West Kaua’i

Tonight: Mostly clear. Isolated showers after midnight. Lows around 71 near the shore to around 62 above 3000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 84 to 90 near the shore to around 75 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Sunday Night: Mostly clear. Lows around 72 near the shore to around 62 above 3000 feet. Northeast winds 10 to 15 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 68 to 75. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Sunday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 79 to 88. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Sunday Night: Partly cloudy. Breezy. Isolated showers after midnight. Lows 68 to 76. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 67 in the valleys to around 59 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 66 above 4000 feet. Northeast winds 10 to 25 mph. Chance of rain 70 percent.

Sunday Night: Windy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 70 in the valleys to around 59 above 4000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 63 to 74. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 68 to 84. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy. Breezy. Scattered showers after midnight. Lows 63 to 74. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 75. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 76 to 84. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy. Breezy. Scattered showers after midnight. Lows 64 to 75. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A ridge to the north, a front to the northeast, a trough to the southwest, and Tropical Storm Pena well south of the state, are all contributing to a breezy trade wind pattern over the islands. Expect breezy trade winds to continue over the next several days. Moisture riding in on the trades will focus showers over the windward and mauka areas. An uptick in shower activity is possible during the latter part of the week.

Discussion

The forecast has been adjusted to align with the latest runs of the National Blend of Models and the REFS, however little change in the forecast was made. The general forecast philosophy remains the same.
The afternoon surface analysis has a cold front to the northeast of the islands, a ridge behind the front to the north of the islands. Both of these features will be moving to the east over the next couple of days. A trough to the southwest of the islands, and Tropical Storm Pena, well south of the islands, will both move to the west over the coming days. The resulting pressure gradient over the islands as a result of these various systems is supporting the breezy trade wind flow. Little change in the winds is expected through tomorrow night, with a bit of a decrease Monday and Tuesday. Moisture being carried in from the front on the trade wind flow will focus shower activity over the windward and mauka areas. However upper level ridging stabilizing the atmosphere will help to limit rainfall amounts.
Winds will be on the uptick again Wednesday as a new ridge builds north of the islands. By midweek, a new cold front will be sinking southwards towards the state, contributing to the uptick in winds. There is general agreement with the GFS and ECMWF with the front reaching the islands Thursday, but differences with regards to the amount of shower activity to accompanying the front.

Aviation

Moderate to breezy trades will continue into Monday. Isolated showers across windward and mountain areas could cause brief MVFR ceilings and visibility.
AIRMET Tango remains in effect for moderate turbulence downwind of terrain below 8000 ft.

Marine

Fresh to strong trade winds will prevail through the remainder of this weekend as high pressure dominates north of the state and Tropical Storm Pena moves westward, several hundred miles south of the Big Island. A Small Craft Advisory (SCA) is in effect through Sunday night for most Hawaiian Waters due to a combination of winds and elevated seas. Winds are expected to ease slightly late Monday and Tuesday as the ridge to our north erodes and Pena moves away to the southwest. The SCA will likely be trimmed back to the typical windy waters around Big Island and Maui at that time. Trade winds are then expected to strengthen again on Wednesday as a new high builds to the north. Wednesday could also see the remnants of a cold front approach from the north and a large northwest swell bringing seas above 10 feet to the exposed coastal waters.
A medium- period swell out of the north- northwest (325 to 340 degree) has been filling on on the outer buoys today, with heights around 5-6 feet at 12-13 seconds. This swell will fill in this evening and peak late tonight into tomorrow morning, briefly reaching advisory levels during its peak. The swell will gradually decrease tomorrow into Monday before another small to moderate swell fills in Monday night, keeping small to moderate surf in place through Tuesday. A large northwest to north- northwest swell is then forecast to arrive late Wednesday into Thursday and could bring surf near or right at warning levels (25 feet).
A small south-southwest swell will keep surf slightly above seasonal average today, then around the average on Sunday before declining Monday through the remainder of the week.
Rough surf along east-facing shores will hold at or above seasonal average through this weekend. Surf will decrease slightly by early next week as trades begin to ease before increasing again by mid week.

Fire weather

Breezy trade winds will continue through tomorrow night, with some weakening of the trades Monday and Tuesday. A new ridge building north of the state midweek will boost trade winds again. A drier airmass moving over the islands due in part to upper level ridging will decrease humidity levels over the next couple of days. Fire weather conditions will remain below critical thresholds into next week. Temperature inversion heights are expected to remain in the 6,500 to 7,500 foot elevation range.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Monday 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