Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 87 to 92 near the shore to around 76 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 74 near the shore to around 63 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tuesday: Breezy. Mostly sunny with isolated showers. Highs 87 to 92 near the shore to around 77 above 3000 feet. East winds up to 20 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 84 to 92. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 73. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 84 to 92. East winds 15 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 76 to 84 in the valleys to around 67 above 4000 feet. East winds up to 15 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 64 to 71 in the valleys to around 61 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 75 to 83 in the valleys to around 68 above 4000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

North Kaua’i

Today: Mostly sunny with scattered showers. Highs 78 to 88. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 75. East winds up to 15 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs 78 to 89. East winds up to 20 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 76 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 76. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 76 to 86. East winds 10 to 20 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy trades will focus showers over windward zones through the period. The greatest coverage of showers through mid- week will be over Windward Maui and Big Island. An approaching trough will then bring potential for an increase in showers during the latter half of the week.

Discussion

Little change expected through mid-week as locally breezy trades deliver occasional waves of low clouds and showers to windward and mauka zones. Passing beneath the northern periphery of a closed low meandering well east of the area, showers upstream of the Big Island and Maui have been receiving an added boost to coverage and intensity between 140-150W prior to their arrival. This will continue to be the case through mid-week as increased moisture depth contributes to greater shower coverage and intensity there. Elsewhere, showers will maintain a more typical character.
The latter half of the week will be characterized by longwave amplification over the northeast quadrant of the Pacific basin. This will in turn force existing mid-level troughing around 35N to dig southward toward the islands Thursday through Friday, potentially cutting off over the islands as it does so. Pressure falls during this time will weaken the local gradient causing trades to ease. There are also hints in both the EC and GFS of a surface reflection developing, a testament to the depth of dynamic forcing associated with the incoming trough. As stability diminishes, any such surface reflection would serve as a mechanism to further organize showers in the trade wind layer and would result in a greater coverage of heavier showers focused chiefly over windward and mauka zones. With that said, the EC, GEM, and their respective ensemble systems remain firm in their depictions of a more progressive solution, leaving the GFS and its much wetter solution the outlier. Regardless, Thursday into the weekend will feature a reduction in stability that will, at the least, contribute to a tendency for heavier trade wind showers. Future forecast packages will also evaluate the potential for thunder over the Big Island on Thursday and/or Friday as the trough moves into the area.

Aviation

High pressure well northeast of the state will maintain moderate to locally breezy trades across the region through the TAF period. Scattered showers will remain focused mainly across windward areas, with limited showers elsewhere. Mainly VFR conditions are expected at TAF locations through tonight, however brief MVFR conditions, accompanying heavier showers, are expected continuing a potential need of AIRMET Sierra for tempo mountain obscuration across some windward locations.
Additionally, strengthening trades today could potentially generate a period of low level mechanical turbulence downwind of mountains.

Marine

Short term change with the morning package was a boost to the winds in the short term. With that change, have expanded the Small Craft Advisory (SCA) to include the Kaiwi Channel and waters to the east. The SCA was also extended through Monday night with this package.
High pressure to the northeast will be replaced midweek by a high currently far north-northwest of the islands. Expect trade winds to prevail into next weekend, however some weakening in speeds is possible at the end of the week. The SCA for the typical windier waters will likely be extended, and its still possible for additional waters to be added to the SCA mid-week.
No advisory level surf is expected through the week. The current northwest and south swells will continue to be on the decline today. North facing shores will see a boost again starting Tuesday as short period energy arrives. This swell is expected to start from the northwest, and transition to a northerly swell by Thursday, and then decline into the weekend. A long period south swell arriving Wednesday will once again provide a boost to south facing shores into the weekend. As the trade winds increase, expect an increase in surf along east facing shores.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Tuesday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov