Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Cloudy with frequent showers and slight chance of thunderstorms in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs around 81 near the shore to around 70 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy early in the evening then becoming mostly clear. Scattered showers and slight chance of thunderstorms in the evening. Haze through the night. Lows around 68 near the shore to around 58 above 3000 feet. Southeast winds around 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 81 near the shore to around 72 above 3000 feet. South winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Cloudy with frequent showers and slight chance of thunderstorms in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 79 to 84. Light winds becoming south around 10 mph in the afternoon. Chance of rain 80 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms in the evening, then partly cloudy with isolated showers after midnight. Haze through the night. Lows around 66. East winds around 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 81. South winds 10 to 15 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Frequent showers and slight chance of thunderstorms. Haze in the afternoon. Highs 71 to 77 in the valleys to around 64 above 4000 feet. South winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy early in the evening then becoming partly cloudy. Haze through the night. Scattered showers early in the evening. Slight chance of thunderstorms in the evening. Isolated showers in the late evening and overnight. Lows 58 to 66 in the valleys to around 56 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with scattered showers in the morning, then mostly cloudy with numerous showers in the afternoon. Haze through the day. Highs 73 to 78 in the valleys to around 65 above 4000 feet. South winds 10 to 15 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Numerous showers and slight chance of thunderstorms in the morning, then frequent showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 73 to 81. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy early in the evening then becoming partly cloudy. Haze early in the evening. Scattered showers and slight chance of thunderstorms in the evening, then isolated showers after midnight. Lows 60 to 68. Southeast winds up to 10 mph. Chance of rain 50 percent.

Friday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs 74 to 82. South winds 10 to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Frequent showers and slight chance of thunderstorms in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Haze in the afternoon. Highs 73 to 82. Light winds becoming southeast around 10 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Haze in the evening. Numerous showers early in the evening. Slight chance of thunderstorms in the evening. Isolated showers in the late evening and overnight. Lows 60 to 70. Light winds becoming south around 10 mph after midnight. Chance of rain 70 percent.

Friday: Partly sunny. Scattered showers in the morning, then numerous showers in the afternoon. Haze through the day. Highs 73 to 82. South winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A series of upper level disturbances passing north of the islands will lead to a more unstable airmass for the next few days, especially over the western end of the chain. These disturbances, combined with moisture riding in on southerly winds, will lead to showers and a slight chance for thunderstorms mainly for Kauai today. Unsettled weather is expected to persist into the weekend, but the atmosphere should become drier and more stable by Sunday as trade winds make a long awaited return to the Aloha State.

Discussion

A surface ridge is just north of Kauai will keep light southeast wind flow across the state. An area of low level clouds and persistent showers has moved over Kauai overnight. A few thunderstorms have popped up along the windward coast as well. 12Z sounding at Lihue shows layered clouds up to around 30 kft with precipitable water of 1.93 inches.
This moisture will begin to feel the influence of a weak, but digging trough aloft to the west of the islands, as well as a weak surface trough which has been lingering northwest of Kauai. All of this will lead to a more unstable airmass across the western end of the chain today. Daytime sea breezes should be quite effective in putting this instability and moisture to work by this afternoon and a slight chance of thunderstorms is in the forecast for Kauai and surrounding waters through the early evening. Oahu will also be on the cusp of the instability and moisture and could also a boost in shower coverage and intensity today.
Meanwhile, Maui county and the Big Island should be relatively drier and more stable air holding on. The models do not show as much moisture advection or destabilization near the Big Island although there should be some afternoon showers over the slopes.
The surface ridge will weaken over the next couple of days and shift south, turning our low level flow around to southerly by tonight, especially for the western islands. The models show the stronger instability from a passing shortwave trough remaining just north of the islands and shifting northward, where most of the deeper convection should focus. The weak southerly flow will keep the weather somewhat unsettled through about Saturday, with bands of scattered showers coming northward especially near Kauai. The upper trough should push east of the islands Friday night, resulting in decreasing instability.
Not to get anyone's hopes up too much, but it still looks like a long-awaited return of trade winds starting about Sunday as a ridge becomes established a several hundred miles N of the islands. Initially the pattern looks like dry, fair weather trades with limited moisture, weak ridging aloft, and a stable atmosphere Sunday and Monday, but a digging upper trough toward the middle of next week may return more instability and lead to wetter, locally breezy trades.

Aviation

A trough northwest of the Hawaiian islands will generate light southeasterly flow across the state today and bring an increase in moisture and instability, mainly to areas west of Oahu. Thus, afternoon sea breezes are expected to initiate scattered shower activity over mainly interior and leeward areas of Oahu and Kauai. The greatest instability will remain near Kauai, however, and allow for a slight chance of thunderstorms thru the day. MVFR ceilings and visibility will likely accompany any of the heavier activity.
Partly cloudy conditions elsewhere with VFR conditions and isolated afternoon showers.
AIRMET SIERRA remains in effect for tempo mountain obscuration above 2500 feet for the entire island of Kauai due to low clouds and showers.

Marine

Weak fronts will clip the northern offshore waters before a stronger front approaches the northwest offshore waters Friday and pushes through the northern offshore waters over the weekend. Isolated thunderstorms are possible over the northern offshore waters as these boundaries move through. There is a chance for thunderstorms entering the coastal waters tonight and Friday.
Winds will be light and variable over the waters near Kauai and Oahu and a touch stronger out of the east-southeast over the waters near Maui County and the Big Island today. Winds will veer to southerlies and strengthen to moderate to fresh ahead of an approaching front Friday and Saturday. Gentle to moderate trades may return Sunday and gradually strengthen to moderate to fresh speeds through early next week as the front dissipates and a new area of high pressure builds north of the island chain. Winds and seas are forecast to remain below Small Craft Advisory thresholds through at least Saturday.
A northwest swell will maintain moderate surf along north facing shores today. A larger northwest swell should bring advisory level surf to north and west facing shores Friday, then dip below advisory levels Saturday. A much larger northwest swell is expected to ramp up quickly Saturday night, peak Sunday, then slowly decline Monday through mid-week next week. Surf heights will reach well above warning thresholds and possibly approach over 40 feet during the peak of the swell along north facing exposures of the smaller islands. The combination of rising surf and the high tides from the new moon Saturday night and Sunday night could produce coastal impacts with waves washing across roads near the shorelines.
Background south swell energy is expected through the weekend. A new small long-period south swell could give south shore surf a minor boost early next week. Surf along east facing shores will remain small due to the lack of trade winds over and upstream of the islands.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov