JACKSONVILLE, Fla. — In previous Tropics in Depth episodes, we spoke about upper-level wind shear and how it’s our friend when it comes to preventing tropical development, or at least stunting the growth of an existing cyclone.
But shear is not our only friend, and we need more friends because our oceans and rivers are definitely warm enough to support tropical cyclones.
We also have Saharan dust and upper-level ridges as good pals.
Saharan dust, also known as the Saharan Air Layer or SAL, is a mass of very dry, dusty air that sweeps off the western coast of Africa during the summer months. This dust travels west in batches across the Atlantic Ocean, typically every three to five days.
The SAL extends between 5,000 and 20,000 feet in the atmosphere. Saharan dust has been known to have significant negative impacts on tropical cyclone development and intensity. The dusty air can sneak into the circulation of a cyclone, which can weaken it. Think of it as the SAL choking off cyclonic development.
However, there have been some studies that suggest as the SAL travels across the Atlantic Ocean it breaks apart. Once the dust is not as concentrated after trekking thousands of miles across the open waters, some researchers suggest the leftover particles can actually help with the formation of clouds.
Simply put, we are confident enough to say Saharan dust is our friend when tracking tropical development. It’s an inhibitor. There is still so much for us to learn though!
Next up on our “friend list” is an upper-level ridge, or surface high pressure along and near the U.S. East coast. When we’re tracking temperatures that are near record heat, or sometimes record breaking, you can think “high pressure!” This is also synonymous with a trough on the West coast, or stormier and cooler weather.
Upper-level ridges not only create shear at 500 mb or the mid-levels of our atmosphere (ranging from 16,000 to 20,000 feet), but they also act as a shield. The high pressure creates a dome of protection in a sense and helps to steer cyclones away and along the outer edge of them.