Weather Forecast

Hawaii County Weather Forecast for September 09, 2021

September 9, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Partly sunny with scattered showers. Highs 78 to 85 near the shore to 64 to 72 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 63 to 71 near the shore to 54 to 59 at 4000 feet. North winds around 10 mph. Chance of rain 60 percent.

Friday: Partly sunny with scattered showers. Highs 78 to 84 near the shore to 63 to 71 at 4000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

Kona

Today: Sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 82 to 87 near the shore to around 68 near 5000 feet. Southwest winds up to 10 mph shifting to the west around 10 mph in the afternoon. Chance of rain 50 percent.

Tonight: Partly cloudy. Scattered showers in the evening, then isolated showers after midnight. Lows 69 to 74 near the shore to 51 to 56 near 5000 feet. Light winds. Chance of rain 50 percent.

ARTICLE CONTINUES BELOW AD

Friday: Sunny with isolated showers early in the morning, then partly sunny with scattered showers in the late morning and afternoon. Highs 82 to 88 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 40 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with scattered showers. Highs 65 to 85. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 70 near the shore to 56 to 63 near 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 64 to 84. Northeast winds around 10 mph. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Breezy. Mostly sunny with scattered showers. Highs 65 to 85. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy with scattered showers. Lows 63 to 70 near the shore to 56 to 63 near 3000 feet. East winds around 10 mph. Chance of rain 50 percent.

Friday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 64 to 84. Northeast winds around 10 mph. Chance of rain 50 percent.

South Big Island

Today: Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 84 near the shore to around 66 near 5000 feet. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Isolated showers in the evening. Lows around 73 near the shore to around 53 near 5000 feet. Northeast winds around 10 mph in the evening becoming light. Chance of rain 20 percent.

Friday: Sunny early in the morning, then partly sunny with isolated showers in the late morning and afternoon. Highs around 83 near the shore to around 65 near 5000 feet. Light winds becoming east around 10 mph in the afternoon. Chance of rain 20 percent.

Puna

Today: Partly sunny with scattered showers. Highs 78 to 85 near the shore to 64 to 72 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Showers likely in the evening, then scattered showers after midnight. Lows 63 to 71 near the shore to 54 to 59 at 4000 feet. North winds around 10 mph. Chance of rain 60 percent.

Friday: Partly sunny with scattered showers. Highs 78 to 84 near the shore to 63 to 71 at 4000 feet. Northeast winds around 10 mph. Chance of rain 50 percent.

Waikoloa

Today: Sunny and breezy. Highs 83 to 89 near the shore to 66 to 73 above 4000 feet. North winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

Tonight: Mostly clear. Lows around 73 near the shore to around 53 above 4000 feet. Light winds.

Friday: Mostly sunny. Isolated showers late in the morning. Scattered showers in the afternoon. Highs 83 to 89 near the shore to 66 to 73 above 4000 feet. Light winds. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trade winds will continue today before weakening tonight and Friday. Trade winds will gradually increase Saturday before becoming breezy again on Sunday. Just a few windward showers are expected today, but an increase in moisture later tonight and Friday will fuel an increase in windward showers that may persist into Saturday.

Discussion

Moderate to locally breezy trade winds will back to a NE direction statewide today and Friday as a surface trough to the distant NE moves slowly W. As the trough draws closer, the low-level pressure gradient over the state will weaken – most notably over the E end of the chain. While winds will trend weaker and become light over most of the state, reaching a minima on Friday, the gradient looks to remain sufficiently tight to support moderate NE trades over Kauai.
As the trough moves closer to the longitude of the islands this weekend, it is expected to weaken while surface high pressure consolidates to the distant NE. The tightening low-level pressure gradient is expected to support a trend toward locally breezy ENE trade winds statewide, although a lingering weakness in the gradient may keep winds from getting all that strong near the Big Island.
A strong low-level subsidence inversion will keep the island atmosphere capped for the foreseeable future. Limited moisture immediately upstream of the islands means a mostly dry day and evening, with just a few small and short-lived showers over windward areas. Later tonight and Friday, an area of increased low-level moisture will arrive from the NE, likely pushing inversion heights upward, thereby fueling an increase in windward showers that may persist into Saturday. The trades may push a few of these showers to leeward areas on the smaller islands. Thereafter, guidance indicates a fairly typical trade wind weather regime into next week, with low clouds and showers occasionally delivering a few showers, mainly windward.

Aviation

Moderate trade winds will carry scattered clouds and isolated showers towards east facing slopes and coasts. Locally gusty winds through channeled areas are expected to persist through early evening then weaken on Friday. AIRMET Tango for low level mechanical turbulence to the lee of higher terrain will likely remain necessary through at least 0600z.
For Leeward Big Island, afternoon sea breezes will focus cloud cover over south and west facing slopes. Clouds will linger through the evening hours then move offshore after midnight. A capping inversion around 07 kft will inhibit vertical development, so few associated showers are expected to develop.
Lastly, numerical models depict a sharp upper level trough anchored just north of the state. SIGMET Tango has been issued for moderate to upper level severe turbulence above FL250 just north and northeast of the smaller islands. The area of turbulence is expected to shift southward later today, possibly impacting Kauai or Oahu this afternoon and the remainder of the smaller islands by late evening.

Marine

High pressure north of the islands will maintain trade winds through the weekend. But a dissipating surface trough nearing the islands from the northeast, will cause the locally strong trades to trend softer over the eastern half of the island chain today. Moderate to fresh trades will continue elsewhere. The Small Craft Advisory has been extended to 6 pm HST for only the Alenuihaha Channel. Although the trough will dissipate before reaching the islands, the pressure gradient will favor the continuing trades in the moderate to fresh range into early next week.
A series of overlapping long period south swells will maintain near seasonal levels through the forecast period. Small surf is expected along the north facing shores from a small north and northeast pulse. This northeast swell, lasting into the weekend, may help to maintain small to moderate surf along exposed east facing shores. Otherwise, no significant swells are expected through early next week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST this evening for Alenuihaha Channel.

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Data Courtesy of NOAA.gov

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