Weather Forecast

Hawaii County Weather Forecast for August 15, 2021

August 15, 2021, 7:16 AM HST
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Photo Credit: James Grenz

Hilo

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 82 to 88 near the shore to around 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 73 near the shore to around 55 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 87 near the shore to around 72 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Kona

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs 81 to 86 near the shore to around 71 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 69 to 74 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 20 percent.

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Monday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 70 near 5000 feet. North winds up to 10 mph shifting to the west around 10 mph in the afternoon. Chance of rain 40 percent.

Waimea

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Today: Breezy. Mostly sunny with scattered showers. Highs 71 to 84. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 83. Northeast winds up to 15 mph. Chance of rain 40 percent.

Kohala

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Today: Breezy. Mostly sunny with scattered showers. Highs 71 to 84. East winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds 10 to 20 mph decreasing to up to 15 mph after midnight. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 83. Northeast winds up to 15 mph. Chance of rain 40 percent.

South Big Island

Today: Sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 86 near the shore to around 76 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Breezy. Isolated showers. Lows around 69 near the shore to around 53 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Monday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 85 near the shore to around 75 near 5000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 40 percent.

Puna

Today: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs 82 to 88 near the shore to around 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 66 to 73 near the shore to around 55 at 4000 feet. Northeast winds up to 10 mph shifting to the west after midnight. Chance of rain 50 percent.

Monday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 81 to 87 near the shore to around 72 at 4000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Waikoloa

Today: Sunny. Isolated showers in the afternoon. Highs 82 to 87 near the shore to 68 to 75 above 4000 feet. North winds up to 15 mph shifting to the northwest in the afternoon. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming mostly clear. Lows around 73 near the shore to 52 to 59 above 4000 feet. East winds up to 10 mph. Gusts up to 30 mph.

Monday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to 68 to 75 above 4000 feet. North winds up to 10 mph shifting to the west in the afternoon. Chance of rain 40 percent.

Detailed Forecast

Synopsis

Trade winds will gradually weaken through tonight, followed by light and variable winds Monday and Tuesday as a weak surface trough passes from east to west to the north of the state. This lighter wind regime will likely allow alternating afternoon sea breezes and nighttime land breezes to develop. The sea breezes may produce clouds and showers over interior and leeward locations each afternoon. A return of locally breezy trade wind conditions is expected later this week.

Discussion

A 1031 mb surface high is centered near 38N 161W, or almost 1100 miles north of Lihue early this morning. The relatively tight pressure gradient south of this feature is maintaining locally breezy trade winds across portions of the state. Elsewhere, a weak north to south oriented surface trough, which appears to be around 750 miles northeast of Hilo, is moving slowly westward. Aloft, upper level ridging is evident in the vicinity of the islands, which is maintaining stable atmospheric conditions across the region.
Loops of satellite imagery and radar reflectivities show areas of scattered to broken low clouds with embedded scattered showers streaming into the windward sides of most islands early this morning. The low-level trade wind flow is expected to continue to transport these low clouds and showers over most windward sections through mid- morning. There may also be a brief shower or two over some leeward sections this morning.
As daytime heating increases during the day, drier conditions are expected to develop across many areas by this afternoon. In addition, the surface trough approaching from the northeast and the surface high shifting to the north are expected to cause some relaxation of the pressure gradient. This will produce a gradual decrease in trade winds speeds through tonight.
Once the surface trough moves north of the islands, it will cause the winds to become light and variable across the state starting Monday. This will likely allow the development of alternating local afternoon sea breeze and nighttime land breeze circulations. The forecast guidance continues to show the main area of low level moisture in the vicinity of this trough will remain just north of the state early this week, but a slight increase in moisture is possible on Tuesday. Regardless, low clouds and a chance of showers can be expected each afternoon, especially across interior and leeward areas of most islands. If the slight increase in moisture occurs, this could enhance the cloud cover and shower activity Tuesday afternoon. Note that the light wind regime will also likely result in very warm and muggy conditions from Monday through Tuesday.
The surface trough is expected to exit northwest of the state by mid-week. This will likely cause a transition back to trades starting Wednesday. Locally breezy trade winds and a relatively dry weather pattern are in the latest forecast from Thursday through Friday. The trade winds may weaken again next weekend.

Aviation

High pressure north of the state will keep moderate to locally breezy trade winds in place. Wind speeds aloft are expected to gradually ease over the next 12 hours. AIRMET Tango for low level turbulence over and downstream of higher terrain may be canceled later today.
Low topped clouds and weak trade wind showers will favor north and east facing slopes and coasts. Isolated spillover showers will impact leeward portions of the smaller islands mainly in the late night and morning hours. Mountain obscuration could become an issue for windward portions of Kauai or Oahu tonight.
Light afternoon sea breezes will encourage inland cloudiness across south and west facing slopes of the Big Island that will linger through the evening hours. A capping inversion will limit vertical development, so little associated precipitation is expected.

Marine

High pressure far N of the islands will support moderate trade winds today, but winds have diminished to the extent that the Small Craft Advisory (SCA) for the windier areas around the Big Island and Maui County has been cancelled. Wind speeds will continue to gradually diminish through Monday as a low-level trough to the distant NE moves W and loosens the low-level pressure gradient. This will also back trade winds to the NE over Kauai and Oahu waters through tonight. As the trough passes N of the islands on Monday and Tuesday, light E/SE winds are expected statewide. As the trough moves NW of the area Wednesday and Thursday, trade winds will strengthen while backing to the ENE.
Observations from NDBC buoy 51101 NW of Kauai indicate that an expected pulse of long-period WNW swell has begun to arrive. This swell will spread to local waters today into Monday, with peak swell heights near 4 feet. The swell’s height and period will diminish on Tuesday. Surf along S facing shores is expected to be trending up today into Monday, as a long-period S swell arrives. Several pulses of swell will likely make this a long- lived event, with a High Surf Advisory likely for S facing shores as the swell peaks Monday into Wednesday. Surf along E facing shores will remain relatively small for the next several days, while a small, long-period E swell from distant Hurricane Linda may arrive by the middle of the upcoming week

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov

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