Weather Forecast

Hawaii County Weather Forecast for August 18, 2022

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Photo Credit: James Grenz

Hilo

Today: Mostly cloudy. Showers likely in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 54 at 4000 feet. Northeast winds up to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Kona

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs 83 to 88 near the shore to around 70 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 69 to 76 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 50 percent.

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Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 83 to 88 near the shore to around 70 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

Today: Partly sunny. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds up to 20 mph increasing to 10 to 25 mph after midnight. Chance of rain 50 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Kohala

Today: Partly sunny. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds up to 20 mph. Chance of rain 50 percent.

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Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 68 near the shore to 56 to 62 near 3000 feet. East winds up to 20 mph increasing to 10 to 25 mph after midnight. Chance of rain 50 percent.

Friday: Breezy. Mostly sunny with isolated showers. Highs around 83 near the shore to 70 to 80 near 3000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

South Big Island

Today: Breezy. Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows around 70 near the shore to around 53 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Friday: Breezy. Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Highs around 87 near the shore to around 74 near 5000 feet. East winds 10 to 25 mph decreasing to up to 25 mph in the afternoon. Chance of rain 20 percent.

Puna

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Today: Mostly cloudy. Showers likely in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 70 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 54 at 4000 feet. Northeast winds up to 15 mph shifting to the northwest after midnight. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to 70 to 75 at 4000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny with isolated showers in the morning, then mostly cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs around 87 near the shore to 71 to 77 above 4000 feet. East winds up to 10 mph shifting to the northwest in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers in the evening, then partly cloudy after midnight. Lows 70 to 76 near the shore to 51 to 58 above 4000 feet. East winds up to 15 mph. Chance of rain 40 percent.

Friday: Mostly sunny. Breezy. Highs around 87 near the shore to 71 to 77 above 4000 feet. Northeast winds up to 20 mph.

Detailed Forecast

Synopsis

A ridge of high pressure north of the state will lift northward and allow for a gradual strengthening of the trade winds during the next couple days. Showers will favor windward slopes and coasts this morning, before transitioning over to leeward and interior areas this afternoon. A more typical, but drier than normal trade wind pattern will return tonight and hold through the weekend, with moderate to locally breezy conditions prevailing. A mid and upper level trough will bring some deeper moisture and an increase in trade wind showers as it moves into the region during the first half of next week, while the trades gradually ease into the light to moderate range.

Discussion

Currently at the surface, a 1022 mb high is centered around 1600 miles northeast of Honolulu, with a ridge axis extending west- southwest to a location around 350 miles north of Kauai. The resulting gradient is producing light to moderate trades early this morning, with land breezes present in many of the more sheltered locales. Infrared satellite imagery shows clear to partly cloudy conditions in most areas, with a bit more cloud cover in some windward and mauka areas, as well as leeward Big Island. Radar imagery shows scattered showers moving into windward areas, with a few decaying showers or sprinkles making it into leeward locales. A few showers also continue to hug the leeward Big Island coast. Main short term focus revolves around trade wind trends and rain chances.
The ridge of high pressure north of the state will lift northward during the next couple days, resulting in an increase in trade wind speeds across the island chain. Light to moderate trades will hold over the western end of the state today, while moderate trades will become locally breezy by late in the day. The trades are expected to be light enough over Kauai and Oahu for sea breezes to develop in the more sheltered leeward areas. The trades will increase to moderate and locally breezy levels statewide tonight, with moderate to breezy conditions then holding in place Friday through the weekend. A front dropping southward toward the islands early next week, should ease the trades to moderate levels on Monday, and into the light to locally moderate range Tuesday and Wednesday, with some land and sea breezes possible in the more sheltered leeward areas once again.
As for the remaining weather details, scattered showers will continue to favor windward areas this morning, before transitioning over to leeward and interior locales this afternoon. Lingering instability could allow for the development of a thunderstorm or two over the Big Island this afternoon as well. The daytime convective showers should end quickly this evening, with a more typical trade wind pattern then taking hold featuring primarily windward and mauka showers. Rather dry trade wind weather will prevail Friday through the weekend, with showers limited primarily to windward slopes and coasts. We should see an increase in trade wind showers during the first half of next week as a mid and upper level trough and some associated deeper moisture moves in from the east.

Aviation

The local weather pattern will be in a transition period today, as the recent light wind regime is gradually replaced by strengthening trade winds across the entire island chain. The strongest trade winds will initially be in the vicinity of the eastern islands this morning. The weaker trades near Kauai and Oahu may allow local sea breeze circulations to develop starting late this morning over the leeward sections of the western islands. However, expect moderate to locally strong trade winds to spread over most areas by late this afternoon or evening. The trades will carry some low clouds and showers into windward sections of the islands, which may produce brief MVFR conditions. If the sea breezes form later today, there may also be clouds and spotty showers over some leeward sections. Otherwise, expect VFR conditions to prevail through this evening.
No AIRMETs are currently in effect, and none are anticipated through this morning. There is a possibility that as the low- level trade wind flow strengthens later today and tonight, AIRMET Tango for mechanical low-level turbulence may eventually be required for portions of the state starting tonight or early Friday morning.

Marine

A weak ridge has persisted north of the islands and has been sustaining light to moderate trade winds. However, the ridge has begun strengthening and shifting north, causing trade winds to increase from east to west across the island chain. A Small Craft Advisory will be posted for the typically windier waters around Maui County and the Big Island by noon HST today.
Small south and southeast swells are expected to produce below typical summertime surf heights along south facing shores into Friday. Forerunners from a new, long-period south swell are expected to arrive late Friday night. This swell will likely produce near to slightly above average surf along south facing shores from this weekend into early next week. Surf will remain small along east facing shores until trade winds strengthen further. As they do, modest, choppy surf will return along east facing shores, lasting from this weekend into early next week. Expect nearly flat conditions along north facing shores. However, small, short-period north-northwest swells beginning later today may provide a slight boost in surf heights along exposed north facing shores through this weekend. Models show a slightly larger and longer period northwest swell arriving early next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory from noon today to 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov

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