Hawaii Vog Direction Trade-Wind Chart Traveler Impact

Hawaii vog is volcanic smog produced when sulfur dioxide (SO2) from Kilauea reacts with sunlight, oxygen, moisture, and dust in the atmosphere. The gas becomes sulfate aerosol within hours, and prevailing winds decide who breathes the plume that day.

On roughly 70% of days between April and October, northeast trade winds carry the plume southwest from the summit and Puʻu ʻŌʻō vents across the Kaʻū Desert and out to sea, then bend north-northwest around South Point and pile up along the Kona coast. During Kona-wind reversals, the plume backs up over Hilo, Puna, and often reaches Maui, Molokai, and Oahu.

This article translates the science into planning decisions for relocating households and travelers: which islands and neighborhoods take the biggest hit, how to read forecasts from the University of Hawaii vog model and the Hawaii Department of Health, and what respirator choices actually filter sulfate particles for asthmatic guests.

How Kilauea produces the sulfur dioxide that becomes vog

Kilauea’s summit caldera vents SO2 whenever magma sits near the surface. During the 2018 lower East Rift Zone eruption, daily emissions peaked above 200,000 tonnes of SO2 per day — roughly ten times what heavy industrial cities produce. That eruption paused emissions until the September 2021 Halemaʻumaʻu return, which averaged 1,500 to 5,000 tonnes daily during active phases.

The 2023 and 2024 summit episodes ran in 12- to 48-hour bursts, each pushing plumes 3,000 to 10,000 feet into the boundary layer before trade winds took over. Between eruptive events, background degassing runs 100 to 500 tonnes daily, still enough to darken the Kona horizon on the third or fourth day of stagnant air.

SO2 gas versus sulfate aerosol

Fresh vog near the vent is dominated by SO2 gas, which irritates airways within minutes at concentrations above 0.2 parts per million. As the plume drifts 20 to 100 miles downwind, sunlight and moisture convert SO2 into sulfate aerosol — fine particles under 2.5 microns. The Kona coast, sitting 90 miles from the summit, sees mostly aged sulfate haze rather than raw gas.

That distinction matters for protective equipment: N95 and KN95 respirators trap sulfate particles at 95% efficiency, but neither filters SO2 gas molecules, which pass straight through the fibers.

The northeast trade-wind default pattern

Northeast trade winds blow across Hawaii between 8 and 25 mph on roughly 70% of days year-round, and closer to 85% of days from April through October. The pattern is set by the North Pacific High pressure system, which parks 800 to 1,500 miles northeast of the islands and drives easterly flow across the archipelago.

When trades are established, Kilauea’s plume leaves the summit heading southwest across the Kaʻū Desert, exits the coast between Punaluʻu and South Point, and wraps around the tip of Hawaii Island in a counterclockwise curl. The vog then piles up along the leeward Kona coast between Miloliʻi and Kailua-Kona, where the Kohala and Hualalai volcanoes block dispersion.

Households living in South Kona subdivisions — Captain Cook, Honalo, Kealakekua — often see the thickest daytime haze, cutting visibility from a normal 60-mile horizon to under 8 miles. Coffee farmers report yields drop 5 to 12% during multi-week high-emission episodes, and afternoon sea breezes push the plume upslope into Holualoa by 2 p.m.

Hilo, sitting 30 miles upwind of the summit under trade flow, usually breathes some of the cleanest urban air in the state during these periods. That inversion is one of the more counterintuitive facts of Big Island living: the town closest to the volcano is often the safest for asthmatic residents.

Puʻu ʻŌʻō legacy plume geometry

Before the 2018 eruption ended East Rift activity, Puʻu ʻŌʻō emitted a lower, more concentrated plume that struck the coastline near Kalapana and mixed with the summit plume around the Kaʻū Desert. Post-2018, the summit is the sole significant source, which simplifies the vog map: one point source at 4,000 feet elevation, one dominant wind vector, one downwind zone.

Visitors driving Chain of Craters Road from the caldera to the coast pass through the source region and often smell a faint sulfur tang inside their vehicle even on low-emission days.

Kona-wind reversals and stagnant air

Kona winds — the local term for southwest to south flow — arrive when a low pressure system disrupts the North Pacific High, typically between October and April. During these reversals, the plume backs up over Hilo, Puna, and the Kaʻū district, then rides north across the Alenuihaha Channel toward Maui and eventually Oahu.

Kona-wind episodes occur on roughly 8 to 15 days per month between November and March, dropping to 1 to 3 days per month in June and July. Each episode typically lasts 24 to 72 hours before the trade winds re-establish and clear the leeward islands.

Air quality monitors in Pahala, 21 miles southwest of the summit, have recorded SO2 spikes above 1,000 parts per billion during reversals — a level the Hawaii Department of Health classifies as hazardous and grounds for staying indoors. Residents of Ocean View and Naʻalehu report similar spikes when the plume settles overnight into low elevations.

When Kona winds reach Oahu

Roughly 4 to 8 times per year, Kona-wind episodes push vog to Honolulu, Waikiki, and Windward Oahu. Under these conditions, Diamond Head can disappear from Ala Moana Beach and visitors experience the same throat irritation Big Island residents describe. The Hawaii Department of Health issues statewide air quality advisories when monitors in Kapolei or Sand Island exceed established thresholds.

Reading IVHHN AQI thresholds

The International Volcanic Health Hazard Network sets the technical benchmarks used by Hawaii forecasters. IVHHN thresholds separate SO2 gas from PM2.5 sulfate particles because they enter the body differently and require different mitigation.

Asthmatic travelers should treat the 101–200 ppb SO2 tier as a hard boundary — the level correlates with measurable drops in FEV1 lung function within 10 to 15 minutes of exertion. Children under 12 and adults over 65 with cardiovascular conditions face elevated risk at moderate tiers as well.

Hawaii Department of Health advisory tiers

Hawaii DOH runs a parallel color-coded advisory system tuned to how the state issues public communications through radio, hotel front desks, and school administrators. The tiers align with IVHHN but add operational guidance for schools, outdoor workers, and event organizers.

• Green: routine conditions; outdoor activities proceed normally.
• Yellow: sensitive groups reduce prolonged outdoor exertion.
• Orange: all groups shorten strenuous outdoor time to under 30 minutes.
• Red: schools cancel outdoor sports; workers move indoors.
• Purple: emergency conditions; shelter in place with sealed windows.

The DOH Interagency Vog Information Dashboard aggregates readings from monitors in Pahala, Ocean View, Kona, Hilo, and Mountain View. Coverage on Oahu, Maui, and Kauai runs through the state ambient monitoring network. A deeper breakdown of these tiers appears in the site’s Hawaii volcano air quality SO2 advisory levels page, which walks through each threshold with case examples.

How schools and workplaces respond

Hawaii County Department of Education activates school-level protocols at the orange tier: recess moves indoors, PE classes shift to gymnasiums, and outdoor sports practices reschedule. At red, most schools within 40 miles of an active monitor cancel outdoor activities entirely and advise students with asthma to remain in classrooms during breaks. State agencies use the same tiers for outdoor road crews and park rangers.

N95 versus KN95 for asthmatic travelers

Respirator selection is the single most consequential decision for travelers with reactive airways. Both N95 and KN95 masks filter 95% of particles down to 0.3 microns, which covers sulfate aerosol well past the aged plume that reaches Kona and Maui. Neither mask filters SO2 gas — that requires an acid-gas cartridge respirator rated for sulfur dioxide.

For a typical Kona vacation during moderate tiers, a properly fitted N95 with headstraps handles the aged sulfate load. Asthmatics planning to hike the summit rim during degassing episodes should carry a half-face respirator with rated acid-gas cartridges — available at Home Depot in Hilo and Kailua-Kona for about $35.

Fit testing matters more than brand. A poorly sealed KN95 with ear loops can leak 30 to 60% of inhaled air around the nose bridge, making the 95% filter rating irrelevant. Beards, deep smile lines, and small facial structures all degrade fit; hospital-grade fit testing at a travel clinic runs $50 to $120.

Children and infants

N95 respirators are not manufactured in true infant sizes. Families traveling with children under 2 during red-tier vog episodes should keep infants indoors with a portable HEPA air purifier running on high — a Levoit Core 300 or equivalent 40-square-meter unit costs $90 to $130 and cuts indoor PM2.5 by 80 to 95% within 30 minutes.

University of Hawaii vog model page

The University of Hawaii vog measurement and prediction project runs an operational atmospheric model that forecasts SO2 and sulfate transport 48 hours ahead. The public page updates twice daily and shows plume trajectories in six-hour intervals overlaid on a satellite base map.

The model ingests Kilauea emission rates from USGS Hawaiian Volcano Observatory, wind forecasts from the National Weather Service, and boundary layer measurements from radiosondes launched in Hilo. Output is color-shaded by SO2 mixing ratio, with contour bands at 20, 100, 200, and 1,000 parts per billion — the same thresholds DOH uses for advisories.

Travelers should check the model 72 hours before Big Island departure to see whether Kona-wind reversals are forecast during the stay. Because the model runs a 48-hour horizon, planning further out requires watching the North Pacific High position on National Weather Service surface charts — a strong high east-northeast of the islands means trades will hold.

What the model shows for typical scenarios

1. NE trades at 15 mph: plume exits over the ocean south of South Point.
2. NE trades at 8 mph: plume stalls over Kona; sulfate builds by afternoon.
3. Kona winds SSW: plume covers Hilo, Puna, and reaches Maui within 12 hours.
4. Calm conditions: plume pools around the summit and Volcano Village.
5. Strong ENE trades: entire island stays clear; sulfate blows west of Kauai.

Island-by-island impact for travelers

Vog exposure varies dramatically by island and, on the Big Island, by neighborhood. The table below shows typical days per year in each advisory tier based on 2019–2024 monitor data, with the caveat that eruption cycles shift the numbers year to year.

Big Island: Kona and Kaʻū versus Hilo

The Kona coast draws the majority of visitors — 1.7 million per year pre-2020 — and takes the heaviest sulfate load. Households considering Kona relocation should visit during August or September to experience worst-case conditions before signing a lease. A drive to the white-sand beach at Kua Bay in Kekaha Kai State Park sits at the northern edge of the typical vog zone and often clears by late morning as onshore winds strengthen.

Hilo, by contrast, offers some of the cleanest air on the island under trade flow. Real estate priced 30 to 45% below Kona reflects that trade-off with cloudier weather and 130 inches of annual rainfall.

Maui, Molokai, and Lanai

Central Maui monitors record moderate vog on 25 to 40 days per year, concentrated in October through February. Upcountry residents in Kula and Makawao see haze at higher elevations first because the plume rides above 3,000 feet during Kona events. The Maui Bill 9 short-term rental phase-out timeline is reshaping accommodation options in the same neighborhoods that experience these episodes.

Oahu and Kauai

Oahu residents encounter vog on 8 to 15 days per year, mainly during winter Kona storms. Kauai remains the cleanest of the main islands because its northern position places it upwind of the Big Island under both trade and Kona flows in most scenarios. Visitors to the north shore refuges near Kilauea Point Lighthouse and its seabird refuge rarely experience measurable SO2 exposure.

Timing a Big Island trip around vog

Trade-wind reliability is highest in June through August, when the North Pacific High parks in its summer position and Kona reversals drop to 1 to 3 days monthly. That season also brings the strongest trades, which disperse the plume most efficiently — Kona sulfate loads tend to be lower per day of active degassing.

Winter months trade cheaper airfare and lower hotel rates for higher vog risk. December through February see 8 to 15 Kona-wind days each month and slower dispersion when trades do blow. Asthmatic travelers who cannot avoid a winter trip should stay in Hilo or on the Hamakua Coast, where trade-flow days keep air quality in the green tier.

Booking flexibility

• Choose refundable hotel rates during September peak vog months.
• Consider trip insurance covering respiratory illness cancellations.
• Ask condos about HEPA filters or portable air purifier loans.
• Confirm rental cars have functioning cabin air filters and recirculation.
• Track UH vog model daily for 72 hours before departure.

Cruise-based itineraries offer a natural hedge — the ship moves 100 to 300 miles between ports, so a single vog day rarely affects the whole cruise. Land-based travelers stuck in Kona during a red-tier episode can drive to Hilo in 90 minutes and move into cleaner air within hours.

Sensitive travelers: preparation checklist

Asthmatic guests, cardiovascular patients, and travelers with COPD should treat a Hawaii trip during active eruption cycles as they would a wildfire smoke event on the mainland. That means portable equipment, prescription refills, and evacuation routes planned before landing.

• Two weeks of rescue inhaler doses beyond expected trip length.
• Peak flow meter with baseline readings from home.
• Prednisone burst prescription from primary physician if history warrants.
• Ten N95 respirators sized for each traveler.
• Portable HEPA purifier rated for room square footage.
• Contact info for two urgent care clinics on the island.

The Honolulu Civil Beat and Honolulu Star-Advertiser newsrooms cover eruption cycles in near real time, often faster than USGS press releases reach mainland outlets. Setting Google Alerts for “Kilauea eruption” and “Halemaʻumaʻu SO2” pushes coverage during travel windows.

Indoor air quality at hotels and rentals

Older Kona condos with jalousie windows leak outdoor air heavily and offer poor protection during red-tier days. Newer sealed-window hotels with central HVAC provide substantially cleaner indoor air. Travelers with severe asthma should book properties built after 2005 with sealed windows and central air, then run any provided air purifier continuously.

Vacation-rental listings rarely disclose window type. A direct email to the owner asking whether the windows are sealed or jalousie style answers the question in most cases. Kona hotels in the Waikoloa Beach Resort and Mauna Lani areas generally use sealed windows and offer better air quality than older Kailua-Kona properties.

Vog and outdoor activities

Certain iconic Big Island activities become risky or unpleasant during moderate to red vog tiers. Hikers should postpone summit-region routes such as the Kilauea Iki crater floor loop when SO2 monitors at Jaggar Museum exceed 200 ppb — the crater walls concentrate gas along the trail. Rangers close specific trails automatically at hazardous thresholds.

Snorkelers and swimmers face fewer direct effects because sulfate particles settle onto the sea surface, but boat operators for the manta ray night encounter at Keauhou Bay occasionally cancel tours when Kona-side visibility drops below 3 miles from surface haze. Confirming operator refund policies at booking prevents disputes.

Coffee farm tours and agritourism

Coffee harvest runs September through January, overlapping peak vog season in South Kona. Kona coffee farm tour operators along the Belt Road continue tours during moderate vog days but recommend N95 masks for guests with reactive airways. The plume sits densest between 800 and 2,500 feet elevation — the exact zone where most farms operate — so exposure during a 90-minute tour can be meaningful.

Emergency escalation and evacuation

Hawaii’s vog rarely rises to evacuation levels, but the 2018 lower Puna eruption forced 2,000 residents from Leilani Estates and disrupted air quality for weeks. The 48-hour hurricane action timeline covers many of the same shelter-in-place mechanics travelers should understand for a severe vog episode: sealed windows, indoor air filtration, medication access, and evacuation triggers.

State-level thresholds for evacuation involve SO2 concentrations sustained above 5,000 ppb for multiple hours combined with wind conditions that will not clear the affected area within 12 hours. Those conditions have not occurred outside the immediate lava flow zones since 2018.

Medical resources on the Big Island

Travelers experiencing acute wheezing, chest tightness, or oxygen saturation below 92% on a portable pulse oximeter should seek emergency evaluation rather than waiting for symptoms to worsen. Kona Community Hospital handles most respiratory presentations from tourists and typically admits within 60 to 90 minutes.

Long-term residents and household planning

For families weighing a permanent move, vog exposure should be part of the decision alongside housing costs, school options, and employment. Data from the Census Bureau’s Hawaii QuickFacts shows Big Island population growth concentrated in Kona-side subdivisions where vog exposure runs highest — a pattern that surprises many buyers.

Real estate valuations reflect vog partially but imperfectly. South Kona properties in the coffee belt trade 8 to 15% below comparable Kohala Coast homes to the north, and part of that gap traces to vog exposure differentials. Prospective buyers should walk properties during an active NE trade day and again during a Kona reversal, if timing allows, before committing.

Insurance and health considerations

Health insurance networks vary by island. Kaiser Permanente Hawaii operates on all main islands but concentrates specialists in Honolulu. Families with children who have severe asthma often prioritize Oahu residency for pulmonology access. Big Island specialist appointments frequently require 90 to 180 day waits or interisland travel to Oahu.

Frequently asked questions

How often does vog reach Waikiki?

Waikiki sees measurable vog on 4 to 12 days per year, almost entirely during winter Kona-wind reversals between November and March. Episodes typically last 24 to 72 hours before trade winds re-establish and clear the leeward Oahu coast. Sensitive travelers can check Sand Island monitor readings on the Hawaii DOH air quality dashboard before outdoor exertion.

Can an N95 mask filter SO2 gas?

No. N95 respirators filter particulate matter down to 0.3 microns at 95% efficiency, which handles aged sulfate aerosol well. Sulfur dioxide is a gas molecule roughly 100 times smaller than the filter can trap, so it passes straight through. Filtering SO2 requires an acid-gas cartridge respirator such as the 3M 6001 with a P100 pre-filter combination.

Is Kona always voggy?

No. Kona typically records 210 green-tier days per year, mostly between April and October when NE trades are strongest. Roughly 45 days annually reach orange or worse tier, concentrated in August and September during peak degassing plus late fall Kona reversals. Travelers checking the University of Hawaii vog model 48 hours out can pick clear windows reliably.

Does vog affect flights into Kona airport?

Occasionally. Kona International Airport ranges from unaffected to briefly reduced visibility during hazardous SO2 episodes, but sustained flight cancellations are rare. Volcanic ash — a separate hazard tied to explosive eruption phases — poses more direct aviation risk than vog. The 2018 summit collapse events produced ash plumes that briefly closed Big Island air traffic corridors.

What is the difference between vog and laze?

Vog forms when SO2 gas from magma reacts in the atmosphere to produce sulfate aerosol haze. Laze — lava haze — forms only where lava enters ocean water, generating hydrochloric acid mist and fine glass particles. Laze was a significant hazard during the 2018 lower Puna eruption but has not been a factor since active flows retreated inland.

Should families with young children avoid the Big Island entirely?

Not necessarily. Healthy children tolerate typical Kona vog levels without lasting effect. Families with asthmatic children should book Hilo or the Hamakua Coast for cleaner trade-flow air, travel between June and August for maximum dispersion, and carry portable HEPA purifiers. Consulting the child’s pediatrician before booking is prudent when the trip includes summit-region hiking.

Where can travelers monitor vog conditions during the trip?

The official Hawaii tourism site links to real-time DOH monitor readings, and the University of Hawaii vog model provides two-day forecasts. Big Island radio stations KWXX and KAPA broadcast hourly updates during elevated advisories. Rental car GPS units and most hotel concierge desks maintain current advisory summaries printed at the front desk.