Saturday, September 13, 2008

How much energy is there in a hurricane?

Thank Gustav It’s Saturday

Yes Gustav is the G word of the day. Why would we thank Gustav for being green when in fact he was the hurricane that hit Louisiana on Labor Day? Well first Gustav is a Swedish name for the “staff of the gods” and maybe the gods were trying to tell us that increasing the ocean temperature helps hurricanes form and intensify. The scale or category of hurricanes is measured from 1 to 5 with 5 being the most powerful. The scale named the Saffir Simpson scale was developed in 1971 by a Structural Engineer named Herbert Saffir and a meteorologist named Bob Simpson. Bob Simpson was the director of the National Hurricane Center and Herb Saffir was interested in designing inexpensive hurricane resistant housing. They could of called their hurricane scale the Herb and Bob scale but then who would have taken them seriously?

The amount of power contained and hence released by a hurricane is proportional to the cube of the velocity of the winds ge nerated by the hurricane. Therefore a category 5 storm with winds of greater than 156 miles per hour has 430 percent of the power of a category 2 storm with winds greater than 96 miles per hour. The residents of the Gulf Coast were indeed fortunate that Hurricane Gustav had lessened in intensity to a Category 2 by the time it hit land. 96 mile per hour winds are still not something to sneeze at. I actually have never tried to sneeze into a powerful wind, perhaps Newton’s laws of motion would cause one to sneeze inward rather than outward.
There are sceptics who believe that the increase in global warming gases in our atmosphere have nothing to do with hurricanes and that all hurricanes just come and go in cycles. There is likely a cycle between periods of fewer hurricanes and periods of increased hurricane activity but the warming of the ocean by a degree or two will have a significant influence on the intensity and severity of each hurricane. The hurricane gains strength when it is over warm water and dissipates its strength by traversing land or cooler waters. All the added carbon dioxide and other greenhouse gases will indeed increase earth's temperature by a degree or more in the next fifty years and folks living in Florida and the gulf coast will have to live with more severe hurricanes. In fact the Saffir Simpson scale may need to expand to a category 6 hurricane but this is purely academic as a category 5 hurricane will damage just about every building in its path.We are fortunate that Gustuv moved across the gulf in pretty rapid fashion with a forward motion of the eye that was between 15 and 18 miles per hour. This more rapid movement prevented Gustav from exceeding a category 2 when it made landfall on the Louisiana coast. Other factors that influence the intensity of the hurricane besides ocean temperature and the speed the eye is traveling is the amount of shear the hurricane experiences in the upper atmosphere by other weather systems. In the case of Gustav there was another weather system that did moderate the hurricane by the presence of counter flowing winds above Gustav. We are indeed fortunate that Gustav only caused $10 billion in damages and there was little loss of life. As Gustav did not reach a category 5 storm his name was not retired and Gustav will live to frighten us again in a future hurricane season. Perhaps the folks who name hurricanes will also use the names herb and Bob in the future.