West Kaua’i

Today: Sunny. Isolated showers in the afternoon. Highs 83 to 89 near the shore to around 75 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 67 to 72 near the shore to around 59 above 3000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs 83 to 88 near the shore to around 74 above 3000 feet. East winds up to 10 mph. Chance of rain 20 percent.

South Kaua’i

Today: Sunny. Isolated showers in the morning. Highs 80 to 87. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows around 71. Northeast winds around 10 mph. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers. Highs 79 to 87. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 81 in the valleys to around 65 above 4000 feet. East winds up to 10 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy with scattered showers. Lows 62 to 68 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 73 to 80 in the valleys to around 65 above 4000 feet. East winds around 10 mph becoming up to 15 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 76 to 85. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 63 to 71. East winds up to 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 75 to 84. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 73 to 84. Northeast winds around 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 75. Northeast winds around 10 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 72 to 84. East winds around 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to locally breezy trades with generally drier weekend weather. There are increasing chances for more inclement, active weather next week.

Discussion

Broad upper ridging west of the region, centered along 20N, will expand eastward and envelope the Hawaiian Islands and its surrounding waters. A 1029 mb surface high pressure located approximately 1,200 miles from Oahu is weakening and settling southeastward. 12Z soundings are depicting very dry mid level air advecting in from the east. All of these factors equate to an evolving stable weather pattern and will result in drier weather under lighter winds. This drier air mass will move across the area early today and assist in ending the overnight persistent windward Big Island precipitation. Many rain gauges in the Hilo and Puna Districts have picked up 2 to 5 inches of rain since early Friday morning. A nice trade wind pattern weekend under partially sunny skies and light trades, locally breezy within higher terrain. Light precipitation will focus along windward upslope mauka with higher nocturnal rain accumulations within an overnight relatively deeper moistened boundary layer squeezed underneath a thick layer of dry air aloft. The next couple of days will be the best weather days of the upcoming week.
A weakness will develop within the upper ridge over the islands on Monday. An upper trough and associated cold front will approach the island chain from the northwest and merge with the weakness channel over the state going ito Tuesday. It is a bit early to determine the evolution of this trough but it will more than likely pull up moist equatorial air while destabilizing the regional atmosphere. The trough or upper low will cool 500 mb temperatures to around -10 C and this instability will increase the probabilities of isolated thunderstorms across the central islands of Oahu and Maui County from late Monday through Tuesday afternoon. Numerous showers that may produce locally heavy rain will be the main theme Monday through Wednesday. Freezing levels falling to around 12k feet, along with the potential of a saturated column between -10 and -20 C Tuesday, implies a frozen mix or brief snow showers atop Big Island's summits. Mid level winds will strengthen east of the upper trough axis going into mid week and this may increase Haleakala and Big Island summit winds to near Wind Advisory levels (in gust) Monday night and Tuesday. The cold front will slow as it approaches the western half of the state Wednesday. This feature, along with a mid level trough moving across from the east within a highly moistened regional air mass, should provide the necessary ingredients of lift and instability to possibly prolong this wet pattern into next weekend.

Aviation

Trade winds are decreasing in magnitude with a diminished threat for regional turbulence over and in the vicinity of the islands. Occasional showers will occur across windward areas and higher terrain. The greatest threat for continued precipitation and mountain obscuration (occasional MVFR) this morning remains over windward exposures, especially Big Island.
AIRMET Sierra remains in effect for windward Big Island. This will continue through mid morning to account for the upstream moist air mass being lifted along windward Mauna Kea and Mauna Loa's slopes.

Marine

Moderate to locally strong easterly trade winds will persist today and gradually weaken as high pressure to the northeast slowly drifts southeast and weakens. A Small Craft Advisory (SCA) has been trimmed back this morning to the typical windy waters and channels around Maui County and the Big Island through this afternoon. Guidance for early next week remains uncertain with the potential for an upper level trough forming southeast of the coastal waters Monday and moving northwest over the islands. The moderate trade winds may veer to the east-southeast and slowly weaken through Tuesday. Additionally, a front looks to move into the offshore waters by Tuesday afternoon, bringing locally strong east-northeast winds behind the front, before weakening over the coastal waters midweek. There is a potential for isolated to scattered thunderstorms over the marine waters Monday through Wednesday.
Surf along north facing shores will remain small through midday before a small to moderate, medium to long period northwest swell looks to fill in this afternoon that will keep surf elevated through the weekend. Tiny long period forerunners have started to show up on the NDBC offshore buoy 51101 early this morning. A moderate long period northwest swell is expected to arrive late Tuesday, and peak Wednesday near High Surf Advisory (HSA) levels before declining by the end of next week.
Surf along east facing shores will continue to decline through the weekend due to the weakening of the local and upstream trade winds. Large choppy short period surf for north and exposed east shores is possible by the middle of next week depending on the evolution of the potential trough and approaching cold front mentioned above. For south shores, tiny background southerly swell will remain through the forecast period.

Fire weather

Recent island wide rain and more overcast skies, along with relatively higher minimum afternoon humidities under light winds, will all help maintain a lower fire weather threat. The potential exists for a wet weather pattern through most of next week. This morning's lower inversion height slopes from near 4k ft the western islands to around 9k ft on Big Island.

HFO Watches/Warnings/Advisories

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