"Definitely a large and powerful storm"

The world was watching Hurricane Irene leave a trail of destruction on the Bahamas and then approach the US East coast before making landfall in North Carolina on early Saturday morning, CET, and passing New York. As of current information, 21 people died through the event, but at least in New York the storm caused less damage than expected. We spoke to our expert Markus Stowasser, meteorologist in the Research and Development team at Allianz Re’s Cat Management, to understand better the characteristics of this event.



Munich, ---

Mr. Stowasser, what type of event is “Irene”?

Markus Stowasser: Irene was definitely a large and powerful storm. At its peak, hurricane-force winds extended outward up to 150 kilometers from the center and tropical storm force winds extended outward to 400 kilometers.

It approached the US East Coast as a Category 2 hurricane when making landfall in North Carolina and then weakened down to a Category 1 storm before it reached the New York area. The storm reached peak wind speed of 195 km/h over the open sea and 140 km/h at is first landfall in North Carolina. In the New York area the winds were down to 95 km/h below hurricane strength.

But the potential danger doesn’t only come from the wind forces, but also from widespread heavy rainfalls in excess of 200 mm, causing extreme flooding. Also the hurricane storm surge causing rising sea levels in coastal areas was a point of concern. Now Irene has significantly weakened and been downgraded to a post-tropical storm.

How typical are these types of events for the area?

Stowasser: Hurricanes affecting the southeast coast of the US are not rare events since warm waters which fuel hurricanes extend far north along the coastline in the hurricane season. Further north, hurricane strikes are less common since cooler waters or interaction with land usually cause a weakening of the hurricanes.

Historically, a total of nine storms have had first landfalls in New England since 1900. There were five storms of Category 3 strength over land: the 1938 Great New England Hurricane, the 1944 Great Atlantic Hurricane, Hurricanes Carol and Edna in 1954, and Hurricane Gloria in 1985.

With the exception of Hurricane Edna, all of these storms made their landfall along New York’s Long Island coastline. Due to the high population density along the northern East Coast these hurricanes had a high damage potential due to their strong winds and storm surges.

What was the reason for the comparably low impact of Irene in the New York City area?

Stowasser: It is a combination of the development of the storm on one the one hand – it weakened as it moved along the coastline mainly due to dry air which was caught into Irene’s circulation – and the prevention and protection measures conducted by the regional authorities. It was certainly important to evacuate at-risk areas to protect lives.

But still, exposed property could only be protected to a certain extent. The power interruptions, for examples, resulted from the fact that in the US, power lines run above the ground. This, of course, exposes them strongly to the elements, and in case of a large storm, power failure is no surprise.

Are there other storms currently building that might have considerable loss potential?

Stowasser: We are still in the most active phase of the Atlantic hurricane season which lasts till October. Significant activity is expected for the remainder of the season since conductive atmospheric and oceanic conditions are in place over the tropical Atlantic Ocean and Caribbean Sea. Sea surface temperatures in these regions are well above the long-term average.

Tropical storm Jose just hit Bermuda and the twelfth tropical depression of this year’s season formed today in the far eastern Atlantic to the south of the Cape Verde islands has now already grown into Tropical Storm Katia. The extent of any damage the upcoming storms may cause certaingly can not be predicted now since this depends strongly on the exact path and strength of the systems.

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