Photo Credit: Tyler Rooke

West Side

Today: Scattered showers after noon. Mostly sunny, with a high near 85. Calm wind becoming west southwest around 5 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Mostly cloudy, with a low around 68. Calm wind.

Wednesday: Isolated showers after noon. Mostly cloudy, with a high near 84. Light and variable wind becoming east northeast 9 to 14 mph in the morning. Winds could gust as high as 18 mph. Chance of precipitation is 20%.

South Side

Today: Showers likely after noon. Increasing clouds, with a high near 85. Light and variable wind becoming west around 6 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers before midnight. Increasing clouds, with a low around 66. Calm wind. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Scattered showers after noon. Mostly cloudy, with a high near 84. Calm wind becoming west southwest around 5 mph in the morning. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

North Shore

Today: Scattered showers, mainly after noon. Mostly sunny, with a high near 84. Breezy, with a light east wind increasing to 11 to 16 mph in the morning. Winds could gust as high as 22 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 67. Breezy, with an east wind 13 to 17 mph, with gusts as high as 24 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Scattered showers, mainly before noon. Mostly cloudy, with a high near 83. Windy, with an east wind 17 to 23 mph, with gusts as high as 32 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Central Maui

Today: Scattered showers, mainly after noon. Mostly sunny, with a high near 84. North northwest wind 6 to 14 mph becoming northeast in the afternoon. Winds could gust as high as 18 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly after midnight. Mostly cloudy, with a low around 66. North northeast wind 7 to 10 mph. Chance of precipitation is 30%.

Wednesday: Scattered showers, mainly before noon. Mostly cloudy, with a high near 84. Breezy, with a northeast wind 10 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 30%.

Upcountry

Today: Showers likely after noon. Increasing clouds, with a high near 71. Calm wind becoming west northwest 5 to 8 mph. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Isolated showers before midnight. Partly cloudy, with a low around 54. Calm wind. Chance of precipitation is 20%.

Wednesday: Scattered showers after noon. Mostly cloudy, with a high near 70. Light west southwest wind. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

East Maui

Today: Showers likely, mainly before noon. Partly sunny, with a high near 82. Southeast wind 7 to 10 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly after midnight. Mostly cloudy, with a low around 65. Calm wind becoming east around 6 mph after midnight. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Showers likely, mainly before noon. Cloudy, with a high near 81. East wind around 7 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Lanai City

Today: Showers likely after noon. Increasing clouds, with a high near 75. Calm wind becoming northeast 5 to 8 mph in the afternoon. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly before midnight. Increasing clouds, with a low around 63. Northeast wind around 10 mph. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Scattered showers, mainly after noon. Mostly cloudy, with a high near 74. Breezy, with a northeast wind 9 to 15 mph, with gusts as high as 21 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Kaunakakai

Today: Scattered showers after noon. Mostly sunny, with a high near 82. Calm wind becoming east northeast around 5 mph in the afternoon. Chance of precipitation is 30%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Mostly cloudy, with a low around 69. East northeast wind around 7 mph.

Wednesday: Isolated showers after noon. Mostly cloudy, with a high near 81. East northeast wind 6 to 13 mph. Chance of precipitation is 20%.

Detailed Forecast

Synopsis

Trade winds will be weak enough for leeward sea breezes today, and showers will become more active, mainly over leeward terrain this afternoon, as an upper level low develops just west of the state. Trade winds will strengthen tonight and Wednesday as the upper low sends thick high clouds overhead. The weakening upper level low will slowly move over the state late Thursday into the weekend, bringing potentially wet and unsettled weather.

Discussion

Trades continue to slowly weaken, and the atmosphere is becoming less stable. A digging upper level trough centered several hundred miles northwest of Kauai is invigorating a decayed front stretching well north of the islands. This is weakening the pressure gradient over the state and causing trade winds to slowly decline. The upper trough is also eroding the upper level ridge over the state, which is leading to decreased stability. As a result, showers have remained somewhat active in the plumes west of the islands, while leeward Big Island had isolated showers through much of the night. The weakening trade wind flow has caused most showers to remain off windward coasts.
Trade winds will become weak enough for sea breezes to develop over sheltered leeward areas in the afternoon, likely triggering a few briefly heavy showers over leeward terrain. Windward areas will experience some showers, but the GFS and ECMWF are suggesting that a band of enhanced moisture will remain just east of the state.
Tonight into Thursday, trade winds will rebuild and high clouds will thicken overhead, as the upper level trough cuts off about 600 miles west of Kauai and surface high pressure passes far north of the state. The GFS and ECMWF show windward showers picking up as a narrow band of moisture moves in on Wednesday, but with the high clouds limiting daytime heating, leeward showers appear less likely each afternoon.
The greatest potential for increased showers and unsettled conditions state-wide looks to be Thursday night and Friday when the weakening upper level low drifts over the islands. Breezy trade winds should hold, keeping the highest chances for rainfall over windward slopes, but spotty, locally heavy afternoon showers will be possible over leeward areas, especially on the Big Island and Maui.
The weak upper level trough will linger over the state through the weekend, creating some uncertainty. Surface high pressure to the northeast will maintain locally breezy easterly trade winds, strongest over the Big Island and Maui. Although the GFS and ECMWF show some drier air pushing in from the east, we could still have some threat for unsettled conditions. Both models show increasingly stable weather next Monday.

Aviation

Light easterly trade winds are expected across the state today. Clouds, showers, and isolated MVFR conditions will favor north through east facing sections of the smaller islands throughout the day, but some clouds and showers will also be possible for leeward areas with sea breezes developing during the afternoon. By tonight, easterly trade winds will increase a bit once again, becoming breezy for the remainder of the week. A low aloft will enhance rainfall chances beginning tonight, though VFR conditions are expected to prevail at most airports throughout the forecast period.
There are currently no AIRMETs in effect, though mountain obscuration may become an issue for interior locations as cloud coverage and showers increase today.

Marine

Weakened trade winds today will restrengthen Wednesday to fresh to locally strong magnitudes through next weekend.
Surf will remain below high surf advisory levels along all shores this week. Returning trade winds will bring choppy seas and surf to windward coastal waters and east facing shores by late Wednesday through the week.

HFO Watches/Warnings/Advisories

None.

Data Courtesy of NOAA.gov