West Side

Tonight: Mostly cloudy. Isolated showers in the evening. Lows 64 to 72. East winds up to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Highs 72 to 84. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon.

Thursday Night: Partly cloudy. Isolated showers after midnight. Lows 64 to 71. East winds 10 to 15 mph decreasing to up to 15 mph after midnight. Chance of rain 20 percent.

South Side

Tonight: Mostly cloudy. Isolated showers in the evening. Lows around 67. Northeast winds 10 to 15 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Highs 74 to 85. East winds 10 to 15 mph.

Thursday Night: Mostly clear. Lows 64 to 69. Northeast winds 10 to 15 mph.

North Shore

Tonight: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 77 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 68 near the shore to around 52 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Central Maui

Tonight: Mostly cloudy. Breezy. Isolated showers in the evening. Lows around 67. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Breezy. Highs 79 to 85. East winds 10 to 20 mph.

Thursday Night: Mostly clear. Breezy. Lows around 66. East winds 10 to 20 mph.

Upcountry

Tonight: Mostly cloudy with scattered showers. Lows around 44 at the visitor center to around 41 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Mostly sunny. Scattered showers in the morning, then isolated showers in the afternoon. Highs 49 to 69. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Partly cloudy. Isolated showers in the evening, then scattered showers after midnight. Lows around 44 at the visitor center to around 41 at the summit. East winds 10 to 15 mph. Chance of rain 50 percent.

East Maui

Tonight: Mostly cloudy with scattered showers. Lows around 68 near the shore to around 53 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday: Partly sunny with scattered showers. Highs 77 to 82 near the shore to around 65 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Thursday Night: Partly cloudy in the evening then becoming mostly cloudy. Scattered showers. Lows around 68 near the shore to around 52 near 5000 feet. East winds 10 to 15 mph. Chance of rain 50 percent.

Lanai City

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Lows 59 to 66. Northeast winds 10 to 15 mph.

Thursday: Mostly sunny. Breezy. Highs 69 to 79. Northeast winds 10 to 20 mph.

Thursday Night: Mostly clear. Breezy. Lows 59 to 66. Northeast winds 10 to 20 mph.

Kaunakakai

Tonight: Breezy. Mostly cloudy with isolated showers in the evening, then partly cloudy after midnight. Lows 54 to 72. East winds 10 to 20 mph. Chance of rain 20 percent.

Thursday: Mostly sunny. Breezy. Highs 67 to 84. East winds 10 to 20 mph.

Thursday Night: Partly cloudy. Breezy. Lows 54 to 71. East winds 10 to 20 mph.

Detailed Forecast

Synopsis

A upper level trough west of Kauai will weaken as it moves east over the Hawaiian Islands the next couple of days. This will create enough instability within a more moist resident air mass to maintain relatively higher rain chances. Breezy trades will focus greater rain amounts and thicker clouds over windward mauka slopes and higher terrain. An approaching front at the end of the week will weaken regional winds and increase shower coverage as the front advances east across the state early next week.

Discussion

Scattered thunderstorms remain focused along the convergent side of a surface trough located approximately 500 miles west of Kauai this evening. This afternoon's local soundings depict a fairly unstable and moist air mass. An elevated inversion with pwats above 1.5 inches is a pretty decent signal that this more wet trade flow will persist through Friday. Widely scattered showers are being caught up within the moderate to fresh maritime trade flow. Better organized, clustering showers will develop within the downstream island plumes.
Thursday's forecast calls for similar conditions as today with more areal precipitation occurring earlier in the day. Windward- facing exposures and upper elevations will experience cooler, overcast conditions along with higher rainfall totals. Interior trades will remain breezy with gusty winds likely occurring along higher elevation ridgelines and valley channels.
.PREVIOUS DISCUSSION (324 PM HST)…. The ECMWF and GFS are in good agreement with the upper level low continuing to weaken into a mid-level trough over the next 24 hours, while remaining nearly stationary. By Friday morning, little remains of the mid level feature, while an upper level trough remains in place. By Saturday morning, mid to upper level ridging pushing in from the west will help to provide some more stability to the region. A surface front approaching the islands from the northwest on Sunday is not expected to have as much upper level support. The cloud and shower band associated with the front is expected to reach Kauai Sunday night, reaching the central islands by Monday afternoon, and slowly moving towards the Big Island Tuesday. The GFS and ECMWF have become better aligned in the handling of this front over the past several model runs, and thus using the National Blend of Models seemed the best course of action.
A drier airmass will move in behind the front, along with a new high far northwest of the islands. The new high will move to the east around 30N as the front moves down the island chain. This will bring a return to more typical trade winds behind the front.

Aviation

Moderate to locally breezy easterly trade winds will prevail across the island chain for the next 24 hours. Radar and satellite imagery continue to show low clouds and showers drifting from east to west into island mountains. AIRMET Sierra remains in effect for mountain obscuration in showers along windward mountain areas of most islands.
A subtropical jet stream over the Hawaiian Islands will continue to produce moderate to severe turbulence statewide. AIRMET TANGO was expanded this evening for moderate with isolated severe turbulence from FL250-380, with SIGMET SIERRA series issued for severe turbulence from FL270-350. These strong winds aloft will likely continue statewide for this severe turbulence threat through the morning hours.

Marine

A ridge of high pressure will remain north of the state through the end of the week generating fresh to locally strong trades across the islands. A Small Craft Advisory remains in effect through Thursday afternoon across the typically windy waters surrounding Maui County and Big Island and will likely be extended into Friday. A front approaching from the northwest will allow winds to gradually weaken and veer slightly out of the east southeast over the weekend becoming light and variable statewide Sunday. Moderate to locally fresh northeast winds will fill in behind the front as it moves through much of the state during the first half of next week.
A small to moderate, medium period northwest (320-330 degrees) swell will continue to slowly lower tonight into Thursday. A new moderate, long period northwest swell (330 degree) will fill in Friday and peak just below advisory levels. A large, possibly extra large, long period northwest swell (330 degree) originating from a developing hurricane force low south of the Kuril Islands is expected to reach the islands Sunday and peak Sunday night into Monday. This swell may produce warning level surf along exposed north and west-facing shores during the peak.
Expect east shore surf to remain elevated and choppy through the rest of the week and ease slightly over the weekend as winds ease. Small south shore surf sets will through the forecast period as several very small, long period south swells move through.

HFO Watches/Warnings/Advisories

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

Data Courtesy of NOAA.gov