Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny with scattered showers and isolated thunderstorms. Highs around 84 near the shore to around 74 above 3000 feet. South winds up to 10 mph. Chance of rain 50 percent.

Tonight: Cloudy with scattered showers and isolated thunderstorms. Lows 67 to 72 near the shore to around 58 above 3000 feet. Southeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

South Kaua’i

Today: Mostly sunny with isolated showers and thunderstorms in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Highs around 82. Southeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Cloudy with scattered showers and isolated thunderstorms. Lows 65 to 71. Southeast winds around 10 mph. Chance of rain 50 percent.

Tuesday: Cloudy with scattered showers and isolated thunderstorms. Highs around 82. Southeast winds up to 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers and isolated thunderstorms. Highs around 77 in the valleys to around 66 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Cloudy with numerous showers and isolated thunderstorms. Lows around 61 in the valleys to around 53 above 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Tuesday: Cloudy and breezy. Numerous showers and isolated thunderstorms in the morning, then showers and isolated thunderstorms in the afternoon. Highs around 77 in the valleys to around 66 above 4000 feet. Southeast winds 10 to 20 mph. Chance of rain 80 percent.

North Kaua’i

Today: Partly sunny with scattered showers and isolated thunderstorms. Highs 77 to 83. Light winds becoming east around 10 mph in the afternoon. Chance of rain 40 percent.

Tonight: Cloudy with scattered showers and isolated thunderstorms. Lows 61 to 70. Light winds becoming southeast around 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Cloudy. Scattered showers and isolated thunderstorms in the morning, then numerous showers and isolated thunderstorms in the afternoon. Highs 77 to 83. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly sunny with isolated showers and thunderstorms in the morning, then partly sunny with scattered showers and isolated thunderstorms in the afternoon. Highs 75 to 81. Southeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Cloudy with scattered showers and isolated thunderstorms. Lows 59 to 72. Light winds becoming south around 10 mph after midnight. Chance of rain 50 percent.

Tuesday: Cloudy with scattered showers and isolated thunderstorms. Highs 75 to 81. South winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A weakening cold front has stalled out several hundred miles northwest of Kauai this morning. Expect light to moderate east to southeast winds to blow across the state today with increasing shower trends over island interiors. By Tuesday a deep cut off low develops far northwest of the state with wind directions veering from a more southerly direction over the western islands, and more stable southeasterly winds blowing over the eastern half of the state. Expect increasing unstable shower trends and thunderstorms from Kauai to Oahu from Tuesday to Thursday. More typical easterly trade winds will spread from east to west across the region from Friday through next weekend.

Discussion

A weakening cold front has stalled roughly 300 miles northwest of Kauai this morning. The linear convergence band that produced heavy showers and thunderstorms just west of Kauai yesterday has diminished and lifted north. Upper air soundings from 2 AM HST this morning at Lihue and Hilo show temperature inversion heights ranging from 5,000 to 8,000 feet respectively. Expect scattered shower activity over most islands today. Increasing instability will continue to lift these inversion heights over the next 24 hours with rising shower coverage trends.
Short range model guidance continues to show a weakening cold front stalled out west of the Hawaiian Islands today with east to southeast winds interacting with island sea breezes during the afternoon hours. Low level convergence between these wind patterns and surface heating will build cloud heights during the daytime hours and increase shower trends into the afternoon and early evening time periods. By Tuesday, a cut off low will deepen as it drifts south, setting up roughly 900 miles northwest of Kauai. This deepening low will weaken the high pressure ridge north of the islands and induce southerly winds for the western islands of Kauai and Oahu from Tuesday through Thursday. Unstable tropical moisture will be drawn up over the western half of the state during this time period with a passing upper level trough on Wednesday that will combine forces to increase rainfall and thunderstorm trends over both islands. Maui County and the Big Island will remain in a more stable southeasterly wind pattern. One exception to this forecast will be lingering chances for isolated thunderstorms each afternoon over the Big Island triggered by strong surface heating above the trade wind inversion and sea breeze moisture advection.
Long range forecast guidance continues to show this deep cut off low far northwest of the state will drift northward from Thursday onward. This change in location will allow the subtropical ridge to strengthen and build back in north of the Hawaiian Islands, allowing a transition back to more typical easterly trade winds from Friday through the upcoming weekend. Expect periods of windward and mountain showers over each island, favoring the overnight to early morning hours. Long range weather models are hinting at a week upper level trough developing near the islands by Saturday, which could enhance trade wind shower activity.

Aviation

Early this morning, a weakening frontal boundary lies northwest of Kauai with a surface ridge far northeast of the islands. This is resulting in light southeasterly background flow across the state. Cloud cover has significantly diminished over Kauai and Oahu overnight, so the AIRMET Sierra for tempo mountain obscuration across these islands has been cancelled. Meanwhile, showers and low clouds continue to impact eastern sections of Maui and the Big Island, where AIRMET Sierra remains in effect.
Light to moderate winds will prevail throughout the day today, which will allow for sea breezes to increase cloud cover and showers over island interiors during the afternoon. Thunderstorms or locally heavier showers cannot be ruled out over Kauai today, where greater instability will be located closer to the stalled frontal boundary to the northwest. Isolated thunderstorms will also be possible over the Big Island this afternoon. Otherwise, VFR flight conditions are expected to prevail.

Marine

The pressure gradient produced by a surface high located off the U.S. West Coast, along with an approaching front from the west, will result in moderate southeast winds. Low pressure northwest of the islands is lifting north with its trailing front just on the fringe of our far western offshore waters this morning. Little eastern movement of this surface low, with Northwest Pacific energy diving down and deepening the upper trough just east of the Dateline, will stall the surface boundary in the vicinity of the west offshore waters. This pattern will support areawide moderate to locally fresh southeast winds, possibly transitioning to light south or variable breezes around Kauai, through the remainder of the week. Convergence ahead of the boundary will keep the threat for western water isolated to scattered thunderstorms alive through mid week. A mid to late week Small Craft Advisory may be required for the notoriously windier zones around Maui and Big Island.
The arrival of a small, medium period northwest swell (310 degree) late yesterday has resulted in slight boost in surf along the smaller island north and west-facing shorelines. This waist to near head high surf along many north-facing shores will continue through the morning before the swell begins to slowly fade from this afternoon through Tuesday. A series of smaller northwest to north swells (310-320 degree) are expected to pass through during the second half of the week. Elevated wind wave chop along eastern exposures generated from a large source region of moderate trades upstream of the islands will persist the next few days. Very small early to mid week bumps along southwest and southeast shores from either background energy moving in from the Southern Hemisphere or from trade belt wind swell, respectively, will keep south-facing shore surf slightly under waist high, at best.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov