Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Mostly sunny with isolated showers. Highs around 80 near the shore to around 68 above 3000 feet. Northeast winds up to 10 mph shifting to the west in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Lows 64 to 69 near the shore to around 57 above 3000 feet. Northeast winds up to 10 mph.

Tuesday: Mostly sunny. Highs around 81 near the shore to around 69 above 3000 feet. East winds 10 to 15 mph.

South Kaua’i

Today: Mostly sunny. Isolated showers in the afternoon. Highs 77 to 84. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows around 66. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 78 to 83. East winds 10 to 15 mph.

Kaua’i Mountains

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 69 to 75 in the valleys to around 60 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 59 to 64 in the valleys to around 55 above 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 20 percent.

Tuesday: Mostly sunny. Isolated showers in the morning. Highs 70 to 77 in the valleys to around 61 above 4000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

North Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 71 to 81. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 30 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Lows 60 to 69. East winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 72 to 82. East winds 10 to 15 mph.

East Kaua’i

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 68 to 81. Northeast winds 10 to 15 mph. Chance of rain 30 percent.

Tonight: Partly cloudy with isolated showers. Lows 60 to 71. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tuesday: Mostly sunny. Highs 70 to 81. East winds 10 to 15 mph.

Detailed Forecast

Synopsis

High pressure to the northwest of the islands will maintain moderate to locally breezy trade winds into Tuesday night. Expect typical trade wind showers to be focused over windward and mauka areas, with fewer showers expected Tuesday. Winds will weaken and turn to the southeast for the second half of the week. An upper level trough will enhance rainfall during the second half of the week.

Discussion

No significant changes to the forecast this morning. Still evaluating the potential for thunderstorms and heavy rainfall starting as early as Wednesday afternoon, and persisting into the weekend.
High pressure to the northeast will continue to bring moderate to locally breezy trades to the islands through tomorrow, with showers being carried in on the trades focused over the windward areas. Little change in the precipitable water (PW) values with the overnight soundings, but the satellite derived PW does show drier air sinking over the islands. Shower activity is on the decline based on radar, and expect this trend to continue over the next 24 hours or so.
The high is expected to starting lifting to the north by Wednesday as a surface low develops to the far northwest. This will weaken the winds and turn the winds to a more southeasterly direction. Expect winds to turn to the southeast near the Big Island Wednesday and then by Thursday for the smaller islands.
The second half of the week continues to look unsettled. The GFS and ECMWF models continue to be in good agreement with an upper level trough being west of the islands near 170W by Thursday morning. The latest run of the GFS continues to depict a much stronger system and cuts off an upper level low to the west of the islands by Friday morning. The ECMWF isn't as strong, but does have a cut off low Thursday. The latest run of the ECMWF brings the cut off low southward as it approaches the islands, which adds another level of uncertainty to how this event is going to play out. The GFS and ECMWF show increasing instability over the islands as early as Wednesday for the western end of the state and adjacent waters. The National Blend of Models (NBM) is still not as completely on- board, but is showing some thunderstorm potential for the second half of the week. Assuming the global model runs continue to show this pattern, expect the NBM thunderstorm probabilities to increase as the event gets closer.
Thunderstorm and heavy rain potential continues to be monitored for this event, but hasn't yet been added to the forecast due to some timing, location and intensity uncertainty with recent model runs with the handling of the upper level feature. This setup will also likely result in increased chances for some heavier showers throughout the time period of Wednesday afternoon into the weekend as the trade wind inversion slips away. The summits of the Big Island will likely see an uptick in winds as the upper trough approaches and moves over the islands. Additionally, temperatures will likely at times be below freezing, so can't rule out some winter weather for the summits either.
That being said, the forecast now reflects showers spreading across the island chain by Wednesday night, and continuing into the weekend.

Aviation

Light to locally moderate trade winds will continue. Clouds and showers will favor north and northeast facing slopes and coasts. Drier air is expected to move into the western half of the state this afternoon in response to high pressure building in from the northwest.
At 2am Monday, satellite imagery revealed thick bands of cumulus draped across most of the state. Radar returns indicated the heaviest showers to be impacting the northeast slopes and coasts of Maui and the Big Island. AIRMET Sierra for mountain obscuration is now in effect for the windward slopes of Kauai, Maui, and the Big Island. Conditions are expected to end over Kauai and Maui by late afternoon, but will likely persist across the Big Island through the evening hours.

Marine

High pressure northwest of the state will keep moderate to fresh trade winds blowing during the next couple days, with locally strong trades in the typically windy waters around Maui and the Big Island. A Small Craft Advisory remains in effect for these windier waters through 6 AM Tuesday but may need to be extended. The trades will gradually ease Wednesday through the end of the work week, with winds potentially becoming light and variable Thursday and Friday as a trough of low pressure develops west of the state.
The current north swell will continue to slowly decline today through the middle of the week. A new moderate sized north- northeast swell is forecast to build Wednesday night, giving a nice boost to north and east shore surf Thursday with a steady decline to follow Thursday night through next weekend.
A series of south-southwest and south-southeast swells will keep south shore surf relatively steady through next weekend, at or slightly below the summertime average.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov