Rains forecast for Hawaii island bring with them the possibility of sulfur dioxide from the volcanic vents mixing with water, creating acid rain.

Acid rain, as defined by the U.S. Environmental Protection Agency, is “a broad term that includes any form of precipitation with acidic components, such as sulfuric or nitric acid that fall to the ground from the atmosphere in wet or dry forms.”

“Acid rain is where the pH, or acidity, of the rain is higher than it should be in a clean, ocean atmosphere,” said University of Hawaii meteorologist and professor Steven Businger. “You get sulfur dioxide that gets converted to sulfuric acid in the plume, so if you are under the plume and it rains, the acidity of the rainfall is going to be substantially higher than it normally is.”

This is a concern primarily for anyone living downwind from the vents, but the rain is not dangerous, he said.

“If you’re wearing clothing, there’s no risk,” he said. “It’s not going to burn your skin … It might irritate your eyes if you look up and get raindrops in your eyes.”

Remain vigilant on air quality, health officials advise public

The National Weather Service forecasts showers and clouds over windward areas through the day today, especially over the eastern end of the state. For Maui and Hawaii island, an east-southeast flow will likely continue to focus clouds and showers over windward locations Thursday through Friday.

As for the vog, some of it may begin pooling northward by Friday due to the weakening of trades, according to forecasters. But it is uncertain how far north the vog will travel.

The northward push toward the smaller islands appears to be short-lived, given that trades are forecast to return as early as Friday night.

“I don’t think we’re going to have a real bad episode of vog,” said Businger, “but there’s a chance of vog on Friday and Saturday.”