Weather Forecast

Hawaii County Weather Forecast for July 23, 2021

July 23, 2021, 7:16 AM HST
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Hilo

Today: Showers likely, mainly before noon. Mostly cloudy, with a high near 81. Light and variable wind becoming east northeast 5 to 9 mph in the afternoon. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Frequent showers. Low around 70. Northeast wind around 6 mph becoming light and variable after midnight. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Saturday: Frequent showers. High near 82. Light and variable wind becoming east northeast 5 to 8 mph in the morning. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Kona

Today: Scattered showers after noon. Mostly sunny, with a high near 82. Light and variable wind becoming west 5 to 10 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Isolated showers before midnight. Mostly clear, with a low around 69. Calm wind. Chance of precipitation is 20%.

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Saturday: Scattered showers after noon. Mostly sunny, with a high near 82. Calm wind becoming west 5 to 9 mph in the morning. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

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Today: Scattered showers. Partly sunny, with a high near 74. Windy, with an east northeast wind 21 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 50%. New precipitation amounts between a half and three quarters of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 61. Windy, with an east northeast wind 21 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 50%. New precipitation amounts between three quarters and one inch possible.

Saturday: Scattered showers. Partly sunny, with a high near 77. Breezy, with an east northeast wind around 22 mph, with gusts as high as 31 mph. Chance of precipitation is 40%. New precipitation amounts between a quarter and half of an inch possible.

Kohala

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Today: Showers likely. Mostly cloudy, with a high near 68. Breezy, with an east northeast wind around 20 mph, with gusts as high as 28 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 59. Windy, with an east northeast wind 20 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Saturday: Showers likely. Mostly cloudy, with a high near 69. Breezy, with an east northeast wind 18 to 20 mph, with gusts as high as 28 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers, mainly before noon. Mostly sunny, with a high near 85. Windy, with an east wind around 23 mph, with gusts as high as 30 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Isolated showers. Partly cloudy, with a low around 76. Windy, with an east northeast wind around 24 mph, with gusts as high as 31 mph. Chance of precipitation is 20%.

Saturday: Isolated showers. Mostly sunny, with a high near 86. Windy, with an east wind around 23 mph, with gusts as high as 30 mph. Chance of precipitation is 20%.

Puna

Today: Frequent showers. High near 77. Breezy, with a northeast wind 10 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 80%. New precipitation amounts between a half and three quarters of an inch possible.

Tonight: Frequent showers. Low around 68. North northeast wind 10 to 13 mph. Chance of precipitation is 80%. New precipitation amounts between three quarters and one inch possible.

Saturday: Showers likely. Mostly cloudy, with a high near 79. Northeast wind 10 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.

Waikoloa

Today: Sunny, with a high near 85. Windy, with a northeast wind 22 to 24 mph, with gusts as high as 34 mph.

Tonight: Mostly clear, with a low around 69. Windy, with an east northeast wind 22 to 24 mph, with gusts as high as 34 mph.

Saturday: Sunny, with a high near 85. Breezy, with a northeast wind around 22 mph, with gusts as high as 31 mph.

Detailed Forecast

Synopsis

Breezy trade winds will continue into the weekend, then ease slightly late Sunday into early next week. Showers will continue to ride in on the trades, with the possibility of more showers to end the weekend and start the new week due the remains of former Tropical Cyclone Guillermo.

Discussion

An overnight ASCAT pass shows winds remain elevated over more than the typical marine areas. A check of the latest high resolution models show several of them expect this uptick to continue through the next 24 hours. Winds have been boosted over the waters, with minimal changes to land. Some tweaks have been made to the PoPs and associated fields for the first 24 hours or so to bring the forecast into better alignment with some of the high resolution models.
A recent day/night band pass of the VIIRS satellite show the remnants of Tropical Cyclone Felicia south of the Big Island. The northern edge of the main cloud area with this surface trough was about 90 miles south of Hilo, and it extends to the south about 300 miles. Additional low clouds just east of the Big Island are loosing associated with this trough, and are expected to help maintain showers over the east side of the Big Island today. The VIIRS pass clearly shows the remnant low that was once Guillermo about 1000 miles east-southeast of the Big Island. The cloud associated with this system extend about 800 miles north. As these clouds and showers move to the east and mover over the islands this weekend and into early next week, we can expect another uptick in shower activity mainly over the windward and mountain areas.
Surface high pressure to the northwest of the islands, with an east to west near zonal flow over the islands will maintain the breezy to locally strong trade winds over the region as we head into the weekend. Some weakening of the pressure gradient over the islands is possible over the weekend. Heading into the middle of next week, the winds are likely to weaken and become more southeasterly as the high moves to the northeast of the islands.

Aviation

Breezy easterly trade winds will continue into the weekend, with clouds and showers favoring windward and mauka locations. MVFR CIGS/VSBYS are possible in and around passing showers, especially over the eastern end of the state where more moisture exists.
AIRMET Sierra remains in effect for mountain obscuration above 1500 feet for north through east sections of Maui and the Big Island. Conditions should gradually improve through the late morning and afternoon hours.
AIRMET Tango remains in effect for low-level mechanical turbulence immediately south through west of island mountains. This AIRMET will continue into the weekend.

Marine

A gradual weakening of the trade winds is expected mainly tonight through Saturday as high pressure north of the islands weaken. The Small Craft Advisory (SCA) covering most of the nearshore waters will continue through today before being scaled down to the normal typical areas of Maui County and waters south of the Big Island. Should this softening trend continues as forecast, we would likely lower the SCA late Saturday afternoon. The trades are expected to hold at light to moderate speeds through the first half of next week.
A blob of warm and humid unstable air belonging to once Tropical Cyclone Guillermo is forecast to settle over the islands between Sunday night and Tuesday. This air mass will be influenced by an upper level disturbance leading to a thunderstorm or two over the offshore waters.
The rough trade wind swell of 6 to 8 ft and 8 seconds will maintain surf along the east facing shores of 5 to 7 feet today. But with the weakening trades through Saturday, look for the surf to be a little smaller each day over the weekend. A long period pulse from the south is being picked up by the buoys far south of the islands. We are looking at 3 to 5 foot surf along the south facing shores today through Saturday before trending lower thereafter. No other significant swells are expected.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 AM HST Saturday for Kauai Northwest Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters.

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Data Courtesy of NOAA.gov

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