Hurricane forecast stays the same

Scientists Philip Klozbach and William Gray from Colorado State University have maintained their predictions made last December that call for another above-normal number of hurricanes in the Atlantic basin in 2006.

In their report issued 4 April, the scientists predict there will be 17 named storms, nine hurricanes and five major hurricanes of Category 3 or above this year. The average between the years 1950 and 2000 has been 9.6 named storms, 5.9 hurricanes and 2.3 major hurricanes.

There is an above-average risk of a landfall of a major hurricane somewhere in the Caribbean, and a 64 per cent risk – more than twice the average for the last century – of a major hurricane making landfall somewhere on the United States East Coast.

The forecasts are based on statistical methodology derived from 52 years of past data and a separate study of analogue years which have similar precursor air circulation features to the current season, the report states.

One of the conditions that statistically contributes to increased hurricane activity in the Atlantic basin is a La Niña condition in the Pacific Ocean.

La Niña, which is a cyclical period of lower than normal sea surface temperatures in the tropical Pacific, reduces vertical sheer in the Atlantic Ocean, providing more favourable conditions for tropical cyclone development.

Mr. Klozbach and Mr. Gray stated that a weak La Niña is being observed, and that neutral or weak La Niña conditions are expected to persist for the next four to six months.

As active as the 2006 hurricane season is forecast to be by the two scientists, it is not predicted to surpass last year’s record-breaking year, which had 27 names storms and 15 hurricanes.

Even though they predict a higher than normal chance of a US landfall of a major hurricane his year, they do not think as many major hurricanes will come ashore in the US as did in the past two years.

‘The historical records and the laws of statistics indicate that the probability of seeing another two consecutive hurricane seasons like 2004-2005 is very low,’ their report states. ‘Even though we expect to see the current active period of Atlantic major hurricane activity to continue for another 15 to 20 years, it is statistically unlikely that the coming 2006 and 2007 hurricane seasons, or the seasons which follow, will have the number of major hurricane US landfall events as we have seen in 2004-2005.’

The scientists note that the probability of a hurricane landfall for any specific location along the US coast is very low, reflecting the fact that most US coastal areas will not feel the effects of a hurricane no matter how active a season is.

‘However, it must also be emphasised that a low landfall probability does not ensure that hurricanes will not come ashore,’ they stated.

Mr. Klozbach and Mr. Gray downplay the possible role of global warming on the increased major hurricane activity in recent years, and instead see it as a result of a cyclical multi-decadal increase in the strength in Atlantic Ocean thermohaline circulation, which is not directly related to global temperature increase.

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

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