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How Saharan Dust impacts development in the tropics

Published: Jul. 15, 2021 at 1:09 PM CDT
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SHREVEPORT, La. (KSLA) - As we have moved into the core summer months and also into Hurricane Season there is a phenomenon that always seems to capture the attention of the ArkLaTex. No, I am not talking about the Barksdale Bubble, but something that has an actual impact on our weather. In fact, it can have an impact on everyone that lives along the coast in the Atlantic Basin. I am talking about Saharan Dust, or the Saharan Dust Layer (SAL). The SAL can have the ability to create hazy skies, and decrease air quality when in high enough levels across the region. But the most crucial effect it has is significantly limiting tropical activity.

This is what sunrises can look like thanks to Saharan Dust from Africa.
This is what sunrises can look like thanks to Saharan Dust from Africa.(KSLA News 12)

The Saharan Dust Layer is air that originates over the desert of the Sahara and thanks to the easterly Trade Winds is transported over the Atlantic Ocean. The very hot and dry Saharan air is less dense than the cooler marine air and is carried higher up in the middle levels of the atmosphere and is able to travel as far west as the continental United States. This is something that will be seen again this weekend across east Texas. There are three major facets of the Saharan Dust Layer that can stop tropical development in its tracks: dry air, easterly wind shear, and the dust particles themselves.

We are tracking increased levels of Saharan Dust across east Texas Saturday.
We are tracking increased levels of Saharan Dust across east Texas Saturday.(KSLA News 12)

Let’s start out with the obvious, the hot and dusty air that starts over the Sahara is going to be very dry. As this air rises into the middle levels of the atmosphere it heads east and then can slam the brakes on tropical convection as the moist unstable air is eaten up by the dry air. Thus the convection of a tropical wave or weak tropical system will not be able to maintain its convection. The higher the dust concentration, the harder it is for tropical moisture and convection to overcome it.

A massive plume of dust emerged off the coast in Africa back in  June of 2020.
A massive plume of dust emerged off the coast in Africa back in June of 2020.(NASA)

Another aspect of the Saharan Dust Layer is the fact that it causes a lot of vertical wind shear. Strong easterly winds in the middle levels of the atmosphere carry the dust west. But it is much stronger than the winds at the surface. Vertical Wind shear is how wind speed changes as you go up in the atmosphere. So the greater the difference in wind speed between the surface and the middle levels of the atmosphere the higher wind shear. This is bad for tropical cyclones as wind shear can rip apart the organization of the convection that power the storm and prevent potential strengthening.

Even though activity has died down in the tropics for now, that will change as we get to August...
Even though activity has died down in the tropics for now, that will change as we get to August and September.(KSLA News 12)

The last aspect of the Saharan Dust Layer that is the bane of tropical weather is the dust particles themselves. On top of the air being dry, the dust particles have been studied to prevent the development of thunderstorms as the moisture is stopped from rising into the upper levels of the atmosphere.

The updated hurricane forecast from Colorado State University calls for a very active second...
The updated hurricane forecast from Colorado State University calls for a very active second half of the season.(KSLA News 12)

So it really is a three legged stool that comes together to really limit the development of tropical cyclones during the Hurricane Season. But while we have the SAL playing a major role in the tropics right now we are still expecting a very active peak season for the tropics. The latest forecast from Colorado State University calls for 20 named storms, 9 of them to become hurricanes, and 4 to become major hurricanes so please make sure you are prepared for the peak season.

The KSLA First Alert Weather team will keep you updated on the latest develops in the tropics as we go through the 2021 Hurricane Season. Here’s how you can stay First Alert to the latest forecast details:

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