West Kaua’i

Tonight: Mostly cloudy. Scattered showers after midnight. Lows around 68 near the shore to around 59 above 3000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Wednesday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 83 near the shore to around 72 above 3000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Wednesday Night: Partly cloudy with isolated showers. Lows around 69 near the shore to around 59 above 3000 feet. East winds around 10 mph. Chance of rain 20 percent.

South Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows around 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 76 to 83. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 69. East winds 10 to 15 mph. Chance of rain 40 percent.

Kaua’i Mountains

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 61 to 67 in the valleys to around 57 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 71 to 78 in the valleys to around 63 above 4000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 61 to 68 in the valleys to around 58 above 4000 feet. East winds around 10 mph. Chance of rain 50 percent.

North Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 62 to 71. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 74 to 82. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Mostly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 62 to 71. East winds 10 to 15 mph. Chance of rain 30 percent.

East Kaua’i

Tonight: Mostly cloudy with scattered showers. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 81. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows 63 to 73. East winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Surface high pressure will continue to build northeast of the state through Wednesday and bring locally breezy easterly trade winds. Brief passing showers will favor windward and mountain areas, mainly during the overnight and early morning hours. Late Wednesday through this weekend, trade winds will ease slightly and veer to a more east-southeast direction, shifting shower activity over east and southeast facing slopes of most islands. However, overall rainfall amounts are expected to remain limited. An approaching front may bring unsettled wet weather by early to mid next week.

Discussion

Visible satellite imagery shows a much drier scene this afternoon compared to this morning, with abundant sunshine across the state and only limited low clouds and isolated light showers moving into windward and mauka areas. Although the trade flow remains primarily out of the east, the low-level steering flow is beginning to take on a slight southerly component, as evidenced by clouds and showers moving more parallel to the island chain in an east-southeast direction.
High pressure to the northeast of the state will continue to build through midweek, bringing increased stability and strengthening trades through Wednesday. Limited clouds and light showers will generally favor windward and mauka areas through this period, especially during the overnight to early morning hours, along with the Kona slopes of the Big Island during the afternoon hours.
By Thursday, winds will veer out of a more east-southeast direction as a cold front approaches from the northwest. In this pattern, showers will favor southeast and east facing slopes of the Big Island and Maui, along with interior portions of the other islands due to the development of sea breezes in the lighter, somewhat blocked flow. Model guidance remains in good agreement through this period, showing this front stalling just to the west of the state as its parent low shoots off to the far northwest.
The evolution of weather features in the Pacific becomes less clear over the weekend as model spread increases. The GFS and the ECMWF both show a deep mid- to upper-level trough developing northwest of the state, spawning a surface low to the west- northwest. Strengthening southerly flow between that low and high pressure to our northeast could draw deep tropical moisture (with precipitable water values near 2 inches) toward or over the western end of the state early to mid next week. The exact placement of this moisture band and the strength of the southerly winds remain uncertain and will be monitored closely in the coming days.

Aviation

Stable trade winds will strengthen to fresh to strong levels and become more easterly tonight into Wednesday, delivering clouds and showers mainly windward and mauka. Pockets of MVFR are likely, but VFR is forecast to prevail during this time. AIRMET Tango for lee turb is in effect and will should remain in place through Wednesday.

Marine

Fresh to strong trade winds will build and become increasingly easterly on Wednesday as surface high pressure strengthens far northeast of the islands. Wednesday night into Thursday, winds will veer out of the east-southeast around Oahu and Kauai as the high drifts eastward and broad low pressure develops northwest of the state. A Small Craft Advisory (SCA) is in effect for the typically windy waters around the Big Island and Maui County today, then expands to windward waters of Big Island and Maui County tonight and Wednesday as veering winds lead to accelerations north of those islands. Minor adjustments will need to be made, but the SCA will likely continue for some areas through the weekend. As low pressure slowly advances toward the islands early next week, local winds could veer increasingly southerly.
The current moderate northwest swell will continue a gradual decline through Thursday. A small west-northwest swell will arrive on Friday and hold through the weekend, followed by a small north-northwest swell early next week. Choppy east shore surf will build to near seasonal average by Wednesday as trade winds strengthen over and east of the islands. Little change is expected along east facing shores through the weekend, followed by a possible decline early next week if winds veer southerly. Surf along south facing shores will remain small to tiny through the weekend, and some islands may an increase in choppy surf if southerly winds develop early next week.
A Coastal Flood Statement remains in effect through early Wednesday morning due to the combination of peak monthly high tides and water levels that are running higher than predicted. This may lead to minor flooding along the shoreline and in low- lying coastal areas during the high tide between midnight and daybreak.

HFO Watches/Warnings/Advisories

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

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Data Courtesy of NOAA.gov