West Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 68 to 73 near the shore to around 60 above 3000 feet. Light winds. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 82 to 87 near the shore to around 73 above 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows 69 to 74 near the shore to around 61 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 71. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 79 to 87. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows around 72. East winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Locally heavy rainfall possible after midnight. Lows 61 to 68 in the valleys to around 58 above 4000 feet. Light winds. Chance of rain 50 percent.

Sunday: Mostly cloudy with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 63 to 69 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Locally heavy rainfall possible after midnight. Lows 64 to 71. East winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 74 to 84. East winds around 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Locally heavy rainfall possible in the evening. Lows 64 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Locally heavy rainfall possible after midnight. Lows 63 to 74. Northeast winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers and isolated thunderstorms. Locally heavy rainfall possible. Highs 72 to 84. East winds around 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers and isolated thunderstorms in the evening, then scattered showers after midnight. Lows 64 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to occasionally breezy trades and relatively dry through late tonight. An approaching cold front from the northwest will graze the Kauai nearshore waters northwest of Kauai during the day tomorrow. The associated upper level trough or low moving in behind the front will increase rain shower and isolated thunderstorm chances for Kauai and its surrounding waters from tomorrow morning through Monday morning. This system will travel west away from the state through the middle of next week. High pressure expanding in its wake will maintain several days of lighter trades and lower rain chances. The greatest rain during the majority of the week will be focused along upslope windward mauka and within high terrain.

Discussion

A fairly dry and breezy afternoon as many sites have remained bone dry since midnight. Only the more typically wet spots along windward zones and over upper terrain have picked up less than a quarter of an inch. After light and variable morning breezes, afternoon breezy trades have returned with the notoriously windier exposures remaining in the 10 mph gusting 15 to 30 mph realm. At 3 PM HST today, a cold front located about 400 miles northwest of Kauai moving at a progressive clip will be in the proximity of the far northwestern coastal waters shortly after Sunday's sunrise. This will significantly strengthen northeast winds over the waters just west of Kauai and Niihau while only subtly veering light trades more east over the remainder of the state through Sunday afternoon. The front is forecast to stall over the far western waters tomorrow afternoon and evening. This will have rain chances steadily rising over the Garden Isle and Niihau over the next 24 to 36 hours.
The associated upper trough to the west of the lower level boundary will dig down over the far northwest offshore waters tonight. Mid to upper layers will cool and destabilize the atmosphere over the western third of the state. Thus, the probability for isolated thunderstorms within periods of scattered showers with locally heavy rain exists for Kauai and Niihau during the daytime hours tomorrow. Deterministic and ensemble guidance from across the board all agree that a cut-off low will pinch off from the base of this trough and travel west southwest over the far west waters from around midnight Sunday through early Monday. Seasonal moisture levels will be on the rise as westerly steering flow directs a more humid southern-based air mass up and over the state ahead of the eventually stalled front. Most of Sunday's precipitation will impact the western third of the state, or mainly Kauai and Niihau, with the potential threat for locally heavy rain that could lead to minor flooding concerns. Oahu will also experience a more cloudy and wet day island-wide with the windward areas of Maui County and Big Island picking up the most rain from this early November system. The boundary layer may become deep enough Monday to throw enough moisture atop Mauka Kea and Mauna Loa to produce either light snow or a wintery mix (with little to no snow accumulation) above 12k feet the next couple of afternoons and evenings.
High pressure ridging will fill in behind the upper low as it progressively travels west. Most island communities will enjoy pleasant weather from Monday afternoon through early Friday as ridging at all levels will return traditional trade weather to the entire state. After this system heads west Monday, the main recurring theme will be for light morning-transitioning-to- afternoon breezy trades and light precipitation confined to windward exposures and upper elevations. A far northern-passing front on Friday may slightly veer and weaken trades.

Aviation

Trades will begin to weaken across the islands tonight as a cold front approaches from the northwest. Expect isolated to scattered to affect much of the area with the greatest coverage over the western-most islands, closest to the approaching front. Some of the more robust showers may bring brief periods of MVFR ceilings and visibility. Expect the possibility of isolated thunderstorms over Kauai on Sunday as conditions become less stable.
No AIRMETs are in effect and none are expected through early tonight. However, an AIRMET for MVFR and/or IFR ceilings from mountain obscuration may be needed for Kauai by Sunday morning.

Marine

A front northwest of the islands will move southeast towards the region and displace the ridge. Isolated thunderstorms will be possible for the northwestern coastal waters tonight as the front approaches the western end of the state. The front is expected to stall and then get pushed to the west as high pressure builds back in by Monday, increasing trade winds to moderate to locally fresh speeds. Winds are expected to remain below SCA levels until Tuesday or Wednesday. By the later half of next week, a front far to the north could potentially disrupt the trade winds.
The approaching front is expected to enter the offshore waters later this evening, with strong (near gale) breezes expected over the extreme northwest portion of the offshore waters tonight and Sunday. The front will also bring the possibility of thunderstorms to the offshore waters.
Surf along north facing shores will hold at HSA levels through tonight as a medium period NNW swell (330) fills in, and a HSA is in place for that time frame for N and W facing shores. Another NNW swell (320-330) is expected to fill in on Sunday, followed by a medium period NNE swell Sunday evening. The NNE swell being associated with an approaching front with near-gale winds, that will primarily impact the western end of the state. This mix of swells may maintain HSA level surf through Sunday before gradually fading early next week. The HSA may be extended through Sunday if buoy readings remain high through tonight. A moderate to large swell is then possible around the middle of next week.
Surf along east facing shores will remain small to moderate through Sunday morning, and then may be impacted by the medium period NNE swell mentioned above. South shore surf will remain small through early next week before building slightly mid to late week as a long period SSW swell (190) 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.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Sunday for Niihau, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.

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