Weather Forecast

Hawaii County Weather Forecast for September 11, 2021

September 11, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy. Numerous showers in the evening, then showers after midnight. Lows 64 to 72 near the shore to 54 to 59 at 4000 feet. West winds up to 10 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 83 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Kona

Today: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 67 near 5000 feet. Northwest winds up to 10 mph shifting to the southwest 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 70 to 75 near the shore to around 54 near 5000 feet. Light winds. Chance of rain 50 percent.

ARTICLE CONTINUES BELOW AD

Sunday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Highs 81 to 86 near the shore to around 67 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

ARTICLE CONTINUES BELOW AD

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 70 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 63 to 83. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

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 70 near the shore to 56 to 63 near 3000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Sunday: Breezy. Partly sunny with scattered showers. Highs 63 to 83. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 83 near the shore to around 65 near 5000 feet. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows around 73 near the shore to around 53 near 5000 feet. Northeast winds up to 15 mph. Chance of rain 20 percent.

Sunday: Breezy. Sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 83 near the shore to around 66 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Puna

Today: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 83 near the shore to 64 to 70 at 4000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Tonight: Cloudy. Numerous showers in the evening, then showers after midnight. Lows 64 to 72 near the shore to 54 to 59 at 4000 feet. West winds up to 10 mph. Chance of rain 90 percent.

Sunday: Mostly cloudy. Numerous showers in the morning, then scattered showers in the afternoon. Highs 77 to 83 near the shore to 63 to 70 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Waikoloa

Today: Mostly sunny. Highs 83 to 89 near the shore to 66 to 72 above 4000 feet. Northwest winds up to 10 mph.

Tonight: Partly cloudy. Lows around 74 near the shore to 51 to 56 above 4000 feet. Southeast winds up to 10 mph.

Sunday: Mostly sunny. Highs 83 to 88 near the shore to 65 to 72 above 4000 feet. Northeast winds up to 15 mph.

Detailed Forecast

Synopsis

A weakened high pressure ridge north of the area and an upper level low roughly 1000 miles northeast of the islands will continue to keep the trade winds in the light to moderate range today. Trade winds will strengthen into the moderate to breezy range on Sunday and Monday as the ridge strengthens. This unstable upper low will slowly drift westward and weaken through early next week, passing just north of the Hawaiian Islands on Wednesday. Periods of enhanced rain showers are likely for all islands into Friday as this unstable system slowly passes through the region.

Discussion

The GOES water vapor satellite imagery this morning shows a narrow upper level trough just north of the state with an unstable upper low roughly 1000 miles northeast of the islands. A subtropical jet stream just south of the upper trough will continue to produce periods of high cirrus clouds, enhancing sunrise and sunset colors through Sunday. The infra-red satellite imagery shows moderately unstable cumulus clouds drifting in on the trade winds. A surface trough northeast of the islands, a reflection of the upper low, will help weaken the trade wind speeds across the region. This surface trough will tend to weaken as the low slowly drifts westward. Local radar imagery shows scattered showers riding in on the trade winds.
The high pressure ridge north of the state is split by a passing cold front moving through the eastern Pacific. The upper level low northeast of the islands continues to produce a surface trough northeast of the islands. Both trough features will reduce the strength of the trade winds today. Expect one more day of light to moderate trade winds across the region with weak daytime sea breezes limited to terrain sheltered areas along western slopes of each island. Trade winds are forecast to increase into the moderate to locally breezy range on Sunday and Monday. Trade wind speeds will decrease again into the light to moderate range from Tuesday onward as the upper low slowly passes by just north of the island chain.
On the rainfall side, enhanced showers are expected through the week for all islands as this upper low slowly passes by north of the state. Model cross sections show trade wind inversion heights around the 8000 foot level, which will produce deeper cloud heights and more shower coverage. All areas will see an increase in shower activity with the highest rainfall totals favoring the typical windward and mountain areas. However, leeward areas will also see periods of enhanced rainfall coverage through next Friday. Deeper moisture will be drawn up from the south on Wednesday and Thursday, producing higher shower coverage, as the upper low center passes by just north of the state. Rainfall coverage was increased in the morning forecast grids for this time period.

Aviation

High pressure north of the state will keep gentle to moderate trade winds in place through tonight. Clouds and showers will favor windward slopes and coasts, with a stray shower drifting into leeward communities from time to time. Brief MVFR cigs/vsbys will be possible in passing showers, mainly along windward slopes and coasts. Otherwise, predominantly VFR conditions will prevail during the next 24 hours.
AIRMET Sierra remains in effect for mountain obscuration across windward sections of Kauai. Conditions should improve here later this morning.

Marine

The weak surface trough northeast of the state resulting in recent light to moderate trades is washing out this morning. The pressure gradient from high pressure centered far north northeast of the state will become more dominant and produce a more healthy moderate to fresh trade wind regime late today through Monday. The only chance for winds reaching Small Craft Advisory thresholds this weekend will be over the east island channels and bays early Sunday, in particular the Alenuihaha Channel. Little change to the regional large scale pressure gradient equates to generally solid moderate northeast to east trades through the middle of the month.
A series of overlapping small, long period south southeast swells will hold slightly below average surf along south facing shores the next couple of days. A slightly larger swell, with more long period energy is passing over the Samoa buoy early this morning. This swell should reach the islands sometime Monday and pick south surf back up to near seasonable heights Tuesday and Wednesday. Recent observations have verified that more southern exposures along western shorelines have and will benefit from some of this south swell wrapping around to the west. Small wind wave swell from slightly stronger trades will maintain choppy surf along many east faces this weekend. A small, medium period northwest swell arriving Sunday may bring surf to just above flat into early next week for north facing shores.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov

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