Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs around 90 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows around 73 near the shore to around 64 above 3000 feet. East winds around 10 mph.

Sunday: Mostly sunny. Highs 87 to 93 near the shore to around 78 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 85 to 92. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 74. East winds around 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny in the afternoon. Highs 85 to 92. East winds around 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 76 to 87 in the valleys to around 68 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 67 to 72 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 77 to 86 in the valleys to around 69 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Partly sunny with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 79 to 90. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 67 to 75. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Mostly sunny with isolated showers. Highs 79 to 90. East winds 10 to 15 mph. Chance of rain 20 percent.

East Kaua’i

Today: Mostly cloudy with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 76 to 88. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows 67 to 78. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 77 to 89. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will deliver passing clouds and showers this weekend, mainly to windward and mauka areas. Weak instability associated with a low aloft may bring an isolated thunderstorm today. Light winds and mostly dry weather are expected next week, with limited showers focused over interior areas during the afternoons.

Discussion

N Pacific surface analysis continues to feature a slow-moving trade- wind-supporting high centered about 1200 miles NNE of the islands, and a pair of strong extratropical lows to the distant N and NW of the area. A fairly typical and relatively benign trade wind weather pattern remains in place this morning, although sounding data indicates that a low aloft several hundred miles NW of Kauai has destabilized the island atmosphere, with a weak/absent subsidence inversion noted in the Lihue and Hilo soundings respectively. Prevailing moisture depth extends as high as 15 kft over the Big Island, and is up to 10 kft near Kauai, but pockets of deeper moisture are moving W over the area. Thin high clouds have diminished somewhat overnight, with radar showing isolated to scattered showers.
Little overall change to the current weather regime is anticipated into Monday, with bigger changes expected thereafter as the trade wind flow breaks down. Until then, low-level moisture will arrive on a moderate to locally breezy trade wind flow that will be gustiest in the afternoons. An area of increased PWAT today will ensure that windward areas receive some showers, while also bringing a slight chance of thunderstorms (CB). The ongoing forecast indicates the potential for isolated CB over the Big Island slopes this afternoon, and over waters around Kauai and Oahu, and this forecast remains unchanged from yesterday.
A trend toward decreasing PWAT is expected Sunday, although mid- level instability will likely linger until Monday. From Monday onward, trade wind speeds will diminish as the low to the distant NW moves E and weakens the surface ridge N of the islands. The associated high will move E, and as a weakening front associated with the low draws closer to the islands, the surface ridge will move over the islands for most of next week.
As a mid-level ridge builds over the area from the W, a mostly dry, light wind pattern is anticipated. Some interior and upslope clouds may develop in response to daytime heating, but little in the way of rainfall is expected, with mostly clear nights and mornings. Depending on the evolution of the parent low N of the islands, the weakening front may move over Kauai over the second half of the week, with deterministic ECMWF guidance continuing this theme over the past 24 hours. Thereafter, significant differences are noted in the reliable guidance, with GFS favoring a weaker low and continued dry with light winds, while ECMWF favors a stronger low driving weak fronts across the area, with the potential for light to moderate NW to N winds. Either way, the recent persistent trade wind flow will have an extended absence.

Aviation

Surface high pressure well northeast of the islands will allow moderate to occasionally breezy trades to persist through the remainder of today. Thus, expect scattered showers to mainly affect windward locations with isolated activity elsewhere. There will be brief periods of MVFR ceilings and visibility associated with any heavier showers.
AIRMET Tango remains in effect for tempo moderate turbulence below 9000 feet for areas downwind (south through west) of island terrain. This AIRMET will likely remain in effect through the weekend before conditions improve early next week.

Marine

The Small Craft Advisory for the windier waters surrounding Maui County and Big Island has been extended through Sunday afternoon. The impetus to these recently moderate to locally strong easterly trade winds, surface high pressure centered to the northeast of the state creating a tight pressure gradient down across the regional waters, will travel east as a cold front moves into the central North Pacific early next week. This will disrupt the upstream pressure gradient and considerably weaken winds to light and variable by Tuesday. The local offshore and coastal waters will generally experience light to gentle winds, with more localized breezes occurring across nearshore waters, from late Monday on through next weekend.
A pair of northern Pacific systems moving south of the Aleutian Islands and into the Gulf of Alaska the next several days will produce a couple of north to northwest swells that will reach the islands Sunday and fill in Monday and then again Tuesday into Wednesday. This will result in heightened north and west-facing shore surf well into next week. The first near 4 foot, medium period northwest (330 degree) swell is timed to fill in during the day on Sunday. This swell should peak Sunday night and Monday surf to or above head high and then slowly fall through Tuesday. A slightly larger, medium period more northwest-turning-north (310 becoming 350 degree) swell is expected to reach the islands and fill in from late Tuesday through early Thursday. This swell will reinforce these head to over head high surf heights from mid to late week.
East-facing short period wind wave chop will significantly fall next week as east trades disappear and light or gentle breezes become the new wind regime. South-facing shore surf will remain around waist high through early next week. There may be a slight bump in southeast low period swell, mixed into weekend background south swell, that originated from a small fetch region far southeast of the island chain. This may lift surf from chest to near head high along more southeastern exposures from Sunday into mid week.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov