Photo Credit: Sebastien Gabriel

West Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 73 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 68 to 73 near the shore to around 59 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Saturday: Mostly sunny with isolated showers. Highs around 86 near the shore to around 74 above 3000 feet. East winds up to 15 mph becoming around 10 mph in the afternoon. Chance of rain 20 percent.

South Kaua’i

Rest Of Today: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 82. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Partly cloudy with scattered showers. Lows 66 to 72. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Rest Of Today: Cloudy with occasional showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 59 to 64 in the valleys to around 54 above 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 73 to 80 in the valleys to around 64 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Rest Of Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 84. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 62 to 72. Southeast winds up to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 76 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

East Kaua’i

Rest Of Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 75 to 83. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Saturday: Partly sunny with scattered showers. Highs 76 to 84. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy easterly trade winds will continue through early next week, with clouds and showers favoring windward and mauka locations. An upper level low will linger near the state through early next week, which will allow for some locally heavy showers over windward areas at times as occasional increases in low-level moisture embedded within the trades move into the islands. An uptick in showers is expected around Sunday and Monday, followed by drier conditions from Tuesday onward.

Discussion

Early this morning, surface high pressure is centered about 1700 miles northeast of Honolulu with ridging extending westward north of the islands. Meanwhile, latest satellite imagery shows a large cluster of showers and clouds across Kauai and its adjacent waters. Observed rainfall totals across the Garden Isle overnight indicate that the showers have been fairly light to moderate in nature, with six hour totals generally less than 0.75″ for most locations. Nevertheless, the light to moderate showers have been persistent early this morning and will continue for the next few hours. Elsewhere, showers are more isolated to scattered and are favoring windward and mauka locations.
The high far northeast of the state will maintain moderate to locally breezy trade winds across the island chain today and throughout the next several days. Showers embedded within the trade wind flow will favor windward and mauka locations, especially through the rest of this morning. Direr air approaching from the east may decrease overall windward shower coverage from this afternoon through Saturday.
The main forecast challenge for Saturday night into early next week will be the evolution of a low aloft that continues to linger over or near the state. Latest guidance continues to suggest that this upper level low may deepen and shift slightly more west by Sunday, which will likely help enhance the trade wind showers. Details still remain uncertain, but some locally heavy showers will be possible for windward areas around the Sunday to Monday time frame as instability and precipitable water increase. With this morning's forecast updates, rain chances were trended up a bit during the Sunday night through Monday morning time frame as this is currently the window of highest confidence, but the overall forecast philosophy remains the same.
Slight variations in the strength of the surface high far northeast of the islands will result in minor day to day fluctuations in trade wind speeds over the next several days, but they are expected to generally remain at moderate to locally breezy levels overall. Drier, more typical trade wind weather could return around Tuesday of next week.

Aviation

A ridge to the north of the islands will maintain a moderate to breezy trade wind flow over the region into the weekend. Expect clouds and showers to favor the windward and mauka areas, however an upper level low just north of the islands will allow some of the showers to be carried to leeward areas. Some MVFR conditions are possible in the clouds and showers, more so over windward locations. No AIRMET Sierra is in effect at this time, but one can't be ruled out for tempo mountain obscuration.
A weak trade wind inversion remains evident on the overnight Hilo sounding. Meanwhile the Kauai sounding shows a moist airmass with no discernible inversion. Satellite and radar show more clouds and showers over the western end of the state closer to the upper level low. The lack of a trade wind inversion over the western end is limiting low level turbulence to the lee of the islands, however the same can not be said for the eastern end. AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of terrain. This AIRMET is expected to remain in place through much of today.

Marine

Surface high pressure anchored roughly 1,200 to 1,500 nm northeast of the islands will maintain moderate to locally strong easterly trade winds through the middle of next week. A Small Craft Advisory (SCA) is in effect for the typically windier waters around Maui County and the Big Island through tonight. The forecast keeps SCA conditions in these same waters through the weekend.
A declining south-southwest swell will drop surf to summertime background levels today. A slight increase in south swell is possible over the weekend, followed by a return to small summertime background level surf early next week. Trades upwind of the state will generate rough choppy seas near leading to moderate surf along east facing shores through the week. An out- of-season, medium period northwest swell from former Northwest Pacific Typhoon Guchol will build on Saturday, peak above June average at 3 to 4 feet Sunday and Monday, then slowly decline Tuesday and Wednesday.

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.

Data Courtesy of NOAA.gov