Photo Credit: Braden Jarvis

West Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 84 near the shore to around 74 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy with isolated showers. Lows 64 to 69 near the shore to around 55 above 3000 feet. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 83 near the shore to around 73 above 3000 feet. Light winds. Chance of rain 50 percent.

South Kaua’i

Today: Mostly sunny with scattered showers. Highs around 82. Northeast winds around 10 mph. Chance of rain 40 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 68. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Thursday: Mostly sunny with scattered showers. Highs around 81. East winds up to 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny with scattered showers. Highs around 77 in the valleys to around 66 above 4000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows around 58 in the valleys to around 50 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Thursday: Partly sunny. Scattered showers in the morning, then showers likely in the afternoon. Highs around 76 in the valleys to around 65 above 4000 feet. Light winds. Chance of rain 70 percent.

North Kaua’i

Today: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 77 to 83. East winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 58 to 67. East winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Thursday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs 76 to 82. East winds up to 10 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 75 to 81. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 56 to 69. Northeast winds up to 10 mph in the evening becoming light. Chance of rain 30 percent.

Thursday: Partly sunny with scattered showers. Highs 74 to 80. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate trades will hold over the eastern islands through Thursday, while lighter trades and leeward land and sea breezes prevail over the western islands. Showers will favor windward slopes and coasts at night and interior and leeward areas each afternoon. More unsettled weather with thunderstorms and localized downpours appear in store as a disturbance aloft moves southeastward across the islands Friday and Saturday. Conditions should improve Sunday through early next week, as the most unsettled weather pushes east of the state.

Discussion

Currently at the surface, a cold front is located around 825 miles northwest of Kauai, while a 1032 mb high is centered 2200 miles northeast of Honolulu. The trade winds have eased to moderate levels overnight as the gradient has relaxed a bit. Infrared satellite imagery shows mostly cloudy conditions in most windward areas and partly cloudy skies in most leeward locales. Radar imagery shows scattered showers moving into windward slopes and coasts, with mostly dry conditions in leeward areas. Main forecast concern continues to revolve around the potential for some active and unsettled weather Friday and Saturday.
The cold front to the distant northwest will shift southeastward and closer to the islands during the next couple of days, eventually weakening into a broad trough over the islands on Friday. As a result, the trades will ease during the next few days. Moderate trade winds will hold over the eastern islands today and Thursday, while lighter trades over the western end of the state allow for land and sea breeze development in leeward areas. The trades ease further on Friday, allowing for sea breeze development statewide. The broad trough then appears to gradually dampen out over the weekend, which could allow some light to moderate trade winds to build back over the islands. By early next week, a new approaching cold front will begin to shift the low level boundary layer flow around to the southeast, maintaining moderate easterly trades over the eastern islands, while land and sea breezes become more dominant over the western end of the state.
As for the remaining weather details, a hybrid trade wind pattern should prevail through Thursday. Showers will favor windward and mauka areas overnight and during the morning, then transition over to interior and leeward areas each afternoon into the early evening. As the boundary layer flow becomes light and variable Thursday night, most of the shower activity should remain offshore or close to the islands coasts.
The weather pattern becomes much more interesting Friday through Saturday as an upper level low swings southeastward across the island chain, with broad surface troughing holding over the state. Precipitable water values don't appear all that high, generally holding at or below 1.5 inches over the smaller islands, while reaching as high as 1.7 inches over southeastern sections of the Big Island. As a result, a widespread heavy rain threat doesn't appear all that high, although some downpours will be possible that could bring some minor flooding impacts. We will continue to monitor the latest model trends as the need for a Flood Watch is still not out of the question, particularly over Maui County and the Big Island.
The more concerning threat revolves around the potential for severe thunderstorms. Mid-level 700-500 mb lapse rates reach 7 to 7.5 C/KM as the upper level low pivots southeastward through the islands, while surface based CAPE values increase to between 1000 and 1500 J/KG, and 0-1 KM MUCAPE values reach as high as 2000 J/KG. This in combination with 0-6 KM Bulk Shear values of 25 to 40 knots could lead to some stronger thunderstorms capable of producing hail and strong gusty winds. The one element that seems to be holding back the potential for well organized convection is the lack of a significant surface trigger aside from sea breezes. Nevertheless, we will need to keep a close eye on how this pattern evolves during the next couple days.
The most unstable airmass slides east of the state Saturday night, which should bring a return of a hybrid trade wind pattern featuring windward and mauka showers at night and interior and leeward showers during the afternoon and early evening hours. This pattern appears to generally hold through early next week.

Aviation

Light to moderate trades are expected to persist through tomorrow. Bands of light showers will continue to favor windward and mauka areas, and be most active during the overnight hours. With the lighter flow, sea breezes will develop across wind- protected leeward areas, bringing an increase in interior clouds and isolated showers by the afternoon. Land breezes may also help to clear out cloud cover across leeward areas overnight. Brief MVFR conditions are to be expected in passing showers, otherwise VFR conditions will prevail statewide.
No AIRMETs are in effect at this time, nor are any expected to be needed today.

Marine

Moderate to fresh trade winds will weaken over the next several days as high pressure northeast of the state moves further away and a front approaches the islands from the northwest. The front will weaken into a trough over the islands Friday as wind speeds look to ease and become light to gentle Friday and Saturday with southeast flow over the eastern half and northeast to east flow over the western half of the state. Gentle to locally moderate east to southeast flow looks to trend into the early half of next week across the coastal waters. An upper level low will move across the island chain Friday through Saturday which will increase the chance for heavy showers and potential thunderstorms.
The current northwest swell will continue to decrease to tiny conditions through Thursday followed by a reinforcing short- period north northwest swell Friday into the weekend. Surf along south facing shores will remain steady through today. Forerunners from a larger and longer lived south- southwest swell are subject to arrive later this afternoon. Surf is trending below High Surf Advisory (HSA) criteria but if nearshore buoy observations come in above guidance, surf could reach HSA criteria when the swell peaks Thursday into Friday before declining into the weekend. Surf along east facing shores should remain small as winds remain light through the rest of the week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov