West Kaua’i

Tonight: Mostly clear. Scattered showers in the evening. Lows 69 to 74 near the shore to around 61 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 30 percent.

Saturday: Mostly sunny with isolated showers. Highs 84 to 89 near the shore to around 75 above 3000 feet. North winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Saturday Night: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 70 near the shore to around 60 above 3000 feet. Light winds becoming northeast around 10 mph after midnight. Chance of rain 50 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 72. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 88. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 71. Northeast winds around 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 63 to 69 in the valleys to around 58 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 82 in the valleys to around 66 above 4000 feet. East winds up to 15 mph. Chance of rain 60 percent.

Saturday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 68 in the valleys to around 57 above 4000 feet. Northeast winds around 10 mph. Chance of rain 70 percent.

North Kaua’i

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 64 to 73. East winds around 10 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 76 to 86. East winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 71. Northeast winds around 10 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 76. Northeast winds 10 to 15 mph. Chance of rain 60 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 74 to 85. Northeast winds around 10 mph. Chance of rain 60 percent.

Saturday Night: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 75. Northeast winds around 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate trade winds will continue through Saturday, with stable conditions and showers focusing along windward and mauka locations. During the second half of the weekend, trades will weaken in response to an approaching frontal boundary and upper- level low advancing southward near the western end of the state. This will bring unsettled weather, particularly for Kauai, Sunday into Monday. Drier conditions are expected through much of the remainder of next week as high pressure becomes reestablished north of the islands.

Discussion

Moderate trade winds are prevailing across the island chain today, driven by surface high pressure centered far northeast of the state. Showers and low clouds have been relatively minimal today, primarily favoring windward and mauka areas and the Kona slopes of the Big Island this afternoon. To our north, latest surface analysis shows a pair of cold fronts in the vicinity of 30N.
For tonight through Saturday, generally stable conditions are expected, with moderate trades and limited shower activity, other than a few passing showers for the typical windward and mauka areas. Skies will remain mostly clear over leeward and interior areas.
Trades will gradually weaken in response to an advancing frontal boundary, shifting out of the southeast near Big Island and Maui, and northeast near Kauai and Oahu Saturday night into Sunday. The front will approach and is expected to reach Kauai late Sunday evening before meandering away from the islands. This boundary will have excess moisture escorted in with it, resulting in increased shower chances, primarily across the western islands.
Immediately behind the frontal boundary, guidance continues to show a low aloft breaking away from upper troughing and drifting south southwest near the western end of the state on Sunday. Southerly flow aloft will draw even more tropical moisture northward across the islands. As previous discussions have mentioned, the heaviest showers associated with this feature are expected to focus over or near Kauai late Sunday into Monday. It should be noted, however, that there remains a great deal of uncertainty regarding the exact placement of the upper low and the associated moisture. Latest ensemble guidance is depicting rainfall amounts lower than the previous forecast. Based on the ensemble guidance, and on the latest NBM Probabilistic Quantitative Precipitation Forecast (PQPF) percentiles, QPF was lowered a bit with this afternoon's forecast updates. However, hesitant to lower it too much at this point given the remaining uncertainty, so the official forecast still remains roughly similar to the 90th percentile of the NBM for now. Additionally, with 500mb temperatures cooling to near -10C to -11C in guidance, have introduced isolated thunder chances for Sunday for Kauai and Niihau and surrounding coastal waters.
High pressure is expected to rebuild into the region from Tuesday through Thursday, allowing trades to become reestablished across the region. With drier air working into the region and stable conditions returning, showers will once again be confined to mainly windward and mauka areas.

Aviation

Moderate trade winds will continue through tomorrow across the state. Embedded showers within the trade winds will bring periods of MVFR conditions over windward slopes. Otherwise, VFR conditions will prevail.
AIRMET Tango is in effect for TEMPO moderate turbulence between FL300 and FL450, from Molokai to the Big Island. The turbulence is expected to weaken this evening, and is not likely to persist through tonight.

Marine

High pressure to the northeast will maintain moderate to locally fresh trade winds through tonight. A Small Craft Advisory (SCA) is in place over typical windy areas around the Big island and Maui through tonight. Winds will decrease Saturday as a front currently to the northwest of the islands moves southeast towards the region and displaces the ridge. Isolated thunderstorms will be possible for the northwestern coastal waters by Sunday as the front approaches the western end of the state. The front is expected to stall and then get pushed to the west as high pressure builds back in by Monday. Resulting easterly trade winds should remain moderate this weekend until Monday where trade winds are forecast to increase to the moderate to fresh range. Winds are expected to remain below SCA levels until Tuesday or Wednesday.
The approaching front is expected to enter the offshore waters Saturday, with the possibility of gale force winds over the extreme northwest portion of the offshore waters Saturday night and Sunday. The front will also bring the possibility of thunderstorms to the offshore waters.
Surf is expected to increase tonight in response to a long period NNW swell (330) with surf peaking at High Surf Advisory (HSA) levels late Saturday morning. Surf will hold at advisory levels through Saturday night, and a High surf advisory is in place for that time frame for N and W facing shores. A short period NNE swell, associated with an approaching front with gale winds, is expected to arrive Sunday, and primarily impact the surf at the western end of the state where it will mix with the longer period NNW swell. This boost will likely bring HSA level surf back to Kauai and Oahu by Sunday afternoon and will gradually fade out next week. A moderate to large swell is then possible around the middle of next week.
Surf along east facing shores will remain small to moderate through Saturday, and then be impacted by the short period NNE swell mentioned above. South shore surf will decrease tonight and remain small through the weekend.

Fire weather

Increased relative humidity values and decreasing trade wind speeds will keep fire weather conditions below critical thresholds into next week.

HFO Watches/Warnings/Advisories

High Surf Advisory from noon Saturday to 6 AM HST Sunday for north and west facing shores of Niihau, Kauai, Oahu, Molokai, and north facing shores of Maui.
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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