Weather Forecast

Hawaii County Weather Forecast for September 26, 2021

September 26, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Cloudy with occasional showers. Highs 79 to 85 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy. Occasional showers in the evening, then showers likely after midnight. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 90 percent.

Monday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to 68 to 73 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. 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 around 86 near the shore to around 73 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 70 to 76 near the shore to around 56 near 5000 feet. Light winds. Chance of rain 50 percent.

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Monday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 86 near the shore to around 73 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Waimea

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Today: Breezy. Mostly cloudy with showers likely. Highs around 81 near the shore to 73 to 80 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 82 near the shore to 73 to 80 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Kohala

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Today: Breezy. Mostly cloudy with showers likely. Highs around 81 near the shore to 73 to 80 near 3000 feet. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Showers likely in the evening, then scattered showers after midnight. Lows around 69 near the shore to 56 to 63 near 3000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Monday: Breezy. Partly sunny with scattered showers. Highs around 82 near the shore to 73 to 80 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly cloudy with scattered showers. Highs around 85 near the shore to around 74 near 5000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows around 70 near the shore to around 55 near 5000 feet. East winds 10 to 25 mph shifting to the northeast after midnight. Chance of rain 20 percent.

Monday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 74 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Puna

Today: Cloudy with occasional showers. Highs 79 to 85 near the shore to 68 to 73 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 90 percent.

Tonight: Mostly cloudy. Occasional showers in the evening, then showers likely after midnight. Lows around 70 near the shore to around 56 at 4000 feet. North winds up to 15 mph. Chance of rain 90 percent.

Monday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs 80 to 86 near the shore to 68 to 73 at 4000 feet. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: Breezy. Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers in the afternoon. Highs around 85 near the shore to 69 to 75 above 4000 feet. North winds up to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 71 to 76 near the shore to 52 to 59 above 4000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 85 near the shore to 69 to 75 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to breezy trade winds will prevail through much of the next week, with the trades strongest today through Monday as a trough passes by to the south of the islands and a strengthening area of high pressure builds southeastward and closer to the state. Fairly typical trade wind weather will persist over the smaller islands today, although some showery weather will affect windward Kauai at times this morning. More unsettled weather is expected over windward sections of the Big Island however, where showery conditions may linger into this evening. Drier trade wind weather should return statewide by late tonight and continue through Thursday. A more showery trade wind pattern could develop Friday into next weekend as a disturbance aloft moves in.

Discussion

Currently at the surface, a trough of low pressure is located around 225 miles south of the Big Island, while a 1030 mb high is centered 1500 miles north-northwest of Honolulu. The resulting gradient is producing moderate to breezy trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions across the state, with cloud cover most prevalent over windward locales. Radar imagery shows scattered showers moving into windward areas, with a stray shower reaching leeward areas from time to time, with shower coverage the highest over windward sections of Kauai and the Big Island. Main short term concern revolves around rain chances during the next 24 hours or so.
High pressure to the north-northwest of the islands will build southeastward and strengthen during the next couple days, while a trough of low pressure passes steadily westward to the south of the state. This will keep breezy trade winds in place across the island chain through Monday, with a slight easing of the trades into the moderate range expected by Tuesday as the ridge north of the state weakens. A cold front passing by to the distant north will further weaken the ridge north of the islands Wednesday, dropping the trades a notch further. The trades should then begin to increase on Thursday as high pressure strengthens to the northeast of the state, with locally breezy conditions returning Friday into next weekend.
As for the remaining weather details, showery conditions will likely affect windward Big Island through this evening, as a slug of deep tropical moisture moves through. More typical trade wind weather is expected over the smaller islands, although some showery weather may continue across Kauai this morning. More typical trade wind weather should then settle in over the whole state by late tonight, with showers favoring windward and mauka areas, mainly during the overnight and early morning hours and a stray shower reaching leeward areas from time to time. A weakness aloft will develop over the state Friday into next weekend, which could bring a more showery trade wind pattern back to the islands.

Aviation

The clouds and showers moving over Kauai and producing some mountain obscuration should be clearing out soon, but AIRMET Sierra remains in effect for the time being. Have recently cancelled the AIRMET Sierra that was in effect for Oahu as conditions have improved there.
Conditions had deteriorated on the Big Island around midnight prompting AIRMET Sierra for mountain obscuration over the east side. However clouds and showers have recently thinned. Another batch of clouds and showers just southeast of the Big Island could bring another spell of MVFR and/or mountain obscuration, so leaving the AIRMET in place for the time being.
Strong high pressure north of the islands will continue to support breezy easterly trade winds across the region into tomorrow. As such, AIRMET Tango remains in effect for moderate mechanical turbulence downwind of the mountains below 9000 ft, and is expected to continue into at least tomorrow.

Marine

A high pressure ridge far north of the region and a surface trough passing steadily westward, to the south of the island chain, will increase trade wind speeds a bit into Monday. Trade winds in the moderate to strong range will last into Tuesday. Wind speeds may weaken a bit from late Tuesday into Thursday due to a reshuffling of the high pressure centers along the ridge far north of the region. A Small Craft Advisory (SCA) was expanded this morning to cover most of the Hawaiian Coastal Waters and Channels. This SCA will decrease in coverage back to the typical windier waters and channels on Monday as the trough passes slowly west of the area. Trade wind speeds will remain just below SCA thresholds for the windier waters near the eastern islands from Tuesday into Thursday.
The north-northwest swell continues to decline this morning, north shore surf will slowly decrease into Monday. A small north swell will build in from Tuesday night into Wednesday with a small bump in surf heights expected along north facing shores. The south swell will drop slightly today and then fade to background level surf heights through at least Wednesday. The trade wind swell will hold surf heights roughly the same for one more day along east facing shores before decreasing slowly on Monday and Tuesday, and then increase back to near average heights on Thursday or Friday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until midnight HST tonight for Kauai Northwest Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov

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