West Kaua’i

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to around 60 above 3000 feet. East winds up to 25 mph. Chance of rain 70 percent.

Friday: Mostly sunny. Breezy. Scattered showers in the morning. Highs 81 to 87 near the shore to around 72 above 3000 feet. East winds up to 25 mph. Chance of rain 50 percent.

Friday Night: Breezy. Partly cloudy with isolated showers. Lows around 69 near the shore to around 59 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then numerous showers after midnight. Lows around 70. Northeast winds 20 to 25 mph. Chance of rain 80 percent.

Friday: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 85. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows around 69. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Breezy. Cloudy with occasional showers. Lows 60 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 25 mph. Chance of rain 90 percent.

Friday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78 in the valleys to around 62 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Friday Night: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 60 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 63 to 70. East winds up to 20 mph. Chance of rain 90 percent.

Friday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 84. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 62 to 69. East winds 10 to 20 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Breezy. Cloudy with occasional showers. Lows 63 to 73. East winds 10 to 20 mph. Chance of rain 90 percent.

Friday: Partly sunny. Breezy. Numerous showers in the morning, then isolated showers in the afternoon. Highs 70 to 82. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Friday Night: Breezy. Mostly cloudy with scattered showers. Lows 63 to 73. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will continue through early next week with clouds and showers generally favoring windward and mauka areas. Enhanced showers will be possible through tonight and again next week as moisture from a dissipated front moves in on the trades and a few upper level disturbances move overhead. By Wednesday, a transition to east-southeast winds may occur and lead to a hybrid east-southeast flow and land/sea breeze pattern.

Discussion

A plume of leftover moisture from a dissipated front continues to stream across the state this afternoon on the moderate to breezy trades. With the instability from the exiting upper level trough, elevated inversion heights, and this current plume of moisture moving across the island chain tonight, clouds and showers will move into windward and mauka areas on the trades with a fair amount of showers passing over the terrain to impact leeward areas, as well.
A 1035mb surface high to the far north of the state will slide eastward over the next couple of days, helping to maintain moderate to breezy trades across the region – with just a slight decline in wind speeds as compared to today. These moderate to breezy trades will deliver clouds and showers to windward coasts and slopes as a long band of moisture reaching far upstream moves across portions of the island chain through the weekend. However, mid-level ridging will temporarily build overhead as the broad upper level trough pushes off to the east, which will help to lower inversion heights, put a slight damper on shower activity, and bring a more typical distribution of windward/mauka showers tomorrow through the weekend.
Early next week, a mid-level low will move over the state from the west with a broad upper level trough quickly following, both of which will act to add some instability back over the area. At the surface, the high to the far northeast will weaken in response to a cold front moving across the eastern Pacific, allowing the local pressure gradient to relax slightly and bring moderate to locally breezy trades across the state. Batches of moisture caught up in the trades will bring periodic clouds and showers that will occasionally spill over to leeward areas at times.
Depending on the progression of a front moving through the Central Pacific midweek next week, wind directions may begin to shift from a more east-southeasterly direction on Wednesday, which would allow land and sea breeze activity to expand in coverage across the state. However, current model guidance is not in good agreement on the pattern that far out at this time.

Aviation

Moderate to breezy trade winds will continue for the next few days with the breeziest winds, both surface and aloft, expected over the western end of the state. AIRMET Tango is now in effect for low level mechanical turbulence to the lee of higher terrain Kauai and Oahu.
Bands of light showers carried by the trade winds will impact mainly windward slopes and coasts and be most active in the late night and morning hours. AIRMET Sierra for mountain obscuration is now in effect for north and east facing slopes of Kauai, Oahu, Molokai, and Maui.
On the Big Island, localized sea breezes along the leeward coast are driving cumulus development over the island's interior. Partial clearing expected after sunset along south and west facing slopes of the Big Island.

Marine

Fresh to strong trade winds will prevail through Friday as robust surface high pressure north of the state creeps eastward, with most waters under a Small Craft Advisory (SCA). The pressure gradient and resulting trades will be strongest along and just north of a band of moisture that will linger around Kauai and Oahu. Winds will ease slightly Friday night and Saturday as the high moves to the east and its associated surface ridge is weakened and displaced southward toward the state. During this time, the SCA will likely be trimmed back to the typically windy waters around the Big Island and Maui County. A further decrease in trades is possible by Tuesday as the surface ridge is pushed closer to the islands.
A series of small northwest to north-northwest swells will produce surf below April average on northern shores through most of the week. A mix of declining north-northwest swell and a fresh northwest swell of around 3 to 4 feet at 12 seconds has been observed on the local PacIOOS buoys at Hanalei and Waimea Bay, maintaining small surf. The new swell will slowly decline Friday afternoon through the weekend. A slightly larger northwest swell is expected to build on Monday and decline Tuesday and Wednesday.
Strong trade winds over and upstream of the islands will produce elevated rough surf along east facing shores through Friday. The largest wind waves have been observed near Kauai, where the PacIOOS buoy has been reporting over 8 feet at 8 seconds, and as these seas peak overnight, east shore surf will be just below the High Surf Advisory level on Kauai. The elevated seas will also contribute to the need for a SCA around Kauai and Oahu. Surf along eastern shores fall to near April average statewide on Saturday and decline below average Sunday into early next week.
South shore surf will be near April average through Friday, then decline to summertime background levels during the weekend.

HFO Watches/Warnings/Advisories

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

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