Huge Saharan dust blob cooling the eastern Atlantic

TAMPA, Fla. (WFLA) — A huge plume of Saharan dust is now visible on satellite loops coming off of Africa into the eastern Tropical Atlantic Ocean. This, combined with stronger than normal easterly winds of the Saharan Desert, is helping cool part of the far Eastern Atlantic, where the seeds for some hurricanes originate.

While the suspended dust makes for hazy skies and—when it falls down—can result in a very dusty ground over land, there is an upside. The haze blocks out the sun and helps cool the ocean surface.

What is Saharan dust and why is it good for Tampa Bay?

That's good because surface ocean temperatures in the main (hurricane) development region of the Atlantic have been running deep into record-hot territory. The map below shows above-normal sea surface temperatures in red, which is basically the whole Tropical Atlantic.

The reason for the dust storm is a very dynamic weather setup in the eastern Atlantic, Africa and Southern Europe. There are two very strong stalled upper-level lows—one west of the Canary Islands and the other over North Africa—ushering some of the airborne dust over southern Europe and the Mediterranean.

How Saharan dust helps keep Atlantic basin quiet

The dust is piling up on top of the snow in the Pyrenees Mountains on the border of France and Spain, and some will invade Rome, Sicily, Athens and Istanbul this week.

However, to the south of the strong Canary Islands upper-level low and the westerly flow associated with it, is the opposite, a vigorous easterly wind—or enhanced trade wind. This is lower to the ground and is what is scooping up the desert dust and propelling it into the Cape Verde Islands area of the eastern Atlantic Ocean.

The easterly winds and suspended dust are a one-two punch for the record warm sea surface temperatures in the Eastern Tropical Atlantic. The strong easterly surface winds are causing upwelling of cooler water near the African coast (you can see the narrow shades of blue along the African coast in the ocean temperature image closer to the beginning of this article).

Also, the blob of dust is blocking some sunlight, cooling the surface waters.

The result is a rapid cooling of the sea surface temperatures, from well above record highs to near record highs, in just the past five days. So, while the cooling is certainly bringing surface ocean temperatures back down to reality, the main development region remains in record territory.

You can see on the far right side of this graph how the Eastern Tropical Atlantic has seen sea surface temps drop (these are anomalies). Problem is it may be short-lived, wind pattern will switch late week, so we will see if temps recover. Tks @cyclonicwx for the graphic! 2/

— Jeff Berardelli (@WeatherProf) April 15, 2024

Note, the fact that surface temperatures can cool so quickly also means they can warm just as quickly when a favorable weather pattern takes shape, so the effect may be fleeting. The weather pattern will switch soon, allowing for weaker trade winds and potentially resumed warming by late week.

Of course, the warmer the tropical ocean waters the more fuel there is for hurricanes once hurricane season rolls around. Certainly, we will take any cooling we can get. But there is still more than a month left until hurricane season and about four months left until what we call Cape Verde season—the time of year when African waves ramp up and hurricanes start emerging from the far eastern Atlantic.

Saharan dust Q&A

And it is worth mentioning that the sea surface temperatures are only one part of the story. This spring, the ocean heat is rich and deep, far above record levels, as evidenced by this Ocean Heat Content graphic from University of Miami researcher Brian McNoldy. With warm water extending deep it is harder to have sustained cooling of the ocean surface temperatures.

The point is don't get too excited about a short-term cooling of the eastern Tropical Atlantic waters yet. This would need to be sustained for many weeks to make a real impact when it counts months from now.

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