Hurricane activity in 2007 is forecast to be below the norm, says Professor Mark Saunders

US landfalling hurricane activity has been running 30%-50% above the long-term norm since 1995. Over this same period, Atlantic basin tropical storm and hurricane activity has been 40%-70% above the long-term norm.

This elevated activity is causing the reinsurance industry concern. Thus it is pleasing to report that hurricane activity in 2007 is likely to be slightly below the 1995-2006 norm levels and certainly well below the record-breaking levels seen in 2004 and 2005. The early-August updated outlook for the 2007 Atlantic hurricane season issued by Tropical Storm Risk (TSR) calls for US landfalling hurricane activity 20% above the long-term norm and Atlantic basin hurricane activity 35% above this norm. The TSR prediction also includes:

• A 72% probability of an above-normal (ie in the top one-third of years since 1950) Atlantic hurricane season, a 24% probability of a near-normal season and only a 4% chance of a below-normal season;

• 15 tropical storms for the Atlantic basin as a whole, with eight of these being hurricanes and three or four intense hurricanes;

• A 61% probability of an above-normal US landfalling hurricane season, a 30% likelihood of a near-normal season and only a 9% chance of a below-normal season;

“Hurricane activity in 2007 is likely to be slightly below the 1995-2006 norm levels and certainly well below the record-breaking levels seen in 2004-2005

• Four tropical storm strikes on the US, of which two will be hurricanes; and

• Two tropical storm strikes on the Caribbean Lesser Antilles, of which one will be a hurricane.

Since March, the TSR prediction for Atlantic basin hurricane activity has fallen slowly but steadily from 75% above-norm to 35% above-norm now. This reduction arises mainly because the outlook for August to September sea surface temperatures (SSTs) in the tropical North Atlantic has progressively fallen. SSTs in this region provide heat and moisture to power incipient storms.

The outlook for US landfalling hurricanes has also fallen from 60% above-norm in March to 20% above-norm now. The August forecast model employs July tropospheric wind anomalies over North America, the East Pacific and the North Atlantic.