Weather Forecast

Hawaii County Weather Forecast for September 17, 2021

September 17, 2021, 7:16 AM HST
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Hilo

Today: Partly sunny with scattered showers. Highs around 84 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs around 84 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 70 percent.

Kona

Today: Partly sunny. 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.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 69 to 75 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

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Saturday: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 69 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 40 percent.

Waimea

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Today: Partly sunny. Breezy. 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 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs around 82 near the shore to 69 to 79 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Kohala

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Today: Partly sunny. Breezy. 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 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Saturday: Breezy. Partly sunny with scattered showers. Highs around 82 near the shore to 69 to 79 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Partly sunny. Breezy. 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.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 70 near the shore to around 53 near 5000 feet. Northeast winds up to 20 mph. Chance of rain 20 percent.

Saturday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to around 73 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Puna

Today: Partly sunny with scattered showers. Highs around 84 near the shore to 70 to 75 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Scattered showers in the evening, then showers likely after midnight. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 15 mph. Chance of rain 70 percent.

Saturday: Partly sunny. Showers likely in the morning, then scattered showers in the afternoon. Highs around 84 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 70 percent.

Waikoloa

Today: Partly sunny. Breezy. Isolated showers in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 70 to 75 near the shore to 51 to 58 above 4000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Saturday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs around 86 near the shore to 70 to 76 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Drier than normal trade wind weather and breezy conditions are expected today, with a periods of high cloud cover continuing to stream overhead. Breezy trades will continue tonight and Saturday, while trade showers increase and high clouds diminish. Moderate to breezy trades will then prevail Sunday through late next week, along with fairly typical windward and mauka favored showers and the occasionally leeward spillover.

Discussion

Currently at the surface, a 1028 mb high centered around 950 miles north of Honolulu, is driving moderate to breezy trade winds across the island chain early this morning. Infrared satellite imagery shows a mix of high and low clouds resulting in partly to mostly cloudy conditions across the state. Radar imagery shows scattered light showers moving into windward areas, with a few of these showers spilling over into leeward communities. Main short term concerns revolve around trade wind trends and rain chances during the next several days.
High pressure to the distant north will shift eastward during the next couple days, keeping rather breezy trade winds in place across the island chain. The trades should ease into the moderate range Sunday and Monday as a front passes by far to the north of the state, and may increase to breezy levels once again Tuesday and Wednesday as a trough of low pressure slides by to the south of the islands. A new front approaching from the northwest may then ease the trades back to moderate levels late next week.
As for the remaining weather details, a drier than normal trade wind pattern should hold in place today, as mid and upper level ridging holds in place over the islands. periods of high clouds will stream through the region however, resulting in partly sunny conditions in many areas today. The ridging aloft will begin to breakdown upstream of the state tonight, which should result in an increase in trade wind showers, particularly as we head toward daybreak Saturday, while the cirrus aloft slowly thins out. Fairly typical trade wind weather should then hold in place through the late next week. Showers will continue to favor windward and mauka areas, particularly at night and during the early morning hours, with a few showers reaching leeward areas from time due to the strength of the trades.

Aviation

Breezy to strong trade winds will lead to low-level turbulence across the state downwind of the island terrain, which will persist into the weekend. AIRMET Tango reflecting this will remain in effect. MVFR CIGS/VSBYS are possible in and around passing showers focusing over windward and mauka areas. Otherwise, VFR conditions will prevail with limited showers expected over leeward areas.

Marine

High pressure north of the state will produce a tight enough pressure gradient down across the islands to maintain fresh to locally strong trades the next several days. Last night’s ASCAT satellite pass caught enough of the island’s nearshore waters to show large 25 knot wind swaths off of the Big Island’s South Point and within the Alenuihaha Channel…along with a few high wind reports around Moloka’i and south of Oahu’s Diamond Head. The eastern movement of the high the next few days will provide very little change to the Central Pacific pressure gradient and therefore result in little variance to these ongoing fresh to locally strong trades. The Small Craft Advisory (SCA) has been expanded westward to encompass all Hawaiian coastal waters through early Saturday morning. The SCA will extend out through early Sunday morning for the typically windier areas on the east end of the state. Trades may subtly weaken to more moderate, locally fresh magnitudes early next week.
The south swell continues to decline with a very small, long period reinforcement filling in today. Small, long period south swell energy originating from current Southern Hemispheric gales southeast of New Zealand is timed to arrive toward the middle of next week. A small, medium period northwest swell is expected to reach the islands late Saturday into Sunday. A series of slightly larger, medium period northwest swells emanating from a weekend North Pacific gale low will come through next week. The return of fresh trades has caused a steady increase in east facing shore surf. East surf should hold at seasonable levels over the next several days per these amped up trades over and upstream of the region.

Fire weather

Gusty winds in combination with dry fuels and low relative humidity levels will result in elevated fire danger today. Any fires that develop will spread rapidly and be difficult to control. Therefore a Red Flag Warning has been posted for leeward sections of Kauai, Oahu, Molokai, Maui and the Big Island through 6 PM this evening.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST this evening for Kauai Windward, Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Central Oahu, Waianae Mountains, Molokai Leeward, Lanai Makai, Lanai Mauka, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Haleakala Summit, Kona, South Big Island, Kohala, Big Island Interior.
Small Craft Advisory until 6 AM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Saturday 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.

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Data Courtesy of NOAA.gov

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