West Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 66 to 71 near the shore to around 60 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Sunday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 82 to 87 near the shore to around 74 above 3000 feet. East winds up to 10 mph shifting to the south in the afternoon. Chance of rain 40 percent.

Sunday Night: Mostly cloudy in the evening then becoming partly cloudy. Lows around 69 near the shore to around 60 above 3000 feet. Light winds.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 68 to 73. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny. Scattered showers in the morning. Highs 76 to 86. East winds up to 10 mph. Chance of rain 40 percent.

Sunday Night: Partly cloudy with isolated showers. Lows 68 to 74. Northeast winds up to 10 mph. Chance of rain 20 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows around 65 in the valleys to around 55 above 4000 feet. East winds up to 15 mph becoming around 10 mph after midnight. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 80 in the valleys to around 66 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows around 65 in the valleys to around 55 above 4000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 72. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning. Highs 69 to 83. East winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 62 to 72. East winds up to 10 mph. Chance of rain 20 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 64 to 73. Northeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny. Scattered showers in the morning. Highs 76 to 84. East winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 64 to 74. Northeast winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate trades give way to expanding land and sea breezes through Sunday. Trades then gradually strengthen through next week. A few light showers may develop over western slopes during the next 36 hours, but otherwise showers remain focused windward and mauka.

Discussion

Height falls associated with a broad cyclone over the NE Pacific will steadily weaken the pressure gradient over the Hawaiian islands through Sunday. This will in turn lead to an expansion of afternoon sea breezes and overnight land breezes, particularly on Sunday when the gradient will be at its minimum. A subtle shearing shortwave trough axis embedded within broader cyclonic flow aloft will pivot through the forecast area late today through Monday. Modest backing of mid-level flow will draw deep moisture northward east of the Big Island by Sunday where weak surface troughing will tend to focus shower activity mostly offshore. From Tuesday onward, ridging over the central and north Pacific will favor a return to breezy trades as governing high pressure strengthens. As these stronger trades return, they will usher this offshore moisture over the islands on Tuesday and/or Wednesday resulting in a brief period of enhanced shower activity windward and mauka. A seasonable trade wind pattern then settles in for the remainder of next week.

Aviation

No AIRMETs currently in effect. Brief/isolated mountain obscurations may occur across island interiors through this evening, and across windward sides of Big Island and Kauai tonight. Possible AIRMET Sierra overnight into Sunday morning if clouds fill in a bit more over either island, but otherwise VFR conditions expected to prevail elsewhere.
Gentle to moderate trade winds expected through tonight becoming lighter on Sunday allowing for sea breezes to set up over the islands.

Marine

Moderate to fresh trade winds will steadily ease into the light to moderate range by Sunday as a surface ridge north of the Hawaiian Islands weakens in response to broad, storm-force low pressure developing south of the Alaska Peninsula. This will translate to localized land and sea breezes near the coasts late this weekend through early next week. A return of moderate to fresh easterly trades is likely by midweek as the ridge restrengthens.
An active pattern is in store for surf along south-facing shores through next week due to a series of recent gale- to storm- force lows passing through our swell window near New Zealand over the past week. Offshore buoys south of the islands continue to observe around a 3.5 ft, 16 second south swell today, which supports continued advisory level surf along south shores tonight. Expect similar conditions to hold through Sunday. The swell will gradually begin to ease on Monday at the same time that long- period forerunners from the next south-southwest swell are expected to arrive. Heights may briefly dip below the advisory level, but as the next swell fills in, surf will likely return to advisory levels Tuesday through midweek as it peaks. A gradual downward trend is then expected through the second half of next week.
A combination of advisory-level surf this weekend and water levels hovering above predicted levels could lead to some wave runup issues, with water sweeping across areas of beaches that typically remain dry during the afternoon peak daily tide cycles. Water levels will steadily lower each day early next week as the next large south swell arrives.
Surf along north-facing shores will remain small through Monday, then likely trends up as a small north swell, originating from the low south of the Alaska Peninsula, arrives by midweek.
Expect surf along east-facing shores to continue to ease for Sunday and Monday when trade winds are at their weakest. Then, a slight increase is likely beginning Tuesday due to a combination of strengthening trades and a wrapping north swell.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Sunday for for south facing shores of all Hawaiian Islands.

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Data Courtesy of NOAA.gov