West Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 67 to 72 near the shore to around 59 above 3000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 81 to 86 near the shore to around 72 above 3000 feet. Southeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 69 near the shore to around 59 above 3000 feet. Light winds becoming northeast up to 10 mph after midnight. Chance of rain 50 percent.

South Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 70. Light winds. Chance of rain 20 percent.

Wednesday: Mostly cloudy with scattered showers. Highs 78 to 85. West winds up to 10 mph shifting to the south in the afternoon. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then isolated showers after midnight. Lows around 70. East winds up to 10 mph shifting to the northeast after midnight. Chance of rain 60 percent.

Kaua’i Mountains

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 61 to 67 in the valleys to around 57 above 4000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 72 to 79 in the valleys to around 64 above 4000 feet. Light winds. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 60 to 67 in the valleys to around 56 above 4000 feet. Light winds. Chance of rain 70 percent.

North Kaua’i

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows 62 to 70. Light winds. Chance of rain 20 percent.

Wednesday: Mostly cloudy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 74 to 83. Light winds becoming southeast up to 10 mph in the afternoon. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 62 to 71. Light winds becoming southeast up to 10 mph after midnight. Chance of rain 70 percent.

East Kaua’i

Tonight: Partly cloudy with isolated showers. Lows 62 to 74. Light winds. Chance of rain 20 percent.

Wednesday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 72 to 83. South winds up to 10 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 62 to 74. Light winds. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A stable southeasterly background flow will persist across much of the state into Wednesday, leading a rather dry land and sea breeze pattern from Oahu to Big Island. A weakening front will stall near Kauai, producing increased clouds and higher rainfall chances on the Garden Isle, mainly Wednesday afternoon and evening. Moderate east to southeasterly trade winds will build across the island chain on Thursday, focusing showers over windward and mountain areas.

Discussion

Stable and mostly dry conditions persist under light winds this afternoon. An advancing front over 200 miles northwest of the state is keeping the subtropical ridge near Kauai, resulting in a generally light southeasterly background flow. This is keeping most islands in the downwind wake of the Big Island and is allowing a land and sea breeze pattern to dominate. A ridge aloft is maintaining a somewhat strong inversion around 6,500 feet, while precipitable water remains below seasonal normal. These ingredients continue to produce scant rainfall, even as afternoon sea breezes generate clouds over interior terrain. The southeasterly flow is also carrying some volcanic emissions from recent activity at Kilauea over most islands. While air quality sensors continue to show somewhat low concentrations and there is no significant restriction to visibility, some haze persists.
Wetter conditions may develop on Kauai Wednesday, while much of the state remains under the rather dry land and sea breeze regime. A trough will develop tonight ahead of the above mentioned front over the coastal waters west of Kauai and Niihau. Expect some increase in shower activity along this feature, but little rainfall is expected over land tonight. The front and trough will merge on Wednesday and drift eastward toward Kauai, bringing increased chances for showers on Kauai during the afternoon and evening. Since there will be little upper level support for the weak front and models depict the feature stalling over or just west of Kauai, widespread heavy showers are not likely, though northern slopes and interior sections of the Garden Isle could experience over an inch of rain in the wettest scenario. Chances for rainfall on Kauai will decrease later Wednesday night as the old frontal band retreats westward.
Moderate east to southeast trade winds will strengthen on Thursday, pushing the deeper moisture away from Kauai. Winds could become locally breezy as shower activity along the old frontal band west of Kauai is enhanced by a shortwave aloft. This will help tighten the local pressure gradient and induce the surging east to southeast winds over the state. Conditions will remain stable, and typical moisture will produce showers over east and southeast slopes.
Moderate easterly trade winds and a typical pattern of mainly windward and mauka showers is expected Friday through early next week.

Aviation

Primarily VFR with increasing chances for showers and MVFR ceilings over Kauai on Wednesday in response to a front stalling in the vicinity of the island. Winds east of the front will have a general light background flow veering more southeast to south from Big Island to Kauai. These large scale winds will remain weak enough to allow local land and sea breezes to survive. Overnight light drainage land breezes developing early this evening will transition back to light onshore winds by late Wednesday morning. As the sea breeze or a more southerly flow builds clouds along leeward-facing slopes, localized MVFR ceilings may briefly occur across these interior areas.
No AIRMETs are in effect and none are expected.

Marine

A weak surface ridge will remain over the area and allow light to moderate southeast background flow to continue through tomorrow. This pattern will allow for daytime sea breezes and nighttime land breezes along waters adjacent to the coasts. A cold front, currently around 200 nm northwest of the state, is forecast to approach Kauai on Wednesday. The front will then stall and weaken into a trough by Thursday before retrograding back westward, away from the state. By Thursday through this weekend, a ridge of high pressure strengthening northeast of the region will bring a return of moderate to locally strong easterly trades. A Small Craft Advisory (SCA) will likely be needed for the typical windier zones surrounding Maui and the Big Island. A moderate to large NW swell could also bring seas to SCA criteria (10 feet) Thursday night into Friday. So at this time, a SCA for winds to 25 kt and seas 10 feet or higher look likely by Thursday afternoon.
The current moderate, medium period, northwest swell (310-330) will continue to slowly decrease tonight. A series of northwest to north-northwest (310-340 degree) swells are expected during the second half of the week, with each pulse becoming slightly bigger with each passing day. The first pulse, a medium period northwest swell, will begin to fill in on Wednesday, and generate surf just below advisory levels. A slightly larger and longer period pulse is expected on Thursday out of the northwest followed by a slightly larger northwest on Friday. Surf heights should exceed advisory thresholds Thursday through through Friday, with the peak approaching warning levels late Thursday into Friday.
East shore surf will remain small through Wednesday due to weak winds, then become choppier by Thursday as trade winds increase from Thursday through the weekend. Expect minimal background energy for south facing shores through much of the week.
There is the potential for minor coastal flooding from December 4th to December 6th. Peak monthly tides combined with water levels that are running higher than predicted could lead to minor flooding along the shoreline and in low-lying coastal areas. Coastal flooding is possible around the daily peak tide, which will be during the early morning hours. This could also magnify effects of the expected high surf on coastal areas around the same time frame.

Fire weather

Critical fire weather conditions are not expected this week. Winds will remain light through Wednesday, with higher rainfall chances on Kauai. The inversion will hold at 5000 to 6500 ft through Wednesday, keeping very dry conditions on the upper elevations of the Big Island and Maui. Moderate east to southeast winds will be below the critical fire weather threshold Friday into early next week. Humidity will be near seasonal normal, and the inversion will lift slightly.

HFO Watches/Warnings/Advisories

None.

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