West Side

Today: Mostly sunny with isolated showers. Haze. Highs 72 to 84. Light winds. Chance of rain 20 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Haze through the night. Lows 63 to 72. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny with isolated showers. Haze. Highs 70 to 83. Light winds. Chance of rain 20 percent.

South Side

Today: Mostly sunny. Haze through the day. Isolated showers in the afternoon. Highs 74 to 86. Light winds. Chance of rain 20 percent.

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

Friday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 73 to 84. Light winds becoming north up to 10 mph in the afternoon. Chance of rain 20 percent.

North Shore

Today: Mostly sunny with isolated showers. Haze. Highs around 80 near the shore to around 68 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 65 to 70 near the shore to around 53 near 5000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Haze. Highs 77 to 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 20 percent.

Central Maui

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

Tonight: Partly cloudy. Isolated showers in the evening. Haze through the night. Lows 63 to 68. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning, then partly sunny with isolated showers in the afternoon. Haze through the day. Highs 79 to 84. Light winds. Chance of rain 20 percent.

Upcountry

Today: Mostly sunny with isolated showers. Highs 55 to 71. Southeast winds up to 15 mph in the morning becoming light. Chance of rain 20 percent.

Tonight: Mostly cloudy with isolated showers. Lows 42 to 53. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Highs 52 to 70. Light winds. Chance of rain 20 percent.

East Maui

Today: Mostly sunny with isolated showers. Haze. Highs around 80 near the shore to around 68 near 5000 feet. Southeast winds up to 15 mph. Chance of rain 20 percent.

Tonight: Mostly cloudy in the evening then becoming partly cloudy. Isolated showers. Haze. Lows 65 to 70 near the shore to around 53 near 5000 feet. Southeast winds up to 10 mph. Chance of rain 20 percent.

Friday: Mostly sunny in the morning then becoming partly sunny. Isolated showers. Haze. Highs 77 to 82 near the shore to around 66 near 5000 feet. Light winds. Chance of rain 20 percent.

Lanai City

Today: Mostly sunny. Haze through the day. Scattered showers in the afternoon. Highs 67 to 78. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Haze through the night. Lows 57 to 64. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Haze through the day. Scattered showers in the afternoon. Highs 68 to 78. Light winds. Chance of rain 30 percent.

Kaunakakai

Today: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 67 to 84. Light winds. Chance of rain 30 percent.

Tonight: Partly cloudy. Isolated showers in the evening. Haze through the night. Lows 53 to 72. Light winds. Chance of rain 20 percent.

Friday: Mostly sunny. Isolated showers in the morning, then scattered showers in the afternoon. Haze through the day. Highs 67 to 84. Light winds. Chance of rain 30 percent.

Synopsis

A stable subtropical ridge over the region will keep cloud cover and shower activity to a minimum until this weekend. Light southeasterly wind flow will allow sea breezes to expand across all islands. 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 of each island.

Discussion

Satellite imagery this morning shows bands of stable low clouds moving into the region from the east-southeast. Most of these clouds are tracking towards the northwest direction, within the lee rain shadow of the Big Island, which tends to block shower activity due to the wind direction. Local radar imagery continues to show southeasterly winds are blowing across the Hawaii region. In this stable environment little clouds or showers show up in either radar or satellite imagery this evening.
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, Kohala Ranch and Honokaa, and as far east as Hilo, based on air quality surface observations this morning. This VOG plume also extends north and west away from the Big Island, riding the southeasterly wind flow into the smaller islands in Maui County, Oahu, Kauai and Niihau. VOG impacts will persist over the smaller islands through Friday afternoon, and will mainly affect people with breathing difficulties. Returning trade winds from late Friday into the weekend should blow much of this VOG plume towards the south, away from the most populated areas.
The surface ridge north of the state remains in a weakened state with light to moderate large scale southeast winds blowing across the region 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, and then 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 enhanced showers moving into the windward and mountain slopes of each island likely lasting into the first half of next week.
The short and long range forecast for the next seven days has remained fairly consistent with little changes expected other than some rainfall amounts and coverage uncertainties associated with the location of the developing upper level low this weekend. The best consensus guidance shows the center of this unstable upper low drifting east to southeast of the Big Island by Sunday night, moderating potential rainfall amounts. Therefore, we used an ensemble modeling approach to boost rainfall totals for this weekend's enhanced shower activity.

Aviation

Weaker trades will allow development of a land/sea breeze regime for the next few days. Low cigs and SHRA may develop across mauka areas each afternoon then decrease overnight. While SHRA should be light ISOL MVFR conds may occur within them, however VFR should prevail. Due to the continuing eruption of Kilauea, leeward portions of the Big Island may see MVFR vsbys due to vog.
No AIRMETs are in effect.

Marine

A return of hazardous marine and coastal conditions is expected across exposed Hawaiian waters as a long-period west-northwest (290-315 degrees) swell rapidly builds down the island chain today. Swell observations at the offshore buoys northwest of Kauai reflected this rising trend through the overnight hours, with the peak energy centered around 18 to 22 seconds. This new swell will drive surf heights to warning levels from today through Friday, prompting an issuance of a High Surf Warning for exposed north and west-facing shores of the smaller islands and for west facing shores of the Big Island.
Following a series of extra-large northwest swells last week, this event is expected to worsen ongoing erosion issues, including the potential for periodic overwash onto low-lying properties and roadways, particularly during high tide cycles. In addition to the coastal impacts associated with the surf, a Small Craft Advisory has been issued to account for seas exceeding 10 feet over exposed waters. This swell will slowly lower over the weekend and into early next week. An upward trend is possible Monday through midweek, as a couple of smaller northwest swells arrive.
Surf along south and east facing shores will remain small through early next week. The exception could be for south facing shores exposed to more westerly swells, which could see a slight rise today as the aforementioned west-northwest builds down the island chain.
Trades will remain disrupted due to the surface ridge weakening in response to a cold front passing to the north over the next couple of days. This pattern will translate a land and sea breeze regime for most coasts through Friday. The background flow will hold out of the southeast, with a shift out of the north over the western end of the state late Friday. Breezy trades are forecast to return over the weekend as the ridge strengthens to the north in the wake of the front stalling near/north of the western end of the state.

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 lasting into early next week.

HFO Watches/Warnings/Advisories

High Surf Warning until 6 PM HST Friday for north and west facing shores of Niihau, Kauai, Oahu, Molokai, and north facing shores of Maui.
High Surf Warning from noon today to 6 PM HST Friday for Kona, Kohala, Big Island South.
Small Craft Advisory until 6 PM HST Friday for most coastal waters and channels.

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Data Courtesy of NOAA.gov