West Kaua’i

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 69 near the shore to around 60 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 40 percent.

Saturday: Mostly sunny with isolated showers. Highs 83 to 89 near the shore to around 74 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday Night: Mostly clear. Breezy. Lows 67 to 72 near the shore to around 60 above 3000 feet. Northeast winds up to 20 mph.

South Kaua’i

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 71. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 80 to 88. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Saturday Night: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 71. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then numerous showers after midnight. Lows 62 to 68 in the valleys to around 57 above 4000 feet. East winds up to 20 mph. Chance of rain 90 percent.

Saturday: Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 72 to 80 in the valleys to around 64 above 4000 feet. Northeast winds up to 20 mph. Chance of rain near 100 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Scattered showers. Lows 62 to 68 in the valleys to around 58 above 4000 feet. East winds up to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 63 to 71. East winds 10 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 85. East winds 10 to 15 mph. Chance of rain 70 percent.

Saturday Night: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 64 to 71. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Tonight: Mostly cloudy with numerous showers. Lows 63 to 74. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Saturday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 72 to 84. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Saturday Night: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 64 to 74. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

High pressure far to our northwest will keep breezy trades blowing through Sunday, with the trades gradually easing next week as the high weakens. An upper level low near the islands will help to enhance showers through tonight. As the upper low moves away over the holiday weekend, drier and more stable air will return to the Aloha State, with fewer showers and lots of sunshine expected.

Discussion

A relatively strong and large 1035 mb surface high is still centered roughly 1300 miles NW of Kauai. This high has been meandering around in the same general area for the past few days, driving breezy trade winds across the islands. Meanwhile, a mid- to upper level low is located on water vapor imagery 250 mi N of Maui. Radar and visible satellite show widely scattered showers carried in from the east by the trades and focusing windward. The instability from the upper low is causing a few of the showers to become a bit more intense, but not very long lasting given the brisk pace westward.
Guidance shows this upper low will start to lift slowly NE away from the islands tonight, gradually taking its pocket of cold air aloft and instability with it overnight. Fine weather is expected for most of the holiday weekend, with any lingering enhancement to incoming trade wind showers fading away on Saturday. In fact, models show quite low precipitable water (PW) over the state for late May pushing in Saturday night, with values maybe even dropping below 1 inch early next week. Although PW increases significantly over the islands toward the middle of the week, forecast soundings show that this PW is largely from abundant high-and mid-level moisture being drawn up by the jet stream from deep convection in the ITCZ far south of the islands, while maintaining a dry and stable boundary layer over us. Thus we are indicating an increase in clouds in the forecast, but not a lot of trade wind rainfall late in the forecast period.
Trade winds should remain breezy over the islands through about Sunday, then start trending downward on Memorial Day as the high gradually shifts south, weakens, and elongates across most of the eastern Pacific becoming a rather weak subtropical ridge by about Wed or Thu when gentle trades are expected, staying locally breezy only in the normal windiest spots.

Aviation

An upper low near the main Hawaiian Islands will continue to enhance incoming trade wind clouds and showers. An increase of showers are expected tonight with TEMPO MVFR ceilings and visibility possible with any SHRA. AIRMET for MTN OBSC may also be needed for select windward N and E facing slopes tonight into Saturday morning. Overall conditions should gradually improve on Saturday (especially in the afternoon) with shower coverage and intensity diminishing as the upper low continues to move away. Moderate to locally breezy trade winds will continue to persist through the weekend.

Marine

High pressure off to the distant north-northwest will maintain moderate to locally strong trade winds through the weekend. The high is expected to weaken early next week, with local winds settling back into the moderate to fresh range. An upper level low lingering near the state will help to enhance trade wind showers through tonight. A Small Craft Advisory for the windier waters and channels around Maui County and the Big Island has been remains in effect through early Saturday morning.
Surf along south facing shores will gradually build through Saturday as a long period south-southwest swell is expected to fill in and generate near-seasonal surf through the weekend before declining early next week. A similarly-sized long-period south-southwest swell is expected to arrive Wednesday into Thursday, bringing another boost to south shore surf.
East shore surf will remain near seasonal average through the weekend as trade winds persist, then gradually decline into midweek as the trades weaken slightly. Tiny surf will prevail along north facing shores through early next week. A small to moderate medium-period northwest swell will arrive late Wednesday into Thursday of next week, bringing above average surf.
Starting Saturday and lasting into Wednesday, we can expect higher than normal tides, which could lead to some coastal flooding during the peak of high tides in the early afternoon hours. As this elevated tide is expected between the aforementioned south swells, this event will likely have minimal impact.

HFO Watches/Warnings/Advisories

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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