Photo Credit: Jeni Ji Cousins

West Side

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs 73 to 81. Northeast winds 15 to 25 mph. Chance of rain 40 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows 65 to 72. Northeast winds 10 to 25 mph. Chance of rain 50 percent.

Monday: Mostly sunny. Breezy. Scattered showers early in the morning, then isolated showers in the late morning and afternoon. Highs 73 to 81. Northeast winds 10 to 25 mph. Chance of rain 40 percent.

South Side

Today: Sunny and breezy. Highs around 84. Northeast winds 10 to 20 mph.

Tonight: Mostly clear. Breezy. Isolated showers after midnight. Lows 64 to 72. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Breezy. Highs around 83. Northeast winds 10 to 25 mph.

North Shore

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 79 near the shore to around 62 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then frequent showers after midnight. Lows around 68 near the shore to 46 to 52 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Breezy. Mostly cloudy with showers likely. Highs 72 to 79 near the shore to around 62 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Central Maui

Today: Breezy. Mostly sunny with isolated showers. Highs 78 to 83. Northeast winds 10 to 25 mph increasing to 20 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 64 to 69. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Monday: Breezy. Mostly sunny with isolated showers. Highs 77 to 82. East winds 10 to 25 mph shifting to the northeast 20 to 25 mph in the afternoon. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 57 at the visitor center to around 53 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Partly cloudy with scattered showers. Lows around 45 at the visitor center to around 42 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

Monday: Partly sunny in the morning then becoming mostly sunny. Breezy. Scattered showers. Highs around 57 at the visitor center to around 53 at the summit. East winds 10 to 20 mph. Chance of rain 50 percent.

East Maui

Today: Partly sunny. Breezy. Showers likely in the morning, then scattered showers in the afternoon. Highs 73 to 79 near the shore to around 62 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Mostly cloudy. Breezy. Numerous showers in the evening, then frequent showers after midnight. Lows around 68 near the shore to 46 to 52 near 5000 feet. East winds 10 to 20 mph. Chance of rain 90 percent.

Monday: Breezy. Mostly cloudy with showers likely. Highs 72 to 79 near the shore to around 62 near 5000 feet. East winds 10 to 20 mph. Chance of rain 70 percent.

Lanai City

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 70 to 78. Northeast winds 10 to 25 mph increasing to 20 to 25 mph in the afternoon. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows around 63. Northeast winds 10 to 25 mph.

Monday: Mostly sunny. Breezy. Isolated showers in the late morning and afternoon. Highs 69 to 77. Northeast winds 15 to 20 mph. Chance of rain 20 percent.

Kaunakakai

Today: Breezy. Mostly sunny with isolated showers. Highs 63 to 84. Northeast winds up to 20 mph increasing to 15 to 20 mph in the afternoon. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows 56 to 72. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Monday: Mostly sunny. Breezy. Isolated showers early in the morning. Scattered showers in the late morning and early afternoon, then showers likely late in the afternoon. Highs 63 to 83. East winds 15 to 20 mph. Chance of rain 60 percent.

Detailed Forecast

Synopsis

Breezy trades will focus clouds and showers over windward and mauka areas today. Developing strong trades will be accompanied by a wetter trade wind pattern beginning late Monday.

Discussion

Trades will steadily strengthen during the next 24 hours or so, becoming locally strong this afternoon. This will support a continuation of the relatively wet trade pattern already in place as weak stability favors locally heavy, but generally progressive showers. Conditions will remain marginally favorable for isolated thunderstorms over the interior slopes of the Big Island during the afternoons, but given the lack of development yesterday will defer to a persistence forecast for now as confidence is too low to warrant inclusion in the forecast. In the meantime, cloud top temperatures of deep trade wind showers spilling over the summits of the Big Island have consistently hovered in the ideal 0C to -5C range for supercooled water while observed surface temperatures are around 30F. The winter weather advisory for freezing rain remains in effect until noon, which should give ample time for temps to warm above the freezing mark.
A cold front delineating the lead edge of strong high pressure is readily evident on satellite imagery pushing south of 30N at press time. This front is forecast to reach Kauai on Monday afternoon and push through the remainder of the area during Monday night. In addition to supporting an uptick in the wet trade pattern, strong winds during this time may approach advisory criteria in favored locales.
The front will slip south of the area by Tuesday, leaving islands in a wet but slightly more stable trade pattern. As the closed low currently northwest of the islands weakens and shears south of the state, the associated band of deep moisture will begin to lift toward the islands from the south. The Big Island in particular appears poised to see a steady dose of trade wind showers, which could be heavy at times, through the mid-week period. For the remaining islands, however, the latest trend in the modeling has been to the delay the arrival the mid-level trough and attendant deep reservoir of moisture resulting in reduced forecast confidence in terms of any organized threat for heavier rainfall.

Aviation

High pressure building to the north of the state will bring breezy trades to the islands through the forecast period. Thus, expect moderate turbulence above the lee sides of mountain ranges. See AIRMET TANGO below. Scattered showers will be focused mainly on windward coasts and slopes and may bring brief periods of MVFR ceilings/visibility. Isolated showers forecast along leeward areas.
AIRMET TANGO remains in effect below 9000 feet over and immediately south through west of mountains for tempo moderate turbulence.
AIRMET SIERRA remains in effect for north through east sections of the Big Island above 2500 ft for tempo mountain obscuration from from low clouds and showers.

Marine

Trade winds will gradually increase over the next couple of days. Strong high pressure far north of the state is currently driving moderate to locally strong trade winds. A Small Craft Advisory (SCA) remains in effect for the typically windy waters around the Big Island and Maui and has been expanded to the Kaiwi Channel for today. The SCA was also expanded to most waters around Kauai, Oahu and Maui for Monday, as trade winds will strengthen along and north of a dissipating front that will drift southward over the islands through Tuesday. The remnants of this frontal boundary are expected to creep northward Thursday or Friday and may cause trade winds to ease and possibly shift to southeasterlies. Instability across the region will potentially trigger heavy showers, or perhaps a thunderstorm, along the remnant front.
Rough seas will accompany the increasing trade winds and will contribute to SCA conditions this week. Large wind waves will be mixed with a relatively short period north-northeast swell, pushing combined seas to the 10 ft SCA threshold over most waters north and east of the islands Sunday night and Monday. Resulting surf along east facing shores may require a High Surf Advisory on some islands by late Monday or Tuesday. Elevated and rough seas may hold through mid week.
A declining northwest swell may receive a reinforcing pulse later today and produce overhead north shore surf. Another small northwest swell is possible mid week. Typical, very small December conditions will persist for south shores.

HFO Watches/Warnings/Advisories

Winter Weather Advisory until noon HST today for Big Island Summits.
Small Craft Advisory until 6 AM HST Monday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

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Data Courtesy of NOAA.gov