Photo Credit: Leosan Miguel

West Side

Today: Breezy. Mostly sunny with isolated showers. Highs 75 to 80. East winds 15 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Breezy. Isolated showers. Lows 64 to 71. East winds 15 to 25 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 73 to 78. East winds 10 to 20 mph. Chance of rain 50 percent.

South Side

Today: Mostly sunny. Highs around 81. Northeast winds 10 to 15 mph.

Tonight: Partly cloudy in the evening, then mostly cloudy with isolated showers after midnight. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly cloudy. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 79. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

North Shore

Today: Breezy. Partly sunny with scattered showers. Highs 73 to 78 near the shore to 58 to 63 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 62 to 68 near the shore to around 51 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Thursday: Breezy. Cloudy with showers likely. Highs 71 to 76 near the shore to 55 to 61 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Central Maui

Today: Breezy. Mostly sunny with isolated showers. Highs 77 to 82. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers in the evening, then mostly cloudy with scattered showers after midnight. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 40 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 75 to 80. East winds 10 to 20 mph. Chance of rain 50 percent.

Upcountry

Today: Mostly sunny with isolated showers. Highs around 52 at the visitor center to around 47 at the summit. East winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 45 at the visitor center to around 39 at the summit. East winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs around 47 at the visitor center to around 42 at the summit. Southeast winds 10 to 20 mph. Chance of rain 50 percent.

East Maui

Today: Breezy. Partly sunny with scattered showers. Highs 73 to 78 near the shore to 58 to 63 near 5000 feet. East winds 10 to 20 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then showers likely after midnight. Lows 62 to 68 near the shore to around 51 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Thursday: Breezy. Cloudy with showers likely. Highs 71 to 76 near the shore to 55 to 61 near 5000 feet. East winds 10 to 25 mph. Chance of rain 70 percent.

Lanai City

Today: Partly sunny. Breezy. Isolated showers in the afternoon. Highs 70 to 77. East winds 10 to 20 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Isolated showers after midnight. Lows around 65. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 68 to 75. East winds 10 to 20 mph. Chance of rain 40 percent.

Kaunakakai

Today: Partly sunny. Breezy. Isolated showers in the afternoon. Highs 70 to 80. East winds 10 to 25 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows 59 to 71. East winds 10 to 25 mph. Chance of rain 40 percent.

Thursday: Breezy. Mostly cloudy with scattered showers. Highs 68 to 78. East winds 10 to 25 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

Locally breezy trade winds will likely continue into Thursday, with trade showers focused mainly over windward and mauka areas. The trades will remain strong enough to carry a few brief showers over to leeward sections of some of the smaller islands. In addition, expect the high clouds to persist during the next several days. An unsettled and very wet weather pattern is forecast to develop from late Thursday through most of the New Year’s Holiday Weekend. Locally heavy rainfall is possible, especially late Thursday night and Friday.

Discussion

The islands remain sandwiched between surface low pressure systems to the west and the east. Far to the north, a large, nearly stationary 1040 mb surface high pressure system continues to dominate the north central Pacific east of the International Date Line. The tight pressure gradient south of this feature is producing locally breezy trade winds across the main Hawaiian Islands early this morning.
Loops of water vapor satellite imagery show an upper level ridge near the eastern end of the island chain, which is maintaining relatively stable atmospheric conditions in the vicinity of the islands. However, a large upper-level low is centered near 17N 171W, or about 825 miles west-southwest of Lihue. The broad circulation around this feature has been bringing a large area of layered mid and high clouds up over the state. Radar reflectivity data show scattered trade showers just east and northeast of the islands from Oahu to the Big Island. There are isolated showers east of Kauai.
The forecast guidance continues to show a rather complex and somewhat complicated weather scenario unfolding as we head toward the New Year’s Holiday Weekend. During the next 24 to 36 hours, expect the surface high to remain far north of the islands. The locally breezy trade winds will likely persist into Thursday. The forecast models show the upper-level low lifting toward the north-northeast later today and tonight. In the meantime, expect mainly windward and mauka trade showers, with a few brief showers being carried over to some leeward sections of the smaller islands by the low-level trade wind flow. Rainfall totals will likely be modest with the relatively stable atmospheric conditions holding for now. In addition, expect the high clouds to continue streaming across most of the state during the next several days.
As the large upper-level low continues to move closer to state, it appears that a new surface low pressure system will develop about 450 miles south-southwest of Kauai late this evening. Once this feature develops, it will likely begin to track toward the north or north-northwest. It will also likely drag a surface trough up toward the state as it approaches late Thursday, which would begin to cause the winds to weaken and shift from the southeast by Thursday evening. This means that increasing moisture will be spreading up over the area at the same time the atmosphere will be less stable due to the approaching upper-level low. The end result will be increasing rainfall coverage starting Thursday, and continuing through Thursday evening.
The global models show the upper-level low may eventually open up into a trough aloft as it gets closer to the state. This will continue to provide instability over the area, especially near the western islands. As the surface low and its associated surface trough approach the islands late Thursday night and Friday, expect an enhancement of the rainfall coverage, with locally heavy rainfall possible. We do not have thunderstorms in the latest forecast, but there is a possibility that some localized deep convection might develop at some point late Thursday night or Friday. We also do not anticipate the potential threat for significant flooding at this time. However, localized flooding may be possible if heavier showers begin to train over vulnerable areas, or if anchoring of heavy showers occurs near some of the higher terrain.
The wet and unsettled weather will likely persist over much of the state from Saturday into Sunday. Lingering instability, ample moisture, and southeasterly winds will keep rainfall chances high, especially over the western islands, which will remain close to the upper-level trough. Heading into the first part of next week, we continue to see some model differences. There are still differences in the background flow according to the model output, so future adjustments to the winds are possible for Monday and Tuesday. Regardless of the background flow, it appears that the mostly cloudy and wet weather pattern might persist for portions of the state from next Monday into Tuesday.

Aviation

Breezy easterly trade winds will persist through today. A pall of high clouds along the eastern flank of a deep low southwest of the main Hawaiian Islands blocks the view of low clouds across the smaller islands. Low clouds and showers will continue to favor windward areas, though VFR conditions are expected to prevail at most locations.
AIRMET TANGO remains in effect below 8000 feet over and immediately south through west of mountains on all islands due to tempo moderate turbulence. Moderate turbulence is expected to continue through today. Additionally, tempo light icing will be possible across the northern half of the state as extensive middle and high cloud cover remains in place.

Marine

High pressure far to the north of the islands will maintain breezy to locally strong trade winds through Thursday. A weakening surface low to the west of Kauai will then move north and shift winds to a more southeasterly direction through the weekend. A Small Craft Advisory remains in effect for most coastal waters through tonight for a combination of breezy trades and swells, and may need to be extended through Thursday for some zones as gradient winds could remain elevated as low pressure south and west of the isles approaches the state.
An east-northeast swell, combined with the breezy trades, will sustain rough and choppy surf along east facing shores. Surf heights, however, are expected to remain just below the advisory threshold.
A moderate west-northwest swell has been declining. Another moderate northwest swell will arrive tonight, being reinforced again Thursday night, and then once more over the weekend.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Thursday for Kauai Northwest Waters, Kauai Windward Waters, Kauai Channel, Oahu Windward Waters, Kaiwi Channel, Maui County Windward Waters, 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 Leeward Waters, Big Island Windward Waters.

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Data Courtesy of NOAA.gov