West Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Isolated showers. Lows around 73 near the shore to around 64 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Isolated showers in the morning. Highs 84 to 89 near the shore to around 74 above 3000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Gusts up to 35 mph. Chance of rain 20 percent.

Monday Night: Partly cloudy. Lows around 73 near the shore to around 64 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 69 to 76. East winds 15 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 79 to 88. East winds 15 to 20 mph. Chance of rain 50 percent.

Monday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Isolated showers. Lows 69 to 76. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with numerous showers. Lows around 68 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs 74 to 81 in the valleys to around 66 above 4000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows around 68 in the valleys to around 61 above 4000 feet. East winds 15 to 25 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 75. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs 70 to 85. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Monday Night: Breezy. Partly cloudy with isolated showers. Lows 64 to 74. East winds 10 to 20 mph decreasing to up to 20 mph after midnight. Chance of rain 20 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 76. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly cloudy with scattered showers. Highs 76 to 84. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday Night: Breezy. Mostly cloudy with scattered showers. Lows 65 to 76. East winds 15 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A high pressure system will strengthen north of the Hawaiian Islands, producing moderate to locally windy trades. Light to moderate showers will focus over windward and mauka areas with brief showers spilling over to leeward areas, especially during the overnight and early morning hours. Confidence is increasing that an upper level trough will deepen to the north of the state from Thursday into next weekend, creating a surface low to our north. This would turn our winds out of the southeast starting around Thursday, and may eventually drive a weak front through the state.

Discussion

Two radars (Molokai and Upolu) remain temporarily out of service, limiting radar coverage from Oahu to northern portions of the Big Island. With that said, the two functioning radars showed isolated windward and mauka showers over Kauai and eastern Big Island. Satellite indicated a typical trade wind pattern of mostly cloudy windward and mostly sunny leeward across most islands. Winds were gusty and mainly out of the northeast. Average speeds were 15 to 20 mph, with gusts of 30 to 40 mph.
A large surface high pressure system was centered near 35N and 155W this afternoon. This high will remain nearly stationary for the next few days, then weaken and begin to move east Wednesday. As it does, a low will move in from the northwest. While the exact track this low ends up taking is not known with confidence at this time (the time frame involved is Thursday into next weekend), it appears there is enough agreement within the model suite to forecast a change to southeast winds sometime around Thursday. After that, if the low drops far enough south, it may push a cold front through the state just after the forecast period ends (so next Sunday or Monday).
In the meantime, we'll see a typical trade wind pattern of mainly windward and mauka showers, with a few making it over to leeward areas due to the relatively strong winds. These showers will be most numerous at night and in the early morning, as usual. Winds will gradually weaken from Tuesday into Wednesday.

Aviation

Breezy trades. Isolated to scattered showers, concentrated mainly along windward and mauka locations, most numerous late at night through the mornings. Showers may produce brief periods of MVFR ceilings and visibility.
AIRMET Sierra remains in effect for north through east sections of the Big Island above 2500 feet due to low clouds and showers.
AIRMET Tango remains in effect for for tempo moderate turbulence downwind of terrain below 9000 ft.

Marine

Robust surface high pressure centered far north of Hawaii will maintain fresh to strong trade winds at current strength for the next couple of days, and a Small Craft Advisory (SCA) remains in effect for all waters except windward Big Island through early Tuesday. Trades will steadily decrease late Tuesday and Wednesday as the high weakens and is displaced eastward by an approaching low far northwest of the islands. The SCA will likely be trimmed back to the typically windy waters around Big Island and Maui at that time. Trade winds will lower to gentle strength, or may become disrupted, as the low passes to the north Thursday and Friday.
A north-northwest swell and a smaller overlapping west-northwest swell will slowly decline through Monday and fade on Tuesday. A very small northwest swell may arrive Thursday, followed by a moderate north- northwest swell next weekend.
The current south swell will continue a slow decline over the next day or so. South shore surf will drop below seasonal average Monday and will remain relatively small through much of the week. A moderate south-southwest swell is expected next weekend.
Rough trade wind swell will produce east shore surf just above seasonal average through Tuesday, then decline later in the week as trade winds decrease.

Fire weather

Fire weather will remain below critical levels for the next several days. Drier air is forecast to move in Tuesday, but wind speeds will be on the decline by then, so we do not expect to meet criteria. The trade inversion should be between 6000 and 7000 feet through Sunday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Tuesday for Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters, Kaiwi Channel, Kauai Channel, Kauai Leeward Waters, Kauai Northwest Waters, Kauai Windward Waters, Maalaea Bay, Maui County Leeward Waters, Maui County Windward Waters, Oahu Leeward Waters, Oahu Windward Waters, Pailolo Channel.

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Data Courtesy of NOAA.gov