Photo Credit: Brendan Stephen

West Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Isolated showers. Highs around 82 near the shore to around 70 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 69 near the shore to around 58 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Highs around 82 near the shore to around 70 above 3000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

South Kaua’i

Today: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 81. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 65 to 70. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 81. Northeast winds 10 to 20 mph. Chance of rain 50 percent.

Kaua’i Mountains

Today: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 77 in the valleys to around 64 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then numerous showers after midnight. Lows 58 to 63 in the valleys to around 52 above 4000 feet. East winds up to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny. Numerous showers in the morning, then scattered showers in the afternoon. Highs 69 to 77 in the valleys to around 64 above 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

North Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 81. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 61 to 70. East winds 10 to 15 mph shifting to the southeast after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 81. East winds up to 15 mph. Chance of rain 50 percent.

East Kaua’i

Today: Partly sunny with scattered showers. Highs 74 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 59 to 71. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Mostly cloudy with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 74 to 81. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Trade winds will gradually decrease during the next couple days as weakening high pressure settles southward and closer to the islands. Showers will favor windward slopes and coasts with the stray leeward spillover. Winds will shift southerly over the weekend as a front approaches from the west. Rather dry weather should prevail Saturday, with the front then bringing some showery weather and shifting winds around to the north and northeast as it pushes southeast through the islands Sunday through Monday. A transition back to trade wind weather is expected Tuesday through the middle of next week.

Discussion

Currently at the surface, a 1028 mb high is centered around 800 miles north of Honolulu, and is driving moderate trade winds across the island chain early this morning. Infrared satellite imagery shows mostly cloudy conditions in most windward areas and partly cloudy conditions in leeward locales. Radar imagery shows scattered to numerous trade showers moving through the islands, with coverage the highest over windward slopes. Main short term focus revolves around trade wind trends and rain chances.
High pressure will weaken as it settles southward and closer to state during the next couple days. The trades will only slowly ease, holding generally at moderate to locally breezy levels through Friday. An approaching front will shift winds around to the south and southwest over the weekend at moderate levels. The front will push southeastward down the island chain Sunday through Monday, with moderate to breezy north shifting to northeast winds developing following the frontal passage. Moderate trades should prevail through Tuesday, then ease slightly next Wednesday as some weak troughing develops in the vicinity of the islands.
As for the remaining weather details, fairly typical trade wind weather will prevail through Friday, with showers favoring windward slopes and a few showers reaching leeward areas at times. As the trades become disrupted and we transition over to southerly flow Saturday, sea breeze development will lead to some interior and mauka showers. Increasing south to southwest flow will bring some showers into leeward areas Saturday night and Sunday, with a band of moisture associated with the front bringing some showery weather as it pushes through the islands, with the shower focus shifting back over to windward areas following its passage. This band of moisture appears to hang up in the vicinity of Maui County and northern sections of the Big Island early next week, keeping windward locales showery. The band appears to break up Tuesday resulting in a return to a more typical trade wind shower regime through the middle of next week.

Aviation

Expect moderate to locally breezy trade winds through Friday as the high pressure system north of the state weakens. Periods of passing showers remain in the forecast mainly over windward and mountain areas during the overnight to early morning hours. Brief MVFR conditions are forecast in any shower activity.
AIRMET SIERRA remains in effect for north through east sections for mountain obscuration. These conditions will diminish in coverage a few hours after sunrise.

Marine

Fresh to strong northeast to east trade winds along with large and rough seas in excess of 10 ft will support Small Craft Advisory conditions continuing today. Seas should dip below the advisory level by tonight, which will allow the advisory to be scaled back to the typical windier locations between Maui County and the Big Island tonight through Friday. Winds are forecast to shift out of the south to southeast Friday night into Saturday and ease, likely enough for localized land and sea breezes to form near the coasts as the ridge settles southward into the area. A cold front associated with a rapidly developing low that is forecast to pass around 1000 NM north of the state this weekend will approach, then advance down the island chain late Sunday into early next week. Moderate south to southwest winds ahead of this front are possible Saturday night through Sunday with a shift out of the north as the front moves through.
Surf along east facing shores will remain elevated and rough at the High Surf Advisory (HSA) level today. As the trade wind generated seas decline on Friday, a northeast swell will linger and likely keep east shore surf just below the HSA level. A downward trend is due over the weekend as the winds shift out of the south and the northeast swell eases.
A tiny, long-period north-northwest swell will move through this weekend. A more significant event is likely Sunday night through early next week as a gale low around 1000 nm to the north generates a large, medium-period north-northwest (340-350 deg) swell. Advisory level surf is expected, but swells from these nearby northerly sources typically come in much larger than predicted, which could produce heights climbing well above advisory levels during the peak on Monday. The swell will linger through midweek as it becomes more northerly. A larger northwest swell will be possible late next week.
An out of season south swell will build on Friday, peak during the weekend, then decline early next week. South shore surf could reach as high as summertime average Saturday.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Olomana, Maui Windward West, Kauai East, Kauai South, East Honolulu, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Kipahulu, Big Island Southeast, Big Island East, Big Island North.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.
Small Craft Advisory until 6 PM HST Friday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov