Photo Credit: James Grenz

Hilo

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to 69 to 74 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 60 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 83 near the shore to around 72 at 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Kona

Today: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 82 to 87 near the shore to around 69 near 5000 feet. West winds up to 10 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 70 to 75 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs 83 to 88 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 83 near the shore to 69 to 80 near 3000 feet. East winds up to 25 mph increasing to 15 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to 70 to 80 near 3000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Kohala

Today: Partly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 83 near the shore to 69 to 80 near 3000 feet. East winds up to 25 mph increasing to 15 to 25 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening, then scattered showers after midnight. Lows around 69 near the shore to 57 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Sunday: Mostly sunny. Windy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 82 near the shore to 70 to 80 near 3000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny in the morning then becoming partly sunny. Breezy. Highs around 86 near the shore to around 73 near 5000 feet. East winds up to 25 mph.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Breezy. Lows around 71 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph.

Sunday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 85 near the shore to 69 to 74 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 15 mph. Chance of rain 60 percent.

Sunday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 83 near the shore to around 72 at 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny. Breezy. Highs around 86 near the shore to 70 to 76 above 4000 feet. North winds up to 20 mph. Gusts up to 40 mph in the afternoon.

Tonight: Partly cloudy. Breezy. Lows around 73 near the shore to 52 to 59 above 4000 feet. East winds up to 25 mph.

Sunday: Mostly sunny. Windy. Isolated showers in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 30 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Strengthening trade winds will usher in drier and more stable weather this weekend. Trades will gradually weaken and trade wind showers will increase during the first half of next week. The winds will become light Wednesday through Friday, allowing a sea and land breeze pattern to develop in most leeward areas, with showers favoring interior and leeward locales each afternoon.

Discussion

Currently at the surface, a trough of low pressure is located around 400 miles north of Kauai, while a 1029 mb high is centered around 1400 miles north-northeast of Honolulu. The resulting gradient across the islands is producing gentle to moderate trade winds early this morning, strongest over the eastern end of the state. Infrared satellite imagery shows some high clouds streaming over the far eastern and western portions of the state, with lower clouds streaming into windward areas with the trades. Radar imagery shows a few light showers moving into windward areas, with very little if any shower activity in leeward locales. Main short term focus revolves around trade wind trends and rain chances.
The trough of low pressure north of the islands will slide westward through the weekend, while the high to the distant north-northeast of the state strengthens. This will allow the trade winds to strengthen today, with moderate to breezy conditions expected this afternoon through the remainder of the weekend, strongest on Sunday. The trades should drop a notch into the moderate to locally breezy range early next week as old frontal remnants north of the islands keep the strongest gradient north of the state. The boundary layer flow then appears to tip east-southeasterly Wednesday through Friday as troughing develops north of the islands. This would ease the trades into the light to locally moderate range, with sea and land breezes common across many leeward areas.
As for the remaining weather details, fairly dry trade wind weather should prevail through the weekend, with showers confined primarily to windward and mauka areas during the overnight and early morning hours. Some more moisture is forecast to get caught up in the trade wind flow Sunday night through early next week as a mid/upper level low approaches the islands from the east. This should lead to an increase in trade wind showers and allow a few more showers to reach leeward areas as well. A convective shower regime could then develop Wednesday through Friday in the lighter wind regime, with showers favoring interior and leeward areas during the afternoon and evening hours.

Aviation

Moderate trade winds will keep clouds and showers focused over windward and mauka areas today and tonight. Webcams over windward Big Island continue to show some low clouds over the area, but coverage continues to wane. Will keep AIRMET Sierra for mountain obscuration going for now, but may drop it with the next issuance. Otherwise, expect mainly VFR conditions across the state the next 24 hours with occasional MVFR cigs possible through the morning hours.

Marine

Easterly trade winds have surged back into the fresh to strong category overnight in response to high pressure building to the north and a weak trough moving away from the region. A Small Craft Advisory is now in effect for the windier waters around Maui County and the Big Island, and may need to be expanded to include other marine areas tonight through Sunday. This pattern will persist through Monday (trades becoming northeast Sunday night), before trending down Tuesday through midweek as the gradient relaxes.
The long-period south swell that filled in Friday will hold today, then ease Sunday into early next week. The next pulse out of the south is expected late Sunday, which will keep the surf up along southern exposures through Tuesday before lowering. After this source fades, not much is shown out in the extended due to a progressive pattern setting up down south within Hawaii's swell window.
Surf along east facing shores will ramp up and become rough over the weekend into early next week due to strong trades locally and upstream. Distant tropical activity in the eastern Pacific may send a small, long-period east swell through the islands around midweek.

Fire weather

Building trade winds this weekend will usher in a dry airmass over the area. The resulting dry and breezy weather will result in elevated fire danger, with red flag conditions possible Sunday afternoon. A Fire Weather Watch remains in effect for all leeward portions of the state on Sunday. Trade winds are expected to gradually decrease Monday through the first half of next week.

HFO Watches/Warnings/Advisories

Fire Weather Watch from Sunday morning through Sunday afternoon for Niihau, Kauai Leeward, Oahu South Shore, Waianae Coast, Olomana, Molokai Leeward, Lanai Makai, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, South Big Island, Kohala, Big Island Interior.
Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov