Photo Credit: Brendan Stephen

West Kaua’i

Today: Showers and isolated thunderstorms in the morning, then showers in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. Southwest winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers early in the evening, then numerous showers in the late evening and overnight. Lows 68 to 73 near the shore to around 59 above 3000 feet. West winds up to 10 mph in the evening becoming light. Chance of rain 80 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. Northwest winds up to 10 mph. Chance of rain 60 percent.

South Kaua’i

Today: Showers and isolated thunderstorms in the morning, then showers in the afternoon. Highs around 83. Southwest winds 10 to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers early in the evening, then numerous showers in the late evening and overnight. Lows 68 to 74. West winds 10 to 15 mph. Chance of rain 80 percent.

Tuesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs around 83. Southwest winds up to 10 mph. Chance of rain 60 percent.

Kaua’i Mountains

Today: Showers and isolated thunderstorms in the morning, then showers in the afternoon. Highs 72 to 78 in the valleys to around 67 above 4000 feet. Southwest winds up to 15 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Showers early in the evening, then numerous showers in the late evening and overnight. Lows around 63 in the valleys to around 55 above 4000 feet. Southwest winds up to 15 mph. Chance of rain 80 percent.

Tuesday: Mostly cloudy with numerous showers. Highs 72 to 78 in the valleys to around 67 above 4000 feet. West winds up to 10 mph. Chance of rain 60 percent.

North Kaua’i

Today: Showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Highs 74 to 83. Southeast winds up to 15 mph shifting to the west in the afternoon. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Numerous showers early in the evening, then scattered showers in the late evening and overnight. Lows 63 to 71. Southwest winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 83. West winds up to 10 mph. Chance of rain 60 percent.

East Kaua’i

Today: Breezy. Showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Highs 74 to 84. Southwest winds up to 20 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Numerous showers early in the evening, then scattered showers in the late evening and overnight. Lows 61 to 74. Southwest winds up to 15 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Tuesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 84. South winds up to 10 mph shifting to the east in the afternoon. Chance of rain 60 percent.

Detailed Forecast

Synopsis

Southwest winds will focus showers and a chance of thunderstorms over and around Kauai into Monday. The chance for thunder then shifts to the Big Island Monday through Wednesday afternoons while the central portion of the state remains largely dry. A land and sea breeze pattern returns by late Tuesday.

Discussion

The morning sounding out of Lihue indicated slightly increased boundary layer moisture depth compared to yesterday, around 10kft, as deep layer southwest flow works to moisten the column. Temperatures aloft have also cooled slightly, to around -6C at 500mb, supporting a modest decrease in instability compared to 24 hours ago. At the surface, moist and weakly convergent southwest flow is organizing bands of light to moderate showers mainly in the vicinity of Kauai. Elsewhere, moisture quality and low-level convergence remain too weak to sustain meaningful shower activity. The exception is portions of Leeward Maui County and adjacent waters where terrain interaction has supported pockets of slow- moving showers, especially around Lanai.
By tonight, showers embedded within southwest flow will increase in coverage, particularly within the corridor of deeper moisture around Kauai. The official forecast has been updated to include categorical (80+%) pops for leeward and upslope portions of Kauai for the balance of the overnight period. As showers expand in coverage, veering flow to WSW and eventually W aloft will be ushering in cooler mid-level temperatures to the tune of about -9C at 500mb per the latest GFS. Combined with the steadily increasing depth of cyclonic flow aloft and a gradually deepening moisture field over the western end of the state, pockets of heavy showers and a few thunderstorms are certainly possible as the night progresses. At this time, the flood threat is considered to be minimal due to the overall lack of deep moisture and sufficiently fast southwest flow to keep convective cells moving along. However, given the flow- parallel nature of the resident moisture band, radar will be worth monitoring for potential training cells and localized nuisance type flooding. The remainder of the state (Oahu through the Big Island) will remain largely dry through tonight owing to the lack of deeper moisture and forcing.
Attention for the Monday through Wednesday period shifts toward the Big Island. As forcing wanes through the day Monday, shower coverage and intensity around Kauai will diminish coincident with a plume of deep tropical moisture (PWATs in excess of 2″) becoming established over the eastern end of the state. Mid-level lapse rates will be rather paltry compared to those over Kauai owing to the warm nature of the incoming airmass, but mid-level heating over the high terrain of the Big Island may help locally steepen those lapse rates and contribute to an afternoon heavy rain or thunderstorm threat on Monday afternoon. Gradual stabilization of the island atmosphere will be well underway by Tuesday and Wednesday as the area settles into another land and sea breeze pattern. However, deep moisture and modest elevated instability may be sufficient for a continued heavy rain or thunderstorm threat over interior Big Island on one or both afternoons. The official forecast handles this potential well and no changes are needed. With few exceptions, winds are modeled to remain light in favor of a sea breeze pattern through the extended portion of the forecast period.

Aviation

South to southwest winds continue through Monday as the cold front approaches the state. Weak instability aloft and enhanced low level moisture will lead to enhanced shower activity over Kauai, with isolated thunderstorms possible over the waters west of Kauai through this evening. Otherwise, isolated showers will continue across the state tonight. Will see another uptick in showers and a slim chance for isolated thunderstorms Monday afternoon over the Big Island as another surge of moisture moves across the region. Expect periods of MVFR or lower conditions across mainly Kauai tonight, with VFR prevailing elsewhere.
No AIRMETs are currently in effect, but AIRMET Sierra for mountain obscurations may become necessary later today over portions of Kauai.

Marine

Expect light southerly winds ahead of an approaching cold front tonight and Monday. The front will stall near Kauai Monday and a slight chance of thunderstorms remains in the forecast along the boundary. The front weakens in place Tuesday and with variable winds through the rest of the work week as another front approaches from the northwest.
A new northwest (320 degree) swell will build in late tonight into Tuesday, then slowly lower through the rest of the week. Surf heights along both west and north facing shores are forecast to peak around the High Surf Advisory threshold on Monday night and Tuesday.
Background surf expected along south facing shores until Monday morning when a long period south swell moves in and lingers through the rest of the week. Surf heights along east facing shores will remain small through much of next week due to light winds across the Hawaii Region.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov