MIAMI – Where are the hurricanes?
I get asked a lot. This is the 7th consecutive year that conditions in the Tropical Atlantic Basin are favorable for an above average season.
NOAA, seeing these signals, once again predicted that we wouldThis year. Yet, so far we’ve only used three and we’re already in August.
So why are things so quiet? Is the Saharan dust I’m talking about the culprit?
Long before I get into that, let’s keep things in perspective.
From a climatological point of view, the majority of tropical activity does not occur until August. In fact, the “peak” of the season is September 10. It is not at all unusual to see a “lull” in July that can continue into early August.
That said, we are likely to see a calm first half of August. So let’s talk about dust, specifically what we call the Saharan Air Layer (SAL).
The orange plumes you see are aerosols in the atmosphere from the Sahara desert in Africa. This sparse air rises to the mean levels of the atmosphere where the easterly trade winds then carry it across the entire tropical Atlantic. As you can see in this image, the plumes are reaching the United States. Our recent dry, foggy days with poor air quality here in South Florida are the result of this transatlantic traveler.
Like all weather phenomena, key ingredients must be present for tropical systems to develop, sustain and intensify, which in our case means hurricanes.
A key ingredient is wind shear (a change in wind speed and/or direction with height) or better, the absence of wind shear. Hurricanes develop from an initial cluster of thunderstorms stacked like pancakes. The wind shear disturbs this essential part of the development, the pancakes fly away.
Tropical systems also need moisture, in large quantities. Any dry air (Saharan dust) removes another critical weather ingredient. So, instead of air particles rising to sustain thunderstorms, which creates instability, dry air creates stable conditions that stop this development. Without these storms, the hurricane “seed” is not present.
No seeds, no hurricanes.
Thus, these continuous Saharan dust plumes largely explain why the tropical Atlantic has so far closed.
So, are we in the clear? Absolutely not.
Clean the dust
Atmospheric circulations moving along the equator are linked to making the atmosphere more favorable for tropical development. They can help reduce wind shear and moisten the development zone in the Atlantic. As a bonus, they can also add spin, another key ingredient in tropical training.
We look for these circulations or “signals” to tell us if we are maintaining the lull or if things are going to get busy. Right now, things will remain quiet for a few more weeks, but further into August and September, signals point to more favorable development conditions.
It also coincides with when, climatologically, the tropical Atlantic is busy producing hurricanes.
I only use one cliché when it comes to hurricane season and it’s one that I and many of you have also experienced: “It only takes one”.