Vog may make its way back to islands

Light to moderate trades winds were helping to keep the vog away from the islands Tuesday, but a shift in the winds expected today may allow the gray haze to return.

A cold front moving in from the northwest is expected to revive the Kona wind conditions that carried a blanket of vog over the islands last week, Maui weather analyst Glenn James said.

“It will be a mirror reflection of last week. Last week the front drove down over Kauai and brought showers to Kauai and Oahu and then stalled,” he said.

“This one is going to be stalling before it gets to Kauai, but the net effect will be the same. It will push the high-pressure ridge right over the islands, and that will knock down our trades and we likely will see the wind pattern shifting from trades to a southeasterly wind flow.

“The southeasterly wind flow is the pattern that brings the vog.”

At the Volcanoes National Park on the Big Island, 15 to 20 mph trade winds on Tuesday resulted in no detectable levels of sulfur dioxide at the Kilauea Visitor Center or Jagger Museum. But the Hawaiian Volcano Observatory said sulfur dioxide and other volcanic fumes are continuing to spew out of the Halemaumau vent and are being blown toward the southwest.

When the winds were blowing from the south, sulfur dioxide levels along East Hawaii led to a vog advisory recommending individuals sensitive to the volcanic fumes to avoid outdoor activities. In Maui County, the Maui District Health Office issued a vog health advisory from Thursday through Sunday.

Even the trade winds that returned over the past weekend did not clear the air around the islands fully, James said.

“People were commenting it never seemed to get as clear as it used to be,” he said.

While the trades returned, they haven’t been as strong as normal for the early summer. Winds at Maalaea were gusting at 25 mph Tuesday morning but backed off to 12 to 19 mph in the afternoon.

At Kahului Airport, the northeast trades were pumping a gusty 24 to 31 mph at 2 p.m., but eased off in the late afternoon to a steady 18 to 21 mph.

The underlying causes of the recurring southeasterly winds and increased haziness are the frontal systems that are continuing to slide across the North Pacific, forcing out of position the high-pressure system that normally sits midocean northeast of Hawaii.

“Last week, I was calling the cold front very unusual for the time of year. . . . I was calling it the last cold front of the season,” James said. “After you say something is very unusual, what can you say about the next one?

“We can call it freaky. It’s unusual to have cold fronts digging down into the tropics less than a month away from the summer solstice,” he said.

James, senior weather analyst with the Pacific Disaster Center, said there is no simple explanation for the unusual conditions.

“It has to do with cold fronts, the way the jet stream airflow is patterned in the middle latitudes and pushing the cold fronts toward us,” he said.

James also produces the Maui Weather Today cable television program at 7:45 a.m. on Channel 55 and the www.hawaiiweathertoday.com weather forecast.