Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs around 82 near the shore to around 71 above 3000 feet. Southeast winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 69 near the shore to around 60 above 3000 feet. Southeast winds up to 15 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers and slight chance of thunderstorms. Highs around 82 near the shore to around 71 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

South Kaua’i

Today: Mostly cloudy. Showers likely in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 82. South winds around 10 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 68. Light winds. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers and slight chance of thunderstorms. Highs 79 to 84. East winds up to 10 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Cloudy and breezy. Showers likely in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs 75 to 81 in the valleys to around 65 above 4000 feet. South winds up to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Showers likely and slight chance of thunderstorms in the evening, then scattered showers and slight chance of thunderstorms after midnight. Lows 62 to 67 in the valleys to around 57 above 4000 feet. South winds up to 10 mph in the evening becoming light. Chance of rain 60 percent.

Friday: Mostly cloudy with showers likely and slight chance of thunderstorms. Highs 74 to 79 in the valleys to around 64 above 4000 feet. Southeast winds up to 10 mph. Chance of rain 70 percent.

North Kaua’i

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 74 to 83. South winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 63 to 70. South winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Highs 74 to 83. Southeast winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Mostly cloudy. Scattered showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs 73 to 83. South winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 62 to 72. Southwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers and slight chance of thunderstorms. Highs 73 to 83. East winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Light to moderate southeast winds will prevail over the islands today. Showers will generally favor southeast facing slopes and coasts, but lingering instability and moisture near Kauai will produce greater shower chances and isolated thunderstorms over the western end of the state for the next couple of days. Thunderstorms also cannot be ruled out over interior Big Island slopes this afternoon. Winds will remain southeasterly through the weekend, then return to a more easterly direction early next week.

Discussion

This morning, a low pressure system remains situated to the northwest of the islands in the vicinity of 30N170W with a surface trough extending to just northwest of Kauai. The surface low is supported by a deep upper low that is producing a broad area of cyclonic flow aloft.
Overnight, thunderstorm activity has diminished across the western end of the state as forcing has weakened. The 12z observed sounding from Lihue shows that there is still instability in the area, but there have been notable drops in 0-6km bulk shear and mid-level relative humidity since the 00z sounding yesterday afternoon. Latest satellite imagery shows that any thunderstorm activity is occurring well away from the state early this morning, both to the far north and far southwest. Rainfall over the Garden Isle has also been minimal overnight with gauges reporting 6 hour totals less than 0.10 inches at most locations as of 12z. Since the axis of highest rainfall potential and convection has shifted away from the state and is expected to remain to the north throughout the day, the Flood Watch that was previously in effect for Niihau and Kauai has been cancelled with this morning's forecast updates.
Meanwhile, light to moderate southeasterly surface flow prevails over the islands. Winds aloft have decreased, and observed wind speeds have dropped below advisory criteria at the Big Island summits. Summit winds will continue to weaken throughout the morning, so the Wind Advisory that was in effect has now been cancelled.
For the central and eastern islands, isolated to scattered light showers embedded within this southeast flow are favoring southeast-facing slopes and coasts. The 12z Hilo sounding shows much more stable air than at Lihue, a strong inversion around 7,000 feet, and drier air aloft resulting in overall drier conditions across the eastern end of the state. Of note, convergent surface flow near Molokai has begun to produce a line of showers as a result of a plume effect, but this activity has remained over the water thus far.
Southeast surface flow will continue for the next several days as the low to the northwest rotates cyclonically through Friday but remains in the same general location. Locally breezy wind speeds are expected around Maui County and the Big Island with light to moderate wind speeds elsewhere. Increased stability will introduce drier conditions across most of the islands, though lingering moisture around Kauai will contribute to increased shower coverage there. Additionally, with ample instability also lingering near Kauai and its adjacent waters, slight chances for thunderstorms were added into the forecast for the next few days over the western end of the state. Isolated thunder produced by afternoon sea breezes coinciding with daytime heating also cannot be ruled out over the Big Island slopes this afternoon, though confidence in this occurring today is less than it has been the previous couple of days.
Models continue to show an upper trough forming over or near the islands early next week. This scenario would increase in showers once again across the state by late Sunday into Monday as a broad surface high far northeast of the state becomes re- established and trade winds return to a more typical easterly direction.

Aviation

A low pressure trough northwest of the state will continue to bring unsettled weather to areas mainly west of Oahu today. A relatively moist southeasterly flow will help to generate scattered showers along windward and eastern portions of the remaining islands. Weak instability aloft, combined with diurnal heating, may spark a couple of thunderstorms this afternoon over Kauai and leeward slopes of the Big Island. MVFR ceilings and visibility will likely accompany any of the more robust shower or thunderstorm activity.
No AIRMETS remain in effect.

Marine

A trough of low pressure will linger west of the state during the next couple days, then shift slowly westward over the weekend into early next week. This will lead to a slow and gradual return of trade winds from east to west across the marine area, with the strongest winds remaining over the eastern end of the state. A Small Craft Advisory (SCA) remains in effect for all waters surrounding the Big Island through 6 PM this evening, and may need to be extended for some of these waters later today.
A small pulse from the northwest (320 degrees) will build this morning, peak this afternoon into tonight, then slowly decline through Saturday. A small northeast swell is expected to fill in Friday into Saturday and decline on Sunday. Otherwise, very little energy is expected from the North Pacific through late next week.
Fresh trades upstream of the state will continue to produce small surf along east facing shores during the next 7 days. Small background energy from the southwest, south and southeast will continue to produce small surf along south facing shores for the foreseeable future.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov