West Kaua’i

Tonight: Partly cloudy. Lows 65 to 70 near the shore to around 57 above 3000 feet. Northeast winds up to 10 mph.

Wednesday: Mostly sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Haze in the late morning and afternoon. Highs 79 to 85 near the shore to around 71 above 3000 feet. East winds up to 15 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Haze. Lows 66 to 71 near the shore to around 59 above 3000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows around 68. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Partly sunny with isolated showers. Haze in the late morning and afternoon. Highs 78 to 85. Southeast winds around 10 mph shifting to the south in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Haze. Lows around 69. Southwest winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 58 to 67 in the valleys to around 56 above 4000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Haze in the late morning and afternoon. Highs 75 to 81 in the valleys to around 64 above 4000 feet. South winds up to 15 mph. Chance of rain 20 percent.

Wednesday Night: Mostly cloudy with scattered showers. Haze. Lows 58 to 68 in the valleys to around 57 above 4000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 61 to 68. Southeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Haze in the late morning and afternoon. Highs 75 to 83. South winds up to 20 mph. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with isolated showers. Haze. Lows 62 to 68. Southwest winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with isolated showers. Lows 62 to 72. Northeast winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Breezy. Partly sunny with isolated showers. Haze in the late morning and afternoon. Highs 73 to 84. South winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 20 percent.

Wednesday Night: Partly cloudy with scattered showers. Haze. Lows 62 to 71. Southwest winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Mostly dry and stable conditions with light and variable winds will prevail overnight as the surface ridge remains to the north. A cold front approaching from the northwest will bring increasing rainfall chances for portions of the state, with moderate south to southeast winds expected Wednesday through Saturday. Drier conditions with light trades could return by the end of the weekend as the surface ridge briefly shifts northward.

Discussion

Guidance remains in good agreement, depicting a progressive pattern with a series of cold fronts passing to the north. Deep-layer ridging over the state has resulted in light and variable winds, maintaining dry and stable conditions with a strong subsidence inversion from 5,000 to 6,000 feet, limiting rainfall chances. Any brief showers that do develop overnight tonight will favor coastal areas due to land breezes.
A transition period is expected Wednesday through the latter half of the week as the next cold front in the series approaches. Low- level winds will veer out of the south to southeast early Wednesday, then shift to a more southerly to south-southwesterly direction over the western end of the state by late Wednesday as the front nears. Increasing moisture and lift ahead of this boundary will enhance rainfall chances, particularly across leeward slopes and mountain areas in the western portion of the state. However, with the front likely stalling or hanging up near or north of Kauai, overall rainfall amounts should remain limited.
Although this pattern may persist into Saturday, a return to light to moderate trades and drier conditions is possible by the end of the weekend as the surface ridge briefly shifts northward. Another cold front passing far to the north on Sunday could drag its tail-end of the boundary into the western portion of the state early next week, bringing another potential increase in rain chances.

Aviation

A surface high pressure will move rapidly eastward to the N of the islands over the next 24 hours. Light E this evening, and then to the SE-S on Wednesday. As a front approaches, winds will veer to the S-SW and increase in strength over Kauai and Oahu, but overall speeds should remain moderate. VFR conds will prevail with ISOL MVFR CIG, with no AIRMETs anticipated.

Marine

Light to moderate east-southeast winds will shift out of the south to southeast through the day Wednesday, then linger through the second half of the week as a cold front approaches and stalls nearby to the north. Localized terrain-induced accelerations will support moderate to fresh speeds periodically in the typical areas with south to southeast winds. A return of light to moderate trades is possible by the end of the weekend.
A large northwest swell is expected to build tonight and peak early Wednesday. As of late this evening, buoy 51001, a couple hundred nm west of Kauai, indicated a 12-foot, long period NW swell entering the local waters which is slightly above guidance. Forerunners have yet to show up at Hanalei buoy, but expecting them to in the next couple of hours. A High Surf Advisory (HSA) is in effect for most north and west facing shores through Wednesday coinciding with the peak of the incoming swell. A Small Craft Advisory (SCA) is posted for high seas due to the swell for most northwest waters exposed to the swell.
As the swell slowly declines Thursday, a large to extra large northwest swell is expected to build late Thursday into Friday, likely reaching High Surf Warning level for most north and west facing shores. The potential for overwash in low lying areas is possible as the swell peaks early Friday morning, but will need to be monitored as the swell nears later this week.
Surf along south facing shores will remain tiny with mainly background energy through the week. Surf along east facing shores will also remain tiny to small through the week due to mostly light background wind flow, with a potential slight uptick early next week with the return of the trade winds.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Wednesday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Windward Haleakala.
Small Craft Advisory until noon HST Wednesday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

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