Weather Forecast

Hawaii County Weather Forecast for December 21, 2021

December 21, 2021, 7:16 AM HST
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Photo Credit: James Grenz

Hilo

Today: Cloudy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 74 to 79 near the shore to around 64 at 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Tonight: Cloudy with occasional showers. Lows around 66 near the shore to around 52 at 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Wednesday: Cloudy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 73 to 78 near the shore to around 63 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Kona

Today: Mostly cloudy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 79 to 84 near the shore to 65 to 71 near 5000 feet. West winds up to 10 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows 66 to 71 near the shore to around 51 near 5000 feet. East winds up to 10 mph. Chance of rain 50 percent.

ARTICLE CONTINUES BELOW AD

Wednesday: Mostly cloudy. Isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 78 to 83 near the shore to 63 to 70 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

ARTICLE CONTINUES BELOW AD

Today: Cloudy and windy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 61 to 77. East winds 10 to 30 mph. Chance of rain 90 percent.

Tonight: Breezy. Cloudy with occasional showers. Lows around 65 near the shore to 51 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Cloudy and breezy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 60 to 76. East winds 10 to 20 mph. Chance of rain 90 percent.

Kohala

ARTICLE CONTINUES BELOW AD

Today: Cloudy and windy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 61 to 77. East winds 10 to 30 mph. Chance of rain 90 percent.

Tonight: Breezy. Cloudy with occasional showers. Lows around 65 near the shore to 51 to 61 near 3000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Wednesday: Cloudy and breezy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 60 to 76. East winds 10 to 20 mph. Chance of rain 90 percent.

South Big Island

Today: Mostly cloudy. Windy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 79 near the shore to around 68 near 5000 feet. East winds 10 to 30 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 68 near the shore to around 52 near 5000 feet. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Wednesday: Mostly cloudy. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs around 78 near the shore to around 67 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Puna

Today: Cloudy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 74 to 79 near the shore to around 64 at 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Tonight: Cloudy with occasional showers. Lows around 66 near the shore to around 52 at 4000 feet. East winds 10 to 15 mph. Chance of rain 90 percent.

Wednesday: Cloudy. Occasional showers in the morning, then occasional showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 73 to 78 near the shore to around 63 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 90 percent.

Waikoloa

Today: Mostly cloudy. Breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 76 to 83 near the shore to 62 to 71 above 4000 feet. East winds 10 to 25 mph shifting to the northeast up to 25 mph in the afternoon. Gusts up to 45 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with scattered showers. Lows around 70 near the shore to 48 to 55 above 4000 feet. East winds up to 10 mph increasing to 10 to 15 mph after midnight. Chance of rain 50 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Locally heavy rainfall possible in the afternoon. Highs 75 to 82 near the shore to 61 to 70 above 4000 feet. Northeast winds up to 10 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A strong surface high pressure system far north of the islands combined with moist and unstable atmospheric conditions will produce a windy and wet trade wind pattern during the next couple of days. Most of the low clouds and showers will favor windward and mauka areas, but the strong trades will also carry some showers over to leeward sections of the smaller islands. Clouds and showers, some with locally heavy rainfall, are also expected to develop over leeward sections of the Big Island each afternoon. The latest forecast indicates slightly weaker winds and a drying trend may develop during the Christmas Holiday Weekend.

Discussion

Winter officially begins in Hawaii ,and the remainder of the Northern Hemisphere, at 559 AM HST this morning. As we transition into the new season, we are seeing a blustery and wet trend in our weather pattern during the next couple of days.
The tight pressure gradient south of a 1039 mb surface high pressure system located far north of the state is producing locally windy trades across the region. Loops of water vapor satellite imagery show the axis of a broad upper-level trough about 550 miles northeast of Hilo. There is also a small upper- level low pressure system centered about 450 miles southwest of Lihue. The close proximity of these features aloft to the state continues to produce unstable atmospheric conditions across the island chain. A band of low clouds and showers associated with a dissipated frontal boundary will continue to bring low clouds and showers across most windward and mauka areas as it moves slowly south today. The gusty low-level trade wind flow will also carry some showers over to leeward sections of the smaller islands today, especially this morning. Note that we currently do not anticipate the need for a Wind Advisory later today. However, some areas will be just below criteria, so we may need to issue one if the wind observations show stronger sustained speeds and/or gusts.
The forecast guidance shows the strong trades will persist into mid-week. The guidance also shows the band of moisture will continue pushing south across the Big Island into this evening. This combined with the lingering instability will likely result in a slight chance of thunderstorms and locally heavy downpours on the Big Island again this afternoon.
The forecast models indicate the moisture from the remnant frontal boundary will eventually stall near, or just south of the Big Island later tonight and Wednesday. This enhanced moisture combined with continued atmospheric instability may result in a prolonged period of wet weather for some areas on the Big Island. The instability will also keep the threat of thunderstorms in the vicinity of the Big Island around mid-week, especially during the afternoon hours. The greatest uncertainty at the moment is where the bulk of the moisture field will end up in relation to the Big Island? If we see a potential threat for widespread heavy rainfall, a Flood Watch may be required for the Big Island starting Wednesday. Elsewhere, there may be a drying trend over some of the smaller islands around mid-week. There may also be some slightly cooler nighttime temperatures in some sheltered locations.
Looking ahead to the long Christmas Holiday Weekend, the latest forecast guidance continues to show a significant low pressure system developing west of the state. There is still some uncertainty in the exact movement of this feature after it develops, but its presence may cause some weakening of the trade winds, especially after Friday. We are also seeing trends in the forecast models now that suggest that the background flow may become east-southeast. The latest model output seems to be trending toward keeping the low far enough west so that significant rainfall may not develop. As a result, we have introduced a frying trend in the weather over most of the state for Christmas Day.

Aviation

Breezy trades will persist through the forecast period and likely generate tempo moderate turbulence over the lee of the mountains. See AIRMET TANGO below. The aforementioned flow pattern will concentrate scattered showers along windward portions of the islands and bring brief periods of MVFR ceilings and visibility. Isolated showers leeward areas.
Relatively deep moisture and instability aloft will drift towards the Big Island this afternoon through tomorrow and bring a slight chance of thunderstorms to areas southeast of Maui. Abundant mid- upper level clouds will persist elsewhere over the island chain.
AIRMET SIERRA remains in effect for northeast thru east facing mountain slopes above 2500 feet for Kauai, Oahu, Maui, Molokai, and the Big Island due to clouds and showers.
AIRMET TANGO remains in effect for all islands over and immediately south through west of mountains for tempo moderate turbulence below 9000 feet.

Marine

nearly stationary, very strong area of high pressure centered far N of the islands will support fresh to near-gale force trade winds this week. A bit of a surge in wind speeds is expected through today as the high pushes the remnants of a front over the islands from the NE. An ongoing Small Craft Advisory includes all waters through Thursday due to a combination of winds and seas. Moisture associated with the frontal remnants may stall near the Big Island today through Thursday, potentially triggering heavy showers and/or thunderstorms as the island atmosphere will remain unstable. A slight chance of thunderstorms is also possible in other coastal waters south of the isles, especially near Kauai.
While the fetch of trade winds to the E of the islands is somewhat limited, a steady supply of short- and medium-period wind waves/swells will be arriving from the N through NE for the next several days, primarily due to the gradient between the high and a slow-moving, gale-force low off the U.S. W coast. This will result in increased seas, with rough and choppy surf along shores exposed to the N and E. High surf along exposed E facing shores is expected, and a High Surf Advisory (HSA) is in effect starting this morning. Surf heights along N facing shores will be similar to those on E facing shores, but differing criteria between shorelines means peak surf heights along N facing shores will remain below HSA heights. Very little swell energy from the NW is expected this week, with increased potential for long-period NW swell to arrive late next weekend.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Wednesday for east facing shores of Kauai, Oahu, Molokai, Maui and the Big Island.
Small Craft Advisory until 6 PM HST Thursday for all Hawaiian waters.

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Data Courtesy of NOAA.gov

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