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Persistent SAL impacting the Hurricane Season - The Galveston County Daily News: Weather Watch

July 29, 2015

Persistent SAL impacting the Hurricane Season

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Posted: Wednesday, July 23, 2014 4:19 pm

With Tropical Depression #2 weakening back into a tropical wave, systems in the Tropical Atlantic Basin continue to have a difficult time developing — not that I am complaining.

There are several reasons for the relatively slow start to the season. One is moderate to strong wind shear (which isn’t too unusual for this early in the season). Another is a stronger than normal high pressure area between Bermuda and the Azores, which is keeping brisk northeast trade winds over much of the Atlantic and Caribbean Sea. This, especially combined with wind shear aloft, tends to send systems rapidly to the west, disrupting their ability to develop into organized systems. It also is an explanation for the abundance of seaweed in the Gulf of Mexico this year.

Another prevalent factor has been the presence of dry, Saharan air (known as the SAL or Saharan Air Layer). With the strong trade winds, surges of dry, stable air have been flowing into the Atlantic and Caribbean and even obscured skies locally last week as the air reached the Gulf of Mexico The presence of large quantities of dry air in the Atlantic and Caribbean Sea has been shown to suppress tropical activity and reduce the number of tropical storms or hurricanes.

The big question for the remainder of the season may well be: Will the SAL continue to inhibit tropical storm formation? Currently, there seem to be no signs of the Atlantic high pressure to weaken, or the trade winds to slacken, though there are some signs of deeper moisture forming off the African coast near the Cape Verde Islands. On the other hand, another surge of dry air seems to be developing over  Mali and Southern Algeria.

Historically, we should see a noticeable uptick in tropical activity as we move into August. Still, I will be watching the Atlantic closely to see if the SAL will continue to influence the weather there!

Below are links related to this blog:

Impact of SAL

Water Vapor image of former T.D.#2 , showing dry air in region

Current status of SAL

Atlantic water vapor loop