Weather Forecast

Hawaii County Weather Forecast for September 18, 2021

September 18, 2021, 7:15 AM HST
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Hilo

Today: 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. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 15 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Sunday: 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. North winds up to 15 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Kona

Today: 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. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Lows 69 to 74 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

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Sunday: 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. West winds up to 10 mph. Chance of rain 40 percent.

Waimea

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Today: 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.

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 decreasing to up to 25 mph after midnight. Chance of rain 50 percent.

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

Kohala

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Today: 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.

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 decreasing to up to 25 mph after midnight. Chance of rain 50 percent.

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

South Big Island

Today: 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 increasing to 10 to 25 mph in the afternoon. 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 10 to 25 mph. Chance of rain 20 percent.

Sunday: 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 10 to 25 mph. Chance of rain 20 percent.

Puna

Today: 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. North winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely. Lows around 68 near the shore to around 54 at 4000 feet. North winds up to 15 mph shifting to the northwest after midnight. Chance of rain 70 percent.

Sunday: 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. North winds up to 15 mph shifting to the east in the afternoon. Chance of rain 70 percent.

Waikoloa

Today: 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.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Lows around 72 near the shore to 51 to 58 above 4000 feet. East winds up to 25 mph shifting to the southeast up to 15 mph after midnight. Chance of rain 20 percent.

Sunday: Mostly sunny. Isolated showers in the afternoon. Highs around 86 near the shore to 70 to 76 above 4000 feet. Northeast winds up to 10 mph shifting to the north in the afternoon. Gusts up to 35 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trades will continue through the weekend, with a slight easing expected Sunday night and Monday. The trades will then increase back to breezy levels Tuesday and Wednesday, before dropping a notch late next week. Fairly typical trade wind weather will prevail through the forecast period. Showers will favor windward and mauka areas, particularly at night and during the early morning hours, with an occasional shower spilling over into leeward communities from time to time.

Discussion

Currently at the surface, a 1028 mb high centered around 1125 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 showers spilling over into leeward communities from time to time. Main short term concerns revolve around trade wind trends and rain chances during the next few days.
High pressure to the distant north will shift eastward this weekend, keeping rather breezy trade winds in place across the island chain. The trades should ease into the moderate range Sunday night through Monday night as a front passes by far to the north of the state. A trough of low pressure will then slide by to the south of the islands Tuesday and Wednesday, and this should boost the trades back to breezy levels once again. A slight easing of the trades is possible late next week as a new front approaches from the northwest.
As for the remaining weather details, the most recent model solutions suggest that an areas of disturbed weather far to the southeast of the islands, may send an area of enhanced moisture toward the Big Island Monday night through Tuesday night. If this occurs, rain chances will likely need to be increased and thunderstorms may need to be added to the forecast as well. Given that this is only a recent trend however, will keep the forecast in line with previous model runs and forecast packages, which suggest this deep moisture will slide by to the south of the island chain. As a result, we expected a fairly typical trade wind weather pattern to prevail throughout the forecast period. Showers will favor windward and mauka areas, particularly at night and during the early morning hours, with a few showers occasionally reaching leeward areas due to the strength of the trades.

Aviation

Breezy to strong trade winds will continue to produce low-level turbulence across the state downwind of the island terrain through much of the weekend. AIRMET Tango remains in effect for this. MVFR CIGS/VSBYS are possible in and around passing showers focusing over windward coasts and slopes. Otherwise, VFR conditions will prevail, with limited showers expected over leeward areas.

Marine

High pressure north of the state will maintain fresh to locally strong trade winds this weekend. Last night’s ASCAT satellite pass over the eastern third of the state continued to verify advisory level winds across the Alenuihaha channel and off of Big Island’s South Point. The eastern movement of the high the next few days will provide very little change to the Central Pacific pressure gradient. This will result in little variance to these fresh to locally strong winds. Today’s Small Craft Advisory (SCA) has been reconfigured to include all waters except the windward Kauai, Oahu and Big Island waters. Tonight through early Sunday’s SCA drops off the western Kauai waters and the Kauai Channel while Sunday’s SCA pares the area further east to just cover the typically windier zones around Maui County and waters south of Big Island.
Medium period background southwest to south swells will hold surf along the south facing shores to slightly below normal summertime averages into early next week. Small, long period south swell energy originating from recent Southern Hemispheric gales southeast of New Zealand is timed to arrive around mid week. These swells may bump surf back up to near summertime averages during the second half of the week. A small, medium period northwest swell is expected to reach the northwest islands later today and travel through the chain Sunday. These swells will lift north and west facing shore surf from near flat to possibly chest high Sunday. A series of slightly larger, medium period northwest swells emanating from a couple of eastern passing North Pacific gale lows will come across the islands next week. A few days of fresh trades over and upstream of the region will support choppy wind waves along most eastern exposures through the middle of next week.

Fire weather

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

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST this evening for 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 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Leeward Waters, Kauai Channel.
Small Craft Advisory until 6 AM HST Sunday for Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters.

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Data Courtesy of NOAA.gov

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