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Monday, May 31, 2010

Oil spill and hurricanes

A question that I have been asked several times is "How will the oils slick in the Gulf of Mexico affect the development or path of an on-coming hurricane?"

The fact is that I do not believe that anyone really knows. Several theories have come about all of which are equally valid.

What will happen when a hurricane tracks through the oil spill? (The Weather Channel)
The high winds and seas will mix and disperse the oil which can help accelerate the biodegradation process.

The high winds may distribute oil over a wider area, but it is difficult to model exactly where the oil may be transported.

Storms' surges may carry oil into the coastline and inland as far as the surge reaches.

Debris resulting from the hurricane may be contaminated by oil from the Deepwater Horizon incident, but also from other oil releases that may occur during the storm.
Where will the oil go? (The Weather Channel)

The rotation of a hurricane dictates the forces that the wind will impart onto the oil. A storm that comes in east of the oil will tend to push the oil out to sea, away from land. A storm in the western portion of the Gulf could drive the oil onshore.

The storm surge will act to bring the oil far onshore. This is primarily true for an approaching storm and for the north-east quadrant of the storm. As stated above, the winds on the western side of the storm will act to force the oil and water away from the shore.

Graphics courtesy of The Weather Channel.

Will the oil slick help or hurt a storm development in the Gulf? (The Weather Channel)
Will the oil have any effect on a hurricane? (The Weather Channel)
Will the hurricane pull up the oil that is below the surface of the Gulf? (The Weather Channel)

One of the issues is whether the storm is developing or is fully developed when it interacts with the oil slick. As discussed above, if a storm is developing, the presence of the oil may reduce the amount of evaporation. This was actually demonstrated in a study at MIT based on work done in the 1960's provided that the windspeed remains low. As the windspeed increases, the oil is more likely to break into smaller droplets which would not block evaporation as efficiently.

Hurricane Season Raises New Fears (New York Times)

A hopeful speculation is that the oil might not be all bad news and that it might sap the storm’s energy. In 1966, a husband-and-wife team of federal hurricane researchers, Joanne and Robert H. Simpson, speculated that spraying an insoluble liquid like oil onto the ocean might even be a way to combat hurricanes by cutting off the evaporation that feeds energy into the storm.

But in a fact sheet issued last week, the atmospheric administration noted that hurricanes span 200 to 300 miles wide, much larger than the current size of the spill, and doubted that the oil could have much effect on the strength or path of a storm.

Hurricane winds would also minimize the evaporation effect.

A few years ago, when researchers at the Massachusetts Institute of Technology built a laboratory experiment to look at the flow of heat from water to air under different conditions, they, almost as a lark, followed up on the Simpsons’ suggestion.

They applied fatty alcohols onto the water, and at very low wind speeds the alcohols did suppress evaporation.

“But when the winds get up to gale force or so, the surface gets torn apart,” said Kerry A. Emanuel, a professor of atmospheric science at M.I.T. “We just didn’t see any effect at high wind speeds.”


One likely scenario is that oil on the surface will be atomized and blown around. An on-shore wind will blow oily residue many miles inland coating everything in the area with a film of oil. A fully developed storm that enters the Gulf may be affected to some extent but would generally push along.

Another concern is if the oil is carried by the Loop current to other areas in the Gulf or out into the Atlantic.

Oil Slick at the Mercy of Winds, Currents and Eddies (AccuWeather)
Light winds continue to allow some of the slick to be captured in the Loop Current, which is a semi-permanent, fast river of warm water circulating through part of the eastern and central Gulf of Mexico. At times this current can reach 3 to 5 mph.

The indications last week were that this current was "pinching off," forming a large eddy.

--snip--

Depending on these winds and storm track, assuming the leak continues, oil that is not broken up by wave action could show up anywhere on the Gulf Coast with time from the Texas and Mexican coasts to the western Florida coast and the Keys.

Outside of this area, the risk of oil transport and landfall are substantially smaller because of the life-expectancy of the oil and tar balls and the even less-probable "hook-up" with more distant currents and eddies.

The development of a closed circulation-Loop Current eddy could allow a general westward migration of some of the oil slick over the central Gulf of Mexico, hence increasing the risk of possible impact on the Mexican and Texas coasts in months ahead.

A hurricane crossing the area could conceivably blow oil into the loop current or one of the eddys promoting the movement of oil into an area that is currently unaffected.

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