Busy ’06 hurricane season predicted

Two leading tropical cyclone forecasters are predicting a very active 2006 Atlantic Basin hurricane season.

In a report released this week, Philip Klotzbach and William Gray from the Department of Atmospheric Science at Colorado State University forecast 17 named storms, nine hurricanes and five intense hurricanes of Category 3 or higher next year.

‘All predictors are calling for an active season,’ said the report, citing warm sea surface temperatures, lower-than-normal sea level pressure in the Gulf of Mexico between September and November of this year, the unlikelihood of an El Niño in the Pacific Ocean in 2006, and other predictors.

Mr. Gray has been making the December tropical season forecast for the following year for 23 years, but this was the first report in which Mr. Klotzbach was listed as first author.

While many of the CSU forecasts have been fairly accurate, last year’s predictions failed to anticipate the record-setting 2005 hurricane season.

Last December Mr. Gray and Mr. Klotzbach predicted 11 named storms (there were 26), six hurricanes (there were 14) and three major hurricanes (there were seven) during the 2005 hurricane season.

The forecasts are based on statistical methodology derived from 52 years of past data.

They are also based on a separate study of analogue, or parallel, years.

‘For this early December extended range forecast, we project atmospheric and oceanic conditions for August through October 2006 and determine which of the prior years in our databases have distinct trends in key environmental conditions, which are similar to current October-November 2005 trends,’ the report stated.

The best analogue years for 2006 in the data base include 1961, 1967, 1996, 1999 and 2003. All of those years except 1967 produced higher than average numbers in named storms, hurricanes and intense hurricanes.

Mr. Klotzbach and Mr. Gray’s forecast tropical cyclone activity for the Atlantic in 2006 is almost double – and in some aspects, more than double – than the average between the years 1950 and 2000.

The forecast also estimated a 98 per cent chance of a 2006 hurricane making landfall in the United States, and an 81 per cent chance of a major hurricane making landfall in the US.

The report discounted the role global warming has played in the increase of major hurricanes in 2004 and 2005.

‘Despite the global warming of the sea surface of about 0.3°C that has taken place over the last three decades, the global number of hurricanes and their intensity have not shown increases in recent years except for the Atlantic,’ the report stated.

‘There have been similar past periods (1940s-1950s) when the Atlantic was just as active as in recent years.’

The authors of the report said the increase in major hurricanes is primarily the result of a cyclical multi-decadal increase in the strength of the Atlantic Ocean thermohaline circulation.

The circulation is not directly related to global temperature increase, and is believed to be driven by changes in ocean salinity, the report said.

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