Photo Credit: Brendan Stephen

West Kaua’i

Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 81 near the shore to around 69 above 3000 feet. Light winds. Chance of rain 40 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 65 near the shore to around 55 above 3000 feet. Light winds. Chance of rain 20 percent.

Wednesday: Sunny. Highs around 81 near the shore to around 69 above 3000 feet. North winds up to 15 mph.

South Kaua’i

Today: Mostly sunny with isolated showers. Highs 77 to 83. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 64. North winds 10 to 15 mph.

Wednesday: Sunny. Highs 78 to 83. North winds up to 10 mph in the morning becoming light.

Kaua’i Mountains

Today: Mostly sunny in the morning then becoming mostly cloudy. Isolated showers early in the morning, then scattered showers late in the morning. Showers likely in the afternoon. Highs 68 to 75 in the valleys to around 62 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 57 to 63 in the valleys to around 53 above 4000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Mostly sunny with isolated showers. Highs 68 to 76 in the valleys to around 62 above 4000 feet. Light winds becoming north up to 10 mph in the afternoon. Chance of rain 20 percent.

North Kaua’i

:

East Kaua’i

Today: Mostly sunny with isolated showers early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 69 to 80. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then mostly clear after midnight. Lows 58 to 69. North winds around 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Sunny. Highs 70 to 81. Light winds becoming north up to 15 mph in the afternoon.

Detailed Forecast

Synopsis

Stable northeasterly trade winds will push shallow bands of showers over windward slopes from Kauai to Maui today and Wednesday. A weak front will move down much of the island chain Thursday and Friday, bringing a modest increase in rainfall over windward and northern slopes.

Discussion

A strong, zonally oriented Pacific jet extending across the Pacific Basin supports an expansive, flat ridge which is dominating the subtropical and tropical latitudes. The fast-moving and southward- displaced storm track has weakened the trade wind belt and forced it south of the islands. This pattern also offers no opportunity for mid-level ridging to amplify and as a consequence offers only fleeting opportunities for trade winds to recover from their current light to moderate state.
At press time, convergence associated with remnant band of frontal moisture resides over the central portion of the state. The resident hostile environment is limiting cloud tops to no more than 6kft with a light showers noted on radar over portions of Windward Maui County. This is in line with expectations, and when the next buckle in the mid-latitude flow sends a decaying front toward the islands late Thursday into Friday, a similar outcome is anticipated. The feature will be shallow and will yield an increase in windward and mauka clouds and slight uptick in NE trades, but will otherwise be inconsequential as convective depths remain squashed.
In the meantime, winds will hover near the tipping point for sea breeze expansion. As the aforementioned decaying front approaches during Wednesday a weakened gradient will likely allow sea breezes to expand during the afternoon resulting in increased interior clouds but little in the way of shower activity. By the end of the week, light to moderate trades take hold behind the front only to be followed by renewed land and sea breeze expansion by Sunday. Drier than normal weather continues through the forecast period.

Aviation

Light winds will give way to moderate northeast trade winds later today as the tail end of a dissipating front approaches and moves into the area from the northwest. With a relatively dry and stable airmass in place, shower activity will generally be limited through the period. However, a band of low level clouds and showers is draped across the central islands early this morning and MVFR conditions have been persistent in those areas over the past few hours. These conditions will likely persist through mid morning today. Otherwise, VFR conditions will prevail.
AIRMET Sierra is in effect for tempo mountain obscuration below 2500 feet across Molokai, Maui and Lanai this morning. This AIRMET will likely be needed for these areas through mid morning before conditions begin to improve.

Marine

A progressive pattern will continue over the northern Pacific through the start of the year featuring a series of powerful gale- to storm-force lows passing north of the state. Large and broad areas of gales focused at the islands down the north to northwest directional bands will accompany these features and drive significant swells through the region. The first system is currently passing north of the area with the head of the fetch digging southward to within several hundred nautical miles of the islands. Recent altimetry data and SOFAR drifter buoy observations in this region showed 25-31 ft seas. Guidance seems to be on track and shows this swell building down the island chain later today, with seas exceeding the Small Craft Advisory (SCA) level of 10 ft over exposed waters. With the next swell on its heels Thursday, that could be larger, expect the SCA seas to persist into the weekend.
Surf along exposed north and west facing shores will quickly build to advisory levels through the day, then to warning levels this evening through Wednesday. The warning will likely need to be extended as the next swell associated with a developing gale trailing this system to the north rolls in later Thursday through Friday. For the upcoming weekend, a mix of north and northwest swell energy impacting exposed beaches will likely support advisory-level surf persisting. For the extended, guidance depicts the next warning-level event arriving Tuesday of next week.
Provided the long duration with advisory/warning level surf expected over the next several days, significant erosion along exposed north and west facing beaches can be anticipated. This erosion combined with our early morning high tides and warning- level surf could translate to overwash onto our vulnerable coastal roadways and impact properties periodically. The most likely time frames for these impacts will be around daybreak Wednesday and late Thursday into Friday as the large overlapping events are near their peak.
Surf along east facing shores will remain small through the week due to the light winds locally. Beaches exposed to northerly swells will begin to pick up Friday through the upcoming weekend as the swell direction shifts out of the north to north-northeast.
Surf along south facing shores will remain around the winter average through midweek. A slight bump is possible during the second half.
The winds over the local waters will fluctuate from light and variable to moderate north to northeast as the tail-end of passing fronts clip the area. For timing, expect the light winds on Wednesday and Friday and the moderate northerly winds today, Thursday, then late Friday through Saturday.

HFO Watches/Warnings/Advisories

High Surf Warning from noon today to 6 PM HST Wednesday for Niihau, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory from noon today to 6 PM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters.

Data Courtesy of NOAA.gov