Weather Forecast

Hawaii County Weather Forecast for August 23, 2021

August 23, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 83 to 89 near the shore to around 74 at 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 65 to 73 near the shore to 56 to 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny with scattered showers. Highs 77 to 85 near the shore to 64 to 71 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Kona

Today: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 82 to 87 near the shore to around 72 near 5000 feet. Southwest winds 10 to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 74 near the shore to 53 to 59 near 5000 feet. East winds up to 10 mph. Chance of rain 50 percent.

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Tuesday: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs 83 to 88 near the shore to around 68 near 5000 feet. Southwest winds up to 10 mph shifting to the northwest around 10 mph in the afternoon. Chance of rain 50 percent.

Waimea

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Today: Breezy. Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 72 to 85. Northeast winds 10 to 15 mph shifting to the east 10 to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 64 to 72 near the shore to 58 to 65 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph after midnight. Gusts up to 40 mph. Chance of rain 70 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 15 to 25 mph. Chance of rain 50 percent.

Kohala

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Today: Breezy. Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 72 to 85. Northeast winds 10 to 15 mph shifting to the east 10 to 25 mph in the afternoon. Chance of rain 70 percent.

Tonight: Breezy. Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 64 to 72 near the shore to 58 to 65 near 3000 feet. East winds up to 20 mph increasing to 10 to 20 mph after midnight. Gusts up to 40 mph. Chance of rain 70 percent.

Tuesday: Breezy. Partly sunny with scattered showers. Highs 65 to 85. East winds 15 to 25 mph. Chance of rain 50 percent.

South Big Island

Today: Breezy. Partly sunny with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs around 87 near the shore to around 77 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 74 near the shore to around 55 near 5000 feet. East winds up to 20 mph shifting to the northeast 10 to 20 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny in the morning then becoming partly sunny. Breezy. Isolated showers. Highs around 85 near the shore to around 68 near 5000 feet. East winds 10 to 25 mph. Chance of rain 20 percent.

Puna

Today: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 83 to 89 near the shore to around 74 at 4000 feet. Southeast winds 10 to 15 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy with showers likely and slight chance of thunderstorms. Locally heavy rainfall possible. Lows 65 to 73 near the shore to 56 to 61 at 4000 feet. Northeast winds up to 15 mph. Chance of rain 70 percent.

Tuesday: Partly sunny with scattered showers. Highs 77 to 85 near the shore to 64 to 71 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Waikoloa

Today: Partly sunny with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 83 to 88 near the shore to 69 to 76 above 4000 feet. Northwest winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 75 near the shore to 52 to 58 above 4000 feet. Light winds becoming east up to 15 mph after midnight. Chance of rain 50 percent.

Tuesday: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 84 to 91 near the shore to 67 to 74 above 4000 feet. North winds up to 25 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

A gale low, which is the left over circulation associated with former Tropical Cyclone Linda, will continue to churn from east to west across the state. The smaller islands from Molokai and Lanai to Kauai appear to be in direct line to experience strong and gusty winds, along with heavy rainfall and thunderstorms that could potentially produce flash flooding. Maui and the Big Island may see locally heavy showers and a slight chance of thunderstorms in the southeast flow after the low moves by.

Discussion

Loops of satellite imagery show the circulation associated with a gale low that appears to be centered near 21N 155W, or just northeast of Hana early this morning. The strong thunderstorms, which had been located in the north quadrant of this low last evening, have dissipated during the past few hours. Rainbands continue to form and rotate counter-clockwise around this low. These rainbands are currently impacting portions of Maui, Molokai, and Oahu. Clouds and showers are also near the northern Big Island.
Based on the latest guidance, the low will continue to track westward across Maui County this morning. The center may pass just south of Oahu this afternoon, and then move south of Kauai this evening. Flooding rains with heavy thunderstorms and gusty winds may accompany this low as it moves through the smaller islands. The current forecast continues to indicate that the coverage of clouds and the intensity of the showers will increase later today, especially over most windward areas. A Flash Flood Watch remains in effect for the entire state through early Tuesday morning. A Wind Advisory, which includes wind gusts to 50 mph, has also been issued for the smaller islands from Molokai and Lanai to Kauai. The confidence in these strong winds occurring is highest for Oahu and Kauai, which will likely be in the stronger northern semicircle of the westward moving circulation. In addition, thunderstorms have been developing at times in the northern side of the gale low during the past couple of days. If these redevelop later today, this may put Oahu and Kauai in some of the heaviest rainfall. Note that for Molokai and Lanai, the steadily backing wind profile as the low passes will lead to highly variable conditions with some areas experiencing light or variable winds with intermittent higher wind gusts, especially in thunderstorms.
If deep convection does develop over Oahu or Kauai later today and tonight, the potential for very heavy rainfall capable of producing flash flooding will increase. This will particularly be the case over windward slopes and the higher terrain. More importantly, the fairly uniform southwesterly flow aloft will give rise to the potential for thunderstorms to anchor along windward terrain. Finally, as the gale low center moves to the west of each of the individual islands, moist southeast flow spreading up over the islands may produce bands of heavy rain within favored zones of leeward convergence through this evening. Looking ahead, a more typical trade wind weather pattern will gradually return from Tuesday into mid-week.

Aviation

A gale low currently bearing down on Maui from the northeast will continue its march due westward, passing just south of Oahu today and rapidly weakening near Kauai tonight. Rain, heavy at times, as well as possible isolated embedded thunderstorms are associated with this feature. Expect widespread MVFR CIG/VIS this morning from Maui to Oahu. Conditions will likely spread to Windward Big Island or Kauai in the afternoon.
AIRMET Sierra is currently in effect for occasional mountain obscuration across Maui, lanai, and windward Oahu, and will likely be expanded later today to included Kauai and the remainder of Oahu. Conditions are expected to persist through the evening hours. Gradual improvement starting in the east beginning after midnight.
AIRMET Tango remains in effect for moderate low level turbulence over and downwind of the terrain of all islands. This AIRMET will continue through the night and will likely remain necessary into early Tuesday.

Marine

As of 3 AM HST, the center of the remnants of TC Linda that is now a gale low is located approximately 100 miles northwest of Hilo. The latest forecast has the low moving almost due west across Maui County and passing just south of Oahu through the day. This may have gale force winds impacting the windward Oahu and Maui zones and their neighboring channels. Thus, a Gale Warning (GLW) is in effect for both the northeast offshore and nearshore windward Maui and Oahu waters including both the Kauai and Kaiwi Channels through this afternoon. A Small Craft Advisory (SCA) is also in effect for the remainder of those waters that may experience strong to near gale force winds and/or high seas. Once the low exits the western offshore waters Tuesday, the north-south pressure gradient from high pressure north of the state will remain tight enough over the state to produce SCA level winds over most marine zones. Thus, once the GLW expires tonight an SCA will be effect for all zones except the Big Island windward zone through Tuesday afternoon.
Thunderstorms north of the gale low may flare back up and impact the surrounding Maui County, Oahu and Kauai waters through Tuesday morning. Gale winds, visibility-limiting heavy rainfall and agitated seas make these storms potentially dangerous to any maritime activity. The low is expected to weaken and move west of the islands Tuesday and be west of the offshore waters by the evening hours. This will introduce the return of mid to late week moderate to locally strong trade winds.
A High Surf Advisory (HSA) remains in effect for the east facing shorelines of Oahu, Molokai and Maui through this afternoon and for the east coast of Kauai through tonight. Higher east wind wave swell from the gale low will increase surf heights along many east facing coasts. Select north and south shores could experience east swell wrap that will produce slightly higher surf. East facing shore surf should quickly decline and fall below HSA thresholds Tuesday as this low moves west and away from the islands. A series of small, lower period south swells will maintain small surf along south facing shores throughout the week. No anticipated incoming north or west swell will keep surf nearly flat along most north and west exposures.

HFO Watches/Warnings/Advisories

Flash Flood Watch through late tonight for all Hawaii islands.
Wind Advisory from 6 AM this morning to 6 AM HST Tuesday for Niihau and Kauai.
Wind Advisory from 6 AM this morning to 6 PM HST this evening for Oahu.
Wind Advisory until noon HST today for Lanai and Molokai.
High Surf Advisory until 6 PM HST this evening for east facing shores of Maui, Molokai and Oahu.
High Surf Advisory until 6 AM HST Tuesday for east facing shores of Kauai.
Small Craft Advisory from 6 PM this evening to 6 PM HST Tuesday for Kauai Northwest Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST Tuesday for Kauai Windward Waters, Oahu Leeward Waters, Maui County Leeward Waters, Maalaea Bay, Pailolo Channel.
Gale Warning until 6 PM HST this evening for Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters.

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Data Courtesy of NOAA.gov

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