12 July 2010

Hurricanes and Oil Will Mix

Posted by Michael McFadden

A hurricane as strong as Katrina may soon be on a collision course with the Gulf oil spill to create a “double-whammy of worst-case scenarios.” That’s the next potential nightmare looming ahead according to Heidi Cullen, one of several scientists who addressed a briefing on 30 June for Congressional staff.

“The Deepwater Horizon oil spill is a worst-case scenario. And, I would say that the fear in the back of many of our minds right now is – we could potentially see the repeat of the 2005 hurricane season,” she explained. Cullen, CEO of Climate Central, spoke at a 30 June 2010 briefing called “Hurricanes and Oil Will Mix: Managing Risk Now.”

With oil spewing nonstop into the Gulf of Mexico from the Deepwater Horizon blowout, Cullen and other researchers described what a large hurricane like Katrina or Ike of 2005 would do if its track took it through the oil slick. Providing a particularly vivid illustration of what might be in store was marine scientist Rick Luettich.

Running a computer model of the Gulf of Mexico that  he and his research team use to simulate hurricanes’ paths and effects, Luettich illustrated how particles floating on the water during Hurricane Katrina would have moved, creating the dramatic image below. The arrows on the left panel indicate the wind direction throughout the hurricane, the colors indicate water elevation above sea level, and the black in the right panel depicts the oil slick.

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“Hurricanes can be real game-changers, and [could] expose areas that have thus far largely escaped impact from the oil,” said Luettich, director of the Institute of Marine Sciences at the University of North Carolina at Chapel Hill, addressing the audience of the standing-room-only briefing.

Luettich also ran the simulation for some other recent major hurricanes: Gustav, Ike, and Rita.

He described three basic consequences of the mixing of oil and hurricanes.

The first brings some much-needed good news: high winds and waves associated with hurricanes cause a lot of mixing in the ocean, which would dilute the oil – like chemical dispersants – but without the potentially toxic side-effects. However, hurricanes only mix the water down to a depth of a few hundred meters, so this won’t do much for deeper oil plumes.

Another scenario depends on the path a hurricane follows as it moves through the Gulf. Hurricanes in the northern hemisphere spin counter-clockwise, which means that winds on the eastern side of the eye blow to the north, while winds on the western side of the eye blow south. So, a storm that tracks west of the oil would push the floating oil onto the shore, whereas a hurricane that passes east of the slick would pull it away from the coast and out to sea.

The third consequence, which operates more-or-less independently of the other two, brings the bad news. All hurricanes that pass through the Gulf of Mexico create winds that circle north up the Florida coast, west across the Louisiana coast, and south down past Texas – only the strength of the wind varies depending on how big, strong, and far away the storm is. These winds will drive water, and the oil floating on it, from east to west around the Gulf of Mexico.

Luettich used his model to illustrate what would happen to floating oil during such an event. “The particles make it all the way around to the Texas coast down to around Galveston. So if a major storm comes along, there will be a very substantial redistribution [from east to west] of where the oil is in the Gulf,” he said.

The oil spill is already devastating the Gulf coast, but with NOAA predictions estimating 14 to 23 named storms, with three to seven of these classified as major hurricanes for this season, it’s likely the Gulf will only get dirtier until this storm season plays itself out.

Colin Schultz, AGU science writer