Bunker atmosphere

As the peak months of the Atlantic hurricane season approach, the National Oceanic and Atmospheric Administration -- the US federal agency that stands sentinel to inclement weather -- is advising coastline dwellers to hunker down.

The organisation is predicting an 85% chance of an above-normal 2007 Atlantic hurricane season, a 10% chance of a near-normal season, and only a 5% chance of a below-normal season.

A perfect storm

The prediction for an above-normal hurricane season reflects the combination of two main climate factors:

• The continuation of conditions that have been conducive to above-normal Atlantic hurricane seasons since 1995. Atlantic hurricane seasons are secular in nature, meaning there are usually decades of generally above-normal or below-normal activity.
• The continued La Niña-like pattern of tropical convection. There is a slightly greater than 50% chance that La Niña will develop during the peak of the hurricane season. La Niña favours more Atlantic hurricanes and El Niño favours fewer hurricanes.

In addition, temperatures in the western tropical Atlantic and Caribbean Sea are warmer than usual. This combination of conditions produces high levels of Atlantic hurricane activity.

Felix, Gabrielle and Humberto

So far this season, there have been five Atlantic named storms -- Andrea, Barry, Chantal, Dean and Erin.  Dean was upgraded to the first hurricane of the 2007 season on August 16.

The 2007 outlook calls for a likely range of 13-16 named storms, 7-9 hurricanes, and 3-5 major hurricanes. If these forecasts prove  to be optimistic, the US National Hurricane Center may even run out of names for the hurricanes and use the Greek alphabet to classify the phenomena.

Tempestuous autumnal weather is now the norm. The 2007 season is expected to become the tenth 'above-normal' season since the current active hurricane era began in 1995. That statistic enhances the sense that the United States escaped lightly last year: meteorologists declared 2006 to be a 'near-normal' season.

Predicting the number, intensity and eventual location of hurricanes remains difficult. There are a couple of certainties: the majority of this year's tropical storms and hurricanes are expected to form over the tropical Atlantic Ocean and track westward toward the Caribbean Sea or the United States as they strengthen.

But the elements are fickle. Hurricane-spawned disasters can occur even in years with near-normal or below-normal levels of activity. If the Americas are lucky, the 2007 hurricane season may consist of several hurricanes hitting sparsely populated areas rather than one major hurricane hitting a heavily populated area.