Photo Credit: James Grenz

Hilo

Today: Mostly cloudy in the morning then becoming mostly sunny. Occasional showers early in the morning, then scattered showers in the late morning and early afternoon. Isolated showers late in the afternoon. Highs 72 to 79 near the shore to 58 to 64 at 4000 feet. North winds up to 15 mph. Chance of rain 90 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 57 to 69 near the shore to around 50 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 50 percent.

Christmas Day: Mostly cloudy. Occasional showers in the morning, then showers likely in the afternoon. Highs 72 to 78 near the shore to 58 to 65 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Kona

Today: Sunny until late afternoon then becoming partly sunny. Scattered showers late in the afternoon. Highs around 80 near the shore to around 63 near 5000 feet. Light winds. Chance of rain 40 percent.

Tonight: Mostly cloudy with isolated showers in the evening, then mostly clear after midnight. Lows 63 to 68 near the shore to 43 to 50 near 5000 feet. Light winds. Chance of rain 20 percent.

Christmas Day: Sunny in the morning, then partly sunny with scattered showers in the afternoon. Highs around 80 near the shore to around 62 near 5000 feet. Light winds. Chance of rain 50 percent.

Waimea

Today: Breezy. Mostly cloudy with showers likely early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 58 to 78. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 56 to 62 near the shore to 49 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Christmas Day: Breezy. Partly sunny with scattered showers. Highs 58 to 78. East winds 10 to 20 mph. Chance of rain 50 percent.

Kohala

Today: Breezy. Mostly cloudy with showers likely early in the morning, then mostly sunny with isolated showers in the late morning and afternoon. Highs 58 to 78. East winds 10 to 20 mph. Chance of rain 70 percent.

Tonight: Breezy. Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 56 to 62 near the shore to 49 to 58 near 3000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Christmas Day: Breezy. Partly sunny with scattered showers. Highs 58 to 78. East winds 10 to 20 mph. Chance of rain 50 percent.

South Big Island

Today: Sunny and breezy. Isolated showers late in the afternoon. Highs around 79 near the shore to around 62 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows around 68 near the shore to around 48 near 5000 feet. Northeast winds up to 20 mph.

Christmas Day: Mostly sunny. Isolated showers in the afternoon. Highs around 78 near the shore to around 62 near 5000 feet. East winds 10 to 15 mph. Chance of rain 20 percent.

Puna

Today: Mostly cloudy in the morning then becoming mostly sunny. Occasional showers early in the morning, then scattered showers in the late morning and early afternoon. Isolated showers late in the afternoon. Highs 72 to 79 near the shore to 58 to 64 at 4000 feet. North winds up to 15 mph. Chance of rain 90 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows 57 to 69 near the shore to around 50 at 4000 feet. Northwest winds up to 15 mph. Chance of rain 50 percent.

Christmas Day: Mostly cloudy. Occasional showers in the morning, then showers likely in the afternoon. Highs 72 to 78 near the shore to 58 to 65 at 4000 feet. Northeast winds 10 to 15 mph. Chance of rain 80 percent.

Waikoloa

Today: Sunny and breezy. Isolated showers late in the afternoon. Highs 76 to 83 near the shore to 62 to 67 above 4000 feet. Northeast winds up to 25 mph. Chance of rain 20 percent.

Tonight: Mostly clear. Breezy. Lows 63 to 68 near the shore to 42 to 50 above 4000 feet. Southeast winds up to 20 mph decreasing to up to 10 mph after midnight.

Christmas Day: Mostly sunny. Isolated showers in the afternoon. Highs 77 to 83 near the shore to around 63 above 4000 feet. North winds up to 10 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trade winds will deliver clouds and passing showers to windward areas, with some briefly spreading leeward, followed by a slight decrease in winds on Christmas Day. A deep low will develop several hundred miles northwest of Kauai on Sunday then dive south and weaken Monday and Tuesday. During this time, local winds will shift out of the east to southeast and an increase in clouds and showers will be possible, especially over the western end of the state. Easterly trade winds will prevail by mid week, though high clouds may persist.

Discussion

Breezy trade winds will continue today with a slight decline expected for Christmas. A blocking pattern remains fixed across the the central Pacific. This is supporting deep and broad high pressure far north of the state that is driving breezy trade winds. Jet stream energy continues to undercut this high and is triggering thunderstorms a couple hundred miles south of the islands, but mid level ridging over Hawaii remains just strong enough to prevent heavy shower development locally. As a result, the main rain makers in the short term are shallow bands of moisture embedded in the trade wind flow that will focus modest showers over windward slopes. One such band has moved in overnight and will clear by mid morning, leading to rather dry afternoon conditions over most areas. Another band will move through tonight. Winds will ease slightly on Christmas Day with typical trade wind weather continuing. Due to the relative weakness of the mid level ridge, we cannot rule out a briefly heavy shower flaring on the leeward Big Island slopes each afternoon.
Deep low pressure will develop several hundred miles northwest of Kauai on Sunday then dive south and weaken Monday and Tuesday. Winds will shift out of the east to southeast on Sunday and Monday as a band of deep moisture develops 200 to 300 miles west of Kauai. Due to the tightening pressure gradient, winds will strengthen over the Big Island and Maui, though the rest of the island chain could be in the “shadow” of these large islands and may not experience much of an increase in southeasterly winds Sunday and Monday. The band of deep moisture will most likely remain west of the state, but the upper level trough supporting the low may may over the islands, leading to increased instability that could support heavy showers and possibly thunderstorms over portions of the state. Given the proximity of the low, Kauai has the greatest chance of unsettled weather, but uncertainty remains somewhat high.
Breezy easterly trade winds will likely return by mid week, though high clouds and some instability will linger over the region.

Aviation

A passing band of trade wind showers will bring periods of MVFR showers to windward and mauka areas through the pre-dawn hours, especially for Oahu through Maui. Conditions will improve early this morning with quick return to prevailing VFR expected.
AIRMET Sierra for mountain obscuration is in effect for Windward Oahu through Maui.
AIRMET Tango for lee turbulence below 9kft remains in effect.

Marine

Fresh to strong trade wind speeds will slowly decrease starting this afternoon into Sunday as the ridge weakens north of the state. The Small Craft Advisory (SCA) was extended for strong winds and high seas across all Hawaiian waters through this afternoon. The SCA will then be scaled back to the typically windy waters around Maui County and the Big Island tonight through Saturday. Borderline SCA conditions may return next week as a surface low develops west of the islands.
Instability from an upper level trough will maintain thunderstorms across the southern offshore waters today. After a lull on Saturday, the threat of thunderstorm activity returns to the western offshore waters from Sunday onward, possibly reach some coastal waters from Monday into Tuesday.
The north-northeast swell will continue to elevate surf along north and east facing shores today and tonight. The High Surf Advisory (HSA) will continue for east facing shores through the afternoon. This HSA will likely be dropped on Saturday as the north-northeast swell diminishes. The continued elevated seas and high surf has also prompted the extension of the Marine Weather Statement for north facing harbor surges today. West facing shores can expect small to moderate surf starting Monday and persist through most of next week as a series of west-northwest swell builds into the region. Surf along most south facing shores will remain nearly flat this week.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST this evening for Olomana, Maui Windward West, Kauai East, Koolau Windward, Molokai Windward, Molokai Southeast, Windward Haleakala, Big Island East, Big Island North.
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters, Kauai Windward Waters, Kauai Leeward Waters, Kauai Channel, Oahu Windward Waters, Oahu Leeward Waters, Kaiwi Channel, Maui County Windward Waters, Maui County Leeward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov