Photo Credit: Sebastien Gabriel

West Kaua’i

Today: Breezy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 84 near the shore to around 71 above 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly clear. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 70 near the shore to around 60 above 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning. Highs around 85 near the shore to around 72 above 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

South Kaua’i

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 79 to 86. East winds 15 to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows around 69. East winds 15 to 25 mph. Chance of rain 70 percent.

Thursday: Breezy. Mostly cloudy with showers likely in the morning, then mostly sunny with isolated showers in the afternoon. Highs 80 to 87. East winds 15 to 20 mph. Chance of rain 70 percent.

Kaua’i Mountains

Today: Windy. Frequent showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 79 in the valleys to around 62 above 4000 feet. East winds 10 to 30 mph. Gusts up to 50 mph in the morning. Chance of rain near 100 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then frequent showers after midnight. Lows 61 to 68 in the valleys to around 57 above 4000 feet. East winds 15 to 25 mph. Chance of rain 90 percent.

Thursday: Mostly cloudy. Breezy. Frequent showers in the morning, then scattered showers in the afternoon. Highs 71 to 80 in the valleys to around 63 above 4000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

North Kaua’i

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 84. East winds up to 25 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 63 to 70. East winds 10 to 20 mph. Chance of rain 70 percent.

Thursday: Breezy. Partly sunny with showers likely in the morning, then mostly sunny with scattered showers in the afternoon. Highs 74 to 85. East winds 10 to 20 mph. Chance of rain 70 percent.

East Kaua’i

Today: Breezy. Cloudy with frequent showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 82. East winds 10 to 25 mph. Chance of rain 90 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 63 to 74. East winds 15 to 20 mph. Chance of rain 70 percent.

Thursday: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 72 to 84. East winds 15 to 20 mph. Chance of rain 70 percent.

Detailed Forecast

Synopsis

Today's strong trade winds will gradually ease Thursday and Friday, delivering low clouds and showers that will favor windward slopes and coasts, especially during nights and mornings. Some light showers will also spread leeward at times with the strong trades. Winds will become light and turn southerly on Saturday as a front approaches. The front is expected to arrive on Sunday, potentially bringing increased showers to leeward areas. Light winds will prevail next week.

Discussion

Strong high pressure due N of the islands is supporting a strong and relatively cool ENE trade wind flow this morning. A Wind Advisory remains posted for areas in Maui and Hawaii Counties where winds are most accelerated by terrain. Although the island atmosphere is quite stable with a strong subsidence inversion based around 8 thousand feet and below-normal PWAT near 1″, steep low-level lapse rates below the inversion are allowing highly efficient warm rain processes to drive the formation of quite a few showers. Radar shows scattered to numerous small showers moving over the islands while satellite imagery shows scattered to broken open-celled (aka showery) low clouds approaching the islands from the ENE.
The high will weaken while moving closer to the islands over the next couple of days, resulting in a slow decrease in trade wind speeds. Model guidance indicates little overall change to the incoming low-level moisture field, so passing showers will favor windward areas during nights and mornings through Friday, with fewer showers spreading leeward as trades ease.
Late Friday, the weakened high will move NE in response to strong cyclogenesis NW of the area. Winds will briefly become light S/SW Saturday as an associated front approaches from the NW. The front is not expected to be particularly strong, but will likely bring some showers as it moves SE down the chain Sunday/Monday. Although some cold advection in the form of moderate N/NE winds may occur immediately after the front passes, winds are expected to diminish rapidly thereafter as the front dissipates over, or just E of, the islands early next week.

Aviation

Locally strong trades will persist through the forecast period. Enhanced low level moisture will bring scattered to numerous showers to the windward sides of all islands this morning, then decrease in coverage by this afternoon. Periods of MVFR ceilings and visibility will likely accompany this activity. In addition, isolated may push over the terrain and affect leeward locations.
AIRMET SIERRA remains in effect for north through east sections of the Big Island for tempo mountain obscuration above 3000 ft.
AIRMET TANGO remains in effect for low-level moderate turbulence over and downwind of the mountains of all islands due to locally strong trades.

Marine

Strong northeast to east trades with near gales over the channels and windier waters around Maui and the Big island will continue today as strong high pressure remains positioned to the north. These winds combined with a large area of strong- to gale-force northeast winds focused at the state between this high and low pressure far northeast of the area support rough seas with heights hovering above the Small Craft Advisory level over exposed waters into Thursday.
Guidance shows the gradient beginning to relax Thursday through Friday as high pressure north of the area settles southward and weakens, which will result in the local winds returning to the fresh to locally strong range. Over the weekend, the progressive pattern over the northern Pacific will continue as low pressure rapidly develops northwest of the state Friday, then lifts northeastward while passing to the north around 1000 NM. A front associated with this feature will approach and potentially reach the western end of the state by the end of the weekend. If this evolves as predicted, moderate south to southwest winds will become a possibility as the front approaches.
Surf along exposed north and east facing shores will remain rough into the second half of the week due to a mix of the locally wind- generated seas and a northeast groundswell from the aforementioned fetch upstream. Heights will hover around the High Surf Advisory criteria for east facing shores into Thursday. A reinforcing swell arriving out of the same direction (050 deg) Friday could be enough to support advisory-level surf returning for eastern exposures. A downward trend is anticipated over the weekend as the winds shift out of the south.
Surf along north and west facing shores will rise over the weekend as a small, long-period north-northwest swell arrives and moves through. A more significant event is possible Sunday night through early next week due to a large area of northerly gales forecast to develop nearby on the backside of the rapidly developing low passing around 1000 NM to the north this weekend. Heights with these nearby northerly sources typically come in much larger than predicted, which could lead to advisory to warning-level surf early next week.
Surf along south facing shores will trend up over the weekend as a long-period south swell arrives.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Thursday for East facing shores of Kauai Oahu Molokai Maui and the Big Island.
Wind Advisory until 6 PM HST this evening for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 PM HST Thursday for all Hawaiian waters.

Data Courtesy of NOAA.gov