West Side

Tonight: Mostly clear. Isolated showers after midnight. Lows 67 to 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Wednesday: Mostly sunny with isolated showers. Highs 78 to 83. East winds up to 15 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

Wednesday Night: Mostly clear with isolated showers. Lows 67 to 73. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

South Side

Tonight: Mostly clear. Breezy. Lows 65 to 74. Northeast winds 10 to 20 mph.

Wednesday: Sunny and breezy. Highs around 87. Northeast winds 10 to 20 mph.

Wednesday Night: Mostly clear. Breezy. Lows 66 to 75. Northeast winds 10 to 20 mph.

North Shore

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 70 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with showers likely. Highs around 80 near the shore to around 65 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 70 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Tonight: Mostly clear. Breezy. Lows 65 to 70. Northeast winds 10 to 25 mph decreasing to 10 to 15 mph after midnight.

Wednesday: Sunny and breezy. Isolated showers in the morning. Highs 81 to 88. Northeast winds 10 to 25 mph. Chance of rain 20 percent.

Wednesday Night: Mostly clear. Breezy. Lows 65 to 70. Northeast winds 10 to 20 mph.

Upcountry

Tonight: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 44 at the visitor center to around 42 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with scattered showers in the morning, then mostly sunny with isolated showers in the afternoon. Highs around 60 at the visitor center to around 64 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday Night: Partly cloudy with scattered showers. Lows around 45 at the visitor center to around 42 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

East Maui

Tonight: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 70 near the shore to around 50 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Wednesday: Partly sunny with showers likely. Highs around 80 near the shore to around 65 near 5000 feet. East winds 10 to 15 mph. Chance of rain 70 percent.

Wednesday Night: Mostly cloudy with scattered showers. Lows around 70 near the shore to around 51 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Tonight: Mostly clear. Breezy. Lows around 64. Northeast winds 10 to 20 mph.

Wednesday: Mostly sunny. Breezy. Highs 72 to 80. Northeast winds 10 to 20 mph.

Wednesday Night: Mostly clear. Breezy. Lows around 64. Northeast winds 10 to 20 mph.

Kaunakakai

Tonight: Mostly clear. Breezy. Lows 57 to 72. Northeast winds 10 to 20 mph.

Wednesday: Breezy. Mostly sunny with isolated showers. Highs 69 to 87. Northeast winds 10 to 20 mph. Chance of rain 20 percent.

Wednesday Night: Mostly clear. Breezy. Isolated showers after midnight. Lows 57 to 73. East winds 10 to 20 mph. Chance of rain 20 percent.

Detailed Forecast

Synopsis

Moderate to locally breezy trades will deliver clouds and showers to windward and mauka areas through the week, with some decaying showers reaching leeward areas as well. A few downpours and even a rumble or two of thunder will be possible Thursday and Friday as a disturbance aloft moves over the island chain. A steady decrease in shower coverage and intensity with progressively nicer weather is expected the latter half of Memorial Day weekend.

Discussion

Current radar and satellite trends show partly cloudy skies, with a few showers riding on the trades. With moderate to locally breezy trades through Wednesday, expect windward and mauka showers with isolated spillover to leeward areas.
Wednesday the weak upper level low that has lingered just to the northeast of the Big Island moves at a glacial pace off to the east- northeast. This slow movement should slightly strengthen trades through Thursday. In the meantime another cut off low pressure system to the northwest of Kauai is moving in, deepening and will be the focus for weather Wednesday evening through the weekend.
As this low moves closer to the western end of the state and deepens temperatures aloft go from around -9C to -12 to -14C, lapse rates around 7.0 C/km and and CAPE values ranging from 900-1500 J/kg a few thunderstorms are possible along with some heavy downpours late Wednesday evening through Saturday. This low weakens and moves off to the northwest Sunday resulting in a reduction of showers and a progressively drier holiday weekend.

Aviation

A locally breezy trade wind flow will persist through the next several days. Some low-level turbulence is expected over and downwind of terrain, but since the inversion is slightly weak and elevated, conditions do not support AIRMET Tango at this time. Pockets of moisture within the trades will produce areas of MVFR conditions along windward slopes, where AIRMET Sierra for mountain obscuration will be possible during the overnight hours. Aside from afternoon clouds and spotty showers over the Kona slopes of the Big Island, VFR will dominate over leeward areas. An upper-level low moving overhead will bring higher chances for heavier showers and a thunderstorm by Thursday.

Marine

Surface high pressure building in far north of the islands will maintain moderate to locally strong trades through Friday. A Small Craft Advisory (SCA) is in effect for the typically windy waters around the Big Island and Maui through Thursday morning, but will likely need to be extended through at least Friday. The high is forecast to retreat westward during the weekend as a series of fronts pass to the far north, favoring a slight decrease in winds across the islands.
Surf along south facing shores will remain just below seasonal average through Thursday. A small, long period, south southwest swell will filter into the area late Thursday and bring surf near the summer average along south facing shores through this weekend. Surf will then slowly decline Sunday through early next week.
East shore surf will remain near seasonal average during the next couple of days. A gradual decline in east shore surf is expected during the weekend and early next week. Tiny surf will prevail along north facing shores this week and into the weekend.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov