Weather Forecast

Hawaii County Weather Forecast for February 21, 2021

February 21, 2021, 7:15 AM HST
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Photo Credit: James Grenz

Hilo

Today: Occasional showers, mainly before noon. High near 78. Light and variable wind becoming east southeast 5 to 8 mph in the morning. Chance of precipitation is 80%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 63. East southeast wind around 5 mph becoming calm after midnight. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 78. East southeast wind 3 to 8 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Showers likely and possibly a thunderstorm after noon. Widespread haze. Partly sunny, with a high near 78. Calm wind becoming west southwest around 6 mph 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: Isolated showers before midnight. Widespread haze. Mostly cloudy, then gradually becoming mostly clear, with a low around 61. Calm wind. Chance of precipitation is 20%.

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Monday: Scattered showers after noon. Widespread haze. Increasing clouds, with a high near 79. West wind 3 to 6 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

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Today: Showers likely, with thunderstorms also possible after 1pm. Widespread haze. Partly sunny, with a high near 74. North northeast wind 11 to 14 mph, with gusts as high as 18 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.

Tonight: Scattered showers and thunderstorms. Widespread haze. Mostly cloudy, with a low around 52. Breezy, with an east wind 13 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.

Monday: Scattered showers. Widespread haze. Partly sunny, with a high near 75. East wind 11 to 13 mph. Chance of precipitation is 40%. 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 21 to 26 mph, with gusts as high as 38 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 46. Breezy, with an east wind around 17 mph, with gusts as high as 24 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 71. Breezy, with an east wind 15 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Isolated showers after noon. Widespread haze. Partly sunny, with a high near 78. Windy, with an east wind 22 to 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Tonight: Widespread haze. Partly cloudy, with a low around 69. Windy, with an east northeast wind around 25 mph, with gusts as high as 33 mph.

Monday: Isolated showers after noon. Widespread haze. Mostly sunny, with a high near 79. Windy, with an east northeast wind around 26 mph, with gusts as high as 34 mph. Chance of precipitation is 20%.

Puna

Today: Occasional showers, mainly before noon. High near 75. East wind 3 to 7 mph. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 61. Northeast wind 8 to 10 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Monday: Scattered showers. Partly sunny, with a high near 76. Northeast wind 8 to 11 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Waikoloa

Today: Scattered showers and thunderstorms after 1pm. Widespread haze. Mostly sunny, with a high near 80. East wind 6 to 8 mph becoming west northwest in the afternoon. Chance of precipitation is 50%. New rainfall amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Tonight: Scattered showers and thunderstorms before 7pm. Widespread haze. Mostly clear, with a low around 61. West northwest wind 6 to 8 mph becoming east after midnight. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch, except higher amounts possible in thunderstorms.

Monday: Isolated showers after 1pm. Widespread haze. Sunny, with a high near 81. East wind around 6 mph becoming north in the afternoon. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

Breezy trade winds will continue for the next couple of days, then become locally strong Wednesday and Thursday. Low clouds and showers will favor windward areas, but coverage and intensity will diminish later today as the atmosphere stabilizes. A brief increase in windward showers is possible on Tuesday, but heavy rainfall is not expected.

Discussion

In summary, trade winds remain in the forecast through next weekend. Breezy trade winds will be veered to a direction slightly S of E through Friday, becoming stronger around mid-week before returning to a more typical ENE direction next weekend while remaining breezy. Low clouds and showers will favor windward areas while most leeward areas will receive little rainfall. The island atmosphere will be somewhat unstable in the short term, but a stabilizing trend over the next day or two means that shower coverage should diminish. However, a slight increase in moisture on Tuesday may bring a brief period of increased showers. A deep-layer trough W of the islands may bring some increase in showers around mid-week. High clouds will clear today, but may return Wednesday and Thursday.
Locally breezy trade winds (supported by a 1039 mb high to the distant NE) are delivering low clouds and showers to windward areas, while a trough aloft near Kauai is producing scattered to broken high clouds over the islands from Oahu to the Big Island. Windward shower coverage increased overnight, likely due to a combination of cloud top cooling and the passage of a trough aloft. As the trough moves steadily E today, high clouds will clear and the island atmosphere will be increasing stable. However, the trough axis is expected to be over the Big Island this afternoon, and then E of all islands by tonight, so there remains a slight chance that a thunderstorm will again develop over the Big Island slopes today.
From Monday through Wednesday mid-level temperatures will warm, leading to increasingly stable conditions. The surface high to the distant NE will change little while a surface front gradually approaches from the NW, thus we expect the locally breezy trade winds to be veered to the ESE. An area of shallow moisture embedded within the trade flow arriving Tuesday may bring a brief period of increased windward showers.
On Wednesday, guidance indicates the dissipating and stalling front to the W will help seed a low-level, N-S oriented trough along 165W, supported by a trough aloft. Meanwhile, the high to the NE will strengthen to near 1047 mb. This is expected to lead to strong ESE winds, but it remains uncertain how much of a moisture and instability increase the trough will bring over the islands, with guidance indicating that it will remain just W of the islands. Closest point of approach of the convergent boundary would be to Kauai around Wednesday before it retreats to the W. The trough will dissipate by next weekend as the high to the NE remains strong, with breezy to locally strong ENE trade winds the result.
The departure of the trough aloft means high clouds will clear the chain today, but they may increase Wednesday/Thursday in association with the new trough aloft NW of the islands.

Aviation

Moderate to breezy trades will continue to push areas of clouds and showers over the islands through the forecast period. Brief MVFR conditions are to be expected, mainly along the windward slopes, with a shower or two being pushed over to leeward areas at times. Otherwise, prevailing VFR is expected through the weekend. In addition, lingering instability will allow for a slight chance of thunderstorms along the leeward slopes of the Big Island this afternoon.
AIRMET Sierra is in effect for tempo mountain obscuration due to an area of enhanced showers moving in on the trade wind flow. This activity should diminish by late morning, with improving conditions.
AIRMET Tango remains in effect for low-level mechanical turbulence over and downwind of terrain for Big Island through Molokai due to the breezy trades.
AIRMET Tango also remains in effect for mid/upper-level turbulence over the entire area between FL250 and FL450.

Marine

Strong surface high pressure located off the mainland west coast has created a tight surface pressure gradient across the eastern Pacific and is directed toward the Hawaiian Islands. This will produce and maintain fresh to strong easterly trades through the week. Healthy trades will further strengthen and increase in areal coverage from Wednesday into next weekend. Strong easterly winds will produce heightened easterly swell and wind waves that will impact the islands the next several days. Rough seas will likely reach Small Craft Advisory (SCA) thresholds for those waters exposed to this combination of easterly swell and wind driven wave action.
An SCA remains in effect for the windward waters, bays and channels surrounding Maui County and the Big Island through Monday afternoon. As large wind driven seas reach SCA thresholds early this week, the advisory will likely need to be extended and expanded westward to include all of the Hawaiian coastal waters. Advisory conditions are forecast to continue into next weekend to account for strong trades and resultant high seas.
In response to strengthened trades over and upstream of the islands, east-facing shoreline surf will be on the rise the next couple of days. Recent satellite ASCAT wind observations verify a large region of strong trades upstream of the state that will generate a long fetch region. High Surf Advisory (HSA) level surf along eastern exposures is expected to develop Monday into Tuesday. These larger wind driven seas will impact eastern-facing shores through next week.
A couple of small, overlapping longer period west northwest swells will travel around the islands in the coming days. The first of these swells is arriving today and be leveling out from tonight through Tuesday afternoon. The second set of similar low west to northwest swells will be moving through during mid to late week. Surf along north and west-facing shores will remain far below HSA levels through Friday. Energy from far Southern Hemispheric gales may clip the islands and provide a subtle bump to south-facing shoreline surf today although much of this energy will pass east of the chain.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Monday 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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