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Thursday, April 29, 2010

Jeff Masters: Unfavorable winds set to push Gulf of Mexico oil spill into Louisiana

Unfavorable winds set to push Gulf of Mexico oil spill into Louisiana

by Jeff Masters, Wunderblog, April 29, 2010

Work crews burned off oil on the surface of the Gulf of Mexico just 20 miles southeast of the Louisiana coast yesterday, in an effort to keep as much oil as possible from moving shoreward and fouling the beaches of the Gulf Coast. Relatively good weather, with moderate southeast winds of 10-15 knots, aided the efforts, and work crews were also able to use skimmers and dispersants to remove and thin the oil spill from the April 20 explosion and sinking of the offshore oil rig Deepwater Horizon. For now, it appears that the fires are not large enough to generate air pollution capable of causing health problems for those living downwind, according to the latest graphics from NOAA's Hazard Mapping System Fire and Smoke Product.

Oil continues to gush from the well head at 5,000 feet depth at a rate five times what was previously estimated -- 210,000 gallons per day. This is equivalent to about 2% of the total spilled oil from the 1989 Exxon Valdez disaster in Alaska entering the Gulf of Mexico each day. If 210,000 gallons per day has been leaking since the disaster began on April 20, over 2 million gallons of oil has already been spewed into the Gulf, about 18% of the 11,000,000 gallons spilled in America's previous worst oil spill, the Exxon Valdez disaster. With the winds expected to begin blowing the oil spill on shore this weekend, the Deepwater Horizon oil spill appears destined to become one of the most disastrous oil spills in U.S. history.

Figure 1. The oil spill on April 25, 2010, as seen by the MODIS instrument on NASA's Aqua spacecraft. Sun glint on the water at this hour happened to be just at the right angle to light up the spill dramatically. Image credit: NASA.

Figure 2. The oil spill on April 27, 2010, as seen by the MODIS instrument on NASA's Aqua spacecraft. The sun angle was not as favorable during this overpass to see the oil spill. The ability to detect oil slicks in photo-like satellite images is very sensitive to the viewing geometry--the angles between the surface, the Sun, and the satellite--at the time of the image. If the slick happens to be located in the sun glint part of the image, it may be very visible, but if not, it can be faint or even impossible to see.

The winds turn unfriendly
The winds have been relatively kind in the week since the Deepwater Horizon explosion, with offshore winds occurring frequently enough to keep the oil spill at least 20 miles from land. However, beginning today (Thursday), NOAA predicts that on-shore winds out of the southeast will increase to 15-20 knots, and strengthen to 20-25 knots tonight through Saturday night. These winds should be able to push the oil slick close to or on the coast by this weekend, along the Louisiana's Mississippi River "bird's foot" visible in the satellite images above. The winds will weaken to 10-20 knots on Sunday through Monday, but remain on-shore. It is not until Tuesday that offshore winds are expected, when a strong cold front should move into the Gulf of Mexico. These offshore winds will last for two days, then high pressure is expected to build in, bringing relatively light winds that should cause little transport of the oil spill for the final portion of next week. My guess is that the winds will not be able to push the oil all the way to the Florida Panhandle coast over the next ten days, but coastal areas from eastern Louisiana to Alabama will be at risk of getting oil.

Oil a long-range threat to southwest and southeast Florida, Cuba, and the Bahamas
The surface ocean currents that transport the oil are driven by the wind and by the large scale ocean current structure of the Gulf of Mexico. The latest surface ocean current forecast (Figure 3) from NOAA's RTOFS model indicates a complicated current structure along the Gulf Coast over the next seven days, making it difficult to predict exactly where the oil slick might go. The warm Loop Current enters the Gulf from the south and loops around to the southeast to exit through the Florida Keys. A counter-clockwise rotating cool eddy is located a few hundred miles south of the Florida Panhandle, and a clockwise-rotating warm eddy is located south of Louisiana's Mississippi Delta. If next Tuesday's cold front brings strong enough northwesterly winds to the oil spill region, it is possible that a portion of the spill will get caught in the circulation of these two eddies and sucked southwards into the Loop Current. If this occurs, the oil would be move relatively rapidly at 2-4 mph to the southeast and then eastwards through the Keys, potentially fouling beaches in the Keys, northwest Cuba, the southwest and southeast coasts of Florida, and the western Bahamas. Based on the movement of the spill earlier this week during offshore winds, I don't think the spill will be able to make it into the Loop Current next week. However, if the oil keeps spewing from the ocean floor for many months, eventually a wind pattern will set up that will take the oil into the Loop Current. This would most likely happen if a persistent trough of low pressure settles over the East Coast in May, or if a tropical storm makes landfall along the Florida Panhandle this summer. We're fortunate that there are no hurricanes to worry about right now, as the strong winds and storm surge of a hurricane would be able to drive the oil far inland along a wide swath of coast.

Figure 3. Surface ocean current forecast for 8pm Thursday from NOAA's RTOFS model. Forecast was made at 8 p.m. EDT on Tuesday, April 27, 2010.

Oil and coal are essential to modern society, and we need to continue extracting and transporting these fossil fuels to sustain our economy. However, we also need to be aware that the price we pay at the pump for gasoline does not include such expenses as the environmental damage from oil spills, nor the pollution from burning fossil fuels. Any debate about the costs of moving to more expensive but cleaner forms of energy needs to be honest about the tremendous costs due to environmental destruction and pollution that the mining and transport of fossil fuels cause -- not to mention the death toll from oil drilling operations, oil refinery accidents, crashes of oil tanker trucks, and wars fought over oil.

Figure 4. Fire boat response crews battle the blazing remnants of the offshore oil rig Deepwater Horizon, April 21, 2010. Note the list of the platform. Image credit: USCG.


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