Photo Credit: Jason Weingardt

West Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 73 near the shore to around 59 above 3000 feet. North winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 61 near the shore to around 51 above 3000 feet. North winds up to 25 mph. Chance of rain 30 percent.

Saturday: Sunny with isolated showers. Highs around 79 near the shore to around 66 above 3000 feet. North winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Mostly sunny. Isolated showers in the morning. Highs around 72. North winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Lows around 60. North winds up to 10 mph in the evening becoming light.

Saturday: Sunny. Highs 75 to 80. Light winds.

Kaua’i Mountains

Today: Breezy. Partly sunny with scattered showers. Highs 61 to 67 in the valleys to around 52 above 4000 feet. North winds 10 to 25 mph decreasing to up to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 54 to 59 in the valleys to around 49 above 4000 feet. North winds up to 20 mph. Chance of rain 30 percent.

Saturday: Mostly sunny with isolated showers. Highs 67 to 73 in the valleys to around 59 above 4000 feet. North winds up to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: Breezy. Partly sunny with scattered showers. Highs 63 to 72. North winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 55 to 64. Northwest winds 10 to 20 mph shifting to the north up to 20 mph after midnight. Chance of rain 30 percent.

Saturday: Breezy. Mostly sunny with isolated showers. Highs 68 to 78. North winds up to 20 mph becoming 10 to 15 mph in the afternoon. Chance of rain 20 percent.

East Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 62 to 72. North winds 10 to 15 mph becoming up to 20 mph in the afternoon. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows 55 to 66. Northwest winds up to 20 mph. Chance of rain 30 percent.

Saturday: Sunny with isolated showers. Highs 67 to 78. North winds up to 15 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

The coolest airmass of the season has settled over the area and dewpoints have fallen into the lower 50s. Gusty northerly winds will add an additional chill to the air and showers will gradually diminish from west to east through the day. Winds will gradually diminish today through Saturday, becoming light and variable by Sunday. Another front will approach the islands early next week, with southerly winds leading to some warming.

Discussion

A deep mid-level low sits northeast of the area, the southern periphery of the cold pool grazing the eastern end of the state early this morning. In spite of relatively shallow moisture, instability provided by the cold pool aloft is supporting pockets of locally heavy post-frontal showers in the vicinity of Maui and the Big Island where NW-NNW winds will focus rainfall over favored slopes through the morning, including the North Kona and Kohala Districts of the Big Island.
Further back in the post-frontal airmass, deep cyclonic flow persists even as low gradually pulls away and the height field begins to rebound. Despite crashing dewpoints into the low and mid 50s at sea level, the cool airmass will tend to easily saturate and will favor a scattered coverage of shallow showers for most areas through the day. The latest modeling does indicate aggressive mid- level/700mb dry advection out of the north working its way east across the area as the day progresses. This dry advection is recognized on IR imagery as the back edge to colder cloud tops that is working toward Kauai at press time. As a result, expect coverage of these shallow post-frontal showers to dwindle over Kauai early this morning followed by Oahu this afternoon and the eastern islands this evening. At the same time, the strong height gradient aloft is supporting powerful mid-level jet that will bring strong winds to the Big Island Summits and Haleakala Summit through today. The relatively low freezing level will may allow deeper showers to deposit freezing rain or graupel on the summits on an isolated basis through early this morning, but shower coverage has sufficiently waned and T/Td remains sufficiently warm (35F/35F) to warrant cancellation of the Winter Storm Warning for Haleakala Summit.
The mid-level dry layer deepens through tonight as northerly dry advection continues. This will bring an effective end to all shower activity across the state. With the exception of a few clouds stacking up along north-facing slopes, light northerlies coupled with low 50s dewpoints will spell another chilly night tonight tonight and a crisp Saturday morning. The gradient will quickly diminish over the weekend as low pressure pulls away and a strong zonal Pacific jet displaces the trade wind belt well south the islands. The resulting land and sea breeze pattern will take hold no earlier than late Saturday night and will be a dry one. A greater- than-normal diurnal temperature range can be expected as daytime temperatures rebound only to be followed by cool overnight land breezes within the resident low dewpoint environment.

Aviation

The cold front is currently making its way across the Big Island (as of 2 AM HST) and will push east of the state later this morning. Moderate showers along and behind the frontal boundary will continue to impact the state through the morning and bring brief periods of MVFR or lower conditions. With a potent upper level trough moving overhead, isolated thunderstorms will continue to be a concern, but the best instability lies north and east of the state.
While winds have begun to drop in some areas overnight, breezy to locally windy northwest winds are still generally prevailing. These winds will generate tempo moderate turbulence downwind of the mountainous terrain. As a result, AIRMET Tango remains in effect across the entire island chain below 8000 feet over and immediately south through east of mountains for tempo moderate turbulence.
In addition, expect areas of moderate to severe upper level turbulence with the strong jet streak rounding the upper level trough. SIGMET Sierra for severe turbulence at mid and upper levels is in effect across the entire island chain early this morning and will gradually move eastward as the upper level trough and jet streak move off to the east. AIRMET Tango for tempo moderate turbulence and isolated severe turbulence aloft is also in effect across the state.
Later this morning, winds will gradually weaken to become moderate to breezy and veer slightly more northerly. Clouds and showers will also decline through the day and allow VFR conditions to prevail through the rest of the forecast period.

Marine

A strong cold front continues to sweep eastward down the island chain and will move over the southeast offshore waters by tonight. A storm force low has developed to the north of the islands, and is bringing gale force winds into the offshore waters. This system will also produce strong to near gale force northerly winds behind the front, bringing high end Small Craft Advisory level winds to the coastal waters. In additional an incoming north to northwest swell will build seas in excess of 10 feet.
The current moderate, medium period northwest (320 degree) swell will continue to build through today and hold through tonight, and combine with a locally generated north (350-020 degree) swell generated by the above mentioned storm-force low. Surf heights will build to high end High Surf Advisory (HSA) levels today along exposed north and west facing shores of Niihau, Kauai, Oahu, Molokai, and north facing shores of Maui and the Big Island. Surf heights for Big Island north facing shores will start off below advisory thresholds in the morning then build to advisory levels by afternoon. Surf heights along west facing shores of the Big Island will build close to HSA levels by tonight. This north swell energy will begin to decline on Saturday, with surf heights falling below HSA levels along west facing shores by Saturday and then along north facing shores by Saturday night.
Lows developing and moving over the northwest Pacific over the weekend and next week will generate additional northwest swells that are expected to reach the islands. These swells will maintain surf along north and west facing shores, with blocks of time when the surf will approach or exceed advisory levels. At this time, the next possible advisory level surf looks to arrive in the islands Sunday afternoon/Monday morning.
Tides are currently running about 0.35 to 0.75 feet above predicted levels. With high astronomical tides near 3 feet, combined with the northwest and north swells, anticipate minor/ nuisance coastal flooding within low lying flood-prone areas during the early morning pre-dawn high tides over the next few days. Additional impacts with these north swells may include harbor surges within both Kahului and Hilo Harbors starting later this evening through Saturday night.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Saturday for Niihau, Kauai Leeward, Waianae Coast, Oahu North Shore, Olomana, Maui Windward West, Kauai North, Koolau Windward, Molokai Windward, Molokai North, Molokai West, Maui Central Valley North, Windward Haleakala, Big Island East, Big Island North.
High Wind Warning until 6 PM HST this evening for Haleakala Summit, Big Island Summits.
Wind Advisory until 6 PM HST this evening for Kona, Kohala, Big Island Interior, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 PM HST Saturday for all Hawaiian waters except Maalaea Bay,

Data Courtesy of NOAA.gov