Sahara Dust

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St. John Weather

Sahara Dust
For the last few days or so we’ve been experiencing a particularly intense Sahara dust condition. The gray skies over St. John are not clouds, but dust that has traveled over the Atlantic all; the way from Africa and will continue as far as the state of Florida in the continental US.

The Good Part:
“Saharan dust is a limiting factor for tropical development in the Atlantic and sunsets are stunning as a result of dust clouds high in the sky with notable, bright red colors on display.

Origin of the Dust
The Sahara is the greatest single stretch of desert in the world, besides the Arctic and Antarctic, stretching about 3.5 million square miles across northern Africa.

Rainfall is rare across much of the Sahara, and sparing across the rest of the desert.

“Persistent high pressure with resultant sinking and drying of air is what tends to limit rainfall across the region. There is likely a ‘feedback’ mechanism at work by which dry, sparsely vegetated earth superheats, thereby further warming the atmosphere and further strengthening the area of high pressure,” AccuWeather Expert Senior Meteorologist Jim Andrews explained.

Persistent northeasterly winds, squeezed between an area of high pressure over the northern Sahara and low pressure over the equator, are often strong enough to stir loose sand and dust in the Sahara. Although the coarser sand is not normally raised far above the land, the smaller dust particles can be lofted 2 or 3 miles high into the sky, Andrews said.

Especially strong winds can blow over thousands of square miles of the desert can scour enormous volumes of dust from the surface. According to a University of Wisconsin-Madison study by Amato Evan, the amount of dust is said to be in the millions of tons….

During a dust storm in the Sahara, which can last for days, the visibility can drop to zero. These long dust storms yield clouds of dust that span one thousand miles or more. Large dust clouds can traverse westward across the Atlantic as they get steered by trade winds.

“Under favorable settings, dust aloft can reach customary tropical cyclone breeding areas, including “Hurricane Alley”, which stretches eastward from the Lesser Antilles,” Andrews said….” From Accuweather.com by Meghan Evans, Meteorologist

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