Photo Credit: Brendan Stephen

West Kaua’i

Today: Mostly sunny. Highs 82 to 87 near the shore to around 71 above 3000 feet. Northeast winds up to 15 mph.

Tonight: Partly cloudy with isolated showers. Lows 65 to 71 near the shore to around 58 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the morning. Highs 82 to 87 near the shore to around 72 above 3000 feet. East winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Breezy. Isolated showers in the morning. Highs 76 to 85. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 69. Northeast winds 15 to 20 mph. Chance of rain 40 percent.

Sunday: Mostly sunny with isolated showers. Highs 76 to 84. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 71 to 82 in the valleys to 60 to 65 above 4000 feet. East winds up to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 65 in the valleys to around 56 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 71 to 82 in the valleys to around 62 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs 74 to 84. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 62 to 70. East winds up to 15 mph. Chance of rain 40 percent.

Sunday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 75 to 84. East winds up to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs 71 to 83. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 63 to 73. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 71 to 82. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A relatively dry moderate to breezy trade wind pattern will continue through Sunday as a high pressure ridge lingers north of the Hawaiian Islands. Light winds are expected through the first half of next week as a cold frontal system approaches from the northwest. This front may drift into the western islands by Thursday, potentially increasing shower trends along the frontal cloud band.

Discussion

The satellite picture this morning shows a fairly stable cloud pattern with pillow shaped clouds moving in on the easterly trade winds. Only brief periods of passing showers are forecast today. A short wave trough in the upper levels is currently approaching Hawaii from the northwest, this upper trough will move over the islands later today briefly increasing local shower trends through Sunday.
The subtropical ridge at the surface will remain locked in place just north of the island chain, keeping moderate to breezy trade winds in the forecast into Sunday. The upper level portion of this subtropical ridge stacks back towards the equator, positioned directly over the Hawaiian Islands. Strong subsidence (downward vertical motions) under this upper level ridge will produce stable conditions, capping cloud heights and limiting shower activity for most days into Wednesday. One wrinkle to this large scale forecast is the approaching upper level short wave trough drifting into the Hawaiian region starting later this afternoon through Sunday. Upper level divergence ahead of this trough will counteract some of the large scale subsidence, decreasing atmospheric stability and producing a brief increase in island shower activity. The best chances for showers are forecast over windward and mountain areas favoring tonight through Sunday mornings.
Two weakening cold fronts will approach the Hawaiian Islands from the northwest from Monday through Wednesday, cold air moving in behind these troughs will help break down the ridge north of the state, and producing variable winds with a stable land and sea breeze regime over all islands. The second cold front will weaken on final approach to the western half of the state. The current timing of the frontal band continues to be based on a model consensus as follows: The frontal band will potentially reach Kauai by Thursday morning, Oahu by Thursday afternoon, and the island of Maui from Thursday night into Friday morning. Less certain if the Big Island will see any noticeable rainfall impacts from this system. Expect a brief period of widespread clouds and showers as the frontal band passes through each island. Rainfall total will likely fall on the low side and be limited to areas along the frontal cloud band. Light to moderate trade winds will then build back into the region as the front passes through each island. The frontal cloud band will then break apart, sending a few pockets of unstable clouds and brief showers into some of our windward mountain slopes lasting into next Saturday morning.
A few uncertainties remain in the track and timing of this next frontal system. Operational forecast guidance between the American (GFS) and the European (ECMWF) models has improved over the past 24 hours. That said, the forward motion on these weak frontal band intrusions are notorious for stalling out at some point and then dissipating as the trade winds build back into the region. This means the frontal cloud band could stall out over any island, limiting the eastward movement of enhanced shower activity. Stay tuned.

Aviation

Breezy trade winds will continue today and tonight. Some brief MVFR cigs/vsbys will be possible in windward areas at times, mainly during the early morning and overnight hours. VFR conditions are expected in leeward areas.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the terrain of all islands and will likely remain in place though the day. AIRMET Tango may also be required for moderate upper level turbulence over the western half of the state tonight.

Marine

Fresh to strong easterly trade winds will prevail through Sunday, easing Sunday night into early next week as the ridge weakens and shifts south due to a series of cold fronts passing to the north. The Small Craft Advisory has been extended through the weekend over the the windier channels and waters around Maui County and the Big Island. Starting late Sunday night, the trades will quickly ease, likely enough for overnight and early morning land breezes and daytime sea breezes. This pattern will persist through the first half of next week as the background flow shifts southeast Sunday night into Monday, then south to southwest Tuesday through midweek as a cold front approaches.
Surf along exposed north and west-facing shores will gradually ease over the weekend as the swell that filled in Friday moves out. By Tuesday, surf will begin to rise again, with a significant upward trend anticipated through the second half of next week. This increase will be driven by a decent-sized fetch developing over the far northwest Pacific, near the Aleutians from the Date Line to the Kuril Islands. Heights could exceed warning-levels late next week if conditions evolve as projected.
Surf along east-facing shores will remain rough through the weekend but will gradually decrease late Sunday and into much of next week as the trade winds diminish.
Surf along south-facing shores will remain near seasonal averages, influenced by a mix of short-period southeast swells and occasional longer-period background south-southwest swells.
Peak monthly tides combined with water levels running higher than predicted could lead to minor coastal flooding issues for vulnerable low-lying coastal areas. The best chance for these impacts will occur during the early morning high tides between midnight and daybreak through the weekend.

Fire weather

Critical fire weather conditions are not expected for the next seven days. Relatively dry conditions will persist statewide through Wednesday. A weakening cold front may drift into the western islands from Thursday to Friday, briefly increasing shower activity especially over the western half of the state.

HFO Watches/Warnings/Advisories

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

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