Weather Forecast

Hawaii County Weather Forecast for September 16, 2021

September 16, 2021, 7:16 AM HST
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Hilo

Today: Mostly cloudy with scattered showers. Highs 79 to 85 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 72 near the shore to around 58 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers. Highs 78 to 85 near the shore to 64 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kona

Today: Partly sunny. Scattered showers in the afternoon. Highs 84 to 89 near the shore to around 70 near 5000 feet. Northwest winds up to 10 mph. Chance of rain 40 percent.

Tonight: Mostly cloudy. Scattered showers in the evening. Lows 71 to 76 near the shore to 53 to 58 near 5000 feet. Light winds. Chance of rain 40 percent.

ARTICLE CONTINUES BELOW AD

Friday: Mostly cloudy. Isolated showers in the afternoon. Highs around 86 near the shore to around 69 near 5000 feet. Light winds. Chance of rain 20 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs 66 to 85. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 71 near the shore to 58 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 66 to 85. East winds 10 to 25 mph. Chance of rain 50 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Breezy. Partly sunny with scattered showers. Highs 66 to 85. East winds up to 25 mph increasing to 10 to 25 mph in the afternoon. Chance of rain 40 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows 65 to 71 near the shore to 58 to 64 near 3000 feet. East winds 10 to 25 mph. Chance of rain 50 percent.

Friday: Breezy. Mostly cloudy with scattered showers. Highs 66 to 85. East winds 10 to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Mostly cloudy in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 85 near the shore to around 68 near 5000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows around 74 near the shore to around 54 near 5000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph after midnight. Chance of rain 20 percent.

Friday: Breezy. Mostly sunny in the morning, then mostly cloudy with isolated showers in the afternoon. Highs around 85 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 20 percent.

Puna

Today: Mostly cloudy with scattered showers. Highs 79 to 85 near the shore to 65 to 71 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Numerous showers in the evening, then scattered showers after midnight. Lows 65 to 72 near the shore to around 58 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Friday: Partly sunny with scattered showers. Highs 78 to 85 near the shore to 64 to 70 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Mostly sunny. Breezy. Highs 84 to 90 near the shore to 68 to 74 above 4000 feet. Northeast winds up to 15 mph shifting to the north up to 25 mph in the afternoon.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy after midnight. Lows around 75 near the shore to 52 to 58 above 4000 feet. East winds up to 25 mph. Chance of rain 20 percent.

Friday: Partly sunny. Highs 84 to 90 near the shore to 67 to 74 above 4000 feet. Northeast winds up to 15 mph.

Detailed Forecast

Synopsis

Unsettled weather will linger mainly over the western islands of Kauai and Oahu today as we transition to a more stable weather pattern. High pressure will build in east of the low as it moves away from the state with strengthening trade winds and drier trends into Sunday. Brief passing showers will develop over the typical windward and mountain areas of each island. Another upper level disturbance may bring increasing showers along with decreasing trade wind speeds from Sunday into early next week.

Discussion

An unstable upper level low, just northwest of Kauai, will continue to drift westward away from the island chain. Lingering instability will keep passing showers over the western islands through the morning hours. Local radar imagery this morning shows a few bands of moderate to heavy showers drifting through the coastal waters from Maui to Kauai. While strengthening easterly trade winds are bringing more stable conditions to the Big Island this morning. The heaviest showers last night were reported over the eastern and southeastern slopes of the Big Island with rainfall totals ranging from 1.00 to 3.00 inches over a six to twelve hour time period. A Flood Advisory was issued for this area to cover minor nuisance flooding concerns.
Today will be a transition day from unstable wet weather with light winds into drier weather trends with strengthening trade winds as the high pressure system north of the islands builds back into the region. Trade winds will strengthen into the moderate to locally breezy range for most areas by afternoon. As the upper low drifts away from the islands a mid level (700 mb) ridge will move into the region from east to west and stabilize the air mass. Forecast guidance suggests trade wind inversion heights dropping down to the 5,000 to 7,000 foot range later this evening, producing fairly stable and dry weather across the state. After some enhanced morning showers, locally heavy at times near Kauai, we will transition into brief passing showers focused mainly over windward and mountain areas.
Friday and Saturday, a high pressure system north of the islands will produce moderate to breezy trade winds with fairly stable and dry weather conditions. Brief passing showers are possible mainly over windward and mountain areas.
Sunday into Tuesday, a weak upper level trough will move into the region from the east, increasing shower trends for all islands with decreasing trade wind trends from Sunday night into early next week.

Aviation

The surface trough should be exiting Kauai County in the next couple of hours, with a east-southeast wind flow following right behind. A trade wind flow, now over the Big Island, will be spreading westward, reaching Oahu around noon, then Kauai late this afternoon. The return of the trades will be moderate to locally strong, as high pressure strengthens north of the islands, leading to an AIRMET Tango by 22z for low level turbulence, south through west of all mountains.
The area of clouds and showers that impacted eastern and windward Big Island continues to break up, resulting in an area of layered clouds between 10k and 25k feet, now moving westward across Maui County. It will continue westward reaching Oahu before sunrise, then dispersing as the morning progresses. There are some lower clouds and showers that will favor the windward and mountain areas of Maui, Molokai, and Oahu during the morning hours, but not widespread enough to warrant an AIRMET Sierra for mountain obscuration.
AIRMET Sierra for eastern and windward Big Island is likely to be lowered at 16z.
Lingering instability and moisture will impact primarily interior and leeward Kauai this afternoon, leading to potential AIRMET Sierra and mountain obscuration. Otherwise, we are looking at the the return of a typical trade wind pattern.

Marine

A surface trough northwest of Kauai is moving west away from the islands this morning. This trough’s exit will allow high pressure north of the state to build down toward the eastern waters and tighten the regional pressure gradient. This will ultimately re- establish primarily fresh to locally strong trades trades the next several days. A Small Craft Advisory (SCA) is in effect for the Kaiwi Channel eastward, including the waters surrounding Maui and Big Island, except for Maalaea Bay. Weakening trades over the windward Big Island waters and a late day strengthening of Maalaea Bay northerlies to advisory thresholds will be the only areal adjustment needed to tonight into Friday’s SCA.
The most recent southwest to south swell will be slowly falling through today with a possible small reinforcement filling in later today into early Friday. The next small southwest south swell may arrive toward the middle of next week. A small, medium period northwest swell is expected to reach the islands later this weekend to then be followed by a series of small, similar to slightly higher period northwest north swell energy through next week. East facing shore surf will trend up to seasonable levels the next couple of days with the return of fresh trades over and upstream of the state.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST this evening for Big Island Windward Waters.
Small Craft Advisory from 6 PM this evening to 6 AM HST Saturday for Maalaea Bay.

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Data Courtesy of NOAA.gov

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