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Black Sea storm causes ecological disaster; powerful Bay of Bengal cyclone forming

By: Dr. Jeff Masters, 3:25 PM GMT on November 12, 2007

At least five ships sunk and five others ran aground yesterday during a fierce storm that swept through the Black Sea, by Russia and the Ukraine. Five sailors drowned and as many as 17 others are missing. The Volganeft-139, an oil tanker loaded with nearly 1.3 million gallons of fuel oil, sank in the Kerch Strait between the Black Sea and the Sea of Azov, dumping over 1/2 million gallons of fuel into the water. The oil spill is a major environmental disaster for the area, and will foul local shores for years to come. The spill is about 1/20 the size of the massive Exxon Valdez oil spill of 1989.

Figure 1. Visible image from the NOAA-18 polar orbiting satellite from Saturday, November 10, 2007, at 11:21 GMT. An "L" marks the center of the developing storm that would move over the Black Sea and sink or ground ten ships. The storm formed at the tail end of a cold front to its north. Image credit: University of Bern, Switzerland.

The storm that sank these ships was an unusually powerful one for the Black Sea. The storm formed over the Mediterranean Sea along the tail end of a very strong cold front. This front was the same cold front that pushed through the North Sea on Friday, bringing winds near hurricane force, flooding in southeast England, and a storm surge over 10 feet high to the coast of the Netherlands. The new storm fed off the relatively warm waters of the Mediterranean and pushed eastward across Greece and Turkey, intensifying to 980 mb as it struck the Ukraine's Crimean Peninsula late in the morning Sunday. Simperopol, Ukraine, on the tip of the Crimean Peninsula, measured sustained winds of 54 mph, gusting to 72 mph, on Sunday afternoon. The pressure bottomed out at 980 mb. Kerch, Ukraine, on the west side of Kerch Strait, recorded sustained winds of 45 mph and a minimum pressure of 988 mb as the storm blew through. On the other side of the strait, in Anapa, Russia, sustained winds of 47 mph, gusting to 65 mph were observed. Waves up to 18 feet high buffeted the waters in the Kerch Strait. This was too much for the Volganeft-139, which was designed for river travel.

The enclosed nature of the Black Sea can produce very steep waves. According to Holquist et al. (2002), steep, short-period waves can be particularly hazardous to large ships, especially when the waves exceed 5 meters (16 feet) in height. The height of waves depends on the wind speed and the fetch or distance over which the wind blows. Also important is the degree atmospheric stability near the surface. A warm ocean with very cold air aloft will produce an unstable atmosphere with very tall turbulent eddies that will mix down the stronger winds that occur aloft. This instability peaks in November, when the air-sea temperature difference is at its greatest.

Hultquist, T.R. M.R. Dutter, and D.J. Schwab, "Reexamination of the 9–10 November 1975 “Edmund Fitzgerald” Storm Using Today’s Technology", Bulletin of the American Meteorological Society, May 2006.

The NASA Natural Hazards team has posted a nice satellite image and description of the storm.

Tropical Update
None of the reliable computer forecast models are predicting tropical cyclone formation in the Atlantic for the next seven days. I'll have a complete analysis of the outlook for the remaining 2 1/2 weeks of hurricane season later this week.

Figure 2. Tropical Cyclone Sidr at 5:30am EST 11/12/07. Image credit: Navy Research Lab, Monterey.

Tropical Cyclone Sidr is headed northwards towards a landfall in Bangladesh or India late this week, and may intensify into a Category 2 or higher storm. The Bay of Bengal has seen the world's deadliest tropical cyclones, and November is one of the region's most dangerous months. On November 12-13, 1970, a Category 4 cyclone struck Bangladesh, causing the greatest tropical cyclone disaster in world history. An estimated 350,000-550,000 people died when a devastating 34-foot storm surge funneled northwards through the Bay of Bengal into Bangladesh. The path of Tropical Cyclone Sidr beyond Wednesday is highly uncertain, with the NOGAPS and ECMWF models taking the storm northwards over a region of high oceanic heat content and into Bangladesh. The GFS model turns Sidr westwards, over a region of low oceanic heat content, into the east coast of India. Wind shear is about 10 knots over the storm, and is expected to remain 10 knots or below for the next three days. Recent satellite observations suggest that Sidr is already of hurricane strength, and may be intensifying rapidly.

Jeff Masters

Winter Weather

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