Weather Forecast

Hawaii County Weather Forecast for July 15, 2021

July 15, 2021, 7:16 AM HST
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Hilo

Today: Showers likely, mainly before 1pm. Partly sunny, with a high near 82. Light and variable wind becoming east northeast 5 to 10 mph in the afternoon. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 67. East northeast wind 5 to 8 mph becoming light and variable after midnight. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Friday: Scattered showers. Partly sunny, with a high near 84. Calm wind becoming northeast 5 to 9 mph in the afternoon. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Scattered showers after noon. Partly sunny, with a high near 80. Light and variable wind becoming northwest 5 to 7 mph in the morning. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly before midnight. Mostly cloudy, with a low around 66. Northwest wind 5 to 7 mph becoming light and variable after midnight. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

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Friday: Isolated showers after noon. Partly sunny, with a high near 80. Southwest wind 5 to 7 mph becoming calm in the afternoon. Chance of precipitation is 20%.

Waimea

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Today: Scattered showers. Partly sunny, with a high near 77. Windy, with a northeast wind 15 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 59. Windy, with a northeast wind 20 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Friday: Scattered showers. Partly sunny, with a high near 79. Windy, with a northeast wind 15 to 25 mph, with gusts as high as 36 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Kohala

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Today: Showers likely, mainly before noon. Mostly cloudy, with a high near 70. Windy, with an east wind 15 to 20 mph increasing to 21 to 26 mph in the afternoon. Winds could gust as high as 38 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 54. Windy, with an east wind around 26 mph, with gusts as high as 38 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Friday: Scattered showers. Partly sunny, with a high near 65. Windy, with an east northeast wind 22 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Isolated showers. Mostly sunny, with a high near 85. Windy, with an east wind around 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Mostly cloudy, with a low around 75. Windy, with an east wind around 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Friday: Isolated showers before noon. Mostly sunny, with a high near 85. Windy, with an east wind 22 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Puna

Today: Showers likely, mainly before noon. Partly sunny, with a high near 79. Light north wind becoming northeast 8 to 13 mph in the morning. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 65. Northeast wind 9 to 13 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Friday: Scattered showers. Partly sunny, with a high near 83. Breezy, with a north northeast wind 9 to 16 mph, with gusts as high as 23 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Waikoloa

Today: Isolated showers after noon. Mostly sunny, with a high near 84. Windy, with a northeast wind 15 to 23 mph, with gusts as high as 33 mph. Chance of precipitation is 20%.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 67. Windy, with an east northeast wind 13 to 23 mph, with gusts as high as 33 mph. Chance of precipitation is 20%.

Friday: Mostly sunny, with a high near 85. Windy, with a northeast wind 21 to 26 mph decreasing to 7 to 12 mph. Winds could gust as high as 37 mph.

Detailed Forecast

Synopsis

High pressure north of the state will keep moderate trades in place this morning, with the trades ramping up to breezy levels this afternoon through Saturday. The trades are expected to become windy Sunday through early next week as high pressure strengthens north of the islands chain. Showers will favor windward and mauka areas through the forecast period, particularly and night and during the early morning hours, with a few showers spilling into leeward communities at times due to the strength of the trades.

Discussion

Currently at the surface, a 1032 mb high is centered around 1250 miles north of Honolulu, and is driving moderate trade winds across the island chain early this morning. Infrared satellite imagery shows partly to mostly cloudy conditions across the state, with cloud cover most prevalent over Kauai and windward sections of the other islands. Meanwhile, radar imagery shows scattered to numerous showers moving into windward areas, with coverage the highest over Kauai and Oahu, with a few showers spilling over into leeward communities at times. Main short term concerns revolve around trade wind and rainfall trends during the next few days.
High pressure north of the state will keep moderate trade winds in place this morning, before ramping up to breezy levels this afternoon as mid-level ridging builds over the islands from the east. The trades should then hold at breezy levels through Saturday. As the surface high strengthens north of the islands Sunday through Tuesday, we should see a further increase in the trade wind speeds locally, with breezy to windy conditions likely statewide. Breezy trades will likely continue through the middle and latter part of next week, but details become a bit less clear as the gradient may be influenced by tropical systems moving into the Central Pacific basin from the east.
As for the remaining weather details, fairly typical trade wind weather can be expected during the next 7 days. Showers will remain active this morning over Kauai as a mid-level trough exits to the west. We should see a more stable and drier trade wind pattern become established statewide this afternoon through Friday night as deep layer ridging aloft builds over the state. Trade wind shower coverage should then increase back to near or slightly wetter than normal levels over the weekend through the middle of next week, as a weakness in the ridging aloft develops over the islands and precipitable water values trend upward. Overall, showers will favor windward and mauka areas through the forecast period, particularly at night and during the morning hours, with a few showers making the trip over the mountains and into leeward communities at times due to the strength of the trades.

Aviation

A nearly stationary 1032 mb surface high located far N of the islands will maintain a strengthening trade wind flow through at least Friday. AIRMET Tango for low level turbulence was issued for the 1000z aviation package, and will remain in effect through 160400z.
The trade winds are carrying a pocket of drier air that will be spreading across the area in the coming hours. In essence, expect somewhat fewer showers and more sun areawide compared to 24 hours ago. AIRMET Sierra for mountain obscuration for Oahu will be lowered by 1600z, then Kauai by 2000z.

Marine

A strong surface high pressure system remains far north of the islands early this morning. A weak surface trough, which currently appears to be located north of Maui, is moving toward the west-northwest at 15 to 20 knots. The departure of this weak system will allow locally strong trade winds to return across most of the state from today into early next week. A Small Craft Advisory (SCA) is currently in effect for the typically windier waters adjacent to the islands of Maui County and the Big Island. In addition, the Oahu Leeward Waters, the Kaiwi Channel, as well as the Maui County Windward and Leeward Waters have all been added to the SCA starting this afternoon. Additional waters, such as the Big Island Windward Waters, may require a SCA starting later today or tonight.
Small background surf due to small south and southeast swells will persist along south facing shores through early Friday morning. A new, slightly larger south swell, which is expected to start spreading across the area late Friday, will likely cause surf heights along south facing shores to return to near the summertime average from Friday night through this weekend. This south swell is expected to gradually diminish early next week. As the trades strengthen during the next couple of days, expect choppy surf to increase along east facing shores. The most recent guidance suggests that surf heights along east facing shores will be above normal from late Friday through early next week. Except for some localized wrap of trade wind waves, surf along most north facing shores will remain nearly flat through early next week.

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 from noon today to 6 PM HST Friday for 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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