West Side

Today: Mostly sunny. Breezy. Highs around 79. East winds up to 20 mph.

Tonight: Partly cloudy. Lows 65 to 72. Southeast winds up to 15 mph in the evening becoming light.

Saturday: Mostly sunny. Highs around 79. Light winds.

South Side

Today: Sunny. Highs around 83. North winds up to 10 mph.

Tonight: Mostly clear. Lows 64 to 73. Northwest winds up to 10 mph in the evening becoming light.

Saturday: Sunny. Highs around 84. Light winds becoming west up to 10 mph in the afternoon.

North Shore

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 79 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 68 near the shore to around 49 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 40 percent.

Saturday: Mostly sunny with isolated showers. Highs around 79 near the shore to around 64 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Central Maui

Today: Sunny and breezy. Highs 79 to 84. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon.

Tonight: Mostly clear. Lows around 66. Southeast winds up to 15 mph in the evening becoming light.

Saturday: Sunny. Highs 80 to 85. South winds up to 10 mph shifting to the east in the afternoon.

Upcountry

Today: Breezy. Mostly sunny with scattered showers. Highs around 60 at the visitor center to around 68 at the summit. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 43 at the visitor center to around 46 at the summit. East winds up to 20 mph shifting to the southeast up to 10 mph after midnight. Chance of rain 40 percent.

Saturday: Mostly sunny. Isolated showers in the morning. Haze in the afternoon. Highs around 59 at the visitor center to around 68 at the summit. Light winds becoming east up to 10 mph in the afternoon. Chance of rain 20 percent.

East Maui

Today: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 79 near the shore to around 63 near 5000 feet. East winds up to 20 mph. Chance of rain 50 percent.

Tonight: Partly cloudy. Breezy. Scattered showers in the evening, then isolated showers after midnight. Lows around 68 near the shore to around 49 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 40 percent.

Saturday: Mostly sunny with isolated showers. Highs around 79 near the shore to around 64 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Lanai City

Today: Mostly sunny. Highs 70 to 77. Light winds.

Tonight: Mostly clear. Lows around 64. Light winds.

Saturday: Mostly sunny. Haze in the afternoon. Highs 71 to 78. Light winds.

Kaunakakai

Today: Sunny. Highs 67 to 84. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon.

Tonight: Mostly clear. Lows 55 to 70. East winds up to 15 mph in the evening becoming light.

Saturday: Mostly sunny. Isolated showers in the afternoon. Highs 68 to 84. Light winds. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Trades will continue through much of the morning and gradually decrease thereafter, veering southeastward. A relatively dry and stable air mass will continue to support only light showers focused windward and mauka through the middle of next week. Late this weekend, a front will move toward the state from the northwest, stalling just outside of Kauai before retrograding back west. By midweek, an upper-level trough moves into the vicinity, increasing instability and producing higher chances for heavy showers ahead of trades rebuilding to ring in the New Year.

Discussion

An elongated area of high pressure and associated ridging extending from southwest from the high toward the Hawaiian Islands will help maintain trades through today. Flanking areas of low pressure on either end of the high remain intact just east of the Dateline and right along the west coast of the US, respectively. Stability is also maintained, limiting any shower activity to mainly windward and mauka areas across the state, with the only exception being the Kona region of the Big Island in the last 24 hours. This stability can visually be seen on the latest 2 AM HST (12Z) upper-air balloon sounding from Lihue and Hilo, depicting a temperature inversion holding steady between 5500 and 6500 feet today.
As all the aforementioned surface features meander eastward, the area of high pressure will lessen the local pressure gradient across the island, leading to trades weakening and veering southeastward. Meanwhile, latest model guidance is in good agreement that the area of low pressure to the northwest will make its way up to the Gulf of Alaska, escorted by a weak cold front advancing toward, but stalling short of, Kauai late Saturday. Guidance continues to depict this front will stall just northwest of Kauai through Sunday, yet close enough where Kauai could see a noticeable increase in shower activity, before retrograding back west on Monday.
Toward the end of the year leading into New Year's Day, model guidance showcases a strong, zonal jet stream west of the Hawaiian Islands splitting, amplifying an upper-level trough and the subtropical jet stream that feeds into the islands. There continues to be a discrepancy between guidance, however, on the strength of the aforementioned trough, leaving quite a bit of uncertainty in the forecast for the days leading into the New Year. The American model (GFS)'s scenario results in increased instability across the state and heavy rainfall potential. Total Precipitable Water (PWATs) normalized anomaly shows a standard deviation of 1 to 2 times above normal precipitation across the Hawaiian Islands. Conversely, the European model (ECMWF) doesn't amplify the upper- level trough as much, and standard deviations are closer to normal. Regardless, shower activity is anticipated during this time, but how much at this time remains uncertain.
That said, what models do seem to agree on is high pressure at the surface developing just north of the state, which leads to a higher confidence that trades will rebuild on Tuesday leading into the New Year, blowing away any firework smoke. At this time, the uncertain pattern seems to favor unstable and wet trades that would place the greatest potential for heavy rainfall over windward and mauka areas. Additional analysis will be necessary to pinpoint which scenario is favored.

Aviation

Trade winds continue through this morning before gradually weakening and veering to southeastward beginning tonight. Shower activity remains limited, but early morning windward and mauka showers are possible, which may lead to brief periods of MVFR conditions. Otherwise, expect VFR conditions to prevail.
No AIRMETS are in effect at this time.

Marine

A low pressure system far north of the islands will drive a trailing shallow cold front into the northwestern offshore waters where it will stall out west of Kauai this weekend. This approaching front will push the surface ridge over the Hawaii region producing gentle to moderate easterly to southeasterly winds across the region through Monday. Easterly trade winds will strengthen again into the moderate to fresh range from Tuesday to Wednesday, as a high pressure system builds in from the north. The Small Craft Advisory remains in effect for windier waters and channels surrounding Maui and the Big Island through tonight.
The current moderate, medium period north-northeast (010-030 degrees) swell will hold through the evening hours. This swell continues to boost surf heights along north facing shores. This swell will decline rapidly from midnight tonight into Saturday. A Marine Weather Statement was extended in time for moderate harbor surges at Kahului and Hilo through tonight. A combination of the declining north-northeast swell and a small long period west- northwest swell will keep smaller surf in the forecast this weekend. The next large medium to long period north-northwest (330-350 degree) swell is expected to arrive in the islands by early Monday morning, peaking at solid High Surf Advisory levels along north and west facing shores from Monday night through Wednesday morning.
Small rough and choppy surf along east facing shores will gradually decline as trade winds ease this weekend. Surf along south facing shores will remain very small through the week.

HFO Watches/Warnings/Advisories

Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay, Pailolo Channel, Alenuihaha Channel, Big Island Leeward Waters, Big Island Southeast Waters.

Data Courtesy of NOAA.gov