Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs around 76 near the shore to around 65 above 3000 feet. Northeast winds 10 to 25 mph shifting to the east up to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows 62 to 69 near the shore to around 52 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Monday: Breezy. Mostly sunny with isolated showers. Highs around 77 near the shore to around 66 above 3000 feet. East winds up to 25 mph. Chance of rain 20 percent.

South Kaua’i

Today: Windy. Mostly cloudy with scattered showers. Highs around 73. Northeast winds 20 to 30 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 59 to 68. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 74. East winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Cloudy and breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 64 to 70 in the valleys to around 56 above 4000 feet. East winds 10 to 25 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then frequent showers after midnight. Lows 51 to 59 in the valleys to around 47 above 4000 feet. East winds 10 to 25 mph. Chance of rain 80 percent.

Monday: Mostly cloudy. Breezy. Frequent showers in the morning, then numerous showers in the afternoon. Highs 65 to 71 in the valleys to around 57 above 4000 feet. East winds 10 to 25 mph. Chance of rain 80 percent.

North Kaua’i

Today: Breezy. Mostly cloudy with scattered showers. Highs 66 to 76. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 56 to 67. East winds up to 15 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs 67 to 77. East winds up to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 65 to 75. Northeast winds 10 to 20 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 52 to 70. Northeast winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy. Breezy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 66 to 76. East winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Strong and gusty easterly trade winds will continue today, as high clouds stream overhead. Showers will favor windward and mauka locations, with a few periodically carrying over leeward areas of the smaller islands. As trade winds ease Monday through Tuesday, a passing disturbance aloft will clear the high clouds and may enhance rainfall. Winds will likely be disrupted late Tuesday into Wednesday, followed by a cold front advancing down the island chain Wednesday night and Thursday. Breezy northerly winds and drier conditions will follow the front.

Discussion

Guidance remains in good agreement and depicts the gusty easterly trades persisting today due to high pressure centered north of the islands. Stable conditions with a subsidence inversion positioned between 6 and 8 kft combined with the strong pressure gradient support the Wind Advisory currently in place for the windier locations of Maui County and the Big Island. Despite the stable conditions, brief showers moving through will favor windward and mauka locations, with some spilling over into leeward areas of the smaller islands periodically. The high clouds streaming over the islands leading to periods of mostly cloudy conditions will persist as an upper low southwest of the state continues to draw mid- to upper-level moisture northward across the region.
Guidance remains in decent agreement and shows a pattern shift through the first half of the week, featuring a cold front approaching from the northwest and the aforementioned upper low to the southwest advancing eastward over the islands. Trade winds will begin to ease Monday, then gradually veer east to southeast on Tuesday. The upper-level trough to the southwest will pass overhead, leading to a decrease in high clouds from west to east and increasing chances for enhanced showers. The GFS and ECMWF are not showing significant mid- to upper-level cooling as the trough moves in on Monday, and though this does not favor a substantial increase in rainfall, locally heavier showers will be possible. As the 500 mb trough axis passes over the Big Island on Tuesday, chances of locally heavy rainfall will be highest across the eastern end of the island chain, and a thunderstorm could flare over the Big Island interior with some winter weather on the high summits.
The winds are expected to diminish and become variable Tuesday night through Wednesday as the front approaches. Increasing moisture and lift ahead of this approaching front will keep the rain chances up, especially through the afternoon periods as sea breezes form. Breezy northerly winds following the front will usher in a cool and rather dry air mass Thursday through Friday, with dew points possibly falling into the low to mid 50s.

Aviation

Surface high pressure north the state will generate strong and gusty trades across the islands through the forecast period. Thus, most shower activity will be limited to windward locations and allow for bring brief periods of MVFR ceilings and visibility. Isolated showers may occasionally push over the higher terrain and onto leeward sides.
AIRMET SIERRA remains in effect for north through east sections of the Big Island above 2500 feet for tempo mountain obscuration due to clouds and showers.
AIRMET TANGO remains in effect below 8000 feet over and immediately south through west of mountains and all islands for tempo moderate turbulence due to the strong trade flow.

Marine

A large area of strong high pressure positioned northwest of the islands will steadily move east through Tuesday. The tight pressure gradient downstream of the high lying across the islands will maintain fresh to strong trade winds through the day. The Gale Warning remains in effect for the channels surrounding Maui County and Big Island through this afternoon as winds will continue to frequently achieve gale force magnitudes. A Small Craft Advisory (SCA) also remains in effect for the remaining waters through the afternoon. Winds in the eastern island bays and channels will fall off to SCA levels tonight into Monday. Early week winds will gradually diminish and veer to the east southeast into mid week as the high moves east and a front approaches from the northwest. The front is scheduled to pass across the local waters from Wednesday through Thursday as moderate north to northeast winds fill in behind the front.
North and west-facing shore surf that peaked yesterday evening will gradually fall through the day with the fading northwest (320 degree) swell. A pair of moderate size, medium to long period north northwest swells are timed to arrive Tuesday into Wednesday and Thursday into Friday. An early week northwest (320 degree) swell originating from a compact hurricane force low east of Japan will begin filling in late Monday and peaking Tuesday. The later week north northwest (330-360 degree) swell coming from a broader area of gale force winds southwest of the Aleutian Islands may arrive and peak Friday. While the first swell origin's source is a deeper low, it is farther away and swell size may be compromised by angular spreading along its long eastern journey. The late week swell fetch area's gales are more in-line with the great circle route aimed toward the islands. This will probably be the larger of the two swells and may push surf to High Surf Warning levels as it arrives from a more northerly direction. Generally strong trades will continue to generate rough, choppy surf along east- facing shores through the day with a gradual early week decline as a result of weakening easterlies. A slight increase in surf along south-facing shores may occur later today and Monday with the arrival of a small, longer period southwest (200-210 degree) swell.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 PM HST this evening for Lanai Mauka, Kohala, Big Island Interior, Lanai Leeward, Lanai South, Maui Central Valley South, Kipahulu, South Haleakala, Big Island South, Big Island Southeast.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Monday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.
Gale Warning until 6 PM HST this evening for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov