Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny with scattered showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 83 near the shore to around 71 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers and slight chance of thunderstorms. Lows around 67 near the shore to around 56 above 3000 feet. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Highs around 82 near the shore to around 70 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 80. East winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers and slight chance of thunderstorms. Lows 63 to 68. Light winds. Chance of rain 50 percent.

Tuesday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Highs around 79. Southeast winds up to 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy. Numerous showers in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 70 to 77 in the valleys to around 61 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms early in the evening, then partly cloudy with scattered showers and slight chance of thunderstorms in the late evening and overnight. Lows 56 to 61 in the valleys to around 49 above 4000 feet. Light winds. Chance of rain 60 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 69 to 76 in the valleys to around 60 above 4000 feet. Light winds becoming southeast up to 10 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny. Numerous showers in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 73 to 83. Southeast winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms early in the evening, then partly cloudy with scattered showers and slight chance of thunderstorms in the late evening and overnight. Lows 59 to 67. Southeast winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 72 to 82. Light winds becoming south up to 10 mph in the afternoon. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 73 to 82. Southeast winds up to 10 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers and slight chance of thunderstorms. Lows 56 to 69. East winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Tuesday: Mostly cloudy. Scattered showers and slight chance of thunderstorms in the morning, then numerous showers and slight chance of thunderstorms in the afternoon. Highs 72 to 81. Southeast winds up to 10 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will ease today, allowing for land and sea breezes across the western islands through midweek, while moderate east-southeast winds remain over the eastern end of the state. A band of moisture drifting across the islands will maintain some showers today, particularly over the western islands. A closed low aloft could bring some unsettled weather with locally heavy rain and thunderstorms to portions of the state tonight through early Wednesday. Breezy trade winds along with more typical windward and mauka showers will become reestablished over the state late Wednesday through the weekend.

Discussion

Currently at the surface, a 1032 mb high is centered around 1500 miles north-northeast of Honolulu, and a cold front is located roughly 750 miles west-northwest of Kauai. The gradient has only weakened slightly since last evening, with moderate trade winds persisting in unsheltered areas early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions across the state. Radar imagery shows scattered to numerous showers moving into windward areas on the smaller islands, with isolated windward showers on the Big Island. Dry conditions prevail in most leeward areas. Main short term focus revolves around rain chances and trade wind trends during the next couple days.
The trades will ease today over the western islands as a cold front approaches from the northwest, while moderate to locally breezy trades persist over the eastern end of the state. The front will then weaken into a trough west of the islands tonight through Tuesday night, while the high to the northeast weakens. Winds will become light and variable over the western islands during this time, with land and sea breezes dominant. Over the eastern end of the state moderate east-southeast winds will prevail. The trough west of the state will dampen out Wednesday through Thursday as high pressure builds north of the islands, bringing a return of moderate to locally breezy trade winds. The high will then settle southeastward Thursday night through next weekend, with breezy to locally windy trades expected.
As for the remaining weather details, a broken band of deeper moisture over the smaller islands will shift westward today. Showers will favor windward areas this morning, and interior and leeward areas this afternoon. Shower coverage will remain highest over the western islands where precipitable water values remain the highest. A somewhat unstable airmass will bring a slight chance of thunderstorms to Kauai and the Big Island this afternoon.
The forecast becomes more interesting tonight through the middle of the week, as a deep upper level trough closes off a southward moving mid/upper level low west of the state. Model guidance continues to show the potential for some deep moisture advecting northward on the southeasterly boundary layer flow into the islands during this time. There remains the potential for some heavy rainfall and thunderstorms, particularly over the western end of the island chain. A flood watch may eventually be needed for portions of the state Tuesday through early Wednesday, but confidence in a widespread heavy rain and flooding threat remains too low to warrant the issuance of a watch at this time.
Both the GFS and ECMWF remain in good agreement showing a return to more typical trade wind weather across the island chain beginning Wednesday afternoon and continuing through the weekend.

Aviation

High pressure far northeast of the islands will generate moderate trades this morning across the region. However, an approaching weather disturbance, currently residing northwest of Kauai, will act to veer flow east southeasterly later today. This flow pattern will advect in an area of enhanced moisture and allow for scattered showers over most islands this afternoon. Expect a slight chance of thunderstorms over Kauai and the Big Island due to the combination of diurnal heating and weak instability aloft. Some of this activity may produce MVFR ceilings and visibility at times.
No AIRMETs are currently in effect.

Marine

Trade winds will remain in the moderate range today across the region. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around Maui and the Big Island through this afternoon. Wind speeds may weaken below SCA levels from later tonight through Wednesday as another cold front approaches the islands from the northwest and winds veer from the southeast direction. Moderate to locally strong trade winds will return from Thursday into next weekend.
The next northwest swell is currently building in at Buoys 51101 and 51001 northwest of Kauai. Surf along the north and west facing shores will build today as this medium sized long period northwest (320 degree) swell spreads southeastward across the islands, peaking on Tuesday, then gradually lowering Wednesday through Friday. Expect a large increase to north and west shore surf heights through Wednesday, approaching High Surf Advisory (HSA) levels as the swell energy peaks on Tuesday.
Small surf along the south facing shores will slowly increase this week as two small long period south-southwest (200-210 degree) and south (180-190 degree) swells build into the region. This southern source swell energy will peak on Wednesday and Thursday near HSA levels. Surf heights along south facing shores will then gradually lower from Friday into the weekend.
Small surf along east facing shores will trend up through the week as trades strengthen east of the islands. East shore surf will return to seasonal levels Thursday through the weekend.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov