Richard Turner: Could a 'superstorm' happen in NZ

Photo / APN

"Superstorm" Sandy was incredibly huge - the largest Atlantic hurricane on record with hurricane-force winds more than 1500km across at its widest point.

Some have dubbed it a "superstorm" because several factors combined to make it so intense over such a big area.

Sea-surface temperatures were warmer than normal for that time of year, it merged with a stalled Arctic front and a huge anticyclone in the Atlantic steered it towards the US East Coast at right angles, allowing for the build-up of a large storm surge.

The important thing to remember about Sandy is that while the winds and heavy rain caused damage and disruption, it was the storm surge - 4m in places - that caused most of the really severe damage and disruption.

Amazingly, heavy snow associated with the Arctic front was also a source of major problems with the storm.

New Zealand is fortunate not to have experienced anything comparable to Sandy. But from time to time we do feel the effects of post-tropical cyclones, such as Bola in 1988, which can cause considerable damage - although not on the widespread scale of Sandy.

We are also lucky that by the time a post-tropical cyclone reaches New Zealand, it has passed over cooler sea-surface temperatures, which help to lessen its intensity.

Assessing the role climate change played in magnifying the effects of Hurricane Sandy - and what that might mean for the future, including New Zealand - is a complex issue and subject to ongoing research.

The Intergovernmental Panel on Climate Change Fifth Assessment report, issued in September, says it is likely that in this century there may be fewer tropical cyclones but that they could be more intense.

Warmer sea-surface temperatures should allow intensities to be sustained for longer and sea-level rise will make storm-surge worse.

In New Zealand, Niwa and GNS Science have developed a tool called RiskScape, which estimates asset impacts and losses for a range of natural hazards.

We are interested in looking at how buildings and infrastructure are affected by extreme weather events and collect survey data after windstorms on building types, cladding characteristics, roof types, windows, exposure to wind and how much and what type of damage occurs.

What we learn from these surveys can help local government understand the vulnerability of buildings and quantify the risk of different natural hazards in their regions.

Dr Richard Turner, meteorologist, National Institute of Water and Atmosphere.