You may have seen all of the reports about an above-average hurricane season that is expected this year, with record amounts of storms. So far, we have had a Category 5 storm, Beryl, which crushed many early season records. But so far, things are quiet now- which is a good thing! But why is that?
July can commonly have a bit of a dry period, but it has been quite some time since we have had any tropical activity worth worrying about. For a fairly consistent period in June and early July, it seemed like the 7-day tropical outlooks were commonly showing multiple risk areas. Now they are not, and it’s been that way for a couple of weeks or more! What has changed?
The Saharan Air Layer- SAL
The SAL- or Saharan Air Layer has been a consistent factor, which is a robust plume of dust that migrates hundreds of miles from Africa and spreads across the Caribbean. The plume can vary in intensity, with pulses or surges of dust, similar to wildfire smoke. This dusty layer is also dry air, and it contains about half the moisture content of normal air.
So, even though sea surface temperatures (SSTs) are already very high, the dry air aloft associated with the Saharan Air Layer is helping to prohibit tropical development. It impacts more than 20% of the Caribbean soundings during peak season, on average. A sounding is a measure of the vertical profile of the atmosphere, for winds, temperatures, and dewpoints.
What does the SAL do?
The SAL helps to reduce thunderstorm activity, and thunderstorms are always the starting point for all tropical cyclone development. It is not uncommon to have a robust SAL happening in July, and then for August and September to be much busier.
Just like with weather, there are plumes of the Saharan Dust that vary in intensity and surge throughout the region. Sometimes they reach as far West as the Gulf of Mexico, and Florida. This can have vast implications for storm development in all areas of the Caribbean and the Atlantic.
This year’s plume of dust seems to be a bit more pronounced than in recent years, which is having even greater impacts. It can also suppress solar activity to a minor extent, which can help prevent the aggressive warming of the ocean below. The suspended mineral content of the SAL can help absorb heat, which keeps the air warm.
The SAL reduces the sun’s energy that reaches the surface of the ocean, which can prevent further warming of the sea surface. It also limits convection, due to the aggressively dry nature of the air. Rich moisture and convective heat are needed for thunderstorms to form. When there is this dry and dusty air aloft, it can slow that process down greatly.
Long-Term Impacts of the SAL?
That said, the ocean was already so warm this year, that there likely won’t be much of an impact from that, but it will assist a bit with further warming. This is a good thing. The sea surface temperatures have also already recovered nicely from Beryl passing through. We don’t need that, but that was inevitable. Hurricanes typically disrupt the surface ocean temperatures as the aggressive waves and winds tend to cause the colder waters to churn up from the sub-surface levels of the ocean.
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Many people have suggested this year is a bust for hurricane activity, but that couldn’t be further from the truth. There still could be explosive development for the remainder of Summer, into early fall. Once this Saharan Air Layer also starts to minimize, development will likely continue to be a major issue.
It’s much too early to let your guard down for this season. In fact, this allows everyone to make greater preparations and to make sure they have everything in order for future storms.
July is moving quickly, and it will soon be August. Time will tell how long the SAL persists, but one thing is certain, above average Hurricane’s are still forecasted for the region. This forecast is still not to be taken lightly. Current projections are that things will definitely heat up with Tropical activity as we head into Mid to late August. The first part of August could remain quiet, but that does not mean that it necessarily will.
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Thanks for checking in!
Meteorologist Bo Cole
