Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Partly sunny with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 84 near the shore to around 72 above 3000 feet. Southeast winds 10 to 15 mph shifting to the south in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows around 73 near the shore to around 67 above 3000 feet. Light winds. Chance of rain 60 percent.

Saturday: Mostly sunny with scattered showers and slight chance of thunderstorms. Highs around 84 near the shore to around 72 above 3000 feet. Light winds. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 81. South winds up to 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows around 73. Light winds. Chance of rain 60 percent.

Saturday: Partly sunny in the morning then becoming mostly sunny. Scattered showers and slight chance of thunderstorms. Highs around 81. Light winds becoming east around 10 mph in the afternoon. Chance of rain 50 percent.

Kaua’i Mountains

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 71 to 78 in the valleys to around 62 above 4000 feet. South winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 66 to 71 in the valleys to around 62 above 4000 feet. Light winds. Chance of rain 60 percent.

Saturday: Partly sunny with numerous showers and slight chance of thunderstorms. Highs 71 to 78 in the valleys to around 62 above 4000 feet. Light winds. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 83. Southeast winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 68 to 74. Light winds. Chance of rain 60 percent.

Saturday: Partly sunny with numerous showers and slight chance of thunderstorms. Highs 74 to 83. Light winds. Chance of rain 70 percent.

East Kaua’i

Today: Mostly cloudy with numerous showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 74 to 82. South winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers and slight chance of thunderstorms. Lows 64 to 75. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Saturday: Partly sunny with scattered showers and slight chance of thunderstorms. Highs 74 to 82. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A kona low west of the islands will bring a continued threat for heavy rain and flooding along with isolated thunderstorms today. Conditions will gradually improve over the weekend with stable trade wind weather expected for the first half of next week.

Discussion

Currently at the surface, a kona low is located around 425 miles west-northwest of Kauai, while a 10 mb high is centered around 1500 miles northeast of Honolulu. A general southeast to south flow prevails across the islands although convection continues to disrupt the wind fields early this morning. Infrared satellite imagery shows mostly cloudy conditions across the state. Radar imagery shows numerous showers and a few thunderstorms moving through Oahu, with limited shower activity across the other islands at the moment. Main short term focus revolves around heavy rain potential and thunderstorms.
The kona low will gradually break down during the next 24 hours or so, weakening into a surface trough by daybreak Saturday. Before it breaks down however, south to southeast boundary layer flow will continue to pump deeper moisture northward into the islands with the upper low and jet forcing continuing to provide forcing for ascent. This will keep the threat for heavy rain and thunderstorms in the forecast, particularly over the western end of the state. We will keep the Flood Watch in effect through this afternoon for all Hawaiian Islands, although the threat for additional heavy rainfall over the Big Island appears to be diminishing.
The unstable airmass will linger over the islands through Saturday with thunderstorms remaining possible across the entire state. More stable weather will then build into the islands on Sunday as trade winds begin to return. The trades will strengthen early next week, with stable trade wind weather prevailing through the middle of the week. The trades may ease late next week as a new front approaches from the west.

Aviation

Deep tropical moisture pooling northward over the state due to the kona low to our west will keep the threat in place for periods of heavy rainfall and thunderstorms today. A band of showers with embedded thunderstorms that has developed overnight will likely continue to impact the western end of the state through much of the day. Expect periods with IFR and MVFR CIGS/VSBYS in the heavier showers moving through. Conditions have improved over the eastern end of the state, which should persist today.
Aside from turbulence and icing associated with any TS that develops, AIRMET for mid-level turb will continue due to wind shear in the 100-FL200 layer. Light icing in layered clouds has also been reported between 120-FL220. AIRMET Sierra for mountain obscuration will persist over some areas, especially over the western end of the state where the band of showers is.

Marine

A kona low west-northwest of the Hawaiian Islands will continue to produce southeast to south winds today with bands of showers, heavy at times, and thunderstorms developing across the region. The kona low will weaken this weekend as the ridge builds in north of the islands. Expect gentle to fresh trade winds spreading across the region from Saturday to Sunday, strengthening to fresh to strong trade winds from Monday onward. A Small Craft Advisory (SCA) remains in effect through today for most coastal waters surrounding Maui and the Big Island. This SCA will likely be cancelled by tonight as wind speeds decrease below advisory thresholds.
The recent small to moderate, medium period northwest (320 degree) swell will gradually decline through Saturday. The next moderate size, longer period northwest (320 degree) swell will arrive and begin to fill in Saturday afternoon and evening. This swell will peak surf to near High Surf Advisory (HSA) heights by Sunday, then slowly subside Monday. A reinforcing north northwest (330-340 degree) swell arriving by Monday night and may lift surf heights well above HSA thresholds and approach High Surf Warning levels on Tuesday and Wednesday.
Expect the short period wind wave chop to persist along south facing shores. Small surf continues along south facing shores with small background south swell pulses next week Monday and Thursday. Strengthening trades through next week will build surf heights along east facing shores.

HFO Watches/Warnings/Advisories

Flood Watch through this afternoon for all Hawaii islands,
Small Craft Advisory until 6 PM HST this evening for Maui County Windward Waters, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov