The Weather Notebook: Tropical Dust

Tropical Dust
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Ah, the beauty of south Florida: swaying palm trees, soft breezes, dust storms. Wait a minute, what's wrong with this picture? Nothing. Florida really does have a dusty season. Hi, I'm Dave Thurlow from the Mount Washington Observatory and this is the Weather Notebook.

American Red Cross photo of high waves caused by a hurricane. Miami, Florida 1948 NOAA Photo Collection

What's even stranger is that Florida's dusty season comes along with the rainy season. The dust and some of the rain comes to Florida each summer from Africa. Each year dozens of low pressure centers called Easterly Waves develop in west Africa, just north of the equator. Some of these waves carry loads of moisture and they drop much needed rain before they move off-shore. Other easterly waves are dry. Their winds pick up tons of dust from the Sahara Desert.

Each wave takes about one week to move west with the trade winds across the Atlantic to the Carribean. In the summer these waves move on a more northerly track that allows them to reach Florida. If the waves start out moist when they leave Africa, they have a shot at becoming hurricanes or at least heavy rainers. If they are dry they can carry dust high above the ocean.

Residens of Miami can see the arrival of these waves several times each year as the sky turns bronze for a day or two. When a shower arrives it can leave a thin coating of mud on cars. Miami's dust is one more thing that can be partially tied to El Niño. Easterly waves tend to be dryer in El Niño years. Which means they're less likely to produce hurricanes. But, more likely to bring dust.

Today's writer is Bob Henson.