Weather Forecast

Hawaii County Weather Forecast for August 17, 2021

August 17, 2021, 7:16 AM HST
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Photo Credit: James Grenz

Hilo

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 65 to 72 near the shore to around 54 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 81 to 87 near the shore to around 72 at 4000 feet. South winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 40 percent.

Kona

Today: Mostly sunny in the morning, then mostly cloudy with showers likely in the afternoon. Highs 82 to 87 near the shore to 68 to 73 near 5000 feet. Southwest winds up to 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 70 to 75 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 50 percent.

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Wednesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 71 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 40 percent.

Waimea

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Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 71 to 84. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 67 near the shore to 55 to 61 near 3000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 70 to 83. East winds up to 15 mph. Chance of rain 50 percent.

Kohala

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Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 71 to 84. Northwest winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 67 near the shore to 55 to 61 near 3000 feet. Light winds. Chance of rain 50 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 70 to 83. East winds up to 15 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs around 86 near the shore to around 76 near 5000 feet. East winds up to 15 mph shifting to the southeast in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows around 68 near the shore to around 52 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Breezy. Mostly sunny with isolated showers 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 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 40 percent.

Puna

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with showers likely in the afternoon. Highs 82 to 88 near the shore to around 73 at 4000 feet. Southeast winds up to 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows 65 to 72 near the shore to around 54 at 4000 feet. Southwest winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 81 to 87 near the shore to around 72 at 4000 feet. South winds up to 10 mph shifting to the southeast in the afternoon. Chance of rain 40 percent.

Waikoloa

Today: Mostly sunny in the morning, then partly sunny with showers likely in the afternoon. Highs 83 to 88 near the shore to 69 to 76 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 60 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy with isolated showers after midnight. Lows around 73 near the shore to 53 to 60 above 4000 feet. Northwest winds up to 10 mph in the evening becoming light. Chance of rain 50 percent.

Wednesday: Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 83 to 88 near the shore to 69 to 76 above 4000 feet. Northwest winds up to 10 mph. Chance of rain 40 percent.

Detailed Forecast

Synopsis

A light wind pattern will hold in place through Wednesday, with showers developing over the island interiors each afternoon, and a few showers possible near the coast each night. More typical trade wind weather will return Thursday through Saturday, with showers favoring windward and mauka areas. The trades appear to become disrupted again Sunday through early next week, with sea breezes favoring shower development over the island interiors during the afternoon hours.

Discussion

Currently at the surface, a slow moving trough of low pressure is located just north of the central islands, and is responsible for the light and variable wind regime across the state early this morning. Infrared satellite imagery shows clear to partly cloudy conditions in most areas, with more extensive cloud cover over some leeward sections of the Big Island. Meanwhile, radar imagery shows a few showers near the island coasts, with the majority of the shower activity out over the water. Main short term concern revolves around rain chances during the next couple days.
The trough of low pressure north of the state will track slowly westward during the next couple days, keeping the trade winds disrupted. As a result, light and variable winds featuring daytime sea breezes and overnight land breezes should prevail through Wednesday. The trades are expected to slowly return across the eastern end of the state late Wednesday, and across the remainder of the island chain Wednesday night as the trough of low pressure exits to the west of the islands and high pressure builds to the distant northeast. Moderate trade winds should then return Thursday through Saturday, although they should be on a downward trend on Saturday. The trades appear increasingly likely to become disrupted Sunday through early next week as the remnants of tropical cyclone Linda pass by to the north of the island chain.
As for the remaining weather details, a convective shower regime should prevail through Wednesday. Showers will favor locations near the coast and night, with scattered to numerous showers developing over the island interiors each afternoon into the early evening hours. A more typical trade wind pattern should become re-established Wednesday night through Saturday, with showers favoring windward and mauka areas. A convective shower regime may develop once again Sunday through early next week as the remnants of Linda pass by to the north of the islands.

Aviation

A light wind regime will allow local scale land and sea breezes to dominate the wind pattern over each island through Wednesday. An upper level disturbance northeast of the Hawaiian Islands will keep the atmosphere fairly unstable into Wednesday.
Overnight to early morning diverging land breezes will push clouds and showers down slope into the coastal waters. Sea breezes will strengthen a few hours after sunrise building clouds over each island. Converging sea breeze winds will produce periods of afternoon to early evening showers favoring western slopes and interior sections. Brief periods of MVFR/IFR conditions over western and interior sections of each island are likely in this pattern.
No AIRMETs in effect. Expect AIRMETs for Mountain Obscuration this afternoon.

Marine

A surface trough passing north of the state the next couple of days will disrupt trade flow…ultimately weakening and varying winds around the islands. The western movement of this trough will subtly veer light to gentle breezes east southeast in time through early Wednesday. A more normal trade wind pattern will begin to take hold Wednesday night into Thursday as the trough moves northwest of the island chain.
The anticipated large, long period south swell has arrived and will produce High Surf Advisory (HSA) surf (peaking 10 foot or greater faces) along south facing shores through Wednesday. Offshore southern buoys are verifying this high south swell arrival…6 to 7 foot swells within the 17-19 second spectral bands. The nearshore PacIOOS Barber’s Point buoy is observing consistent 3 foot or greater swell heights within the high 18-22 second spectral bands. The HSA will be in effect through Wednesday afternoon as the enhanced southern swell energy drives this high south shore surf event through mid week.
The fairly low, moderate period northwest to west swell will be slowly declining through Tuesday. This will have north and west facing shore surf gradually falling through late this afternoon. Surf along east facing shores will remain small the next several days. Swell within the small captured fetch from Hurricane Linda in the East Pacific might reach the east facing shores of the eastern most islands late this week as small, moderate period east swell.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Wednesday for Niihau, Kauai Leeward, Waianae Coast, Kahoolawe, Maui Leeward West, Kona, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Molokai Southeast, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast.

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Data Courtesy of NOAA.gov

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