West Kaua’i

Today: Mostly cloudy with scattered showers and isolated thunderstorms. Highs 82 to 87 near the shore to around 73 above 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 69 to 74 near the shore to around 61 above 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 84 to 90 near the shore to around 76 above 3000 feet. East winds up to 10 mph. Chance of rain 40 percent.

South Kaua’i

Today: Partly sunny with scattered showers and isolated thunderstorms. Highs 79 to 87. Northeast winds around 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 72. East winds around 10 mph. Chance of rain 50 percent.

Monday: Partly sunny with scattered showers. Highs 81 to 88. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Today: Mostly cloudy with numerous showers and isolated thunderstorms. Highs 72 to 79 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows 63 to 69 in the valleys to around 59 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Monday: Mostly cloudy with scattered showers. Highs 75 to 83 in the valleys to around 66 above 4000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly cloudy with numerous showers and isolated thunderstorms. Highs 74 to 84. East winds around 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 73. East winds 10 to 15 mph. Chance of rain 60 percent.

Monday: Partly sunny with scattered showers. Highs 77 to 87. East winds 10 to 15 mph. Chance of rain 40 percent.

East Kaua’i

Today: Mostly cloudy. Numerous showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Highs 72 to 84. East winds around 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 64 to 76. East winds 10 to 15 mph. Chance of rain 60 percent.

Monday: Mostly cloudy with scattered showers. Highs 74 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A rapidly weakening cold front approaches the Hawaiian Islands from the north today. This low level frontal cloud band will stall out near the island of Kauai and weaken into a trough later today. The stronger upper low will begin to drift slowly westward, enhancing shower activity over windward mountain areas into Monday. A weak ridge aloft will slowly fill in over the region decreasing shower trends a bit from Tuesday into Thursday. An upper level trough will drop in from the northwest on Friday, likely enhancing trade wind showers before a shallow front moves into the northwest islands by next weekend.

Discussion

In the big picture satellite imagery this morning we see a weakening cold front approaching the island of Kauai at the surface, while a cold unstable upper low enhances shower activity over windward mountain areas statewide. A few thunderstorms are possible near Kauai and Niihau today as the low level frontal trough interacts with the unstable upper low. Subsidence temperature inversion heights, measured at 2 AM HST (12Z) this morning at Hilo and Lihue, range from 7,000 feet and 10,000 feet respectively. These higher inversion heights over the western half of the state are due to the closer proximity to the unstable upper level cold core low. Rain shower activity today will remain the highest over Kauai County with more passing showers forecast to spread across the rest of the island chain.
The surface cold front will weaken into a trough later today and the surface trough will follow the upper level low as the system begins to drift westward away from Hawaii through Monday. Cloud tops may briefly reach the highest summits of Mauna Kea and Mauna Loa on the Big Island on Monday and Monday night. Freezing temperatures at summit level may produce some light rime icing concerns during this time period as supercooled cloud drops freeze on contact with roadways, vehicles and buildings above the 11,000 foot elevation level. A Winter Weather Advisory for the Big Island summit zones may be needed for Monday due to this potential icing threat.
Global models continue to show a weak ridge filling in aloft over the state with a slight decrease in statewide shower activity from Tuesday through Thursday. Trade wind will also see a subtle increase into the moderate to locally breezy range during this mid week time period.
Another upper level trough moves in from the northwest on Friday, divergence aloft will spread over the islands lifting trade wind temperature inversion heights, and increase shower trends from Friday into the weekend. Another weakening cold front will approach the islands from the north and stall out near Kauai and Oahu next weekend. Islands within this stalling frontal band will see cloudy skies and showers. More island by island forecast details as the time period grows shorter. Stay tuned.

Aviation

Moderate trade winds will continue through Monday as a weakening cold front and unstable upper level low moving in from the northwest stalls out near the island of Kauai. A few thunderstorms are possible today near Kauai and Niihau today and tonight with this system. Wet weather conditions with periods of MVFR conditions remain in the forecast for Kauai and Niihau. Additional periods of showers should be expected across windward airfields over all islands with brief periods of MVFR conditions in any shower activity. Expect improving trends on Monday as this system begins to drift westward away from the state.
AIRMET Sierra was issued for mountain obscuration over the island of Kauai, as a weak cold front and unstable upper low moves into the region.

Marine

A front is sagging southward over the northwest portion of the offshore waters early this morning, bringing pockets of strong (near gale) breezes, along with isolated to scattered thunderstorms. Some of these thunderstorms may enter the coastal waters near Kauai later today through tonight. The front is expected to stall and then get pushed to the west as high pressure builds to the north by Monday, increasing trade winds to moderate to locally fresh speeds. Winds will likely remain below SCA levels until Tuesday or Wednesday. However, seas are expected to reach SCA levels later this morning as a mix of northwest and north swells build into the northwestern end of the island chain. By the later half of next week, a front far to the north could disrupt the trade winds once again.
Surf along north facing shores will build today as a mix of medium to long period north-northwest swells (320-330 degrees) fill in across the area. A medium period north-northeast swell will fill in later today into the evening hours associated with the approaching front with near-gale winds, that will primarily impact the western end of the state. This mix of swells is expected to maintain HSA level surf through tonight before gradually fading early this week and so a HSA is in effect through 6 AM HST Monday for most north and west facing shores of the smaller islands. A moderate long period north-northwest swell (340 degrees) is then possible around the middle of next week.
Surf along east facing shores will remain small to moderate through the morning, and then may be impacted by the medium period NNE swell mentioned above. South shore surf will remain small through early next week before building slightly mid to late week as a long period south-southwest swell (190 degrees) fills in across the region.

Fire weather

Increased relative humidity values and light trades will maintain below critical fire weather conditions the next several days. Temperature inversion heights near the Big Island and Maui will range from 7,000 to 8,000 feet today.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Niihau, Waianae Coast, Oahu North Shore, Maui Windward West, Kauai North, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala.
Small Craft Advisory until 6 AM HST Monday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

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