Photo Credit: Tyler Rooke

West Side

Today: Mostly sunny with isolated showers. Highs 78 to 90. Northeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with scattered showers. Lows 70 to 77. East winds up to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 79 to 89. Northeast winds around 10 mph. Chance of rain 50 percent.

South Side

Today: Mostly sunny. Isolated showers in the afternoon. Highs around 89. North winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows 69 to 77. North winds up to 15 mph. Chance of rain 30 percent.

Wednesday: Partly sunny in the morning then becoming mostly sunny. Scattered showers. Highs around 89. North winds around 10 mph. Chance of rain 40 percent.

North Shore

Today: Mostly cloudy with scattered showers. Highs 77 to 85 near the shore to around 66 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 72 near the shore to 51 to 56 near 5000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Wednesday: Showers in the morning, then scattered showers in the afternoon. Highs 77 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Central Maui

Today: Mostly sunny with isolated showers. Highs 81 to 88. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 69 to 74. Northeast winds up to 10 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 83 to 89. Northeast winds around 10 mph. Chance of rain 50 percent.

Upcountry

Today: Mostly sunny with isolated showers. Highs around 59 at the visitor center to around 54 at the summit. East winds up to 10 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Isolated showers. Lows around 46 at the visitor center to around 44 at the summit. East winds up to 10 mph. Chance of rain 20 percent.

Wednesday: Partly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Highs around 56 at the visitor center to around 53 at the summit. Southeast winds around 10 mph. Chance of rain 50 percent.

East Maui

Today: Mostly cloudy with scattered showers. Highs 77 to 85 near the shore to around 66 near 5000 feet. East winds up to 15 mph. Chance of rain 50 percent.

Tonight: Mostly cloudy with numerous showers. Lows around 72 near the shore to 51 to 56 near 5000 feet. East winds up to 10 mph. Chance of rain 70 percent.

Wednesday: Showers in the morning, then scattered showers in the afternoon. Highs 77 to 86 near the shore to around 67 near 5000 feet. East winds 10 to 15 mph. Chance of rain near 100 percent.

Lanai City

Today: Mostly sunny with isolated showers. Highs 73 to 82. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 65. Northeast winds up to 15 mph. Chance of rain 30 percent.

Wednesday: Partly sunny with scattered showers. Highs 74 to 82. Light winds becoming northeast up to 10 mph in the afternoon. Chance of rain 40 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 68 to 89. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows 59 to 76. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers. Highs 68 to 89. Northeast winds 10 to 15 mph. Chance of rain 50 percent.

Detailed Forecast

Synopsis

An upper level low northeast of the islands will drift slowly west-southwest through the week, weakening the trade winds starting tonight through early Thursday morning. Localized sea breezes may develop over sheltered western slopes each afternoon through Wednesday. Instability associated with the upper low will lead to periods of showers and the potential for localized heavy rain on Wednesday and Thursday. Drier weather should return from Friday onward as the trade winds strengthen across the region.

Discussion

The satellite water vapor imagery this morning shows the unstable upper low continues to drift slowly westward and is roughly 600 miles north-northeast of Oahu. Isolated to scattered thunderstorms are developing within the cold core center of the low. The instability around this low is producing fairly unstable clouds across the region and showers are developing as these clouds move into each island on the trade winds.
Broad instability associated with this low and a weaker high pressure ridge north of the islands will keep the trade wind temperature inversion in the 7,000 to 10,000 foot range for the next few days. Cumulus cloud heights will rise to the inversion level with deeper clouds keeping periods of enhanced showers in the forecast through Thursday.
For today, moderate trade wind speeds will start to weaken with localized land and sea breezes forming along terrain sheltered western slopes of Kauai and Oahu. Wind convergence between the afternoon sea breezes and the lighter trade winds may cause afternoon showers to develop over leeward areas. This light to moderate trade wind pattern with localized land and sea breezes will continue through Wednesday.
On Wednesday and Wednesday night, the upper low will drift westward, passing just north of the Hawaiian Islands with the potential for a few heavy showers in some locations. Expect slower moving shower bands in lighter trade wind flow. Isolated thunderstorms are possible by Wednesday afternoon over the higher elevations of the Big Island. Chances for locally heavy showers will continue for all islands into Thursday.
Thursday will be a transition day, as the trough begins to move away from the state, and high pressure builds north of the island chain. Showery conditions are still expected as the breezy trade winds fill back from east to west. Shower coverage will decrease a bit over the eastern islands as more stable trade winds move into the eastern half of the state.
By Friday, the trade winds will strengthen across the region with drier weather trends in the forecast. Expect a more typical windward and mountain shower pattern favoring the overnight to early morning hours through Monday.

Aviation

High pressure northeast of the state will allow for persistent moderate trades across the island chain today. Thus, the highest concentration of showers will likely be confined to the windward coasts and slopes. Isolated activity expected elsewhere.
Some of the heaviest showers may generate brief periods of MVFR ceilings and visibility.
There are currently no AIRMETs in effect.

Marine

High pressure north of the state will keep moderate to fresh trade winds in place today. The trades will briefly ease tonight and Wednesday as a surface trough slides by to the north of the islands. As this trough exits to the northwest of the state Wednesday night and Thursday, the trades will gradually ramp back up to locally strong levels, with winds reaching Small Craft Advisory (SCA) thresholds over the typically windy Maui and Big Island waters by Thursday. The strong SCA level trades are expected to expand to most if not all waters Friday and Saturday, before dropping a notch Sunday into early next week.
A series of long period south and southwest swells will keep surf along south facing shores near to slightly above the September average through Thursday. South shore surf will then gradually lower through the weekend into early next week. Small surf will prevail on north facing shores through most of the week, with a small bump from a northwest swell possible this weekend. East shore surf will remain well below normal through Wednesday. As trade winds ramp up Thursday through Saturday, surf along east facing shores will become rough and rise to near seasonal levels, before lowering gradually Sunday into early next week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov