West Kaua’i

Tonight: Partly cloudy. Isolated showers after midnight. Lows 69 to 74 near the shore to around 62 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs 84 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.

Friday Night: Mostly clear. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds up to 10 mph.

South Kaua’i

Tonight: Partly cloudy. Scattered showers after midnight. Lows around 73. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 81 to 89. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with scattered showers. Lows around 72. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy with scattered showers. Lows 64 to 69 in the valleys to around 59 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 83 in the valleys to around 67 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Friday Night: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows 63 to 69 in the valleys to around 59 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 66 to 73. East winds up to 10 mph. Chance of rain 40 percent.

Friday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 85. East winds up to 15 mph. Chance of rain 40 percent.

Friday Night: Partly cloudy with scattered showers. Lows 65 to 72. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 65 to 76. Northeast winds around 10 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 86. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday Night: Mostly cloudy with scattered showers. Lows 64 to 75. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy trades become strong this weekend into next week delivering limited clouds and showers mainly to windward and mauka areas.

Discussion

Closed mid-level low positioned west of the islands at press time is transitioning to a weak and sheared out low amplitude shortwave as it's partially absorbed back into mid-latitude westerlies. This low remains of little consequence other than the attendant subtropical jet which is gracing area skies with occasional cirrus. Near the surface, observed soundings indicate a very firm trade wind inversion anchored near 6kft at Lihue and Hilo, though slightly weaker in the vicinity of Kauai courtesy of closer proximity to the low. This has kept a kept a lid on overnight showers while the daytime diurnal max has maintained dry predominantly dry conditions each afternoon. Little change expected going forward as showers remain light and ridging north of the islands strengthens. This will only reinforce stable trade wind conditions as trades become strong this weekend into early next week. Given the strength of the inversion and strengthening background trades, it will be worth monitoring favored downslope areas for gusty wind potential as early as Friday, mainly in Maui County and the Big Island.
Shear-induced upper low development is anticipated over the islands this weekend which may diminish stability a bit, especially over the western end of the state, but the shallow boundary layer moisture field will likely be unable to capitalize leading to a rather uniform scattered coverage of light-intensity showers each night.

Aviation

A stable, moderate to locally breezy trade wind flow will persist through Friday, followed by an increase in winds during the weekend. Periods of MVFR ceiling and visibility in SHRA will focused along windward slopes, and during the overnight and early morning hours AIRMET Sierra for mountain obscuration may be needed. VFR will dominate over most leeward areas, but sheltered terrain will experience isolated MVFR conditions each afternoon, especially on the Kona slopes of the Big Island. The stable trade wind flow will produce light turbulence below 7,000 feet, but these conditions should not require AIRMET Tango through Friday. An upper-level low to the west may produce some light turbulence above FL300 into early Friday.

Marine

High pressure far northeast of the islands will remain nearly stationary through the remainder of this week and bring moderate to locally strong trade winds. High pressure will then re-center north of the region this weekend and help to further strengthen trades. Thus, a Small Craft Advisory for the windier waters and channels around Maui County and the Big Island remains in effect through at least Sunday.
Surf along south facing shores will be tiny to small over the next several days. A small, long period, south swell originating from a fetch near New Zealand will build late this weekend and help to boost surf heights through early next week.
Rough and choppy surf is expected for east facing shores through the forecast period due to the moderate trades. Tiny seasonal surf is expected for North facing shores.

HFO Watches/Warnings/Advisories

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

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