Weather Forecast

Hawaii County Weather Forecast for October 09, 2021

October 9, 2021, 7:15 AM HST
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Hilo

Today: Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 78 to 83 near the shore to around 70 at 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Occasional showers in the morning, then showers likely in the afternoon. Highs 79 to 85 near the shore to 68 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain near 100 percent.

Kona

Today: Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 86 near the shore to around 73 near 5000 feet. West winds up to 10 mph with gusts to 50 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 69 to 74 near the shore to around 55 near 5000 feet. Light winds. Chance of rain 20 percent.

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Sunday: Mostly sunny in the morning, then mostly cloudy with scattered showers in the afternoon. Haze through the day. Highs around 86 near the shore to around 73 near 5000 feet. West winds up to 10 mph with gusts to 50 mph. Chance of rain 30 percent.

Waimea

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Today: Windy. Mostly cloudy with showers likely. Highs 68 to 83. East winds 15 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Windy. Scattered showers in the evening, then showers likely after midnight. Lows around 68 near the shore to 55 to 62 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Sunday: Windy. Mostly cloudy with showers likely. Highs around 81 near the shore to 73 to 80 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Kohala

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Today: Windy. Mostly cloudy with showers likely. Highs 68 to 83. East winds 15 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Windy. Scattered showers in the evening, then showers likely after midnight. Lows around 68 near the shore to 55 to 62 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

Sunday: Windy. Mostly cloudy with showers likely. Highs around 81 near the shore to 73 to 80 near 3000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 70 percent.

South Big Island

Today: Windy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 85 near the shore to around 74 near 5000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 30 percent.

Tonight: Windy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Haze through the night. Lows around 69 near the shore to around 54 near 5000 feet. East winds 10 to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Sunday: Windy. Mostly sunny in the morning, then partly sunny with scattered showers in the afternoon. Haze through the day. Highs around 85 near the shore to around 74 near 5000 feet. East winds 15 to 30 mph with gusts to 50 mph. Chance of rain 30 percent.

Puna

Today: Breezy. Occasional showers in the morning, then showers likely in the afternoon. Highs 78 to 83 near the shore to around 70 at 4000 feet. Northeast winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain near 100 percent.

Tonight: Breezy. Occasional showers. Lows around 69 near the shore to around 55 at 4000 feet. North winds up to 20 mph. Chance of rain near 100 percent.

Sunday: Occasional showers in the morning, then showers likely in the afternoon. Highs 79 to 85 near the shore to 68 to 73 at 4000 feet. Northeast winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain near 100 percent.

Waikoloa

Today: Mostly sunny in the morning then becoming partly sunny. Windy. Isolated showers. Highs around 85 near the shore to 69 to 75 above 4000 feet. Northeast winds up to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Tonight: Windy. Partly cloudy with isolated showers. Lows around 72 near the shore to 51 to 58 above 4000 feet. Southeast winds up to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Sunday: Sunny in the morning then becoming partly sunny. Windy. Isolated showers. Highs around 85 near the shore to 69 to 75 above 4000 feet. Northeast winds up to 30 mph with gusts to 50 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A very windy trade wind pattern will hold in place during the next couple days, as strong high pressure builds north of the islands. Clouds and showers will favor windward and mauka areas with the strong trades sending brief passing showers over to leeward areas more regularly. A wet trade wind pattern will develop late Monday and continue through early Wednesday as a disturbance aloft combines with a plume of deep moisture moving in from the east. A drier and more typical trade wind pattern is forecast to return Wednesday afternoon through late next week.

Discussion

Currently at the surface, a 1032 mb high is centered around 1250 miles north-northeast of Honolulu, while a trough of low pressure is located around 900 miles east-southeast of Hilo. These features are producing a very tight pressure gradient and windy conditions across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions across the state, with cloud cover most prevalent in windward areas. Radar imagery shows numerous showers moving into windward areas, with quite a few showers spilling over into leeward communities as well. Main short term concerns revolve around rain chances and trade wind trends during the next couple days.
A series of reinforcing highs building to the north of the islands will keep strong trade winds in place through most of the forecast period. The trades will remain very strong through the weekend, and the Wind Advisory has been extended through 6 PM Sunday. The gradient will ease ever so slightly early next week, but breezy to locally windy conditions will likely continue Monday through Wednesday. The trades should drop a notch lower by late next week, with moderate to locally breezy conditions expected Thursday and Friday.
As for the remaining weather details, we should see fairly showery conditions to start the morning, as a band of higher moisture with precipitable water (PW) values of 1.3 to 1.6 inches moves through the islands. Most of the showers will focus over windward and mauka areas, but the strong trades will allow these showers to reach leeward communities as well. After a showery start to the day, a more typical trade wind shower regime should take hold this afternoon and continue through Monday. Showers will continue to favor windward slopes and coasts, although the strong trades will also deliver passing showers to leeward areas at times. Moisture will remain deeper over the eastern islands during this time, and this should result in higher shower coverage over windward sections of Maui and the Big Island.
A plume of deeper tropical moisture should begin to slide into the eastern islands late Monday, then overspread the remainder of the island chain Monday night through Tuesday night, before exiting to the west Wednesday morning. PW values climb into the 1.5 to 2.0 inch range, with low level inversions getting eliminated as mid and upper level troughing to the southwest of an upper level low moves over the islands. This should result in wet trade wind weather across the islands, with some downpours likely, particularly over windward slopes and coasts. The strong trades will continue to carry showers into leeward communities more regularly as well. A more typical trade wind regime is then forecast to return Wednesday afternoon and continue through late next week.

Aviation

Surface high pressure building far north of the state will cause the trade winds to gradually strengthen today. AIRMET Tango remains in effect for sustained wind speeds of 30 knots or higher across Maui and the Big Island, as well as the adjacent waters. The strongest sustained winds will likely be in the channels adjacent to these islands, where gale force winds are expected. AIRMET Tango also remains in effect for TEMPO low-level mechanical turbulence below 8 thousand feet south through west of the higher terrain on all islands.
A westward moving band of broken low clouds with embedded showers is currently in the vicinity of the islands. This will likely continue to cause periods of MVFR conditions over windward facing slopes and coastlines into mid-morning. The strong trade winds will also likely transport some low clouds and brief trade showers over to leeward sections of some of the smaller islands this morning. AIRMET Sierra remains in effect for mountain obscuration above 2500 feet along north through east facing sections of all islands.
The band of low clouds and showers will eventually depart the area later this morning, so AIRMET Sierra may be lowered for some islands west of Maui later today. Note that the forecast guidance continues to show additional low clouds and showers streaming into the windward Big Island and Maui into tonight, so portions of these islands may continue to experience occasional MVFR conditions during the next 18 to 24 hours.

Marine

Hazardous boating conditions will continue statewide through the holiday weekend due to strong- to gale-force winds and large seas ranging from 10 to 15 feet. The gales and largest seas can be expected over the typically windier waters and channels from Maui County to the Big Island. Guidance suggest this pattern will continue through early next week before slowly notching down Wednesday onward.
Surf along east facing shores will remain rough through the first half of next week due to the aforementioned winds and seas. In addition to the locally strong trades, guidance shows a large area of strong breezes upstream between the islands and the west coast. As a result, a High Surf Advisory remains in effect for exposed east facing shores statewide through Sunday, which may need to be extended through Monday in later packages. Although a slow downward trend is anticipated next week, rough conditions will continue at exposed beaches each day.
Surf along south facing shores has trended up overnight due to a new, long-period south swell filling in from a recent storm southeast of New Zealand. The offshore NDBC buoys and nearshore PacIOOS buoy at Barbers are reflecting this new source this morning with the peak energy holding within the 18 to 22 second bands. Surf will likely hit the new advisory-level threshold of 10 ft on the face at the standout spots today, which will continue through Sunday. This will be a long-lived event, lingering through early next week as it slowly eases.
Surf along north facing shores will remain small through early next week. The exception will be at north facing locations exposed to the trade wind energy, which will result in rough conditions. For the long range, guidance does show a gale racing eastward across the Kamchatka Peninsula and southern Bering Sea early next week with a short-lived fetch setting up within the 315 to 330 directional band relative to Hawaii late Monday through Tuesday. WAVEWATCH III reflects this and depicts a small, long-period northwest swell arriving Thursday night into Friday.

Fire weather

With KBDI values above 600, low daytime relative humidities and windy trades, the Red Flag Warning has been extended through 6 PM Sunday, and may need to be extended through Monday as well.

HFO Watches/Warnings/Advisories

Red Flag Warning until 6 PM HST Sunday for Kauai Leeward, Oahu South Shore, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Molokai Leeward, Maui Leeward West, Maui Central Valley, Leeward Haleakala, Kona, Kohala, Big Island Interior.
High Surf Advisory until 6 PM HST Sunday for Niihau, Kauai Leeward, Waianae Coast, Olomana, Kahoolawe, Maui Leeward West, Kona, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Molokai Windward, Molokai Southeast, Molokai Leeward South, Lanai Leeward, Lanai South, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island East, Big Island North.
Wind Advisory until 6 PM HST Sunday for Kauai Leeward, Kauai Mountains, Waianae Coast, Oahu North Shore, Olomana, Central Oahu, Waianae Mountains, Lanai Mauka, Kahoolawe, Maui Windward West, Maui Leeward West, Kohala, Big Island Interior, Kauai North, Kauai East, Kauai South, East Honolulu, Honolulu Metro, Ewa Plain, Koolau Windward, Koolau Leeward, Molokai, Lanai Windward, Lanai Leeward, Lanai South, Maui Central Valley North, Maui Central Valley South, Windward Haleakala, Kipahulu, South Maui/Upcountry, South Haleakala, Big Island South, Big Island Southeast, Big Island North.
Gale Warning until 6 PM HST Sunday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Sunday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov

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