Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Tonight: Partly cloudy with isolated showers. Lows 71 to 76 near the shore to around 62 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 74 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny with isolated showers. Highs around 83. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows 71 to 77. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 83. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs 72 to 78 in the valleys to around 67 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows around 66 in the valleys to around 58 above 4000 feet. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 70 percent.

Sunday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 78 in the valleys to around 67 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 83. Southeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with scattered showers. Lows 66 to 74. Southeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 74 to 83. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 77. Northeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 74 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

The trades will ease today then hold at gentle to moderate levels through the remainder of the weekend, with passing showers affecting mainly windward and mauka areas. A slug of deeper moisture will bring the potential for some locally heavy rain and a few thunderstorms to the state early next week, particularly over the eastern islands. A front will stall out over or just north of the islands around the middle of next week, while a new high builds to the north of the front. This is expected to bring a period of wet trades and breezy to locally windy weather to the islands Wednesday through the end of the work week.

Discussion

Currently at the surface, a 1027 mb high is centered around 1000 miles north-northeast of Honolulu, while a trough of low pressure is located around 950 miles east-southeast of Hilo. The gradient locally is producing moderate trade winds across the island chain early this morning. Infrared satellite imagery shows partly cloudy skies in most areas across the smaller islands, while mostly cloudy conditions prevail over a good chunk of the Big Island. Radar imagery shows isolated to scattered showers moving into windward sections of the smaller islands, with mainly dry conditions in leeward locales. Shower coverage is much higher over windward Big Island with a few showers noted in leeward sections as well. Main short term focus remains on trade wind trends and rain chances during the next few days.
High pressure north of the islands will shift eastward during the next couple days, as a front approaches, stalls out, and gradually dissipates to the distant northwest of the islands. As a result, the trades will ease today, then hold generally in the gentle to moderate range through the remainder of the weekend. The trades may re-strengthen Sunday night and Monday as a trough of low pressure slides by to the south of the state, before easing again on Tuesday as a stronger front approaches from the northwest. A new high building in north of the front Tuesday night and Wednesday is expected to lead to a resurgence in the trades, with breezy to locally windy conditions developing by late Wednesday and holding through the end of the work week.
As for the remaining weather details, fairly typical trade wind weather will prevail through the weekend, with bands of low clouds and showers affecting windward areas, particularly at night and during the early morning hours. A few of the showers will reach leeward areas, and the weakened trades could allow a few showers to develop over leeward terrain with the assistance of localized sea breezes each afternoon.
A trough passing by south of the state will send a slug of deeper moisture into the eastern end of the state Monday through Tuesday, which may spread to the western islands at least to some extent. Meanwhile, upper trough west of the islands will send some shortwave energy across the state, increasing instability and leading to the potential for some locally heavy rainfall and even potentially some thunderstorms. At the moment the eastern islands appear to have the highest potential for both locally heavy rain and thunderstorms during this time, with a good amount of ensemble support.
Beyond Tuesday details become more less clear. The majority of the GFS/ECMWF/CMC ensembles support a front approaching from the northwest and hanging up over or just north of the islands. This along with strengthening trades and troughing aloft should set up an extended period of wet trades which looks to continue through the end of the work week.

Aviation

Breezy easterly trade winds weaken and veer slightly to the ESE direction into the weekend. Low clouds and showers will persist along the eastern windward slopes of the Big Island through the early morning hours. Clouds and showers will then decrease in coverage statewide later this morning.
AIRMET Sierra for mountain obscuration remains in effect for the N thru E sections of the Big Island.

Marine

Fresh to strong easterly trades will ease slightly over the weekend as a weakness forms in the ridge northwest of the area. Expect the highest winds and roughest conditions over the windier waters and channels from Maui County to the Big Island. Guidance does suggest the potential for Small Craft Advisory level winds holding in these windier zones over the weekend, which has led to extending the advisory for today. Looking ahead to next week, guidance shows a cold front approaching and entering the area around midweek, with strong north to northeast winds returning through the second half.
Surf along exposed north and west facing shores will build through the weekend, with a peak expected Sunday as overlapping north-northwest pulses arrive from a recent low pressure system that formed over the far northwest Pacific earlier this week. The nearshore and offshore buoy observations reflect this fresh, long-period north-northwest swell within the 17-21 second bands this morning, with heights coming in above predicted levels. Surf heights will likely reach the advisory levels beginning today, then hold at these levels through Sunday as the next pulse arrives. A downward trend is expected briefly early next week as this swell fades before trending back up through the second half.
Surf along east-facing shores will lower over the weekend as the trades back off slightly. Expect small and choppy conditions through early next week. An upward trend is possible later next week.
Surf along south-facing shores will remain small, with mainly a mix of short period southeast and background medium-period south swell energy.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Sunday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov