Thick vog blanketing the islands is expected to dissipate by Sunday with the return of tradewinds.

National Weather Service meteorologist Jon Jelsema said tradewinds will return tonight, and by Sunday the vog will be south of the islands.

“It should be on a downward trend on Saturday, and by Sunday it should be outta here,” he said.

There has been a large concentration of vog due to southeast winds blowing volcanic emissions from Hawaii island to the rest of the state, said Steve Businger, professor of atmospheric sciences at the University of Hawaii-Manoa School of Ocean and Earth Science and Technology.

Businger and a team of scientists developed a computer dispersion model that measures the amount of sulfur dioxide emissions from Kilauea volcano and wind predictions to forecast vog movement. The model has been a useful tool for the National Weather Service.

Vog causes irritation to the eyes, nose, throat and lungs, primarily aggravating those with breathing problems such as emphysema, bronchitis or asthma. Dr. Franklin Yamamoto, an allergist of Hawaii Asthma Allergy Associates in Aiea, said vog could trigger spasms in the airways for asthmatics.

Although they have not experienced an increase in patients seeking treatment, they have been receiving calls from existing patients to ensure they are well supplied with medication. “It’s very important that they have their medications and use them as directed by their physician,” said Yamamoto.

Yamamoto and Kim Nguyen, executive director of the American Lung Association in Hawaii, offered the following precautions:

>> Make sure you have a sufficient supply of medication.

>> Drink lots of fluids.

>> Avoid outdoor physical exertion.

>> Stay indoors. If possible, use an air conditioner.

>> Monitor weather reports.