When the Trades Drop: Kona Winds, Vog and the Hazy Week

Maui's default weather is a northeast trade wind, and almost everything about the island assumes it: which coast is dry, why boats sail in the morning, why Hoʻokipa is a windsurfing capital.

Several times a year, particularly between roughly October and April, the trades break down and the wind swings round from the south or southwest. Locals call these kona winds, from kona, the leeward direction.

What changes

The air gets still and humid. The normally dry leeward coasts — Kīhei, Wailea, Lāhainā, Kāʻanapali — lose their breeze and warm up. Cloud builds over the leeward slopes instead of the windward ones, and afternoon showers can turn up in places that are usually dry.

A deeper version, a kona low, can sit over the islands for days and produce heavy rain, thunderstorms, flash flooding and landslides. Those are the systems that close the Hāna road and put brown water plumes off the river mouths.

Vog

The other thing kona winds bring is vog: volcanic haze, mostly sulphur dioxide and fine particulate, carried up the island chain from Kīlauea on Hawaiʻi Island. Under normal trades it blows away to the southwest. Under kona winds it drifts north over Maui.

What it looks like is a flat, milky haze that dulls the horizon, softens sunsets into something oddly beautiful, and makes distant ridgelines disappear. What it feels like depends on you. Most visitors notice nothing beyond the view. People with asthma, other respiratory conditions or unusual sensitivity can get a sore throat, itchy eyes or tightness in the chest.

What to do about it

If you are sensitive: carry your inhaler, keep exertion lower on hazy days, use air conditioning rather than open windows, and drink more water than usual. The Hawaiʻi Department of Health publishes air quality information and a vog forecast, which is the thing to check rather than a general weather app.

For everyone else, the practical effect is photographic. If you want the sharp, deep-blue Maui of the brochures, a trade wind day is what you need. A vog day is the one where the sunset over Lānaʻi is the best you will see all week.