SAHARAN DUST ON SOUTH FLORIDA’S DOORSTEP

The core of the massive plume of dust from the Sahara Desert in Africa will push by well south of Florida today. But the northern fringe is forecast to move over the southern part of the peninsula.

We may see a milkiness to the sky later today, becoming more noticeable tomorrow. As the dust moves farther west, it should add some color to our sunrises and sunsets. If the dust gets too thick, the sun becomes a fuzzball at sunset, and is unattractive. But with a thinner dust layer, we see more dramatic reds and oranges.

The dust is a regular occurrence from June to August across the tropics. The thunderstorm complexes over Africa that move into the Atlantic and become tropical disturbances – the seeds of hurricanes later in the year – kick up the dust. The same flow that propel the disturbances west, sometimes brings along the dust. In this case, a strong high-pressure system over the Atlantic has provided a perfectly situated river of air to create an unusually thick plume.

Scientists in Puerto Rico have calculated that the density of the dust in the air is the highest in at least 50 years.

NASA simulates the dust’s path in a special computer forecast model. It shows the core of the plume, which passed over Puerto Rico and the northeastern Caribbean islands, staying to our south and moving into the Gulf of Mexico before curving north and affecting much of the Gulf coast.

The flow around the western nose of the big Atlantic high should loop the dust back to the west as it disperses across much of the Southeast U.S. The bottom line is, the dust will be with us for a while – likely through the weekend at least.

While the dusty air is very dry, most of it is a mile or higher in the atmosphere. That does a good job of squashing tropical activity because storm cells can’t grow. But underneath that dry air, very moist tropical air builds up, and humidities are higher than normal. Because we get fewer thunderstorms, there is less stirring of the atmosphere, which is one of the things that would normally give us nice summer evenings after afternoon storms.

When afternoon storms do occur with dust in the atmosphere, they can be quite strong and gusty. Most thunderstorms that are able to develop should be inland and toward the west coast for the next several days.

Elsewhere in the Atlantic, the daughter system of the upper-level low that sat over the eastern U.S. all last week finally organized enough off the Northeast U.S. coast to be called a Subtropical Depression. It moved right over the warmest part of the Gulf Stream yesterday and is heading for cold water and North Atlantic oblivion. It has a little window of time today to strengthen just slightly and be called Subtropical Storm Dolly before that happens. In any case, it’s nowhere near land.

Otherwise, nothing threatening is expected in the tropics through the weekend, at least.