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Friday, April 30, 2010

Jeff Masters' Wunderblog: Gulf of Mexico oil spill hits Louisiana coast

  Gulf of Mexico oil spill hits Louisiana coast

by Jeff Masters, Wunder Blog, April 30, 2010

The oil slick from the ruptured well due to the April 20, 2010, explosion and sinking of the offshore oil rig Deepwater Horizon has reached the Louisiana coast near the mouth of the Mississippi River. Strong southeasterly winds blowing at 20-25 knots will continue through Sunday, which will push a large amount of oil onto most of the eastern Louisiana coast from the mouth of the Mississippi River northwards to the Mississippi border. It is likely that the Mississippi coast will see the arrival of oil by Saturday night or Sunday. 

On Monday, the winds shift to southwesterly, but weaken. The wind shift will allow oil to move eastwards towards Alabama and the Florida Panhandle, but at just 1 mph or so. The winds remain southwesterly through Tuesday, which should allow the oil to reach Alabama by Monday and possibly the extreme western Florida Panhandle by Tuesday. On Tuesday night, a cold front is expected to move over the Gulf of Mexico, bringing offshore northwesterly winds. These offshore winds will last for two days and blow the oil slick 5- 10 miles offshore. High pressure is expected to build in late next week, bringing relatively light offshore winds that should cause little transport of the oil spill for the final portion of next week.

Figure 1. The oil spill on April 29, 2010, as seen by the MODIS instrument on NASA's Terra spacecraft. A tendril of oil is beginning to touch the Mississippi River "bird's foot" in Louisiana. Sun glint on the water at this hour happened to be just at the right angle to light up the spill dramatically. Image credit: University of Wisconsin.

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 America's worst oil spill, 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 20% of the 11,000,000 gallons spilled in the Exxon Valdez disaster.

Figure 2. Previous location and forecast location for today of the Deepwater Horizon oil spill. Image credit: NOAA Office of Response and Restoration.

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 shows a complicated current structure along the Gulf Coast over the next seven days. By Tuesday night, when the winds shift to northwesterly (offshore), the forecast calls for surface currents of about 1 m/s (roughly 2 mph) to transport oil to the southeast from the site of the blowout. There is a danger that the oil thus transported could make it all the way south to the Loop Current, since offshore winds are now expected to last Tuesday through Friday of next week. The warm Loop Current enters the Gulf from the south and loops around to the southeast to exit through the Florida Keys, where it becomes the Gulf Stream. Oil caught in the Loop Current would 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. I don't think the spill will be able to make it into the Loop Current next week, since it has to travel about 120 miles south-southeast from the blowout location to reach the Loop Current. The duration and strength of next week's offshore winds are probably capable of pushing the oil slick only half way to the Loop Current. However, that may be close enough so that the oil will reach the Loop Current the following week, unless strong onshore winds develop again. The long range wind forecast is too uncertain to put odds on the possibilities at this point. If the oil keeps spewing from the ocean floor for many months, though, 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. Any oil that does make it into the Loop Current will suffer significant dispersion before it makes landfall in Cuba, Florida, or the Bahamas, and far less oil will foul these shores compared to what the Louisiana coast is experiencing this weekend.

Figure 3. Surface ocean current forecast for 8pm EDT Tuesday, May 4 from the NOAA's RTOFS model run made at 8 pm EDT on Wednesday, April 28, 2010. Note that on Tuesday, northwest winds are expected to create surface currents of about 1 m/s (roughly 2 mph) from the site of the spill towards the southeast. It is possible that these currents will be strong enough to transport oil far enough south that it will enter the Loop Current, which would then transport the oil into northwest Cuba, the Florida Keys, and South Florida.


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