BP claims to be capturing 5,000 barrels of oil a day from the leaking well at the bottom of the Gulf of Mexico, but more continues to gush into the water. Meanwhile, the annual hurricane season begins on June 1, and some scientists are predicting an above-average year with 15 named storms and eight hurricanes (PDF). It sounds like a deadly combination—but what would actually happen if a storm like Katrina tracked across the spill in the Gulf?
It could make things even worse. At least one forecast team puts the chance of a strong hurricane hammering some part of the Gulf Coast this year at 44 percent, and any such storm would threaten to disrupt ongoing containment or environmental protection measures. In an absolute worst-case scenario, powerful hurricane winds might drive the oil slick towards land and push some of it ashore with the ensuing storm surge.
Much depends on the angle at which the storm crosses the slick. In the Northern Hemisphere, hurricanes rotate counterclockwise, with the largest storm surge occurring where the winds blow in the direction the storm as a whole is traveling—that's in front of the eye and off to the right. (Meteorologists worry over a hurricane's dangerous "right-front quadrant.") So if a powerful storm approached the slick from the southwest, say, its most potent winds would push the oil forward, instead of sweeping it off to the side and out of the storm's path. If the storm then plowed into the Gulf Coast, you'd expect an oily landfall.
The strength, movement, and size of the storm would also make a difference. Fortunately, the height of the Atlantic hurricane season, featuring the strongest storms, doesn't arrive until August. We might reasonably hope to have cleaned up the oil by that point.
So the storm could move the slick. Could the slick affect the storm? Hurricanes draw their energy from the evaporation of warm seawater—that's why they occur over the summer and into the fall. Given that fact, you might think that oil on the surface of the ocean would interfere with a hurricane's access to its power source. Indeed, some have proposed to combat hurricanes by coating the ocean surface with an oily substance (not crude oil, of course) in order to reduce evaporation and quench a storm's strength.
Alas, this scheme probably wouldn't work, nor should we expect the oil spill to slow down any hurricanes very much this season. The first problem is that most hurricanes span an enormous area of the ocean. According to the National Oceanic and Atmospheric Administration, the typical storm is 300 miles wide, dwarfing even this large spill. Even if a hurricane passed directly over the slick, the oil would cover just a fraction of the relevant sea surface.
What's more, by the time winds reach hurricane force (greater than 74 mph), they cause so much ocean mixing that any oil slick on the surface would be driven down into the depths and generally broken up. MIT hurricane expert Kerry Emanuel has tested the phenomenon on a small scale using an enclosed tank, half filled with water, with an air rotor at the top capable of generating hurricane force winds. When the rotor turned at high speeds, the surface of the water was torn apart, and the scientists observed no difference in the amount of evaporation that occurred with or without an oily surface film.
It's even possible that an oil slick could make a powerful hurricane a little stronger. Oil is darker than water, and so it absorbs more sunlight while also blocking evaporation from the sea surface. That means the spill could be trapping heat in one part of the ocean. If a storm passed over and churned up the surface of the water, that potential hurricane energy might then be released.
There is a small silver lining here: A hurricane of sufficient force might cause enough ocean mixing to help disperse and "weather" the oil slick, which could in turn speed up the process of biodegradation.
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Explainer thanks Kerry Emanuel of MIT and Dennis Feltgen of the National Hurricane Center.