West Side

Today: Mostly sunny with isolated showers. Highs 72 to 85. East winds up to 15 mph. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze after midnight. Lows 63 to 72. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Haze. Highs 71 to 84. Light winds. Chance of rain 20 percent.

South Side

Today: Sunny. Isolated showers in the afternoon. Highs 75 to 86. North winds up to 10 mph shifting to the northeast in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Haze after midnight. Lows 63 to 69. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs 74 to 85. Light winds. Chance of rain 20 percent.

North Shore

Today: Breezy. Mostly sunny with isolated showers. Highs around 80 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Haze after midnight. Lows around 68 near the shore to around 54 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Haze. Highs around 80 near the shore to around 67 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Central Maui

Today: Mostly sunny. Breezy. Isolated showers in the afternoon. Highs 81 to 86. East winds up to 20 mph increasing to 10 to 20 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy. Breezy. Isolated showers in the evening. Haze after midnight. Lows 63 to 68. East winds up to 20 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs 80 to 86. East winds up to 10 mph. Chance of rain 20 percent.

Upcountry

Today: Breezy. Mostly sunny with isolated showers. Highs 54 to 71. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Lows around 45 at the visitor center to around 43 at the summit. Southeast winds up to 20 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Highs 53 to 71. Southeast winds up to 15 mph in the morning becoming light. Chance of rain 20 percent.

East Maui

Today: Breezy. Mostly sunny with isolated showers. Highs around 80 near the shore to around 67 near 5000 feet. East winds up to 20 mph. Chance of rain 20 percent.

Tonight: Breezy. Partly cloudy with isolated showers. Haze after midnight. Lows around 68 near the shore to around 54 near 5000 feet. Southeast winds up to 20 mph. Chance of rain 20 percent.

Thursday: Mostly sunny with isolated showers. Haze. Highs around 80 near the shore to around 67 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Lanai City

Today: Mostly sunny. Isolated showers in the afternoon. Highs 69 to 79. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Haze after midnight. Lows 58 to 65. Light winds. Chance of rain 20 percent.

Thursday: Mostly sunny. Haze through the day. Scattered showers in the afternoon. Highs 68 to 79. Light winds. Chance of rain 30 percent.

Kaunakakai

Today: Mostly sunny with isolated showers. Highs 67 to 86. East winds up to 15 mph increasing to 10 to 15 mph in the afternoon. Chance of rain 20 percent.

Tonight: Partly cloudy with isolated showers. Haze after midnight. Lows 55 to 72. East winds up to 15 mph in the evening becoming light. Chance of rain 20 percent.

Thursday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 68 to 85. Light winds. Chance of rain 30 percent.

Synopsis

Lighter large scale east-southeast winds forecast through Friday will allow an expansion of daytime onshore sea breeze winds over all islands. A stable subtropical ridge over the region will keep cloud cover and shower activity to a minimum until this weekend. On Saturday and Sunday a shallow cold front and upper level disturbance will move into the islands and combine forces, as high pressure builds in from the northwest. Expect periods of enhanced trade wind showers across the Hawaiian Islands this weekend, favoring the overnight to early morning hours along windward and mountain slopes.

Discussion

Weather satellite imagery this morning continues to show a very stable weather pattern locked in place across the Hawaii region with a cold frontal cloud band slowly approaching from the northwest. Infra-red satellite imagery clearly shows a small thermal hot spot on the Big Island over Halemaumau Crater associated with the ongoing Kilauea volcanic eruption. Sulfur dioxide (SO2) emissions from the Kilauea eruption are producing a plume of VOG (Volcanic fOG or smOG) over large areas of the Big Island drifting as far north as Waimea and Kohala Ranch based on air quality observations this morning. This VOG plume also extends westward away from the Big Island and will slowly creep northward, riding the southeasterly wind flow into the smaller islands by late tonight through at least Thursday, and possibly Friday. Returning trade winds this weekend should blow much of this VOG plume towards the south, away from the most populated areas.
The surface ridge north of the state is weakening today in response to a cold front approaching the islands from the northwest direction. Trade winds have diminished as large scale east-southeast winds are weakening in response to the fading surface ridge. This wind direction shift places the smaller islands from Kauai to Maui in the leeward wind and rain shadow of the Big Island, allowing local scale land and sea breeze winds to strengthen and expand in coverage across all islands through Friday. Upper level stability from the subsidence (downward moving air) under the descending limb of the subtropical ridge and the rain shadowing effects for islands in the lee of the Big Island will limit cloud cover and rainfall activity until this weekend.
By Saturday morning, a shallow cold front slowly drifts into Kauai and Oahu. The forward motion on this front will stall out at some point, perhaps as far east as Oahu or Molokai, and the shallow frontal cloud band will start to break apart. High pressure will build in rapidly across the dissipating front with moderate to locally breezy trade winds blowing across the region. An upper level trough will also be riding in above this shallow front, colder air aloft and wind divergence ahead of this upper trough will help to lift the low level boundary layer and over- ride the stabilizing effects of the large scale subtropical ridge. This means low level cloud bands from the dissipating front and upstream moisture will produce periods of showers moving into the windward and mountain slopes of each island on the strengthening trade winds. These enhanced shower trends will likely last into the first half of next week.
A period of enhanced showers will start on Saturday over the western half of the state and then expand in coverage statewide by Sunday morning as the upper level trough deepens into an upper level low near the Big Island. Rainfall amounts will highly depend on the position of this upper low, setting up farther east of the islands would be a drier solution. However, if the low center sets up over the eastern islands then we may see considerably more rainfall activity over the eastern half of the state. Forecast confidence is growing in a period of statewide wet trade wind trends as weather model run to run consistency improves.
Colder air aloft associated with this upper low and enhanced shower activity may lead to a brief period of ice and snowfall over the summits of Mauna Loa and Mauna Kea on the Big Island early next week. The best chance for summit level snowfall to develop will be next week Monday. Summit level impacts will be driven by the location and intensity of the upper level low.

Aviation

Weakening trades will allow the return of the sea/land breeze regime. Any SHRA that do develop should be light with the ISOL possibility of some MVFR conds. VFR should generally prevail. The one exception is leeward Big Island, where vog may lead to MVFR vsbys.
No AIRMETs are in effect.

Marine

The trades will continue to ease as they gradually shift more east-southeasterly today. Fresh trades will persist over the eastern waters, while light to moderate trades hold over the western end of the state. The Small Craft Advisory (SCA) has been cancelled as winds have dropped below advisory thresholds. The winds will become light and variable over the western waters tonight through Friday, meanwhile, east to southeast winds will slowly ease over the eastern islands, becoming gentle to moderate by Friday. A new high building north of the islands will allow moderate trades to gradually fill back in Friday night, and become locally strong over the weekend.
A large, long period northwest swell will fill in tonight, peak Thursday and Thursday night, then gradually lower Friday through the weekend. This swell is expected to produce warning-level surf along most north and west facing shores as it peaks, and a High Surf Warning will likely be required later today. The swell will also elevate seas above the 10 foot SCA threshold across a good chunk of the marine area beginning late tonight and continuing into the weekend. A couple small to moderate sized northwest and north swells will move through early next week, but surf should remain below advisory levels.
Surf along east facing shores will trend slightly lower today through Saturday as the winds locally and upstream of the islands diminish. East shore surf will then rebound back to near normal levels late Sunday through early next week as the trades return.

Fire weather

No critical fire weather conditions are expected for the next seven days. Mostly dry weather remains in the forecast across the state with limited shower activity as the dry spell continues through Friday. Shower trends increase starting Friday night with enhanced trade wind showers into early next week.

HFO Watches/Warnings/Advisories

None.

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Data Courtesy of NOAA.gov