Vog Forecasting on Big Island

It’s sunny, with a chance of sulfate aerosols.

Illustration: Elizabeth Baddeley

It’s not hard to tell when it’s voggy outside. The sky gets hazy, eyeballs get itchy, the asthma inhalers all come out and you know the volcanic smog is back. But suppose you’re a vog-sensitive soul trying to plan your weekend. How do you know if you’ll be better off going on a hike or shutting yourself inside an air-conditioned building? Easy—check VMAP.

VMAP, which stands for Vog Measurement and Prediction, is a project of UH-Manoa meteorologists bent on taking the mystery out of the movements of Kilauea volcano’s massive plume of caustic gasses, a.k.a, vog. Their forecasts, posted at weather.hawaii.edu/vmap, use animated models to show where the plume is expected to travel as it wanders and swirls around the Hawaiian Islands, irritating bronchial tubes from Kau to Kauai. Written summaries also describe where the vog is expected to appear, and why. The forecasts are updated twice a day and look 60 hours into the future.

Steven Businger, a meteorology professor and the principal VMAP investigator, says the forecasts have proven to be very good at predicting where vog will appear. But predicting how thick the vog will be—well, that’s been trickier. “It’s akin to precipitation,” Businger says. “It’s not difficult to say if it’s going to rain or not, but it’s very difficult to predict how much it’s going to rain. We’re good at determining whether you’re going to be in the plume or not, but the concentrations still need work.”

VMAP’s best concentration guesstimates are indicated by color coding the animated plume along a six-point scale, which ranges from green for “good” (only the most vog-sensitive people beware) to maroon for “hazardous” (imagine sticking your head into Puu Oo vent). Vog consists mainly of sulfur dioxide, which pours straight out of the volcano, and sulfate aerosols, which are created when sulfur dioxide reacts with oxygen and sunlight. VMAP forecasts both, based on emissions readings from Hawaii Volcano Observatory. The next step is for the researchers to untangle the complex chemistry needed to make those forecasts more accurate.

Meanwhile, VMAP fans across the Islands have been emailing thank-yous to the meteorologists for their work. “We’re getting a lot of positive feedback, mostly from people troubled with asthma,” Businger says. But you don’t need a chronic respiratory disease to put a vog forecast to use. There are aesthetic considerations. Think of those redder-than-red sunsets you occasionally see. Why so red? Often it’s the vog. When’s the next one? No one can say for sure, but you can always check VMAP.