Photo Credit: James Grenz

Hilo

Today: Scattered showers. Partly sunny, with a high near 82. Light and variable wind becoming east 6 to 11 mph in the morning. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely, mainly after 7pm. Mostly cloudy, with a low around 68. East wind 5 to 8 mph becoming calm after midnight. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Showers likely, mainly before 1pm. Mostly cloudy, with a high near 81. Calm wind becoming north northeast around 6 mph in the morning. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Kona

Today: Scattered showers, mainly after 1pm. Mostly sunny, with a high near 82. West northwest wind 6 to 11 mph. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers, mainly before 1am. Mostly cloudy, with a low around 66. Northwest wind 5 to 7 mph becoming calm in the evening. Chance of precipitation is 40%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Scattered showers, mainly after 1pm. Mostly cloudy, with a high near 81. Calm wind. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Waimea

Today: Showers likely after noon. Increasing clouds, with a high near 75. Calm wind becoming north northeast 5 to 9 mph in the afternoon. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.

Tonight: Scattered showers. Mostly cloudy, with a low around 55. Breezy, with a northeast wind 10 to 18 mph, with gusts as high as 25 mph. Chance of precipitation is 50%. New precipitation amounts between a tenth and quarter of an inch possible.

Wednesday: Scattered showers. Mostly cloudy, with a high near 74. Breezy, with a northeast wind 18 to 22 mph, with gusts as high as 31 mph. Chance of precipitation is 40%. New precipitation amounts between a tenth and quarter of an inch possible.

Kohala

Today: Showers likely after noon. Increasing clouds, with a high near 68. Calm wind becoming east southeast around 5 mph in the afternoon. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Showers likely. Mostly cloudy, with a low around 53. Breezy, with an east northeast wind 5 to 10 mph increasing to 13 to 18 mph after midnight. Winds could gust as high as 25 mph. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Wednesday: Showers likely, mainly after noon. Mostly cloudy, with a high near 67. Breezy, with an east northeast wind 18 to 20 mph, with gusts as high as 28 mph. Chance of precipitation is 70%. New precipitation amounts of less than a tenth of an inch possible.

South Big Island

Today: Scattered showers, mainly before noon. Mostly sunny, with a high near 79. Breezy, with an east wind around 18 mph, with gusts as high as 23 mph. Chance of precipitation is 30%.

Tonight: Scattered showers. Mostly cloudy, with a low around 70. Breezy, with an east northeast wind 17 to 20 mph, with gusts as high as 25 mph. Chance of precipitation is 30%.

Wednesday: Scattered showers. Mostly cloudy, with a high near 79. Breezy, with an east wind 20 to 22 mph, with gusts as high as 28 mph. Chance of precipitation is 30%.

Puna

Today: Showers likely, mainly before noon. Partly sunny, with a high near 80. Light and variable wind becoming east 5 to 10 mph in the morning. Chance of precipitation is 60%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Occasional showers. Low around 65. Calm wind becoming west around 6 mph. Chance of precipitation is 80%. New precipitation amounts between a tenth and quarter of an inch possible.

Wednesday: Showers likely. Cloudy, with a high near 79. Light north wind becoming north northeast 5 to 10 mph in the morning. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.

Waikoloa

Today: Scattered showers after noon. Mostly sunny, with a high near 81. Light and variable wind becoming west northwest 5 to 7 mph. Chance of precipitation is 50%. New precipitation amounts of less than a tenth of an inch possible.

Tonight: Scattered showers before midnight. Increasing clouds, with a low around 67. East wind 5 to 10 mph becoming light east southeast after midnight. 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 80. Light and variable wind becoming north northeast 9 to 14 mph in the morning. 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.

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