West Kaua’i

Tonight: Breezy. Partly cloudy with isolated showers. Lows 66 to 71 near the shore to around 60 above 3000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 87 near the shore to around 73 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 71 near the shore to around 59 above 3000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 69. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy. Showers likely in the morning, then scattered showers in the afternoon. Highs 78 to 86. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 69. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then occasional showers after midnight. Lows 60 to 69 in the valleys to around 57 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Sunday: Mostly cloudy. Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 73 to 79 in the valleys to around 64 above 4000 feet. East winds 10 to 20 mph. Chance of rain 80 percent.

Sunday Night: Mostly cloudy. Showers likely in the evening, then occasional showers after midnight. Lows 59 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 63 to 70. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 74 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 62 to 69. East winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Mostly cloudy with showers likely. Highs 71 to 83. East winds 10 to 15 mph. Chance of rain 70 percent.

Sunday Night: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows 63 to 72. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Breezy trade winds will continue for the next several days, with passing clouds and showers favoring windward slopes and coasts. Lighter winds are expected by the middle of next week, with fewer windward showers, and a greater chance for afternoon interior showers.

Discussion

Strong high pressure NE of the islands supports breezy to strong trades locally. The latest visible and radar loops are roughly in line with expectations as scattered to numerous showers are evident over windward and mauka portions of Oahu through Big Island. Greater coverage of showers lurks immediately offshore and is taking its time arriving courtesy of southeasterly steering flow at 850mb tending to drive cell motion northwestward parallel to the island chain. This moisture will nonetheless work its way through the forecast area eventually with another uptick in shower coverage anticipated tonight.
Low pressure aloft is expected to gradually move E and pass over the islands Sunday into early next week, supporting a somewhat unstable island atmosphere, and the notion that orographic lift will also trigger some shower formation. Leeward areas may see some brief showers, but only minor rainfall totals are expected.
The longer range forecast anticipates of winds weakening by the middle of next week as strong low pressure far N of the area forces the surface ridge near/over the islands. Winds may remain light into next weekend. In this regime, island-scale land/sea breezes are likely to be the strongest modulator of island weather, with mostly clear nights and mornings giving way to afternoon clouds and showers over interior/leeward areas. Mid- level temperatures are expected to be cooler than normal due to a trough aloft, so briefly heavy downpours are not out of the question at this time.

Aviation

Breezy trades will continue for the next few days and bring in scattered low clouds and showers focusing over windward slopes.
AIRMET Tango is posted for tempo moderate turbulence below 8000 feet on the leeward sides of the islands due to the breezy winds. This AIRMET will continue through at least tonight.
Expect the low clouds and showers to fill in again by sunset across windward slopes with the expectation AIRMET Sierra will go into effect again for tempo mountain obscurations across windward slopes through the night.

Marine

A surface high far northeast of the state will maintain moderate to locally strong trades through late Monday. A Small Craft Advisory (SCA) has been extended through Monday afternoon for the typically windy waters around the Big Island and Maui County. By mid- week, a front approaching from the northwest will act to weaken the pressure gradient across the local waters and allow for much weaker southeasterly flow.
Expect elevated rough surf along east facing shores through Monday, due to the breezy trades. Surf should then subside Tuesday into mid-week as winds ease locally and upstream of the state.
Small surf is expected along north and west facing shores through the remainder of this weekend. A moderate, medium period northwest swell is due to enter the local waters on Monday. This swell will push surf to near the April average, followed by a decline Tuesday and Wednesday. A slightly larger north northwest swell is progged to arrive Thursday and could produce surf that approaches advisory levels through Friday.
Surf along south facing shores will remain near or below April average as typical background south swell moves through, keeping surf from going flat through much of next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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