Vog from the eruption of Kilauea Volcano on Hawaii island could reach the smaller islands in the western half of the state later this week, the National Weather Service said.

Jon Jelsema, a National Weather Service forecaster, said tradewinds from the east-northeast could weaken and winds could shift to the east-southeast enough for a vog plume to reach the smaller islands by Thursday night.

“It’s not a slam dunk, but we can’t rule it out,” he said, adding that better predictions will be possible closer to that time. “I’m not sure it’s even going to make it up here.”

If vog from sulfur dioxide emitted by volcanic activity reaches Oahu, it could stick around until tradewinds return Friday. Tradewinds should continue through the weekend, keeping the vog plume to the southwest of the state.

Today, the weather service received reports that parts of Kona were voggy, but it was unclear whether the pollution was caused by increased volcanic emissions, burning structures, melting asphalt or other sources.

At about 9 p.m. today, the U.S. Environmental Protection Agency’s air quality website showed moderate air quality for Kona and Ocean View on the Big Island.

Exposure to vog can lead to asthmatic symptoms for people with respiratory conditions and breathing difficulties for people without respiratory conditions where there is a high level of sulfur dioxide in the air, according to the International Volcanic Health Hazard Network. Other vog-related symptoms include eye, nose, or throat irritation and headaches.