West Kaua’i

Tonight: Mostly clear in the evening then becoming mostly cloudy. Lows 67 to 72 near the shore to around 60 above 3000 feet. Northeast winds up to 10 mph.

Saturday: Mostly cloudy. Isolated showers in the afternoon. Highs 83 to 90 near the shore to around 76 above 3000 feet. East winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows around 70 near the shore to around 60 above 3000 feet. Light winds becoming northeast up to 10 mph after midnight.

South Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 71. Northeast winds around 10 mph. Chance of rain 20 percent.

Saturday: Mostly cloudy with isolated showers. Highs 81 to 89. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows around 71. Northeast winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 61 to 67 in the valleys to around 57 above 4000 feet. East winds up to 10 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy with scattered showers. Highs 75 to 81 in the valleys to around 66 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 62 to 68 in the valleys to around 58 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 63 to 72. Southeast winds up to 10 mph. Chance of rain 20 percent.

Saturday: Mostly cloudy with isolated showers. Highs 76 to 85. East winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy with isolated showers. Lows 64 to 72. Southeast winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 74. North winds up to 10 mph. Chance of rain 40 percent.

Saturday: Mostly cloudy with isolated showers. Highs 74 to 85. Northeast winds up to 10 mph. Chance of rain 20 percent.

Saturday Night: Mostly cloudy with scattered showers. Lows 63 to 74. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will ease over the weekend as the high pressure system to the northeast weakens. With a weak upper low passing just north of the state, instability should contribute to the development of windward showers overnight and a few leeward and interior sea breeze showers in the afternoons, as well. More stable conditions with drier trends will return next week as high pressure builds in over the region and trade winds will strengthen to become moderate to locally breezy by midweek.

Discussion

This afternoon's radar and satellite imagery show a few clouds and showers moving into windward and mauka areas on the moderate trades, and building over leeward and interior areas, thanks mostly to sea breeze activity. This hybrid trade wind/sea breeze pattern will persist through the weekend as an Aleutian low pressure system weakens the high to the far northeast of the state, and hence, keeps the trade wind speeds on the lighter side locally. Aloft, a weak upper level low can be seen passing just north of the state on water vapor imagery this afternoon. General upper level troughing will remain in the vicinity through the weekend, supporting brief windward and sea breeze shower development as batches of moisture pass through.
Heading into next week, we'll transition to a more stable, slightly drier trade wind pattern as ridging builds in aloft and drier air filters in at the lower levels. High pressure will gradually build at the surface and become more established northeast of the state through the week, gradually strengthening the trade wind speeds to locally breezy levels by mid to late week. Brief showers will favor windward and mauka areas, especially during the overnight and early morning periods, and sea breeze induced leeward and interior showers will become less common as the week progresses due to the strengthening trades.

Aviation

High pressure to the northeast of the area will keep moderate trade winds in place through the weekend. Trade winds could weaken slightly over the weekend which could give way to localized land and sea breezes. A pocket of dry air moving through the region this afternoon and tonight should limit shower activity and keep them isolated over windward and mountain areas through the forecast period. Overall VFR conditions will prevail.
No AIRMETs are in effect and none are expected over the next 24 hours.

Marine

High pressure to the far northeast will slowly weaken, maintaining gentle to locally fresh trade winds through the weekend. By early next week, high pressure looks to rebuild north of the islands as a surface trough develops west of the waters, potentially veering trade winds to the east to east southeast by the middle of next week.
Surf along south facing shores have begun to build slowly today as long period energy from the south-southwest trickles in this afternoon. Due to the observations in Samoa from the same swell outperforming the model guidance, surf heights are expected to peak through the day on Saturday at High Surf Advisory levels and hold through the day Sunday before declining into early next week. A High Surf Advisory has been issued for all south facing shores starting Saturday morning through 6 AM HST Sunday.
East shore surf will remain moderate as the northeast swell slowly declines through the weekend. Surf along north facing shores will remain tiny to small through the forecast period, except for select areas that may be exposed to the northeast swell tonight into Saturday.

HFO Watches/Warnings/Advisories

High Surf Advisory from 6 AM Saturday to 6 AM HST Sunday for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.

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