading Wednesday. A larger, moderate, long period swell (330-340 degree) could produce advisory level surf for north and west facing shores late Wednesday into Thursday.
Background, medium- to long-period south to southwest swells will continue to filter into the area today through the upcoming week, keeping surf along south facing shores from going flat. Rough, choppy surf along east facing shores will persist through today before dropping a notch Monday as trades trend down slightly through mid week.

Fire weather

Moderate to locally breezy trades will prevail through this morning under slightly unstable conditions that will produce some enhanced moisture and increase humidity levels keeping fire weather conditions below critical levels. Trades are expected to gradually ease through Wednesday and strengthen thereafter for the remainder of the week. Temperature inversion heights near Maui and the Big Island will range from the 5,500 to 6,500 feet today.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.