West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with isolated showers. Highs 84 to 90 near the shore to around 76 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Monday Night: Mostly cloudy. Lows 70 to 75 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph.

South Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows around 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 89. East winds 10 to 20 mph. Chance of rain 40 percent.

Monday Night: Cloudy with isolated showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 83 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Monday Night: Cloudy with isolated showers. Lows 64 to 70 in the valleys to around 59 above 4000 feet. East winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 72. East winds 10 to 15 mph shifting to the southeast after midnight. Chance of rain 70 percent.

Monday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 87. East winds up to 15 mph. Chance of rain 40 percent.

Monday Night: Cloudy with isolated showers. Lows 65 to 74. Southeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 75. Northeast winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 70 percent.

Monday: Mostly cloudy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Monday Night: Cloudy with isolated showers. Lows 65 to 77. Northeast winds around 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

An upper low and surface trough to the west will slide further to the west allowing trades to build in. An area of tropical moisture will clip the Big Island Monday and Monday night and bring showers to windward and southeast slopes. A cold front will approach the islands next weekend.

Discussion

Water vapor imagery shows an upper low just west of the state digging towards the south-southwest. This low is reflected at the surface as a trough with the axis passing just north of Kauai. Moderate east-southeast winds encompass the state with the trough separating strong northeast winds just offshore of the north and west sides of Kauai.
The trough will move west tonight and winds will back easterly by Monday. Moderate trades will begin to usher in drier air across the smaller islands. The northern edge of a band of tropical moisture will clip the Big Island Monday and Monday night. Cloud tops may briefly reach the highest summits of Mauna Kea and Mauna Loa on Monday and Monday night bringing a chance for freezing rain, but confidence is not high enough for a Winter Weather Advisory at this time. Rain chances also increase across windward and southeast Big Island low elevations.
Global models continue to show a weak ridge filling in aloft over the state with a decrease in showers Tuesday through Thursday. An upper level trough moves in from the northwest on Friday, divergence aloft will spread over the islands lifting trade wind temperature inversion heights, and increase shower trends from Friday into the weekend. A cold front will approach the islands from the north and stall out near Kauai and Oahu next weekend.

Aviation

Moderate trades will continue through tomorrow as a weakening cold front stalls out near the island of Kauai. A few TSTMS are possible near Kauai and Niihau through tonight. IFR conds possible in heavier SHRA on Kauai. Additional SHRA expected across windward and mauka locations of all other islands. MVFR conds possible in SHRA otherwise VFR prevails.
AIRMET Sierra for IFR is in effect for mtn obsc for the entire islands Kauai and Oahu. This may be expanded to other islands overnight with an increase in SHRA.

Marine

A trough that is currently over the northwest waters near Kauai is expected to push west of the area tonight into Monday as high pressure builds to the north. Small Craft Advisory (SCA) level winds behind this feature have prevailed over the northwest coastal waters today, and these will linger into the evening hours before weakening overnight. Moderate to locally fresh easterly trades will return thereafter, and persist through much of this week. Additionally, seas remain above 10 feet across portions of the north and northwest coastal waters. A SCA remains in effect due to a combination of winds and seas, and has been extended through Monday afternoon to account for lingering SCA seas into at least the first half of Monday.
A High Surf Advisory (HSA) remains in effect through 6 AM HST Monday for most north and west facing shores of the smaller islands. A mix of medium to long period north-northwest swells (320-330 degrees) have filled in across the area today. Latest buoys and observations show surf well into advisory levels across north and west facing shores this afternoon. A medium period north-northeast (020 degrees) swell generated by distant gale force winds associated with the decaying front to our north will also fill in this evening, primarily impacting the western end of the state. This mix of swells is expected to maintain advisory level surf through tonight before dropping below advisory levels on Monday. Surf along north and west facing shores will then gradually fade during the first half of the week. A moderate long period north northwest swell (340 degrees) is possible around the middle of the week.
Surf along east facing shores will remain moderate through the next couple of days, influenced by the medium period NNE swell mentioned above. South shore surf will remain small through the first half of the week before building slightly mid to late week as a long period south-southwest swell (190 degrees) fills in across the region.

Fire weather

Increased relative humidity values and light trades will maintain below critical fire weather conditions the next several days. Temperature inversion heights near the Big Island and Maui will be around 10,000 feet with unstable conditions on Kauai and Oahu. Expect a gradual return to more stable weather Monday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for north and west facing shores of Niihau, Kauai, Oahu, Molokai and for north facing shores of Maui.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

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