Photo Credit: Brendan Stephen

West Kaua’i

Today: Breezy. Mostly sunny with isolated showers. Highs 87 to 92 near the shore to around 76 above 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 74 near the shore to around 63 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 86 to 92 near the shore to around 76 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Scattered showers. Highs 84 to 92. East winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 73. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 83 to 91. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 83 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with showers likely. Lows 64 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 75 to 83 in the valleys to around 67 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 78 to 89. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Cloudy with showers likely. Lows 66 to 75. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Breezy. Cloudy with showers likely in the morning, then partly sunny with scattered showers in the afternoon. Highs 77 to 88. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 76 to 86. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Cloudy with scattered showers. Lows 66 to 76. East winds 10 to 20 mph. Chance of rain 50 percent.

Wednesday: Cloudy in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 75 to 86. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trades will become locally strong today into Wednesday as they deliver frequent showers to windward and mauka zones. Showery conditions, mainly for windward areas, will continue through the week as winds decrease and an upper low brings decreased stability during the latter half of the week.

Discussion

With the islands positioned between shower bands, the next poised to arrive later this evening, shower activity and cloud cover has diminished considerably this morning. This brief period of dry advection in the boundary layer is coinciding with the descent of strong 1040mb north Pacific high pressure from around 45N to 40N, and will bring a period of locally strong trades to the area today into Wednesday. No change to overall expectations today with the typical windy locales in Maui County and the Big Island potentially flirting with wind advisory criteria at times. A greater coverage of trade wind showers is then expected tonight through Wednesday night as an organized band of upstream showers works through the islands. This band of showers has shown organization for a couple of days now and originated within a corridor of convergent easterly flow beneath an upper low residing well east of the area. This lends confidence in model depictions of very showery weather over windward and mauka slopes through this time. The increased moisture depth combined with breezy to strong trades will likewise ensure frequent leeward drift of showers, particularly overnight and during the early morning.
Upper troughing then approaches islands from the north Thursday into Friday. Strong consensus exists among the global models that a closed low will develop somewhere in the vicinity of the islands this weekend. The guidance remains touchy with respect to the ultimate location of the closed low, though the overall trend has been for a more progressive initial trough passage followed by closed low development east or northeast of the islands. The initial wave of dynamic forcing associated with the passing trough axis accompanied by steeper lapse rates will be favorable for diurnal thunderstorm development over the Big Island on Thursday and/or Friday. Moved the forecast in this direction for the morning forecast package with the introduction of schc thunder for the Big Island on Thursday afternoon. As the closed low develops near/east of the islands late this week, stability will decrease and moderate trades will focus frequent showers over windward zones for the remainder of the week with occasional waves of showers reaching leeward areas as well.

Aviation

High pressure far northeast of the state will maintain a trade wind weather pattern across the islands through tonight, with trade winds strengthening to locally strong through Wednesday. Scattered showers will remain focused mainly across windward areas, while showers remain limited elsewhere.
Mainly VFR conditions are expected into Wednesday morning. However, MVFR conditions accompanying heavier showers remain possible, generating potential brief periods of tempo mountain obscuration across some windward locations.
AIRMET Tango remains in effect for moderate low-level mechanical turbulence downwind of island terrain toady.

Marine

No significant changes to the forecast this morning. High pressure to the north and northeast of the region will maintain the fresh to locally strong trade winds through tonight, before we see a bit of a decrease. A Small Craft Advisory (SCA) is now in effect for waters near Oahu and to the east. At this time, the SCA is in effect through tonight. Models indicate the winds will weaken some Wednesday, and even further Wednesday night. At this time don't have the best confidence, so going to leave the SCA as it, but likely will need to extend it for some areas.
A recent gale north of the region will be sending a series of northwest to north swells today and tomorrow, which will boost surf north and west- facing shores. Additional northerly swells are possible this weekend into early next week. Generally background, medium period south swell will hold through the week, but a larger and longer period south swell is expected to arrive Friday. This will bump surf along south facing shores for the weekend. As the trades strengthen in the next couple of days, expect more elevated and choppy surf along east- facing shores.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Wednesday for Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov