Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs around 83 near the shore to around 70 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows around 66 near the shore to around 56 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs around 83 near the shore to around 70 above 3000 feet. North winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 77 to 83. Northeast winds 15 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 67. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 78 to 84. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Mostly cloudy. Breezy. Occasional showers early in the morning, then scattered showers in the late morning and afternoon. Highs 70 to 77 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph decreasing to up to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 65 in the valleys to around 55 above 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers. Highs 70 to 77 in the valleys to around 62 above 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 72 to 83. East winds up to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 69. Southeast winds up to 15 mph. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers. Highs 73 to 83. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Highs 69 to 81. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 60 to 73. Northeast winds 10 to 15 mph decreasing to up to 10 mph after midnight. Chance of rain 40 percent.

Sunday: Partly sunny with scattered showers. Highs 70 to 82. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Breezy easterly trade winds will gradually ease later today into Sunday as a high pressure slowly drifts far northeast and weakens. Drier and more stable conditions will fill in later this afternoon, with light showers favoring windward and mountain areas. Rainfall chances could trend up again Monday through mid week as a disturbance develops just northwest of the state. Strong easterly trades with a more typical trade shower regime may return toward the end of next week.

Discussion

A 1032 mb high has moved slightly more northeast overnight and is now located 1200 miles northeast of Kauai. Winds have eased overnight and are now in the more gentle to locally breezy range. However, model guidance continues to show slightly stronger winds filling in later this morning and afternoon that will keep breezy conditions in the forecast today. Current satellite and radar imagery shows a stratocumulus deck moving in from the east with light to moderate scattered showers embedded. These showers will focus along windward and mauka areas with a few showers spilling over to leeward areas at times through the morning hours.
Drier and more stable conditions will fill in later today and Sunday as upper and mid level ridging builds overhead and precipitable water dips around or below an inch. Tradewinds are expected to ease to a more gentle range Sunday and Monday as the high weakens further northeast of the state and a front approaches from the far northwest. This could allow for a more hybrid land/sea breeze pattern to develop, with clouds and showers developing along select sheltered leeward and interior areas in the afternoons and clearing overnight.
Guidance from both the ECMWF and the GFS continues to show a surface trough developing between the state and an anomalously strong high (around 1050 mb) building to the far north early next week. The placement of this trough has been generating some differences between each model run with winds being stronger/weaker or more easterly/southeasterly. The latest forecast has been updated with a blend of 00Z ECMWF and 06Z GFS which has been more consistent with the previous run, showing easterly trades strengthening late Monday and Tuesday before further strengthening and veering out of the southeast by mid week as the trough develops to the northwest of the state. Meanwhile, an amplified upper level wave pattern will deepen a trough just northwest of the state and that could pinch off a closed low by mid-week. This upper level closed low will could produce a surface low along the surface trough boundary northwest of the state. The combination of these features may allow for precipitable water to significantly increase and provide enough instability to allow for development of heavier showers and the potential for a few thunderstorms, especially over the western half of the state. The focus of this potential heavy rain will depend on where the surface trough sets up in relation to the islands and the strength of the resulting winds. Inconsistency between and within the models are keeping confidence in the sensible weather details relatively low for this event at this time, but the situation bears close monitoring over the next few days.
During the second half of next week, the surface trough and low may move far west of the state, allowing a strong surface ridge to build in from the east. This could bring a return breezy to strong trades along with a more stable tradewind shower pattern.

Aviation

Trade winds will gradually ease into the moderate to breezy category today as the surface ridge continues to push off to the northeast and a front approaches from the northwest. Low clouds and showers will favor windward and mauka areas, bringing periods of MVFR conditions, especially during the overnight to morning hours. Otherwise, VFR conditions should prevail.
AIRMET Sierra for tempo mountain obscuration is in effect for windward portions of the state and is expected to be needed through the morning hours.

Marine

High pressure northeast of the state continues to weaken and slowly move northeast as fresh to locally strong trade winds will continue today. Trades look to gradually ease through the rest of the weekend and into early next week as the surface ridge weakens north of the state. A Small Craft Advisory (SCA) is in effect for the typically windier waters of Maui County and the Big Island through tonight. It is likely trade winds will drop just below SCA criteria on Sunday.
Beyond Monday, there remains some uncertainty in the forecast as a strong ~1050 mb high becomes established north of the state. Although typically we would anticipate strong to gale force trade winds, guidance suggests a surface trough building to the northwest between the high and the coastal waters setting up the potential for moderate southeast winds over Kauai and Oahu waters, and fresh to strong southeast winds over Maui County and Big island waters. Inconsistencies in the models are resulting in the unusual degree of uncertainty regarding the forecast for the middle of next week, so changes over the next several days are possible as the details become more clear.
Surf along exposed north and west facing shores will remain small through early next week, with mainly overlapping small medium period northwest swells moving through. An upward trend is possible beginning Tuesday as a potential moderate sized, short- to medium- period north swell arrives, though confidence for this set up remains low at this time.
Surf along east facing shores will remain rough and choppy due to the strong trades impacting the area locally and upstream today before slowly easing on Sunday. Similar to north facing shores, an upward trend is possible by midweek depending on how the scenario evolves, particularly for shores exposed to north to northeast swells.
Surf along south facing shores will remain small for the next several days. By late next week/weekend, a small medium-period southeast swell cannot be ruled out.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov