Photo Credit: Sebastien Gabriel

West Kaua’i

Rest Of Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 81 near the shore to around 67 above 3000 feet. East winds 10 to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 65 near the shore to around 55 above 3000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with isolated showers. Highs around 80 near the shore to around 66 above 3000 feet. East winds around 15 mph. Chance of rain 20 percent.

South Kaua’i

Rest Of Today: Partly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 76 to 81. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 64. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 75 to 81. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Rest Of Today: Breezy. Mostly cloudy with numerous showers. Highs 69 to 75 in the valleys to around 59 above 4000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with occasional showers. Lows 57 to 63 in the valleys to around 53 above 4000 feet. East winds 10 to 25 mph decreasing to up to 25 mph after midnight. Chance of rain 90 percent.

Wednesday: Mostly cloudy. Breezy. Occasional showers in the morning, then numerous showers in the afternoon. Highs 69 to 75 in the valleys to around 58 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

North Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers. Highs 70 to 81. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 66. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 70 to 81. East winds 15 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Rest Of Today: Breezy. Partly sunny with scattered showers. Highs 68 to 78. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 69. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 68 to 78. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

High pressure to the north of Hawaii will maintain breezy trade winds into the weekend. Clouds and showers will favor windward and mauka areas, with the gusty winds carrying some showers over leeward areas at times.

Discussion

As expected, no significant changes to the forecast with the morning package. The 1037 mb high remains about 1200 miles north of Oahu early this morning, and continues to bring a stable and breezy trade wind patter to the region. The overnight sounding at Lihue continued to show a trade wind inversion around 8000 ft, while the Hilo sounding inversion was around 11,000 ft. In part to showers in the area at the launch time, the Hilo sounding reported precipitable water (PW) to be about 1.33 inches, while Lihue had 0.98. The Lihue value is near normal, while Hilo's was on the high end of normal. A showery low cloud band is moving onto the windward sides of Maui and the Big Island early this morning, with showers expected to thin out there later this morning. With the trade winds, expect showers to be focused over the windward slopes of all the islands, with a few additional spotty showers possible over the Kona slopes of the Big Island.
No significant change is expected through tomorrow as the high is expected to weaken slightly and drift southward, but the pressure gradient over the region will change little, maintaining the breezy and gusty trade winds. Another high setting up far north of islands tomorrow will keep breezy trades in place through at least Friday. Random patches of moisture in the stable trade wind flow will bring periodic boosts in mainly windward rainfall over the next couple of days. Chances for more widespread shower activity, some briefly heavy, and thickening high clouds will increase on Thursday and Friday as an upper-level trough passes over the islands.
There is some uncertainty heading into the weekend. Trades should persist, but the GFS and ECMWF differ significantly on the strength, with the GFS leaning towards breezy and gusty conditions. The GFS and ECMWF are trending toward another upper level trough moving in from the west, potentially bringing an increase in high clouds and shower activity on Sunday.

Aviation

Breezy trade winds will remain in place through the remainder of the week. Clouds and light showers will favor windward coasts and slopes and be most active in the late night and early morning hours.
In the afternoon and early evenings, lee-side sea breezes and daytime heating will encourage cumulus build-ups along south and west facing slopes of the Big Island, but a strong inversion aloft around 8000 ft will limit their growth and rainfall potential.
AIRMET Sierra for mountain obscuration is currently in effect for portions of Maui and Windward Big Island. Conditions are expected to improve by late morning.
AIRMET Tango remains in effect for moderate low-level turbulence, and will likely be needed through midweek. Additionally, moderate upper level turbulence could become an issue for the western half of the state later today thanks to a passing upper level jet streak.

Marine

Rough conditions will continue across the Hawaiian waters through the week due to fresh to strong easterly trades. Seas will remain around and just above the 10 ft Small Craft Advisory threshold over exposed waters into early Wednesday due to a combination of a medium-period northeast swell and locally generated wind waves. Seas will drop slightly through the second half of the week as the northeast swell moves out.
Surf along exposed east facing shores will remain rough through the week, with heights hovering around the advisory level through tonight. Heights should dip below the advisory level Wednesday as the northeast swell begins to move out.
Surf along north facing shores will remain small into Friday, except for shores exposed to northeast swells. An upward trend is expected late Friday through the weekend due to a combo of a medium- to long-period north-northeast swell and a long-period west-northwest swell expected. The north-northeast swell should steadily fill in late Friday, then peak over the weekend. The west-northwest swell is forecast to build down the island chain through the day Saturday, then peak near the advisory levels for exposed north and west facing shores late Sunday.
Surf along south facing shores will remain small through midweek with mainly background energy moving through. An upward trend is expected Friday as a long-period south-southwest swell arrives. This swell will peak late Friday into Saturday, then ease Sunday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Olomana, Maui Windward West, Kauai East, Kauai South, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST Wednesday for all Hawaiian waters,

Data Courtesy of NOAA.gov