Hilo

Tonight: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 64 to 70 near the shore to 51 to 58 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Frequent showers early in the morning, then scattered showers in the late morning and afternoon. Highs 79 to 85 near the shore to around 67 at 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Sunday Night: Cloudy. Frequent showers in the evening, then numerous showers after midnight. Lows 64 to 69 near the shore to 51 to 58 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 90 percent.

Kona

Tonight: Mostly cloudy with isolated showers. Haze. Lows around 73 near the shore to 47 to 52 near 5000 feet. Light winds. Chance of rain 20 percent.

Sunday: Mostly cloudy. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 84 to 90 near the shore to around 67 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 50 percent.

Sunday Night: Cloudy with isolated showers. Haze. Lows around 73 near the shore to 48 to 53 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 72 near the shore to 54 to 62 near 3000 feet. East winds up to 20 mph shifting to the southeast up to 10 mph after midnight. Chance of rain 70 percent.

Sunday: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Haze in the afternoon. Highs around 81 near the shore to 71 to 78 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Sunday Night: Cloudy and breezy. Numerous showers in the evening, then scattered showers after midnight. Haze through the night. Lows 63 to 71 near the shore to 54 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Kohala

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then numerous showers after midnight. Lows 63 to 72 near the shore to 54 to 62 near 3000 feet. East winds up to 20 mph shifting to the southeast up to 10 mph after midnight. Chance of rain 70 percent.

Sunday: Mostly cloudy. Breezy. Numerous showers early in the morning, then scattered showers in the late morning and afternoon. Haze in the afternoon. Highs around 81 near the shore to 71 to 78 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

Sunday Night: Cloudy and breezy. Numerous showers in the evening, then scattered showers after midnight. Haze through the night. Lows 63 to 71 near the shore to 54 to 63 near 3000 feet. East winds up to 20 mph. Chance of rain 70 percent.

South Big Island

Tonight: Breezy. Mostly cloudy with isolated showers. Haze. Lows around 73 near the shore to around 51 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Sunday: Breezy. Mostly cloudy with isolated showers. Haze. Highs around 86 near the shore to around 66 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Sunday Night: Cloudy and breezy. Isolated showers in the evening. Haze through the night. Lows around 73 near the shore to around 52 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Tonight: Mostly cloudy. Numerous showers in the evening, then frequent showers after midnight. Lows 64 to 70 near the shore to 51 to 58 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Frequent showers early in the morning, then scattered showers in the late morning and afternoon. Highs 79 to 85 near the shore to around 67 at 4000 feet. East winds up to 15 mph. Chance of rain 90 percent.

Sunday Night: Cloudy. Frequent showers in the evening, then numerous showers after midnight. Lows 64 to 69 near the shore to 51 to 58 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 90 percent.

Waikoloa

Tonight: Mostly cloudy. Isolated showers in the evening, then scattered showers after midnight. Haze through the night. Lows around 74 near the shore to 50 to 55 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Sunday: Partly sunny in the morning then becoming cloudy. Scattered showers. Haze through the day. Highs 84 to 89 near the shore to 64 to 71 above 4000 feet. Southeast winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

Sunday Night: Cloudy. Scattered showers in the evening, then isolated showers after midnight. Haze through the night. Lows around 74 near the shore to 51 to 56 above 4000 feet. Southeast winds up to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to breezy easterly trade winds will briefly shift out of the east-southeast tonight through Monday as a broad surface trough develops far northwest of the islands. Increasing moisture and instability may lead to enhanced shower activity Sunday into Monday, particularly over the western end of the state. Breezy easterly trades and drier conditions are expected to return during the first half of next week as the trough weakens and shifts away from the region.

Discussion

Moderate to breezy trades will veer east-southeast tonight through Monday as a strengthening high well to our northeast interacts with a broad trough approaching from the northwest. This slightly veered wind direction will disrupt the trade wind flow across the smaller islands and allow for the development of land and sea breezes across leeward areas. An upper-level trough approaching from the northwest will lower 500 mb heights and temperatures, introducing some instability over the western half of the state Sunday through early next week. The instability associated with this feature and an influx of low level moisture may help to enhance windward showers overnight and sea breeze- induced clouds and showers over leeward areas during the afternoons, particularly over the western half of the state. This east-southeasterly flow may also transport vog to a majority of the island chain through early next week.
A return to breezy and more stable trade wind conditions is expected by Monday night as upper-level heights rise, drier air filters in from the east, and the surface trough weakens and moves away from the state. This will result in a more typical easterly trade wind pattern through Thursday, with showers favoring windward and mauka areas and generally dry conditions prevailing elsewhere.
For the latter end of the week and into the weekend, a weak upper-level trough will move overhead, introducing some more instability to the region. However, the instability and available moisture look rather unimpressive, so not expecting much more than perhaps a slight enhancement of trade wind showers for the end of the forecast period at this time.

Aviation

AIRMET Tango in effect for tempo moderate turbulence below 7000 feet south through west of mountains due to breezy trade winds. The winds will maintain strength into Sunday, but veer southeasterly and partially block some leeward areas from the full strength of the winds, and moving the main turbulence area to the northwest sector of the islands. LLWS possible through the rest of this afternoon and Sunday afternoon at near PHOG terminal.
Low clouds and showers may fill in a bit overnight with possible MVFR ceilings and visibility across all windward areas.

Marine

Moderate to locally strong trade winds will veer out of the east to east-southeast late tonight and Sunday as the subtropical ridge is pushed closer to the islands by a developing trough northwest of Kauai. The Small Craft Advisory (SCA) has been adjusted slightly from the typically windy waters around the Big Island and Maui to account for enhanced winds north of these islands. On Monday, the trough will move westward, and the surface ridge to the north will rebuild, causing trade winds to shift back to a more easterly direction. The SCA will likely be reconfigured to the typically windy waters by Monday and should remain in place through at least midweek.
A late season northwest swell is peaking this afternoon, bringing surf well above seasonal average. Nearshore PacIOOS buoys at Hanalei and Waimea Bay showed the 320-330 degree swell at 6 to 7 feet at 13 to 14 seconds, producing surf just below High Surf Advisory levels. The swell will decline tonight and Sunday, with north shore surf dropping to near June average for the first half of the work week. Tiny surf is expected by Thursday.
Surf along south-facing shores will continue to see a mix of small background swell for the next few days, followed by a small inconsistent southwest swell late Tuesday and Wednesday. A storm low moved into the Hawaii swell window southeast of New Zealand yesterday and is generating seas in excess of 30 feet today. The resulting long-period south-southwest swell will build on Friday and peak next weekend, leading to surf well above June average.
Surf along east-facing shores will remain small and choppy through Sunday, then gradually build to near or above seasonal average Monday through Wednesday due to a return of fresh to strong trades over and upstream of the islands.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Monday for Maui County Windward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters.

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Data Courtesy of NOAA.gov