Photo Credit: Jeni Ji Cousins

West Side

Today: Windy. Mostly sunny with isolated showers. Highs 75 to 80. East winds 20 to 30 mph. Chance of rain 20 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows 64 to 71. Northeast winds 20 to 30 mph. Chance of rain 50 percent.

Tuesday: Windy. Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs 73 to 78. Northeast winds 20 to 30 mph decreasing to 15 to 20 mph in the afternoon. Chance of rain 50 percent.

South Side

Today: Breezy. Mostly sunny with isolated showers. Highs around 81. Northeast winds 10 to 25 mph with gusts to 45 mph. Chance of rain 20 percent.

Tonight: Partly cloudy early in the evening then becoming mostly cloudy. Breezy. Scattered showers. Lows around 65. North winds 10 to 25 mph with gusts to 45 mph. Chance of rain 40 percent.

Tuesday: Breezy. Mostly sunny with isolated showers. Highs around 79. Northeast winds 15 to 25 mph. Gusts up to 45 mph in the morning. Chance of rain 20 percent.

North Shore

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 78 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Tonight: Windy. Showers likely early in the evening, then occasional showers in the late evening and overnight. Lows 62 to 68 near the shore to around 50 near 5000 feet. East winds 15 to 30 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Mostly cloudy with showers likely. Highs 71 to 76 near the shore to around 61 near 5000 feet. East winds 10 to 25 mph becoming around 15 mph in the afternoon. Chance of rain 70 percent.

Central Maui

Today: Windy. Mostly sunny with isolated showers. Highs 77 to 82. Northeast winds 15 to 30 mph. Chance of rain 20 percent.

Tonight: Breezy. Mostly cloudy with scattered showers. Lows around 65. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Tuesday: Partly sunny in the morning then becoming mostly sunny. Windy. Scattered showers. Highs 75 to 80. Northeast winds 15 to 30 mph. Chance of rain 50 percent.

Upcountry

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 54 at the visitor center to around 51 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy early in the evening then becoming mostly cloudy. Breezy. Isolated showers early in the evening, then scattered showers in the late evening and overnight. Lows around 43 at the visitor center to around 39 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

Tuesday: Partly sunny with scattered showers. Highs around 54 at the visitor center to around 51 at the summit. East winds 10 to 15 mph decreasing to up to 15 mph in the afternoon. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 78 near the shore to around 62 near 5000 feet. East winds 10 to 25 mph with gusts to 45 mph. Chance of rain 70 percent.

Tonight: Windy. Showers likely early in the evening, then occasional showers in the late evening and overnight. Lows 62 to 68 near the shore to around 50 near 5000 feet. East winds 15 to 30 mph. Chance of rain near 100 percent.

Tuesday: Breezy. Mostly cloudy with showers likely. Highs 71 to 76 near the shore to around 61 near 5000 feet. East winds 10 to 25 mph becoming around 15 mph in the afternoon. Chance of rain 70 percent.

Lanai City

Today: Windy. Mostly sunny with isolated showers. Highs 70 to 77. Northeast winds 10 to 30 mph. Chance of rain 20 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows around 64. Northeast winds 20 to 30 mph. Chance of rain 40 percent.

Tuesday: Windy. Partly sunny with scattered showers early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 68 to 75. Northeast winds 20 to 30 mph shifting to the east 15 to 20 mph in the afternoon. Chance of rain 40 percent.

Kaunakakai

Today: Windy. Mostly sunny with isolated showers in the morning, then partly sunny with scattered showers in the afternoon. Highs 70 to 80. Northeast winds 10 to 30 mph. Chance of rain 40 percent.

Tonight: Windy. Mostly cloudy with scattered showers. Lows 58 to 70. Northeast winds up to 30 mph increasing to 15 to 30 mph after midnight. Chance of rain 50 percent.

Tuesday: Breezy. Partly sunny with scattered showers early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 68 to 78. East winds 15 to 25 mph with gusts to 45 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

A surface high pressure system building far north of the state will provide a windy and wet trade wind weather pattern across the islands through mid-week. Expect numerous trade showers over most windward and mauka sections. The gusty trade winds will carry scattered trade showers over to leeward sections of some of the smaller islands. Clouds and showers, some with locally heavy rainfall, will also likely develop over leeward sections of the Big Island each afternoon. The trade winds may weaken as we head into the Christmas Holiday Weekend.

Discussion

A 1046 mb surface high is located far north of the main Hawaiian Islands early this morning. The diffuse leading edge of a band of broken to locally overcast low clouds with embedded showers associated with a weakening frontal boundary is evident about 180 miles north-northeast of Honolulu. This leading edge is moving toward the south at about 10 mph. The pressure gradient across the islands remains very tight, so locally breezy trade winds are occurring across most of the state.
Loops of water vapor satellite imagery show the axis of a broad upper-level trough less than 900 miles northeast of Hilo. There is also a smaller upper-level low centered near 21N 171W, or about 750 miles due west of Lihue. The close proximity of these features is producing relatively unstable conditions across most of the state early this morning. The precipitable water (PW) values in the vicinity of the islands indicate that relatively abundant moisture is across the area. As a result, there are broken low clouds with embedded scattered showers across many parts of the state, especially over windward and mauka sections.
The forecast guidance shows the surface high far north of the state will continue to build. This will push the remnant frontal boundary down toward the islands from later today into Tuesday. The arrival of this feature will likely cause trade wind speeds to increase, and there is a possibility that a Wind Advisory may be needed for some of the typically windier land areas, especially over portions of the Big Island and Maui County. Also, expect the coverage of low clouds and showers to increase. Note that there appears to be enough instability near the eastern end of the state to allow for a few thunderstorms and locally downpours to develop across the Big Island during the time of maximum daytime heating again this afternoon, as well as Tuesday afternoon.
Beyond Tuesday, the unstable atmospheric conditions are expected to persist. If so, this will likely maintain the wet trade wind pattern through mid-week. The forecast guidance appears to show the highest PW values will be over the eastern end of the island chain, so the rainfall chances are expected to be greatest near the Big Island from Wednesday into Friday.
As we head into the long Christmas Holiday Weekend, the forecast models continue to show a surface low pressure system nudging slowly eastward towards Kauai. Assuming this scenario were to unfold, it would likely cause the trade winds to eventually weaken, and the background flow might shift out of the east- southeast. However, the effects of the approaching surface low on our sensible weather remain uncertain at this time due to differences in the output from the global models. Stay tuned to future updates as we fine tune the weekend forecast.

Aviation

Breezy trade winds will persist through the remainder of this morning. Therefore, expect tempo moderate turbulence over the lee of the mountains. See AIRMET TANGO below. Scattered to occasional showers will mainly be limited to windward areas and will likely bring periods of MVFR ceilings and visibility.
AIRMET SIERRA remains in effect for northeast thru east facing mountain slopes above 2500 feet for Big Island due to clouds and showers.
AIRMET TANGO remains in effect for all island over and immediately south through west of mountains for tempo moderate turbulence below 9000 feet.

Marine

A nearly stationary, very strong area of high pressure centered far N of the islands will support fresh to strong trade winds for most of the week. A surge in wind speeds is expected tonight and Tuesday, resulting in near gale-force winds in some areas for a couple days as the high pushes the remnants of a front over the islands. A Small Craft Advisory (SCA) has been expanded in time and area, and now includes nearly all waters through Thursday due to a combination of winds and seas. The one zone, Big Island Windward Waters, currently not included in the SCA may be added later as winds and seas increase further. Moisture associated with the frontal remnants may stall near the Big Island by midweek, potentially triggering heavy showers and/or thunderstorms as the island atmosphere is likely to remain unstable.
While the fetch of trade winds to the E of the islands is somewhat limited, short- and medium-period wind waves/swells will be arriving from the NE and NNE over the next day or two, due to the strong high, and the strong gradient between it 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. Surf along exposed E facing shores may become large enough to warrant a High Surf Advisory by tonight or Tuesday. Very little swell energy from the NW is expected this week, but a small pulse of swell will persist through today, with another pulse possible Thursday and Friday.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 PM HST Thursday for all Hawaiian Waters, except the Big Island Windward Waters.

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Data Courtesy of NOAA.gov