Weather Forecast

Hawaii County Weather Forecast for March 20, 2021

March 20, 2021, 7:16 AM HST
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Hilo

Today: Showers likely, with thunderstorms also possible after 1pm. Cloudy, with a high near 79. Calm wind becoming north 5 to 8 mph in the afternoon. Chance of precipitation is 70%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely and possibly a thunderstorm, then frequent showers after 7pm. Low around 66. North northeast wind 3 to 6 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Sunday: Frequent showers. High near 79. Light and variable wind becoming northeast 5 to 8 mph in the morning. Chance of precipitation is 90%. New precipitation amounts between a tenth and quarter of an inch possible.

Kona

Today: Scattered showers and thunderstorms after 1pm. Partly sunny, with a high near 80. Light and variable wind becoming west southwest 5 to 8 mph in the afternoon. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before 7pm, then isolated showers. Mostly cloudy, with a low around 61. Calm wind. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

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Sunday: Scattered showers, mainly after noon. Partly sunny, with a high near 80. Calm wind becoming west northwest around 5 mph. Chance of precipitation is 30%. New precipitation amounts between a tenth and quarter of an inch possible.

Waimea

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Today: Scattered showers, with thunderstorms also possible after noon. Mostly cloudy, with a high near 76. Very windy, with an east northeast wind 24 to 32 mph, with gusts as high as 47 mph. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 55. Windy, with an east wind 26 to 28 mph, with gusts as high as 40 mph. Chance of precipitation is 60%. New precipitation amounts between a quarter and half of an inch possible.

Sunday: Showers likely, mainly before 11am. Partly sunny, with a high near 76. Breezy, with an east northeast wind 17 to 21 mph, with gusts as high as 31 mph. Chance of precipitation is 60%. New precipitation amounts between a half and three quarters of an inch possible.

Kohala

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Today: Showers likely, with thunderstorms also possible after noon. Cloudy, with a high near 72. Very windy, with an east northeast wind 28 to 31 mph, with gusts as high as 45 mph. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Frequent showers. Low around 48. Very windy, with an east wind around 32 mph, with gusts as high as 47 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Frequent showers. High near 72. Windy, with an east wind 21 to 24 mph, with gusts as high as 39 mph. Chance of precipitation is 90%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers, with thunderstorms also possible after noon. Partly sunny, with a high near 79. Windy, with an east northeast wind around 29 mph, with gusts as high as 37 mph. Chance of precipitation is 30%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Isolated showers. Partly cloudy, with a low around 71. Windy, with an east northeast wind around 29 mph, with gusts as high as 37 mph. Chance of precipitation is 20%.

Sunday: Isolated showers before 11am. Mostly sunny, with a high near 79. Windy, with an east northeast wind 26 to 29 mph, with gusts as high as 37 mph. Chance of precipitation is 20%.

Puna

Today: Showers likely, with thunderstorms also possible after noon. Cloudy, with a high near 78. West northwest wind 7 to 13 mph becoming north northeast in the afternoon. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Frequent showers. Low around 64. North northeast wind 11 to 13 mph. Chance of precipitation is 100%. New precipitation amounts between a tenth and quarter of an inch possible.

Sunday: Frequent showers. High near 78. Breezy, with a north northwest wind 11 to 15 mph becoming northeast in the afternoon. Winds could gust as high as 21 mph. Chance of precipitation is 100%. New precipitation amounts between a half and three quarters of an inch possible.

Waikoloa

Today: A 20 percent chance of showers and thunderstorms after noon. Increasing clouds, with a high near 81. Very windy, with an east northeast wind 26 to 32 mph, with gusts as high as 47 mph.

Tonight: Partly cloudy, with a low around 61. Windy, with an east northeast wind around 30 mph, with gusts as high as 44 mph.

Sunday: Isolated showers after 11am. Mostly sunny, with a high near 81. Breezy, with an east northeast wind 9 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

Showery conditions will remain in place for windward and mountain locations through tonight due to a band of moisture drifting southward into the area and an upper disturbance. Northeast trade winds will reach advisory levels through this time while gradually becoming more easterly by Sunday. Winds will ease through the day Monday, then shift out of the south Monday night through midweek as a cold front and upper disturbance approach and move into the area. The potential for another round of wet conditions will increase Tuesday through midweek, especially over the western end of the state where the front could stall.

Discussion

Satellite imagery showed a band of low clouds drifting southward into the area this morning, which supports increasing shower coverage for windward and mountain locations through tonight. Some of these showers will occasionally carry over into leeward sections – best chances being through the early morning periods. In addition to the showery conditions, lowering upper heights associated with the upper trough could trigger a few thunderstorms over the eastern end of the state as the trough sharpens and potentially closes off into an upper low.
Northeast trade winds are expected to reach advisory levels today due to this band of moisture moving in and strong high pressure passing to the north. A Wind Advisory has been posted for most of the state (with the exception of a few areas on Maui and the Big Island that are normally not exposed to the trade wind flow) that continues through tonight. Saturated soils from recent rainfall combined with wind gusts potentially reaching 45 mph in exposed areas could down trees and large branches. Strongest winds will be felt near mountain tops and passes, trade wind exposed areas and around incoming showers.
Drier weather is expected later Sunday with breezy trades holding. A cold front will approach the islands and begin to weaken the trade winds further on Monday. Background winds will veer southerly and become light and variable for many areas around the state Monday night into Tuesday. The front will arrive Tuesday night or Wednesday on Kauai and then stall somewhere over the smaller islands Wednesday and Thursday. Showers will increase along and ahead of the boundary as early as Tuesday across the state, with Wednesday and Thursday likely being the wettest days. Model solutions begin to diverge late next week, which reduces forecast confidence.

Aviation

A high pressure system passing north of the state will produce breezy to windy trade winds lasting through Sunday. An upper level trough over the region will continue to enhance shower activity across the area. Unstable cloud bands are moving into the islands from the east this morning, with deeper moisture moving into the Big Island from the southeast direction.
Expect periods of MVFR conditions through the early morning hours along north and east facing slopes of some islands with unstable showers driven up the mountain slopes by strong trade winds. Isolated thunderstorms remain in the forecast over the eastern end of the state this afternoon.
AIRMET Sierra remains in effect for Mountain Obscurations over the north and east slopes of Kauai and the Big Island. This AIRMET may expand today to cover additional islands.
AIRMET Tango remains in effect for low level Moderate Turbulence over and south through west of all island mountains due to strong trade winds. This AIRMET will remain in effect at least through Sunday. AIRMET Tango for strong surface winds greater than 30 knots was also issued this morning.

Marine

High pressure north of the state moving east into the East Pacific will maintain a tight enough pressure gradient back across the Hawaiian Island waters to produce fresh to strong trade winds this weekend. A north northeast swell, along with strong trades, will have an all water Small Craft Advisory (SCA) in effect through Sunday. The lone exception to the SCA will be in the Alenuihaha Channel where a Gale Warning (GLW) is in effect through tonight. This enhanced trade wind and north northeast swell tandem will also support the High Surf Advisory (HSA) for exposed east-facing shoreline surf through Sunday. Eastern Pacific high pressure will be pushed farther east as a cold front approaches the state from the northwest early next week. The result will be weakened winds that will veer more southerly ahead of the front Monday night. Winds are forecast to weaken late Sunday through Monday and will likely fall below SCA criteria Monday.
The next appreciable northwest swell is scheduled to pass around the islands Wednesday and Thursday. This moderate height, lower period northwest swell may push surf along north and west-facing shores to HSA levels Wednesday and Thursday. Periodic small, long period southwest to south swells emanating from gales south of New Zealand will produce a modest boost to mid week south-facing shore surf.

HFO Watches/Warnings/Advisories

Wind Advisory until 6 AM HST Sunday for Niihau, Kauai, Oahu, Molokai, Lanai, Kahoolawe, Maui Windward West, Maui Leeward West, Maui Central Valley, Windward Haleakala, Leeward Haleakala, South Big Island, Big Island North and East, Kohala.
High Surf Advisory until 6 PM HST Sunday for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, Big Island North and East.
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, Maalaea Bay, Pailolo Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.
Gale Warning until 6 AM HST Sunday for Alenuihaha Channel.

Data Courtesy of NOAA.gov

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