Weather Forecast

Hawaii County Weather Forecast for September 30, 2021

September 30, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Rest Of Today: Frequent showers in the morning, then frequent showers and slight chance of thunderstorms in the afternoon. Highs 79 to 84 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy with showers likely. Lows 64 to 72 near the shore to 55 to 60 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with scattered showers. Highs 79 to 85 near the shore to 64 to 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Kona

Rest Of Today: Sunny in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs 84 to 89 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 73 near the shore to 52 to 58 near 5000 feet. Light winds. Chance of rain 20 percent.

ARTICLE CONTINUES BELOW AD

Friday: Partly sunny. Scattered showers in the afternoon. Highs 84 to 89 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Rest Of Today: Mostly cloudy. Frequent showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs 66 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 66 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Rest Of Today: Mostly cloudy. Frequent showers in the morning, then showers likely and slight chance of thunderstorms in the afternoon. Highs 66 to 85. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy with scattered showers. Lows 64 to 71 near the shore to 57 to 64 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Friday: Partly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 66 to 86. East winds 10 to 15 mph. Chance of rain 50 percent.

South Big Island

Rest Of Today: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 85 near the shore to around 69 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Lows around 73 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph.

Friday: Partly sunny. Breezy. Isolated showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Puna

Rest Of Today: Frequent showers in the morning, then frequent showers and slight chance of thunderstorms in the afternoon. Highs 79 to 84 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 10 mph. Chance of rain near 100 percent.

Tonight: Mostly cloudy with showers likely. Lows 64 to 72 near the shore to 55 to 60 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 70 percent.

Friday: Mostly cloudy with scattered showers. Highs 79 to 85 near the shore to 64 to 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Rest Of Today: Sunny with isolated showers in the morning, then partly sunny with scattered showers and slight chance of thunderstorms in the afternoon. Highs 84 to 90 near the shore to 67 to 73 above 4000 feet. North winds up to 10 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Lows around 75 near the shore to 52 to 57 above 4000 feet. East winds up to 10 mph.

Friday: Mostly sunny in the morning then becoming partly sunny. Highs 84 to 90 near the shore to 67 to 73 above 4000 feet. North winds up to 10 mph.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will continue through the weekend as high pressure holds north of the state. A plume of moisture will bring showery conditions over windward Big Island today with scattered clouds and showers elsewhere across the state. A disturbance aloft may enhance rainfall over some areas this weekend.

Discussion

A ridge of high pressure far north of the state will continue to produce moderate to locally breezy trade winds through the weekend. Passing clouds and showers will continue to ride in with the trade winds and will produce some light to moderate rainfall over windward and mauka areas over the smaller islands. Over on the Big Island and east Maui, satellite imagery is showing a plume of moisture moving in from the east this morning. Showery conditions are expected today and we could see a few thunderstorms pop up during the afternoon over the Big Island slopes. This mornings sounding from Hilo shows a weakened inversion with an increase of low level moisture. Showers should be generally on the decrease by this evening for the Big Island. Friday looks to be a fairly typical trade wind day with some passing showers across the state.
Some enhancement in shower activity is possible for the weekend, mainly for the western end of the state. An upper level low is expected to approach the state from the north and will likely stall about 200 miles north of Kauai or Oahu. The upper low will be close enough to destabilize the atmosphere over the western end of the state and produce brief heavy showers within any pocket of moisture moving with the trade winds. Also, the high terrain on the Big Island will experience higher rainfall chances, mainly during afternoon hours. The disturbance aloft will weaken on Monday and Tuesday, bringing back stable conditions. Stay tuned as the forecast for the weekend can evolve due to the erratic nature of upper level lows.
Also we did issue a Special Weather Statement (SPSHFO) yesterday evening due to several pilots reporting areas of volcanic glass or Pele’s hair near the Halemaumau summit. This morning’s sounding from Hilo shows a weakened inversion at around 10000 feet. An upper level disturbance slowly approaching the area will continue to keep a somewhat unstable atmosphere through the weekend. This could possibly allow volcanic emissions to travel elsewhere across the Big Island depending on the strength of the volcanic emission. Winds will generally be out of the south or southwest as you get above 10,000 feet and out of the east to northeast below 10,000 feet.

Aviation

High pressure north of the state will keep moderate trade winds in place during the next 24 hours. MVFR cigs/vsbys will remain common in showers over most windward areas through mid morning. An area of enhanced moisture could keep reduced cigs/vsbys in place over windward sections of Maui and the Big Island through much of the day. Meanwhile, windward sections of Kauai and Oahu should see improvement by late this morning, and leeward sections of all islands should see prevailing VFR conditions during the next 24 hours.
An unstable airmass over the Big Island could allow for the development of a thunderstorm or two over the Big Island slopes this afternoon.
AIRMET Sierra is now in effect for mountain obscuration across windward sections of Kauai, Oahu, Molokai, Maui and the Big Island. This AIRMET will likely remain in place through mid morning, and possibly though much of the day over windward sections of Maui and the Big Island.

Marine

Surface high pressure positioned far northeast of the state is weakening as it shifts further east toward the U.S. West Coast. A new, slightly stronger high building in north of the region today will subtly tighten the pressure gradient down across the area. This will produce moderate to locally strong trade winds the next couple of days. A Small Craft Advisory (SCA) has been issued for those typically windier waters surrounding Maui County and south of Big Island starting at noon today and continuing through Friday afternoon. This SCA may need to be extended into Friday evening or early Saturday morning.
A couple of late week into early next week small, short to medium period north northwest swells will come through beginning tonight into Friday, as well as Sunday into Monday, that will maintain low end north and west facing shore surf. A small, long period west northwest swell being generated by Northwest Pacific Typhoon Mindulle may reach the islands by Tuesday of next week. A small, medium to long period south southwest swell will arrive by tonight and peak Friday. This swell will keep south surf from going completely flat during the remainder of the week. Choppy wind wave surf along most eastern exposures will remain small the next couple of days. A more late week persistent, stronger trade fetch upstream of the islands may increase weekend east facing shore surf.

HFO Watches/Warnings/Advisories

Small Craft Advisory from noon today to 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

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