Weather Forecast

Hawaii County Weather Forecast for September 14, 2021

September 14, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Mostly cloudy with scattered showers. Highs 78 to 84 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Cloudy with showers. Lows 64 to 72 near the shore to around 56 at 4000 feet. Light winds. Chance of rain 90 percent.

Wednesday: Cloudy with numerous showers. Highs 79 to 85 near the shore to 65 to 71 at 4000 feet. Southeast winds around 10 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 84 to 89 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 50 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Scattered showers. Lows 70 to 75 near the shore to 51 to 56 near 5000 feet. Light winds. Chance of rain 50 percent.

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Wednesday: Mostly sunny in the morning then becoming partly sunny. Scattered showers. Highs around 86 near the shore to around 68 near 5000 feet. Light winds becoming southwest up to 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

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Today: Partly sunny with scattered showers. Highs 64 to 84. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 57 to 64 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 66 to 85. East winds up to 10 mph. Chance of rain 70 percent.

Kohala

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Today: Partly sunny with scattered showers. Highs 64 to 84. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 71 near the shore to 57 to 64 near 3000 feet. East winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 66 to 85. East winds up to 10 mph. Chance of rain 70 percent.

South Big Island

Today: Sunny in the morning then becoming mostly cloudy. Isolated showers. Highs around 84 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows around 74 near the shore to around 53 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 30 percent.

Wednesday: Partly sunny with scattered showers. Highs around 85 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain 40 percent.

Puna

Today: Mostly cloudy with scattered showers. Highs 78 to 84 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Tonight: Cloudy with showers. Lows 64 to 72 near the shore to around 56 at 4000 feet. Light winds. Chance of rain 90 percent.

Wednesday: Cloudy with numerous showers. Highs 79 to 85 near the shore to 65 to 71 at 4000 feet. Southeast winds around 10 mph. Chance of rain 70 percent.

Waikoloa

Today: Sunny in the morning then becoming partly sunny. Isolated showers. Highs 83 to 90 near the shore to 66 to 72 above 4000 feet. North winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Lows around 74 near the shore to 50 to 56 above 4000 feet. East winds up to 10 mph in the evening becoming light. Chance of rain 20 percent.

Wednesday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs 85 to 90 near the shore to 67 to 73 above 4000 feet. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper level low northeast of the islands will drift slowly west-southwest through the week, weakening the trade winds starting tonight through early Thursday morning. Localized sea breezes may develop over sheltered western slopes each afternoon through Wednesday. Instability associated with the upper low will lead to periods of showers and the potential for localized heavy rain on Wednesday and Thursday. Drier weather should return from Friday onward as the trade winds strengthen across the region.

Discussion

The satellite water vapor imagery this morning shows the unstable upper low continues to drift slowly westward and is roughly 600 miles north-northeast of Oahu. Isolated to scattered thunderstorms are developing within the cold core center of the low. The instability around this low is producing fairly unstable clouds across the region and showers are developing as these clouds move into each island on the trade winds.
Broad instability associated with this low and a weaker high pressure ridge north of the islands will keep the trade wind temperature inversion in the 7,000 to 10,000 foot range for the next few days. Cumulus cloud heights will rise to the inversion level with deeper clouds keeping periods of enhanced showers in the forecast through Thursday.
For today, moderate trade wind speeds will start to weaken with localized land and sea breezes forming along terrain sheltered western slopes of Kauai and Oahu. Wind convergence between the afternoon sea breezes and the lighter trade winds may cause afternoon showers to develop over leeward areas. This light to moderate trade wind pattern with localized land and sea breezes will continue through Wednesday.
On Wednesday and Wednesday night, the upper low will drift westward, passing just north of the Hawaiian Islands with the potential for a few heavy showers in some locations. Expect slower moving shower bands in lighter trade wind flow. Isolated thunderstorms are possible by Wednesday afternoon over the higher elevations of the Big Island. Chances for locally heavy showers will continue for all islands into Thursday.
Thursday will be a transition day, as the trough begins to move away from the state, and high pressure builds north of the island chain. Showery conditions are still expected as the breezy trade winds fill back from east to west. Shower coverage will decrease a bit over the eastern islands as more stable trade winds move into the eastern half of the state.
By Friday, the trade winds will strengthen across the region with drier weather trends in the forecast. Expect a more typical windward and mountain shower pattern favoring the overnight to early morning hours through Monday.

Aviation

High pressure northeast of the state will allow for persistent moderate trades across the island chain today. Thus, the highest concentration of showers will likely be confined to the windward coasts and slopes. Isolated activity expected elsewhere.
Some of the heaviest showers may generate brief periods of MVFR ceilings and visibility.
There are currently no AIRMETs in effect.

Marine

High pressure north of the state will keep moderate to fresh trade winds in place today. The trades will briefly ease tonight and Wednesday as a surface trough slides by to the north of the islands. As this trough exits to the northwest of the state Wednesday night and Thursday, the trades will gradually ramp back up to locally strong levels, with winds reaching Small Craft Advisory (SCA) thresholds over the typically windy Maui and Big Island waters by Thursday. The strong SCA level trades are expected to expand to most if not all waters Friday and Saturday, before dropping a notch Sunday into early next week.
A series of long period south and southwest swells will keep surf along south facing shores near to slightly above the September average through Thursday. South shore surf will then gradually lower through the weekend into early next week. Small surf will prevail on north facing shores through most of the week, with a small bump from a northwest swell possible this weekend. East shore surf will remain well below normal through Wednesday. As trade winds ramp up Thursday through Saturday, surf along east facing shores will become rough and rise to near seasonal levels, before lowering gradually Sunday into early next week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov

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