Photo Credit: Allen Tate

West Side

Today: Cloudy and breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs 74 to 85. Northeast winds 20 to 25 mph with gusts to 45 mph. Chance of rain 40 percent.

Tonight: Cloudy and breezy. Scattered showers and slight chance of thunderstorms in the evening, then slight chance of thunderstorms and isolated showers after midnight. Lows 67 to 73. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

Wednesday: Breezy. Partly sunny with scattered showers. Highs 75 to 86. Northeast winds 10 to 20 mph. Chance of rain 40 percent.

South Side

Today: Cloudy and breezy. Scattered showers in the morning, then scattered showers and slight chance of thunderstorms in the afternoon. Highs around 85. East winds 10 to 25 mph shifting to the north in the afternoon. Gusts up to 45 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy. Breezy. Slight chance of thunderstorms and isolated showers in the evening, then isolated showers after midnight. Lows 66 to 73. North winds 15 to 20 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs around 86. North winds 15 to 20 mph. Chance of rain 20 percent.

North Shore

Today: Breezy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 73 to 82 near the shore to around 62 near 5000 feet. East winds 15 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 69 near the shore to 47 to 53 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Wednesday: Breezy. Mostly cloudy with occasional showers. Highs 74 to 82 near the shore to around 63 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Central Maui

Today: Breezy. Cloudy with scattered showers and slight chance of thunderstorms. Highs 79 to 85. Northeast winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Cloudy and breezy. Scattered showers and slight chance of thunderstorms in the evening, then slight chance of thunderstorms and isolated showers after midnight. Lows 65 to 70. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Breezy. Isolated showers in the morning, then scattered showers in the afternoon. Highs 80 to 87. Northeast winds 15 to 20 mph. Chance of rain 50 percent.

Upcountry

Today: Mostly cloudy. Breezy. Scattered showers and slight chance of thunderstorms in the morning, then slight chance of thunderstorms and isolated showers in the afternoon. Highs around 57 at the visitor center to around 52 at the summit. East winds 15 to 20 mph. Chance of rain 50 percent.

Tonight: Breezy. Mostly cloudy with scattered showers and slight chance of thunderstorms. Lows around 45 at the visitor center to around 42 at the summit. East winds 10 to 25 mph. Chance of rain 50 percent.

Wednesday: Mostly sunny. Breezy. Scattered showers in the morning, then isolated showers in the afternoon. Highs around 59 at the visitor center to around 54 at the summit. East winds 10 to 25 mph. Chance of rain 50 percent.

East Maui

Today: Breezy. Occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Highs 73 to 82 near the shore to around 62 near 5000 feet. East winds 15 to 20 mph. Chance of rain near 100 percent.

Tonight: Breezy. Cloudy with occasional showers and slight chance of thunderstorms. Locally heavy rainfall possible. Lows around 69 near the shore to 47 to 53 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Wednesday: Breezy. Mostly cloudy with occasional showers. Highs 74 to 82 near the shore to around 63 near 5000 feet. East winds 15 to 20 mph. Chance of rain 90 percent.

Lanai City

Today: Breezy. Partly sunny with scattered showers in the morning, then cloudy with scattered showers and slight chance of thunderstorms in the afternoon. Highs 71 to 80. Northeast winds 15 to 20 mph. Chance of rain 30 percent.

Tonight: Mostly cloudy. Windy. Slight chance of thunderstorms and isolated showers in the evening, then isolated showers after midnight. Lows around 64. Northeast winds 15 to 30 mph. Chance of rain 20 percent.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 72 to 80. Northeast winds 15 to 25 mph. Chance of rain 20 percent.

Kaunakakai

Today: Breezy. Partly sunny with scattered showers in the morning, then cloudy with slight chance of thunderstorms and isolated showers in the afternoon. Highs 65 to 85. East winds 15 to 25 mph. Chance of rain 50 percent.

Tonight: Breezy. Cloudy with slight chance of thunderstorms and isolated showers. Lows 57 to 73. East winds 15 to 20 mph. Chance of rain 20 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Breezy. Isolated showers. Highs 66 to 86. East winds 15 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Breezy trade winds will be rather wet for most of this week, with some locally heavy downpours, and possibly a thunderstorm, the next couple of days. Most of the showers will focus over windward communities, but a few showers will occasionally drift to leeward areas. Thickening high clouds are expected statewide from Wednesday night through Friday. Fewer clouds and showers, and lighter winds, are anticipated by the weekend.

Discussion

A ridge of high pressure well N of the islands will support breezy to locally strong trade winds this week. A front approaching from the NW by the end of the week will force the ridge southward, leading to some weakening of the winds, while also veering them to the ESE. Light to moderate trade winds are then expected to continue into early next week.
Of greater significance to island weather the next couple of days is a closed low aloft that is currently just N of Kauai, and its associated trough aloft, now over the island chain. This low and trough will keep the island atmosphere destabilized this week as it moves slowly toward the WSW. It has already led to 8 to 10 inches of rain over the last 48 hours in windward portions of Maui and the Big Island, where water levels in streams and rivers are elevated.
The core of the 500 mb low (with temperatures as low as -16C) will pass directly over Kauai and Oahu today and tonight, acting to thermodynamically destabilize the atmosphere to the point that a few thunderstorms are likely to develop, and they are included in the forecast. Deep moisture reaching the Big Island Summits, where temperatures are below freezing, has led to a wintry mix of precipitation, and a Winter Weather Advisory remains in effect through today. As the cold core of the mid-level low drifts away to the W late Wednesday and Thursday, mid-level temperatures will warm, reducing the amount of thermodynamically-induced instability, and the potential for winter weather over the Big Island Summits.
Although thermodynamic instability is expected to diminish, latest GFS and ECMWF guidance indicate periods of large-scale dynamic lift supported by divergence aloft E of the trough axis on Wednesday, and again on Friday, as the trough aloft becomes negatively tilted. While confidence in the timing is not high, confidence is fairly high that the island atmosphere will remain relatively unstable for most of the week, especially so over Kauai and Oahu today and tonight. Although high clouds over Maui County and the Big Island may diminish somewhat tonight and Wednesday, thicker high clouds are expected to blanket island skies from Wednesday night through Friday.
With trade winds persisting in the low-levels, the threat of flash flooding is somewhat reduced as most showers will move quickly westward. The potential for heavy rain to become terrain-anchored can't be entirely ruled out, especially if the trough aloft works it's way closer to the surface. While a Flash Flood Watch is not deemed necessary at this time, it may be required later in the week, when model guidance depicts a vertical wind profile that may be more conducive for terrain-anchored cells to develop.
A trend toward increased atmospheric stability is expected over the weekend as the mid- and upper-level low weakens and lifts NE of the islands. A mid-level ridge will build over the area from the SW, and PWAT will trend toward normal, so just a few trade wind showers are expected. In the meantime, expect a rather wet pattern, especially for windward areas.

Aviation

With high pressure persisting north of the islands, trade winds will remain moderate to breezy, and locally strong, through the day. Also, a nearby upper low and trough will continue to destabilize the atmosphere. Showers and isolated thunderstorms, with accompanying MVFR and IFR conditions, are likely until these features depart the area, with the eastern part of the state being most susceptible to heavier precipitation.
AIRMET Sierra for mountain obscuration remains in effect for all windward zones.
AIRMET Tango for lee turbulence below 090 remains in effect for the entire area.

Marine

High pressure north of the state will continue to produce strong trade winds across the area over the next several days. The Small Craft Advisory (SCA) has been extended for all Hawaiian Coastal Waters through tonight. The combination of strong trades and a late- season northwest swell will keep SCA conditions in place across many areas through the middle of the week. In addition, an upper low over the area has destabilized the local airmass, producing isolated thunderstorms. This low is expected to linger over the state through the middle of the week.
A long-period northwest swell will continue to fill in across exposed north and west waters today, then get a reinforcement late tonight into Wednesday. With the reinforcement arrival, surf heights could reach low-end advisory levels, then lower gradually through the remainder of the week.
The current long-period south swell is expected to hold today. An even larger south swell will fill in later today, peak Thursday then slowly lower through rest of the week. A High Surf Advisory is in effect through Thursday 6 PM HST for all south facing shores as these south swells maintain elevated surf.
Trade winds over and upwind of the state will continue to produce above normal, short-period surf along east facing shores through this next week. Surf heights are expected lower during the second half of the week as the trade winds weaken some.

HFO Watches/Warnings/Advisories

High Surf Advisory until 6 PM HST Thursday for South facing shores of all islands.
Winter Weather Advisory until 6 PM HST this evening for Big Island Summits.
Small Craft Advisory until 6 AM HST Wednesday for all Hawaiian waters.

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Data Courtesy of NOAA.gov