Hilo

Tonight: Cloudy with occasional showers. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Sunday: Numerous showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 76 to 82 near the shore to around 63 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Sunday Night: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. Northeast winds around 10 mph becoming up to 15 mph after midnight. Chance of rain near 100 percent.

Kona

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 71 near the shore to 45 to 51 near 5000 feet. East winds around 10 mph. Chance of rain 20 percent.

Sunday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 67 near 5000 feet. East winds around 10 mph shifting to the west in the afternoon. Chance of rain 30 percent.

Sunday Night: Partly cloudy. Isolated showers in the evening. Lows 68 to 73 near the shore to 45 to 51 near 5000 feet. East winds up to 10 mph. Chance of rain 20 percent.

Waimea

Tonight: Windy. Mostly cloudy with occasional showers in the evening, then partly cloudy with scattered showers after midnight. Lows 62 to 70 near the shore to 53 to 61 near 3000 feet. East winds 15 to 35 mph with gusts to 55 mph. Chance of rain 90 percent.

Sunday: Very windy. Mostly sunny with isolated showers in the morning, then mostly cloudy with numerous showers in the afternoon. Highs 62 to 82. East winds 10 to 40 mph. Chance of rain 70 percent.

Sunday Night: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 61 to 71 near the shore to 53 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Tonight: Windy. Mostly cloudy with occasional showers in the evening, then partly cloudy with scattered showers after midnight. Lows 62 to 70 near the shore to 53 to 61 near 3000 feet. East winds 15 to 35 mph with gusts to 55 mph. Chance of rain 90 percent.

Sunday: Very windy. Mostly sunny with isolated showers in the morning, then mostly cloudy with numerous showers in the afternoon. Highs 62 to 82. East winds 10 to 40 mph. Chance of rain 70 percent.

Sunday Night: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows 61 to 71 near the shore to 53 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Tonight: Windy. Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 72 near the shore to around 50 near 5000 feet. East winds 15 to 30 mph. Chance of rain 20 percent.

Sunday: Mostly sunny. Windy. Scattered showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. East winds 15 to 35 mph. Chance of rain 30 percent.

Sunday Night: Breezy. Partly cloudy with isolated showers. Lows around 72 near the shore to around 50 near 5000 feet. East winds 15 to 25 mph. Chance of rain 20 percent.

Puna

Tonight: Cloudy with occasional showers. Lows 61 to 68 near the shore to 50 to 56 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Sunday: Numerous showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 76 to 82 near the shore to around 63 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain near 100 percent.

Sunday Night: Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 61 to 68 near the shore to 51 to 56 at 4000 feet. Northeast winds around 10 mph becoming up to 15 mph after midnight. Chance of rain near 100 percent.

Waikoloa

Tonight: Partly cloudy. Windy. Isolated showers in the evening. Lows around 72 near the shore to 48 to 53 above 4000 feet. East winds 10 to 35 mph with gusts to 55 mph. Chance of rain 20 percent.

Sunday: Windy. Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 88 near the shore to 65 to 70 above 4000 feet. Northeast winds 10 to 30 mph with gusts to 50 mph. Chance of rain 50 percent.

Sunday Night: Partly cloudy with isolated showers. Lows around 72 near the shore to 48 to 53 above 4000 feet. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Gusts up to 35 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Gusty trade winds are expected to prevail through the remainder of the weekend. An upper low will move over the Big Island and bring periods of heavy rain and isolated thunderstorms across the eastern end of the state. Winds will weaken and the atmosphere stabilizes by Tuesday as the low moves away.

Discussion

High pressure north northeast of Hawaii will drive strong trade winds statewide, especially across wind-prone locations including valleys and channels where downsloping and funneling effects are most prominent. The Wind Advisory is extended through the day Sunday for portions of Maui County and the Big Island.
Visible satellite and radar show a band of clouds and light showers moving onto the islands carried in by the trade winds from the east. Showers will focus over windward slopes tonight before this band is broken up and moves west by Sunday morning. A decrease in trade wind showers is expected through midday Sunday. Wind speeds begin to taper off beginning Sunday night as the driving high pressure weakens, but will still remain breezy into Monday.
An upper-level low will move southwestward over the Big Island and persist from Sunday through Monday night before moving away to the east. 500 mb temperatures will lower to around -12C, and this cold pool aloft will likely be enough to trigger heavier trade wind showers and a slight chance of thunderstorms across Maui and Big Island Sunday afternoon into Monday. Precipitable water will be a fairly average 1.3 inches during this time, so with the winds expected to carry most showers on not expecting any flood highlights at this point. A wintry mix or a light dusting of snow is possible across the summits of Mauna Kea and Mauna Loa.
While conditions stabilize Tuesday, winds will weaken becoming light and variable across the state by midweek as the driving high is vanquished by a strong cold front moving across the Northeast Pacific. Periods of light afternoon showers may develop but the general consensus is much drier conditions are expected through the remainder of the week.

Aviation

Strong trade winds continue to blow over the state this afternoon, driven by high pressure to the northeast and a tight pressure gradient over the the state. Quite a few low-level wind shear and moderate low-level turbulence PIREPs have been received from Maui today, and this will continue to be an issue into late afternoon/early evening. Meanwhile, a band of moisture moving into the islands on the trade winds has increased clouds and showers along windward areas this afternoon, particularly for the eastern end of the state.
This evening, expect continued showers along north through east sections of the islands. MVFR ceilings and visibility will be common, but then prevailing VFR conditions will return Sunday morning for most locations. Winds will remain strong through the rest of the weekend.
AIRMET Sierra remains in effect for mountain obscuration across north through east sections of the Big Island and Maui this afternoon. It is likely that this AIRMET will need to be expanded to include other islands as well by the evening. Additionally, AIRMET Tango remains in effect for moderate low-level turbulence over and downwind of island terrain. This AIRMET will likely be needed at least through Sunday.

Marine

Strong high pressure will remain far northeast of the islands through Sunday. The high should then weaken and drift southeast Sunday night into Monday as a low passes far north of the state. A Gale Warning remains in effect through Sunday night for the windier waters and channels around Maui County and the Big Island. A Small Craft Advisory (SCA) remains in effect for all remaining coastal waters through Sunday night for strong winds and seas greater than 10 feet. Winds are expected to drop below SCA thresholds by Tuesday or Wednesday as a ridge of high pressure drifts closer to the state.
Surf along north facing shores will remain small through the weekend as the short period north swell levels off. A small, medium period northwest swell is expected to fill in Sunday night and linger through Tuesday. A similar pulse from the northwest is possible Wednesday night into Thursday. Into the long range, a series of small to moderate swells from the north is possible towards the end of next week into the weekend due to a complex low pressure system developing far northeast of the state Tuesday through the 2nd half of next week.
Surf along east facing shores will continue to remain large, rough, and choppy through Sunday night coinciding with the strong trade winds. The High Surf Advisory remains in effect through Sunday night for all east facing shores. Surf will likely linger near advisory thresholds through Monday then steadily decline rest of next week as the trade winds ease.
Surf along south facing shores is expected to remain small through the forecast period. Shorelines exposed to the easterly wind wave on south and north facing shores may continue to see an uptick over the weekend.
Peak monthly tides are forecasted in the early morning hours through Monday morning. These high tides combined with elevated seas from strong trade winds may increase coastal inundation impacts for vulnerable locations during the morning high tides. This has prompted a Coastal Flood Statement which will continue through early Monday morning.

Fire weather

Red Flag Warning is cancelled as of this afternoon. Relative humidity levels are not at the critical fire threshold this afternoon, and are expected to remain above 45 percent into Sunday. Wind speeds will remain strong into Sunday and a Wind Advisory has been extended through the day Sunday for portions of Maui County and the Big Island.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 AM HST Monday for Olomana, Maui Windward West, Kauai East, Koolau Windward, Molokai Southeast, Windward Haleakala, Kipahulu, South Haleakala, Big Island Southeast, Big Island East, Big Island North.
Wind Advisory until 6 PM HST Sunday for Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Molokai North, Molokai West, Molokai Leeward South, Lanai Windward, Lanai Leeward, Maui Central Valley North, Maui Central Valley South, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Small Craft Advisory until 6 AM HST Monday 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.
Gale Warning until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov