Photo Credit: Jason Weingardt

West Kaua’i

Today: Mostly sunny until late afternoon then becoming partly sunny. Scattered showers until late afternoon, then isolated showers late in the afternoon. Highs 77 to 82 near the shore to around 68 above 3000 feet. Northwest winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with isolated showers. Lows 64 to 69 near the shore to around 55 above 3000 feet. West winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Breezy. Scattered showers until late afternoon, then frequent showers late in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. Southwest winds 10 to 20 mph. Chance of rain 80 percent.

South Kaua’i

Today: Sunny until late afternoon then becoming partly sunny. Isolated showers until late afternoon. Highs around 80. West winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the late evening and overnight. Lows around 65. West winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Breezy. Scattered showers until late afternoon, then numerous showers late in the afternoon. Highs 75 to 80. Southwest winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Numerous showers until late afternoon, then isolated showers late in the afternoon. Highs 70 to 76 in the valleys to around 63 above 4000 feet. West winds 10 to 20 mph. Chance of rain 60 percent.

Tonight: Breezy. Mostly cloudy with isolated showers. Lows 57 to 63 in the valleys to around 52 above 4000 feet. West winds 10 to 20 mph. Chance of rain 20 percent.

Tuesday: Mostly cloudy. Breezy. Scattered showers until late afternoon, then frequent showers late in the afternoon. Highs 69 to 76 in the valleys to around 59 above 4000 feet. Southwest winds 10 to 25 mph. Chance of rain 80 percent.

North Kaua’i

Today: Partly sunny until late afternoon then becoming mostly sunny. Scattered showers until late afternoon. Highs 70 to 79. West winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Isolated showers in the late evening and overnight. Lows 59 to 67. West winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny early in the morning then becoming cloudy. Breezy. Scattered showers in the morning, then numerous showers in the afternoon. Highs 70 to 79. Southwest winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Mostly sunny until late afternoon then becoming partly sunny. Isolated showers until late afternoon. Highs 72 to 82. West winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers in the late evening and overnight. Lows 57 to 68. West winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Partly sunny. Scattered showers until late afternoon, then numerous showers late in the afternoon. Highs 68 to 80. Southwest winds 10 to 15 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Showers will diminish in coverage over Kauai early this morning as a cold front advances toward Oahu this morning and Molokai and Maui late today into tonight. A second cold front will move into the state Tuesday night bringing a brief period of showers followed by strong westerly winds on Wednesday. Lighter winds and drier conditions are then expected for the second half of the week.

Discussion

The first of two well-advertised cold fronts is crossing the island of Kauai at press time. Scattered showers have developed well ahead of the front and are lifting over leeward portions of Maui County. A higher coverage showers with pockets of embedded higher rates is lifting northeastward over Kauai and Oahu. Moderate WNW winds will fill in behind the front bringing drier to Kauai for the remainder of the day. The front will clear Oahu during mid-afternoon. The mid-latitude trough responsible for depositing this front over the islands in the first place is slightly stronger than anticipated and it now appears that the deepest moisture will be forced away from the islands as the front reaches Maui tonight. This will also cause the front to be more progressive, potentially clearing Maui as early as tonight resulting in a shorter duration of moderate to heavy rainfall. A shallower version of the frontal moisture band is then modeled to set up over Leeward Big Island tonight. However, its arrival during the stable nocturnal period coupled with shallower moisture and modest southwest winds leads to uncertainty regarding shower coverage. The forecast is accordingly conservative tonight through Tuesday. Showers will redevelop over Leeward Maui County and possibly Leeward Big Island late Tues into Wednesday as the frontal moisture band reactivates and lifts northward in response to a digging upper trough.
The forecast remains unchanged with respect to the second cold front. It is forecast to arrive with greater dynamic support, but also in a more stable environment courtesy of ongoing southwesterly warm advection. Regardless, it will also be a very progressive feature and will ultimately kick the preceding stalled front east of the state late Wednesday or Wednesday night. Breezy southwesterly winds will develop in advance of the front, but increasing low-level stability and a marginal wind field limit any wind advisory concerns.
Attention then turns to the post-frontal period on Wednesday when strong and well-mixed WSW flow pushes into the area. Ambient winds will be strong in their own right, especially over the western end of the state. Coupled with local accelerations through channels and around terrain, A wind advisory (gusts to 50 mph) is likely for favored zones statewide on Wednesday. Rapidly developing subsidence will help to further accelerate winds over and consequently downwind of terrain while a strong push of low-level dry advection (dewpoints falling into the 50s) adds an additional component of downward forcing to help stronger winds reach the surface. Forecast soundings offer little support for higher end wind gusts (i.e. high wind warning) for most areas. They do indicate winds around 60 mph hovering near and above the top of the boundary layer on Wednesday. These won't reach the surface, except where it could potentially be drawn downward as the flow is forced over prominent terrain features. This would be an issue for only the most favored locales such as Windward Oahu, but doesn't appear particularly likely at this time.
Gusty westerly winds coupled with dewpoints falling well into the 50s will bring a chill to the air Wednesday night through Thursday. Mostly dry weather will continue into the weekend as winds steadily weaken and dewpoints remain comfortably in the 50s.

Aviation

A cold front will move through Kauai prior to daybreak, through Oahu around noon, and into Maui County this afternoon. The front will then stall out over the eastern islands tonight. Showers and increasing south to southwest winds can be expected along and ahead of the front as it pushes steadily eastward today and tonight. Conditions will improve with winds shifting around to more of a westerly direction behind the front. Widespread MVFR cigs/vsbys can be expected in showers as the front moves through, with isolated IFR conditions possible.
AIRMET SIERRA is now in effect for mountain obscuration over all of the smaller islands. Conditions will likely improve over Kauai later this morning and over Oahu around noon. The AIRMET will likely continue over Maui County through the day.
AIRMET Tango remains in effect for moderate upper level turbulence over the entire state. This AIRMET will likely continue through the morning, with conditions improving this afternoon. See SIGMET VICTOR series for severe turbulence area over the islands.

Marine

A weak cold front near Kauai will produce moderate to locally fresh southwest winds with widespread clouds and showers ahead of it this morning. After the front moves through the western islands, expect a brief period of moderate to locally fresh west to northwest winds immediately behind the front. A much stronger front will approach the state from late tonight into Tuesday, which will produce fresh to locally strong southwest winds starting Tuesday. Winds may reach the Small Craft Advisory (SCA) criteria ahead of the front over some waters adjacent to Kauai and Oahu starting Tuesday afternoon. Strong to near gale force west winds and elevated, rough seas are forecast to develop behind the front by Wednesday. Therefore, expect SCA conditions over most coastal waters, with Gale Warnings possible over some marine zones Wednesday. Even though the winds will likely shift out of the northwest, and weaken slightly by Thursday, large seas will result in SCA conditions persisting over most Hawaiian waters from Thursday into Friday.
The buoys northwest of Kauai (51001 and 51101) are showing a northwest swell of 5 to 6 feet with a period of 10 seconds, so this swell appears to be close to the model guidance. This small, medium-period northwest swell (315 degrees) is expected to arrive in the islands later today, and peak on Tuesday. A much larger, long-period northwest swell (310 degrees) is forecast to arrive late Tuesday night, and peak from Wednesday night into Thursday. This will likely cause surf heights to reach the High Surf Warning criteria along most north and west facing shores, including the leeward Big Island, for an extended period of time. Therefore, expect the potential for overwash and coastal erosion to greatly increase from Wednesday evening through Thursday morning along exposed north and west facing shores. Waves could periodically overtop some vulnerable roads during the peak of this event, especially during high tide. This extra-large northwest swell is forecast to gradually lower, and veer more northerly from Thursday through next weekend.
Surf along east facing shores will continue to lower today, with minimal trade wind swell expected this week. Note that there is a potential for localized wave wrap along some east facing shores with an exposure to the large swell as it veers more northerly later this week. Rough and choppy surf may increase along some south facing shorelines with a westerly exposure through Tuesday night due to the strengthening southwest to west winds associated with the second front. Otherwise, no significant long-period swell energy is expected along south facing shores this week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov