Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 79 near the shore to around 71 above 3000 feet. Southeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy in the late evening and overnight. Lows around 68 near the shore to around 56 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs around 81 near the shore to around 72 above 3000 feet. Northeast winds around 10 mph shifting to the southwest in the afternoon. Chance of rain 40 percent.

South Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 80. Southeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy early in the evening then becoming partly cloudy. Scattered showers and slight chance of thunderstorms early in the evening. Lows 63 to 69. Southeast winds around 10 mph shifting to the north after midnight. Chance of rain 30 percent.

Wednesday: Mostly sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Highs around 81. North winds around 10 mph shifting to the southeast in the afternoon. Chance of rain 20 percent.

Kaua’i Mountains

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 70 to 75 in the valleys to around 64 above 4000 feet. Southeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Lows 56 to 61 in the valleys to around 51 above 4000 feet. East winds around 10 mph shifting to the southwest after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny early in the morning then becoming partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 72 to 77 in the valleys to around 65 above 4000 feet. Southwest winds around 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 71 to 78. Southeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Lows 59 to 68. East winds around 10 mph shifting to the south after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny with isolated showers early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 72 to 80. South winds around 10 mph shifting to the north in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 72 to 80. Southeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms early in the evening, then partly cloudy with isolated showers in the late evening and overnight. Lows 56 to 69. Southeast winds around 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny early in the morning then becoming partly sunny. Isolated showers early in the morning, then scattered showers in the late morning and afternoon. Highs 73 to 81. West winds around 10 mph shifting to the east in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light winds will prevail for the next couple of days, with the island atmosphere remaining moist and unstable. Low clouds will generally clear over the islands during the night and morning, with afternoon sea breezes leading to cloud and shower formation over island interiors. Some showers could be briefly heavy before diminishing by evening. Trade winds are expected to return by the end of the week, bringing clouds and showers that will primarily focus over windward areas. Stronger trade winds are anticipated by early next week.

Discussion

Morning soundings show that a moist and unstable air mass remains in place, mainly due to a cutoff low aloft SW of the islands. The light to moderate low-level flow is generally out of the SE due to the presence of a persistent but gradually weakening surface trough near Kauai, and a surface high to the NE. Skies are mostly cloudy due to a combination of cloud layers, and regional satellite imagery shows scattered thunderstorm clusters associated with the low aloft.
While most land areas remained dry overnight, an area of heavy showers and thunderstorms somewhat unexpectedly developed over leeward waters and moved northward. While some rain and high- elevation snow fell over the Big Island, precipitation totals remained very low. Some briefly heavy showers did clip leeward Oahu, but the bulk of the rainfall remained offshore and has been gradually dissipating since. Some of these showers may move ashore on Kauai early this morning, but otherwise fairly quiet (albeit somewhat cloudy) conditions to start the day statewide, with light winds prevailing.
The low aloft will linger SW of the islands, and an associated trough will extend overhead, maintaining the potential for some locally heavy downpours and a few thunderstorms the next couple of days. The low-level trough will linger N of the islands as it becomes increasingly broad and diffuse, and light and variable winds are expected to develop by tonight as the low-level gradient becomes quite loose. This will allow island-scale land and sea breezes to modulate weather over land the next couple of days.
Most likely outcome in this regime is that skies will generally clear (of low clouds at least) over the islands at night and remain that way through the morning as land breezes prevail. Afternoon sea breezes converging over the islands will lead to cloud and shower development over island interiors, with the lingering moist and somewhat unstable island atmosphere allowing some heavy showers to develop, with potential for a few thunderstorms, mainly over the Big Island slopes. Mid- and high-level clouds are expected to gradually thin, but in areas they don't, the sea breeze convection may be muted. Additionally, exceptions to the land/sea forecast may occur. As we saw overnight, showers and thunderstorms may develop along lingering boundaries that are difficult to anticipate, but generally expect the overnight land breezes to keep them from moving ashore.
We expect trade winds to return by the end of the week as the trough dissipates and high pressure builds to the N. This high may push moisture associated with a dissipated front over the islands from Friday into the weekend, as a weak trough aloft lingers. The long range outlook features stronger trade winds that may trend drier early to midweek next week.

Aviation

An upper level low anchored about 420 nm southwest of Kauai continues to be a source of instability and mid level moisture. Meanwhile, light trade wind flow has begun to pull in drier air in the lower levels, especially over the eastern half of the state.
As of 2 am Tuesday, radar imagery revealed a band of light to moderate showers extending from southwest Oahu to Kahoolawe and across leeward Big island. This band is expected to move swiftly north and westward, passing over most of the state by late morning. Brief MVFR CIG or VIS is to be expected in these quick moving showers. Isolated thunderstorms associated with this band.
In the afternoon, shower activity across the smaller islands will be limited and focused over island interiors. On the Big island, showers will briefly increase in both coverage and intensity during the afternoon then taper off after sunset. Isolated thunderstorms over interior Big Island in the afternoon.
Light icing in layered clouds above 14 kft will remain a concern through the morning hours, and possibly beyond.
AIRMET Tango for moderate mid and upper level turbulence remains in effect due to the proximity of the upper level low. Conditions are expected to persist through this evening and possibly beyond.

Marine

A surface trough near Kauai will weaken and drift westward away from the state today as high pressure weakens northwest of the state. Winds will become light to moderate later today into Thursday before trade winds rebuild Friday. The strong northeast winds around Kauai, as well as east winds around Big Island have come down considerably overnight. The large northwest swell and northeast wind waves are declining as well. Therefore, the Small Craft Advisory (SCA) has been dropped for all waters. An SCA may be required again by this weekend as trades rebuild.
The aforementioned northwest (310 degrees) swell and short-period northeast wind waves around Kauai have declined enough this morning to drop the remaining High Surf Advisory (HSA) as well. A small pulse of northwest swell is due Wednesday and Thursday, followed by a moderate north-northwest swell (350 degrees) this weekend. An out of season south swell will provide surf around summertime average today into Thursday.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov