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A look at the hurricane and typhoon season
An assessment of the cyclone season of 2011
Last Modified: 22 Sep 2011 11:30
The aftermath of Tropical Storm Nanmadol in Pingtung, China {Getty/Gallo]

There is always great interest in the predicted number of hurricanes and typhoons each season. In recent years the predictions have taken on added significance because of the links between this cyclone activity and global warming. So how does the 2011 season measure up?


Looking first at the Atlantic hurricane season: here, activity was expected to be above average. Yet, for the first time in more than 150 years, the first eight storms failed to attain hurricane status (mean wind speeds of 119 kph).


Since the beginning of June, when Tropical Storm Arlene developed in the Gulf of Mexico, there have been just three hurricanes.  Two were major hurricanes: Irene – the strongest, so far, with winds of 195 kph - and Katia, plus the less intense Maria.


NOAA defines a ‘normal’ season as one with nine to 12 named storms, of which five to seven reach hurricane strength and one to three develop into major hurricanes (winds in excess of 180 kph). Totals for 2011 stand at 15, five and two respectively.


With the season not officially over until November, there is plenty of time for totals to reach those predicted by NOAA before the start of the season:  12 to 18, six to 10 and three to six.


In the Pacific Ocean, where there is a year-long season, the current tally stands at 16 cyclones, seven typhoons and three super typhoons. These figures are open to some debate as different meteorological agencies have slightly different criteria for their definition.


There are many organisations issuing forecasts for the Pacific, but the general trend has been for the predicted activity to be around average. The London-based Tropical Storm Risk Consortium, for example, predicted 28 tropical storms, 18 typhoons and eight super typhoons.


It is too early in the season to predict the likely outcome for the Pacific season at this time, but interest in the numbers of cyclones has become heightened as a result of links to climate change and the possibility that both hurricanes and typhoons will become more intense as the world become warmer.


On this point, there is very little evidence to suggest that the actual number of these cyclones is  linked to climate change. In any event, climate prediction models are not able to resolve these vortices sufficiently well to produce any reliable indications.


What is suggested by a warmer world, however, is that cyclone intensity will increase.  According to research at the Massachusetts Institute of Technology, over the last 30 years, the energy released by all cyclones has increased by a staggering 70 percent.  This has equated to a 15 percent increase in maximum wind speeds and a 60 percent increase in storm longevity.


With the global death toll from all cyclones in 2011 standing at around 500 and the damage estimated to be $US 12 billion, any potential increase in energy must be a cause for concern.

Source:
Al Jazeera
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