Photo Credit: Braden Jarvis

West Kaua’i

Today: Partly sunny. Breezy. Scattered showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 66 near the shore to around 55 above 3000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs around 79 near the shore to around 67 above 3000 feet. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

South Kaua’i

Today: Breezy. Occasional showers in the morning, then partly sunny with scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs around 78. Northeast winds 15 to 25 mph. Chance of rain near 100 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Numerous showers and isolated thunderstorms. Lows 62 to 67. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs around 78. Northeast winds 15 to 25 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Breezy. Occasional showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 66 to 74 in the valleys to around 61 above 4000 feet. East winds 10 to 25 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with numerous showers and isolated thunderstorms. Lows 55 to 60 in the valleys to around 49 above 4000 feet. Northeast winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Windy. Numerous showers and isolated thunderstorms in the morning, then numerous showers in the afternoon. Highs 66 to 74 in the valleys to around 61 above 4000 feet. Northeast winds 10 to 30 mph. Chance of rain 70 percent.

North Kaua’i

Today: Breezy. Occasional showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Locally heavy rainfall possible in the morning. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with numerous showers and isolated thunderstorms. Lows 58 to 67. East winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Partly sunny. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs 71 to 78. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Occasional showers and isolated thunderstorms in the morning, then scattered showers and isolated thunderstorms in the afternoon. Locally heavy rainfall possible in the morning. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Mostly cloudy with numerous showers and isolated thunderstorms. Lows 56 to 68. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Wednesday: Mostly cloudy. Breezy. Numerous showers and isolated thunderstorms in the morning, then scattered showers in the afternoon. Highs 71 to 78. Northeast winds 10 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

A wet trade wind pattern with isolated thunderstorms and locally heavy rain, especially over windward areas, will prevail through Wednesday night. Breezy trades will further strengthen during the middle part of the week.

Discussion

Overall the forecast seems to be on track, so no changes to the short term forecast with the morning package. Overnight saw showers carried in on the trades focused over the windward and mauka slopes. Kauai, Maui and the Big Island experienced the heavier showers, and on the Big Island, a few of the area stream gages did respond. Fortunately there has been enough of a break in the showers for the streams to periodically get a break an
High pressure to the north, and a weakening surface trough moving west away from the main Hawaiian islands is helping to bring breezy trade winds to the region. An upper level trough sinking southward over the islands is responsible for the unstable airmass, allowing trade wind showers to be more intense than normal. In addition, this instability could trigger a few thunderstorms.
This set up over the next couple of days will continue the wet trade wind weather with the potential for moderate to locally heavy rain focused windward and mauka, particularly over the western end of the state through early Tuesday morning and the Big Island and Maui Tuesday and Wednesday.
The Winter Storm Warning remains in effect through Tuesday night for the Big Island, with the primary concern being freezing rain leading to ice accumulation.
As the above mentioned upper level trough lingers over the islands, a couple more rounds of moderate to locally heavy rain potential exist both Tuesday night and Wednesday night. In both cases, the focus is expected to be mainly over Maui and the Big Island, but can't completely rule out Oahu and Kauai from seeing additional showers.
Trade winds will linger through the week with high pressure to the north. Winds are expected to increase mid-week so the above mentioned surface trough dissipates. Toward the end of the week, the high will move to the east, and be replaced by a new high, which will maintain the moderate to locally windy trade winds.
From Thursday on into the weekend the upper level trough lifts to the north and northeast, just enough to cut off some of the instability that is leading to the heavier showers. As such look for a return to a more typical trade wind pattern.

Aviation

Moderate to breezy trade winds will persist for the next several days as strong surface high pressure holds north of the state. Clouds and showers will favor windward slopes and coasts. Periods of MVFR conditions with low ceilings and visibility in showers are expected mainly over windward airfields, especially in the late night and morning hours.
A deepening upper level trough will enhance convective activity. There is a slight chance of thunderstorms statewide through forty- eight hours and possibly beyond.
AIRMET Sierra is now in effect for northeast facing slopes of Kauai, Oahu, and the Big Island. Conditions are expected to improve later this morning.
AIRMET Tango is in effect for moderate leeward mountain wave turbulence over all islands due to breezy trade winds, and is expected to remain necessary through twenty-four hours and possibly beyond. Additionally, areas of moderate upper level turbulence remain an issue for the eastern third of the state. Upper level turbulence conditions are expected to rapidly improve this morning as the subtropical jet shifts to the east.

Marine

A strong high pressure system will drift eastward, slowly passing north of Hawaii over the next few days. Expect strong to near- gale east-northeast trade winds through much of this week as another strong high pressure system builds into the region from the west as the first one retreats eastward on Thursday. A Small Craft Advisory remains in effect for all waters, and will likely remain in place through much of this week. A persistent trough aloft will keep the island atmosphere unstable, with briefly heavy showers producing periods of strong wind gusts and low visibility. Isolated thunderstorms are also in the forecast into Thursday.
The persistent trade winds will generate rough and choppy surf along east facing shores through the week. Gradually diminishing medium period swells out of the northwest and north will continue to trend down today. A small, medium period northwest swell will arrive on Wednesday. Followed by a larger and longer period northwest swell, building surf heights to near advisory thresholds along exposed north and west facing shores from Friday to Saturday.
South shores will remain seasonably small with mainly medium period background swell energy pulses.

HFO Watches/Warnings/Advisories

Winter Storm Warning until 6 AM HST Wednesday for Big Island Summits.
Small Craft Advisory until 6 AM HST Thursday for all Hawaiian waters,

Data Courtesy of NOAA.gov