Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 88 near the shore to around 77 above 3000 feet. Northeast winds around 10 mph. Chance of rain 30 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 71 near the shore to around 61 above 3000 feet. Northeast winds around 10 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Highs around 89 near the shore to around 77 above 3000 feet. Northeast winds around 10 mph.

South Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 82 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

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

Thursday: Mostly sunny. Scattered showers in the morning. Highs 83 to 90. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 74 to 85 in the valleys to around 66 above 4000 feet. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Occasional showers in the evening, then showers likely after midnight. Lows 64 to 70 in the valleys to around 58 above 4000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Thursday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 75 to 85 in the valleys to around 68 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 77 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 74. East winds 10 to 15 mph. Chance of rain 70 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 77 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 75 to 86. Northeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with showers likely. Lows 65 to 75. Northeast winds around 10 mph. Chance of rain 70 percent.

Thursday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will gradually relax just a bit over the next few days, as high pressure far to our north moves slowly northeast. Dry and stable air over the state should limit windward showers, which will favor the overnight and early morning periods. Isolated afternoon showers can be expected to form on the sea breeze over the lower slopes of leeward Big Island. A weak trough aloft moving over the state from east to west this weekend could bring a minor increase in showers for portions of the state. Stronger trades are expected to return again early next week.

Discussion

Surface high 1030 mb is located about 1400 mi NW of Kauai. The high is moving toward the ENE very slowly. A ridge extends SE from the high, helping to maintain the pressure gradient over the state for breezy trades. Over the next few days the high will move very slowly NE and the ridge will weaken, while a weak, stationary surface trough develops 600 mi NE of the islands and lingers through Sat. This should allow the trades to gradually relax just a bit. Starting Sunday, the trough will begin moving W and weaken, allowing the now-stronger high to build back toward the S, far N of the islands. This will allow locally windy trades to return about Mon.
The 12z RAOBs showed a strong inversion remaining over the islands from about 5500 ft at Lihue to 6500 ft at Hilo. This is due in part to weak mid-level ridging over the islands, accompanied by warm temperatures aloft. GOES-derived TPW shows a wedge of drier than normal air for this time of year over the islands as well. All of this spells generally fair weather this predawn, with just a few mainly light windward showers.
This general cycle is expected to continue for the next few days. Models show a weak trough at 700 mb moving in from the E over the weekend. This will be enough to raise the inversion a bit, and bring in some additional moisture (a small pocket of 1.5-1.8 inch precipitable water), allowing for an increase in mainly windward showers starting Friday night, especially for Maui and the Big Island. There are some differences in the model guidance by Sunday as to how much moisture will get entangled with the smaller islands, but the multi-model ensemble mean PW does seem to suggest some increase in showers lingering for the smaller islands into Sunday. Not a washout weekend by any means, but additional showers to contend with, mainly windward, and mainly during the nights and mornings. The leeward slopes of the Big Island should see an increase in sea breeze showers each afternoon this weekend as well as moisture wraps around that island and gets trapped in the leeside eddy.
Models and ensembles are in good agreement that drier and more stable air will return briefly for Mon, then suggest another influx of moisture is possible about Mon night or Tue. This moisture would be associated with a surface trough, the remnant of whatever is left of a current tropical disturbance near 17N 125W, which is unlikely to develop further, per NHC.

Aviation

Breezy trades will gradually ease through the end of the week. SHRA and low cigs will favor windward and mauka areas and could bring brief periods of MVFR. Otherwise, VFR should prevail.
AIRMET Sierra is in effect for mtn obsc for Oahu and Molokai. Conds should improve by mid-morning.
AIRMET Tango for mod low-level turb lee of island terrain remains in effect and will continue through today.

Marine

Overnight ASCAT pass showed mostly moderate tradewinds across the state with borderline Small Craft Advisory (SCA) winds around the typical windier waters of Maui County and the Big Island. The forecast remains on track with the pressure gradient weakening around the state today and thus wind speeds easing below SCA criteria. Thus the SCA has been cancelled. SCA conditions may return over the weekend and into early next week as the trough dissipated and a strong high builds north of the state.
Surf along south facing shores will remain elevated today with a gradual downtrend through Thursday. Background south swell energy is then expected Friday through the rest of the forecast period.
Rough, choppy surf along east facing shores begin to trend down today through the rest of the week as the tradewind swell eases and the small northeast swell fades.
Tiny surf along north facing shores will linger through today from the combination of a small, medium period northwest swell and the small northeast swell mentioned above but should return to nearly flat summertime conditions Thursday.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov