Weather Forecast

Hawaii County Weather Forecast for February 20, 2021

February 20, 2021, 7:16 AM HST
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Photo Credit: James Grenz

Hilo

Today: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 78. West southwest wind around 6 mph becoming calm. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely. Cloudy, with a low around 64. East southeast wind around 6 mph becoming calm in the evening. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 76. Light and variable wind becoming east southeast 5 to 8 mph in the morning. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Kona

Today: Scattered showers and thunderstorms after 1pm. Partly sunny, with a high near 79. Calm wind becoming west around 6 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 62. Northwest wind 5 to 7 mph becoming light and variable. 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: Isolated showers before 7am, then scattered showers and thunderstorms after 1pm. Partly sunny, with a high near 78. Calm wind becoming west southwest around 6 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.

Waimea

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Today: Scattered showers, with thunderstorms also possible after 1pm. Partly sunny, with a high near 74. Breezy, with a northeast wind 11 to 16 mph, with gusts as high as 22 mph. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms. Mostly cloudy, with a low around 53. Northeast wind 6 to 13 mph. Chance of precipitation is 40%. New precipitation amounts between a quarter and half of an inch possible.

Sunday: Scattered showers, with thunderstorms also possible after 1pm. Mostly cloudy, with a high near 73. North northeast wind 11 to 14 mph, with gusts as high as 20 mph. Chance of precipitation is 40%. New rainfall amounts between a quarter and half of an inch possible.

Kohala

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Today: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 70. Windy, with an east wind 24 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 60%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely. Mostly cloudy, with a low around 46. Windy, with an east wind 21 to 26 mph decreasing to 11 to 16 mph after midnight. Winds could gust as high as 38 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Sunday: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 69. Windy, with an east wind 17 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 70%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

South Big Island

Today: Isolated showers, with thunderstorms also possible after noon. Partly sunny, with a high near 79. Windy, with an east northeast wind 23 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Tonight: Isolated showers. Mostly cloudy, with a low around 70. Windy, with an east northeast wind 21 to 25 mph, with gusts as high as 32 mph. Chance of precipitation is 20%.

Sunday: Isolated showers, with thunderstorms also possible after noon. Partly sunny, with a high near 78. Windy, with an east northeast wind 22 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Puna

Today: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 77. West wind 5 to 9 mph becoming east in the afternoon. Chance of precipitation is 60%. New rainfall amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Tonight: Showers likely. Cloudy, with a low around 62. East wind 5 to 9 mph becoming calm in the evening. Chance of precipitation is 70%. New precipitation amounts between a quarter and half of an inch possible.

Sunday: Showers likely, with thunderstorms also possible after noon. Mostly cloudy, with a high near 75. Light northeast wind becoming east northeast 5 to 10 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.

Waikoloa

Today: A 20 percent chance of showers and thunderstorms after 1pm. Partly sunny, with a high near 80. East southeast wind 5 to 8 mph becoming west northwest in the afternoon.

Tonight: A 20 percent chance of showers and thunderstorms before 7pm. Mostly cloudy, with a low around 62. Calm wind becoming east around 6 mph after midnight.

Sunday: Scattered showers and thunderstorms after 1pm. Partly sunny, with a high near 79. East wind 6 to 8 mph becoming west northwest 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.

Detailed Forecast

Synopsis

High pressure northeast of the state will keep moderate to breezy trade winds in place through the weekend, with showers favoring windward and mauka areas and a stray shower reaching leeward areas from time to time. Dry trade wind weather is expected to build back in Sunday night through Monday night. Trade showers should increase in coverage and intensity Tuesday through late next week as old frontal remnants move through the islands and moisture moves in from the southeast. Quite windy weather could develop statewide Wednesday through late next week as a very strong high builds northeast of the island chain.

Discussion

Currently at the surface, a broad 1038 mb high is centered around 1400 miles northeast of Honolulu, and is driving moderate trade winds trade winds across the island chain early this morning. Infrared satellite imagery shows high cloud streaming over the state, resulting in mostly cloudy conditions in most areas. Radar imagery shows a fairly typical trade wind shower regime, with scattered showers moving into windward areas, and a few of these showers making the trip over the mountains and into leeward communities. Main short term concerns revolve around trade wind trends and the potential for a few pop up thunderstorms on the Big Island this afternoon and again Sunday afternoon.
Strong high pressure will remain far northeast of the islands through the weekend and the first half of next week, while a front slowly approaches from the northwest, stalling out around 400-500 miles west of the state by Wednesday. This will keep a moderate to breezy trade wind pattern in place across the islands, with the trades strongest over the eastern islands. Additionally, the low level boundary layer flow may shift east-southeasterly enough to allow for some local land and sea breeze development over the western islands at times, most likely Monday through Tuesday. The trades appear to ramp up to breezy and windy levels Wednesday through late next week, as a very strong high (1045-1048 mb) is forecast to develop far to the northeast of the state as the front west of the islands weakens into a trough and begins to retrograde westward and away from the area.
The airmass over the islands will continue to stabilize through the weekend as the upper troughing breaks down and upper level ridging begins to become more dominant. With precipitable water values hovering in the 1.2 to 1.5 range through the weekend however, we should continue to see a bit more trade wind shower coverage than normal. The showers will continue to favor windward and mauka areas with a few showers making the trip into leeward communities at times. Additionally, the airmass appears unstable enough that daytime heating could allow a thunderstorm or two to develop over the Big Island this afternoon and again Sunday afternoon.
A drier and more typical trade wind pattern should settle over the islands Sunday night through Monday night as precipitable water values lower to around 1 inch. Model solutions then show an increase in trade wind shower coverage Tuesday through late next week, as some old frontal remnants move through and some moisture advects into the region on east-southeasterly boundary layer flow. Showers will continue to favor windward and mauka areas, with a few showers reaching leeward locales at times.

Aviation

Moderate to breezy easterly trade winds will focus clouds and showers over windward and mountain locations through the weekend. MVFR ceilings and visibilities are possible in and around these showers.
AIRMET Sierra is currently in effect for mountain obscuration over the windward slopes of Kauai and Oahu.

Marine

Large, strong high pressure off the mainland west coast will produce a tight enough pressure gradient across the eastern Pacific to produce and maintain fresh to strong trades over the local Hawaiian waters the next several days. A Small Craft Advisory (SCA) is still in effect for those notoriously windier channels and bays surrounding Maui County and waters south of the Big Island, with the inclusion of the Maui and Big Island windward waters, through Sunday afternoon. This SCA will likely need to be extended into next week and possibly expanded westward to account for these strengthened trades. Seas will eventually climb to and exceed SCA level heights under this persistent trade flow next week.
A couple of small, longer period west northwest swells will travel around the islands in the coming days. The first of these swells will be arriving today and be leveling out from Sunday night through Tuesday afternoon. The second set of similar low west to northwest swells will be moving through around mid week. In response to strengthened trades over and upstream of the islands, east-facing shore surf will increase going into early next week. Recent satellite observations verify a large region of strong trades upstream of the state that will likely generate a long enough fetch region to produce near advisory level surf along eastern exposures by Monday. Energy from far Southern Hemispheric gales clipping the islands this weekend will provide a subtle boost to south-facing shoreline surf.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Sunday for Maui County Windward Waters, Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Windward Waters, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov

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