Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny with isolated showers. Highs 83 to 88 near the shore to around 74 above 3000 feet. Northeast winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 72 near the shore to around 58 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Saturday: Mostly sunny with isolated showers. Highs around 84 near the shore to around 73 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 80 to 85. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Mostly cloudy with scattered showers. Highs 73 to 80 in the valleys to around 65 above 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with numerous showers. Lows 60 to 66 in the valleys to around 56 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Saturday: Cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 75 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 75 to 84. Southeast winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 70. Southeast winds up to 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 74 to 82. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 73 to 83. Northeast winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 72. East winds up to 10 mph. Chance of rain 50 percent.

Saturday: Mostly cloudy with scattered showers. Highs 72 to 82. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate trade winds will continue today through the weekend, maintaining showers across windward areas. A system developing northwest of the state late in the weekend, may increase moisture and strengthen southeast winds, potentially enhancing shower chances next week across the islands.

Discussion

A slight chance of showers and thunderstorms remains in the forecast over the Mauna Loa summit through the weekend, where lava-induced extreme heating of the lower atmosphere will spur occasional development of pyrocumulonimbus clouds.
Current radar trends show limited showers across the state this morning, with a majority of showers concentrated just offshore, over the marine areas, as low level winds shift east to southeast this morning.
Today through the Sunday afternoon…easterly trade winds will strengthen to moderate to locally breezy and continue through the weekend, as a ridge of high pressure lingers north of the state. This will generate a trade wind weather pattern across the state, with showers embedded in the trades focused across mainly windward and mauka zones. The areal coverage of showers will increase slightly during the overnight and early morning periods. Showers may occasionally drift to leeward locations at times. Rainfall rates will remain limited through Sunday afternoon, as surface and upper level ridging in place over the state, maintains a mainly stable airmass.
Sunday night through next week…deterministic guidance remains in agreement with a mid-latitude trough rapidly amplifying east of the Dateline Sunday night and closing off northwest of Kauai Monday. Additionally, at the surface, a low is forecast to develop and strengthen northwest of Kauai Monday, with current forecast trends suggesting this feature will remain west of Kauai and drift slowly westward, causing winds to become mainly southeasterly across the island chain. This will potentially increase moisture and enhance rainfall chances across much of the state through the middle of next week. GEFS ensemble data trends are currently showing rainfall assoicated with the developing surface and upper features, slowly overspreading the western islands Monday evening, while the grandensemble shows rainfall chances increasing slowly by Monday afternoon/evening. Ensemble data trends also support more widespread areal coverage of rainfall uniformly spreadings across the state by midweek, though keeping the heaviest rainfall amounts north and west of the state through mid week. This time period certainly bears monitoring, especially over the western end of the state.

Aviation

A high pressure ridge far north of the region will keep light to moderate trade winds in the forecast through Saturday. Expect brief passing showers along windward slopes of all islands today with increasing low cloud and shower trends from late afternoon through the overnight hours as a low level trough drifts into the islands from the east.
No AIRMETs in effect.

Marine

Large surface high pressure centered approximated 1,350 miles northeast of the islands and expanding southeast will maintain a pressure gradient tight enough to support moderate easterly trade winds the next few days. A large west northwest swell that peaked overnight lifted combined seas to near the 10 foot Small Craft Advisory (SCA) criteria over those nearshore seas surrounding Kauai, the Kauai and Kaiwi Channels, along with the windward Oahu and Maui waters. The SCA has been extended until 10 AM HST this morning to account for the slow subsidence of this swell over these more west coastal waters. The approach of an early week cold front from the northwest may hang up just west of the state as low pressure developments along it northwest of the Hawaiian offshore waters. As this occurs, high pressure moving in from the north will re-tighten the pressure gradient upstream and over the local waters. This will strengthen next week's winds as they veer to more of a southeasterly direction.
The large, long period west-northwest (300-310 degree) swell that peaked last night into early this morning will slowly begin to subside through this weekend. Early morning nearshore buoy observations at Hanalei still displayed High Surf Warning (HSW) level swell while, over in Waimea Bay, swell was supporting High Surf Advisory (HSA) surf along north and west beaches. Thus, to account for this slow decline int he swell, the HSW will remain in effect for Niihau and Kauai through 10 AM and then drop to a HSA, along with the north and west-facing shores of Oahu and Molokai, through this afternoon (6 PM HST today). A HSA is also in effect for the west-facing shores of Big Island until 6 PM HST today to account for the slow fade of this more westerly swell. A moderate size, medium period northeast swell moving into our nearshore windward waters Saturday is expected to increase north and east- facing shore surf across the state to near or slightly over HSA levels.

HFO Watches/Warnings/Advisories

High Surf Warning until 10 AM HST this morning for Niihau, Kauai Leeward, Kauai North.
High Surf Advisory from 10 AM this morning to 6 PM HST this evening for Niihau, Kauai Leeward, Kauai North.
High Surf Advisory until 6 PM HST this evening for Waianae Coast, Oahu North Shore, Kona, Kohala, Molokai Windward, Molokai North, Molokai West.
Small Craft Advisory until 10 AM HST this morning for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

Data Courtesy of NOAA.gov