Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny. Highs around 83 near the shore to around 72 above 3000 feet. Northeast winds around 10 mph shifting to the west in the afternoon.

Tonight: Partly cloudy with isolated showers. Lows around 66 near the shore to around 55 above 3000 feet. North winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83 near the shore to around 72 above 3000 feet. Light winds becoming southwest around 10 mph in the afternoon. Chance of rain 40 percent.

South Kaua’i

Today: Sunny. Highs around 81. Northeast winds 10 to 15 mph.

Tonight: Partly cloudy with isolated showers. Lows 62 to 67. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Partly sunny with scattered showers. Highs around 81. East winds around 10 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Mostly sunny with isolated showers. Highs 73 to 78 in the valleys to around 64 above 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 59 in the valleys to around 51 above 4000 feet. Northeast winds 10 to 15 mph in the evening becoming light. Chance of rain 40 percent.

Thursday: Partly sunny with scattered showers. Highs 73 to 78 in the valleys to around 64 above 4000 feet. Light winds becoming northeast 10 to 15 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with isolated showers. Highs 75 to 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows 58 to 67. Northeast winds 10 to 15 mph in the evening becoming light. Chance of rain 40 percent.

Thursday: Partly sunny with scattered showers. Highs 75 to 82. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 40 percent.

East Kaua’i

Today: Mostly sunny with isolated showers. Highs 73 to 80. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows 57 to 69. Northeast winds 10 to 15 mph in the evening becoming light. Chance of rain 40 percent.

Thursday: Partly sunny with scattered showers. Highs 73 to 81. Light winds becoming northeast around 10 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A nearly stationary trough will slowly dissipate near Maui County the next couple of days, supporting the formation of widespread showery low clouds. Associated moisture will spread to Oahu and potentially the Big Island at times, favoring windward areas. Gentle to locally moderate trade winds will prevail over Kauai and Oahu, while light winds continue over Big Island and Maui as this feature slowly weakens. As the trough dissipates by the weekend, strengthening trade winds will bring just a few windward showers to all islands.

Discussion

What was a nearly stationary cold front over Maui County is now analyzed as a trough, with associated low-level convergence and moisture becoming increasingly diffuse. Latest IR satellite images show that stable and showery broken to overcast low clouds have increased in coverage NE of all islands except the Big Island and Kauai, where nearly clear skies prevail. Radar shows light to moderate showers, in greatest coverage over windward portions of Maui, Molokai, and Oahu and adjacent waters. Some small heavy rain cores are leading to very low cloud bases in select areas.
On Oahu and Kauai, light to moderate NE winds prevail, supported by a weak high pressure cell centered about 1000 miles NW of Kauai. A ridge extending over the Big Island from a high to the NE, combined with the lingering trough, is leading to light and variable winds over Maui County and the Big Island. Overnight soundings show a dry and stable air mass over Kauai and the Big Island, but are likely not representative of conditions over the central islands.
Little significant change is expected over the next couple of days, as the trough moves very little and weakens. Associated moisture will become increasingly diffuse near and upstream of the islands, potentially bringing periods of increased low clouds and showers to Oahu and/or the Big Island, especially windward. NE trade winds on Kauai and Oahu will weaken on Thursday as the high to the NW dissipates. Wind speeds may diminish sufficiently to allow afternoon leeward sea breezes to prompt some cloud and shower development. The surface ridge lingering near the Big Island will keep a light wind pattern in place, with generally clear skies in the morning giving way to upslope clouds in the afternoon tomorrow.
From Friday into the weekend, a surface high to the distant NW will move rapidly E, passing well N of the islands. This high will support a strengthening trade wind flow as the lingering trough and associated moisture finally dissipate. Breezy trades with passing windward showers can be expected. Early next week, guidance indicates that a significant trough aloft will move toward and over the islands from the NW. This feature may lead to the formation of a surface trough to the W of the islands, which would turn the low- level flow to the SE and/or lead to some weakening of the trade flow. Forecast grids lean toward the latter solution, representing a blend of GFS and ECMWF guidance. As far as sensible weather, the trough aloft may bring instability that could bring increased shower coverage/ intensity.

Aviation

The stalled front weakened to a trough over Maui County overnight, and will slowly dissipate across the central portion of the island chain through the rest of the week. Lingering moisture with this trough will allow enhanced showers to continue over the central islands through tonight, especially over windward areas in the north- northeast flow on the backside of the trough. Therefore, AIRMET Sierra for mountain obscuration remains in effect for the islands of Maui County, as well as northeast slopes of Oahu, and will likely continue into this afternoon.
Gentle to moderate north-northeast winds will continue for the next couple of days from Molokai westward. Elsewhere, light southeast flow will keep a land/sea breeze regime over the Big Island and portions of Maui, with isolated MVFR conditions in low clouds/-SHRA across leeward slopes again this afternoon.

Marine

Moderate to locally fresh northeast winds will continue over the Kauai and Oahu waters through Thursday as a trough lingers over and around Maui County. Light to moderate southeast winds will hold east of this boundary over the waters from Maui to the Big Island. A return of fresh to locally strong easterly trades is forecast late Friday through the weekend as high pressure builds north of the state.
Surf along north facing shores will remain small through the upcoming weekend with mainly a mix of short to medium period north and northwest swells moving through. For the long range, guidance is advertising a gale low emerging over the far northwest Pacific and tracking east-southeast Friday into the weekend. Gales associated with this system are shown locked in down the 300-320 degree directional band relative to the islands driving seas into the 25-30 ft range. If this materializes, a long-period northwest swell arriving locally next Monday would result.
Surf along south facing shores will ease today as a south swell that recently peaked moves out. A new long-period south arriving, however, should lead to a slight upward trend later today through Thursday as it peaks. Surf will return to background levels Friday through Monday. For the long range, guidance shows a solid south- southwest swell arriving next Tuesday with a peak likely through the midweek time frame from a source currently evolving within our swell window southeast of New Zealand.
Surf along east facing shores will remain small through the weekend due to the lack of trades locally and upstream. For the long range, an upward trend appears possible beginning early next week as the trades return.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov