West Kaua’i

Tonight: Partly cloudy with isolated showers. Lows around 73 near the shore to around 63 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 88 near the shore to around 76 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday Night: Partly cloudy. Lows around 73 near the shore to around 62 above 3000 feet. Northeast winds around 10 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 74. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 81 to 90. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Mostly cloudy with numerous showers. Lows 65 to 71 in the valleys to around 60 above 4000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 75 to 84 in the valleys to around 66 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 64 to 71 in the valleys to around 60 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 74. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 77 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy with scattered showers. Lows 66 to 74. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 66 to 77. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

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

Sunday Night: Mostly cloudy with scattered showers. Lows 65 to 78. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A locally breezy and slightly unstable trade wind flow will ease slightly late Sunday through Tuesday. Showers will be focused along windward areas, though some will briefly pass over leeward communities. Heavier showers, and possibly a brief thunderstorm, will form along the Kona slopes of the Big Island each afternoon. Trades are expected to strengthen on Thursday and Friday.

Discussion

A locally breezy and slightly unstable trade wind flow remains in place this afternoon. An upper-level low that passed near Kauai during the past couple of days is moving off to the west, carrying thunderstorms away from the islands, but the axis of its associated upper-level trough is drifting over the northern end of the island chain, maintaining some instability that is keeping the inversion elevated and very weak. Building high pressure far north of the area is driving a locally breezy trade wind flow, and while the upwind trades only contain a mix of scattered to locally broken cumulus clouds, instability is enhancing the showers as they encounter island terrain. This has resulted in roughly a quarter to a half of an inch of rainfall across many windward gages during the past 12 hours, with a few standouts measuring around 1.5 inches. Some of these showers have been carried over leeward areas, but the breezy trades have produced scant leeward accumulation. A band of high clouds that had been draped over the Big Island has thinned considerably this afternoon, but diminished heating on the Kona slopes has slightly suppressed afternoon shower activity, though spotty heavy showers remain possible there into the evening.
Breezy trades will persist into Sunday as the robust surface high passes far north of state, followed by a very gradual easing later Sunday and Monday as the high travels to the east. A sharp upper- level trough will linger near or just northwest of Kauai through Tuesday then swing southward Wednesday, maintaining enough instability for some heavier showers in the trade flow, mainly over windward slopes. No highly organized areas of moisture are seen, but models are hinting at some pockets of potentially enhanced rainfall favoring windward areas of the Big Island and Maui on Monday and Tuesday. Most leeward areas will only experience a brief passing shower, but the Kona slopes of the Big Island will likely have spotty afternoon and evening showers, some heavy with a slight chance of a thunderstorm.
Guidance is in fairly good agreement that trade winds will strengthen Thursday and Friday. Even though a sharp upper-level trough may persist near the islands, mid-level ridging should bring increased stability, favoring less intense showers.

Aviation

High pressure to the north will keep moderate to locally breezy trade winds through tomorrow. An upper level low just west of Kauai will move west slowly while a second upper low forms to the north tomorrow. These upper level disturbances will allow bands of passing trade wind showers to be more intense with MVFR ceilings and visibilities. Showers will also favor night time and early morning hours. Overall VFR conditions should prevail at most airports with the exception of windward Big Island and Kauai where lingering moisture could bring MVFR through much of the night and early tomorrow morning.
AIRMET SIERRA is not in effect, but could be issued tonight due to potential low clouds and showers causing mountain obscuration.
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 remain in place over the Hawaiian coastal waters through the weekend. Trades then weaken into the moderate to locally fresh range through much of the upcoming week. A Small Craft Advisory (SCA) is now in effect over the windier waters and channels surrounding Maui County and the Big Island through Sunday evening.
Surf along N and W facing shores will continue to slowly trend down through Sunday as two moderate, long-period NW and NNW swells fade. A developing hurricane force low near the dateline will bring another round of moderate, long-period NW (330 deg) swell into the islands towards the middle of the upcoming week leading to building surf along N and W facing shores. This next long- period swell may reach low-end High Surf Advisory thresholds late Wednesday into Thursday.
A series of small, medium- to long-period S to SW swells will continue to filter into the area through the upcoming week keeping surf along S facing shores from going flat. Short-period surf along E facing shores remains steady through Sunday due to the stronger trades, then trends down slightly early next week.

Fire weather

Locally breezy trade winds will persist into Sunday, while slight instability and somewhat enhanced moisture and humidity keeps fire weather conditions below critical levels. Expect slightly weaker trade winds late Sunday through Wednesday, followed by stronger trades Thursday and Friday. A weak inversion will be based between 8,000 to 10,00 feet over the next few days.

HFO Watches/Warnings/Advisories

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

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