Science
6:36 pm
Tue November 26, 2013

How We Left Hurricanes In Our Dust This Year – Literally

What we dodged this year: Haitians struggle through Hurricane Sandy's devastating floods last year.
What we dodged this year: Haitians struggle through Hurricane Sandy's devastating floods last year.
Credit Carl Juste / Miami Herald

It’s hard to be a fan of hurricanes. Two out of three Haitians don’t have enough food to eat these days – thanks largely to storms like last year’s Hurricane Sandy and how they’ve ravaged Haiti’s agriculture.

And yet we need hurricanes once in a while. They’re a sort of planetary thermostat that cools oceans and redistributes hot air. Their rains more effectively alleviate droughts, and that can be a help instead of a horror to impoverished countries like Haiti.

I know, I know, they say the same thing about wildfires and how nature rises like a phoenix from their ashes. Which is fine if you’re a forest but lousy if you’re a nearby homeowner. But the point is, we’ve got a lot to be grateful for this Thanksgiving when it comes to hurricanes – and a little to be wary of too.

That’s because the Atlantic Basin hurricane season that ends on Saturday was one of the quietest in decades. So tame that it saw only two hurricanes – the fewest since 1982 – and no storm reached even Category 2 strength, which hasn’t happened since 1968.

Only one tropical storm made landfall in the United States, and its effects in Florida were relatively minor. Ditto for the neighboring Caribbean islands. They usually get hit like bowling pins; but from Port of Spain to Pinar del Rio this year, nature threw hurricane gutter balls. (Mexico, however, did get slammed by deadly Atlantic and Pacific storms.)

“It was a surprise to us as forecasters,” says Chris Landsea, science and operations officer at the National Hurricane Center in Miami. “We had anticipated a very busy [season] and we were completely wrong.”

Believe me, we're not complaining. But the natural question is, Why? How did we get off so lightly, especially since we’re supposedly in an active hurricane cycle that could last another decade?  And especially since scientists say much of the water in the Atlantic Basin (including the Caribbean and Gulf of Mexico) was very warm this year, which is usually jet fuel for hurricanes.

Experts like Landsea cite factors such as dry, sinking air – which can smother a storm’s energy – as well as strong wind shears, which can decapitate a hurricane like an atmospheric guillotine. “Fortunately,” Landsea notes, “hurricanes are kind of like people: they very rarely live up to their potential, and the reason why is that the atmosphere doesn’t cooperate.”

But one of the newer and most intriguing causes may well have been dust.

Specifically, dust clouds from Africa’s Sahara Desert. They’ve been floating across the Atlantic into Florida and the Caribbean Basin for thousands of years. This year they seemed especially robust, and that’s got atmospheric scientists like Joseph Prospero thinking:

“When you have a great deal of dust in the atmosphere it’s going to intercept some of the solar radiation that reaches the sea surface,” says Prospero, emeritus professor at the University of Miami’s Rosenstiel School of Marine and Atmospheric Sciences. That keeps the waters cooler, he adds, which reduces water-vapor energy for tropical cyclones.

Click here to see the image below in animated form, showing the progress of Saharan dust storms.

Credit Space Science and Engineering Center / University of Wisconsin-Madison

Prospero points to a computer map of the Atlantic that looks like a tie-dye T-shirt. It indicates the density of recent dust clouds – and shows how heavily they sat around the Cape Verde Islands off Africa’s west coast, where so many hurricanes are spawned.

Did that dust stifle hurricanes this year? “That could very well have been one of the factors,” says Prospero.

But before we start the calypso party music in this part of the world, it’s premature to declare dust our savior from hurricanes – or, for that matter, from the yolk of Citizens and other windstorm policy writers. “The smoking gun of a direct link” between greater dust and fewer hurricanes “is still somewhat elusive,” Prospero warns. “And anticipating what dust levels might be in the future is very difficult.”

If you think that’s a buzzkill, Prospero points out that dust particles can also facilitate cyclone formation if atmospheric conditions are right.

Which brings us back to that question of how hurricanes do good. Scientists say global warming is having the two-fold effect of producing fewer but stronger hurricanes. (Fewer because it yields more of the atmospheric conditions that thwart storm development, stronger because higher sea surface temperatures feed storms that do form.)

If we have too few hurricanes, they say, that could leave the waters in regions like the Caribbean too warm – and make the hurricanes that do get out the gate all the more potentially destructive.

In other words, be careful what you wish for, even with hurricanes. But for the moment, even though 2013 was an aberration, it’s more than OK to be thankful that we left those storms in our dust.

Tim Padgett is WLRN's Americas editor. You can read more of his coverage here.