Photo Credit: James Grenz

Hilo

Today: Partly sunny with numerous showers. Highs around 80 near the shore to around 68 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 65 near the shore to around 51 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Friday: Mostly sunny with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 65 to 70 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 72 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 65 to 71 near the shore to around 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 80 to 85 near the shore to around 71 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Numerous showers. Highs 65 to 81. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Lows around 64 near the shore to 50 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs 64 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Numerous showers. Highs 65 to 81. East winds 10 to 25 mph. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with numerous showers in the evening, then partly cloudy with scattered showers after midnight. Lows around 64 near the shore to 50 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Friday: Breezy. Mostly sunny with scattered showers. Highs 64 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 84 near the shore to around 73 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows around 67 near the shore to around 51 near 5000 feet. East winds up to 20 mph.

Friday: Breezy. Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 83 near the shore to around 72 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny with numerous showers. Highs around 80 near the shore to around 68 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 65 near the shore to around 51 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Friday: Mostly sunny with numerous showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to 65 to 70 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Breezy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 83 near the shore to 67 to 74 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 69 near the shore to 47 to 55 above 4000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Friday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 82 near the shore to 66 to 73 above 4000 feet. Northeast winds up to 20 mph. Chance of rain 20 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.

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Data Courtesy of NOAA.gov