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Oil Slick at the Mercy of Winds, Currents and Eddies

By By Alex Sosnowski, Expert Senior Meteorologist
June 10, 2010, 9:29:36 AM EDT

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While light winds and waves will cooperate for surface containment operations of the oil slick over the northern Gulf of Mexico through the holiday weekend, questions remain as to where the slick could wind up next.

A flow from the east and southeast in recent weeks brought a big part of the oil slick along the Louisiana and Mississippi coasts during the past couple of weeks.


Oil slick depicted is approximate based on most recent satellite photos available.

Loop Current and Eddies

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.


The Loop Current as portrayed by the U.S. Navy's HYCOM model on Thursday, May 27, 2010.

This and other eddies of various size are a common occurrence within, along the edge of, and outside of the ocean currents throughout the world's oceans.

These eddies come and go, change shape, meander, intensify, and weaken at random.

There is some skill forecasting the large eddies and seasonal shifts of the currents. Forecasting the smaller "come-and-go" eddies is more difficult.

The Loop Current and nearby smaller eddies have been capturing part of the large oil slick, creating streamers and smaller patches of oil. The currents and eddies have also been protecting much of the eastern shores of the Gulf of Mexico thus far.

Oil Breakdown

Once the oil is exposed to the water and the air, it is attacked and slowly broken down by the environment. However, tar balls remain.

According to Malcolm Spalding, Professor of Ocean Engineering, University of Rhode Island, the toxic nature of the oil begins to diminish after three days, then begins to convert to tar balls. As the tar balls age, they too become less toxic.

The oil breakdown process adds another variable to the complex equation of where and when the oil may show up next.


Image taken May 25, 2010, appears courtesy of NASA.

Small patches of non-evaporated oil and tar balls could be carried great distances by the currents and other smaller eddies, especially if strong winds are introduced during storm/hurricane situations.

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.

While some impacts on the environment and economy are already apparent, it may take months for full effects to surface, and years to recover from this disaster.

One thing is for sure, stopping the leak sooner rather than later would go a long way toward reducing the threat to shorelines not yet impacted by the oil spill and reducing the damage to areas already hit.

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