West Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows around 70 near the shore to around 60 above 3000 feet. Light winds. Chance of rain 20 percent.

Saturday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 82 to 88 near the shore to around 75 above 3000 feet. Light winds. Chance of rain 40 percent.

Saturday Night: Partly cloudy. Isolated showers after midnight. Lows around 70 near the shore to around 61 above 3000 feet. Light winds. Chance of rain 20 percent.

South Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 68 to 73. Northeast winds around 10 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 87. Northeast winds up to 10 mph. Chance of rain 30 percent.

Saturday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 68 to 74. Northeast winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 65 in the valleys to around 58 above 4000 feet. Light winds. Chance of rain 40 percent.

Saturday: Partly sunny with scattered showers. Highs 73 to 80 in the valleys to around 66 above 4000 feet. Light winds. Chance of rain 50 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 66 in the valleys to around 58 above 4000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 62 to 72. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs 70 to 84. East winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 72. East winds up to 10 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 64 to 73. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs 76 to 84. Northeast winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 74. Northeast winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will weaken through Saturday, then gradually begin to strengthen Sunday and into next week. Sea-breeze showers will develop Saturday and again Sunday in some leeward areas before we return to mainly windward and mauka showers from Monday through next week. There is a decent chance of increased moisture showing up toward the end of next week.

Discussion

Satellite shows partly to mostly cloudy skies over the islands, as is typically the case in the afternoon. Radar was showing showers over North Kona on the Big Island earlier this afternoon, but most of those have dissipated. As of 3 PM HST, isolated showers were over South Puna and Ka'u, but otherwise it was dry. Winds were mainly out of the northeast in windward areas, but otherwise highly variable in direction due to an abundance of sea-breezes, and were averaging 5 to 15 mph.
We'll see a weak upper level low form to our northeast this weekend, then slowly weaken and move away through midweek. At the surface, a weakened pressure gradient will lead to weak winds this weekend. There will be sea-breeze showers, especially Saturday afternoon and early evening, over some leeward areas. And of course the windward and mauka areas will still see their share of showers, too.
Trade winds will increase Sunday into Monday, then hold pretty steady into at least the middle of next week. This will bring an end to the stronger sea breezes, and return things to a more typical trade wind pattern with showers mainly over windward and mauka areas. Some of the latest model guidance suggests an area of enhanced moisture will move into the state Sunday night and perhaps hang around the area – close enough to supply additional moisture for showers through most of next week. But there is uncertainty in both how much moisture there will be and how long it will linger. Overall, changes to the forecast today have been minor.

Aviation

Gentle trades with localized land and sea breezes will persist through Saturday. A drier airmass will lead to mostly VFR condition. Brief MVFR ceilings will remain possible over leeward and interior areas during the afternoons and windward areas during the overnight hours.
No AIRMETs are in effect.

Marine

Gentle to moderate east-northeasterly winds are expected through Saturday as a weak front passing far north of the state displaces the ridge and keeps the trade winds tempered. Moderate to fresh easterly trades will return Sunday through early next week as the surface ridge strengthens north of the area.
Small pulses of southerly swell will bring somewhat below average surf to south facing shores into Saturday. Surf will begin to trend up on Saturday afternoon as forerunners arrive from a large, long-period swell originating from a storm- to hurricane- force low that moved up along Hawaii's swell window south and just east of New Zealand. This swell peaked at the American Samoa buoys around 12 feet 17 seconds Thursday afternoon. Surf is expected to peak locally Sunday into Monday, approaching warning levels, but most likely to remain at high-end advisory levels. This swell will also coincide with the peak monthly tides which may lead to significant wave runup and minor coastal flooding during the first half of next week, particularly during the peak daily high tide cycles each afternoon. South shore surf will remain elevated through much of next week due to the slow decline of this large south swell and a series of continued overlapping southerly swells.
Very little swell energy is arriving along north facing shores today, keeping surf tiny to flat. A small bump in surf is possible along north facing shores with the arrival of a small northwest swell and a smaller north swell early next week. Weaker than average trade winds near and upstream of the islands will produce below average surf along east facing shores through the weekend and into early next week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov