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What precisely do we mean by a storm surge: what are its key indicators?

The following question is the first of two from a public body dedicated to disaster planning and preparedness:

What precisely do we mean by a storm surge: what are its key indicators?

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Storm surge is associated with low pressure weather systems: Storms and Cyclones. There is also a special type associated with earthquakes called a Tsunami.

Normal storm surge is made up of two components:

  1. 'pressure surge' which is an increase in the sea level due to the lower atmospheric pressure allowing the sea water to expand.

  2. 'wind surge' which is the larger of the two components is caused by strong winds on the surface of the sea forcing water in one direction causing it to 'pile up' near the centre of the storm.

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As a storm nears land strong winds create large waves which when breaking can also add to the storm surge. If the storm makes land near an estuary then the large amounts of rainfall from the storm can enter the river system and also raise water levels prior to the storm surge hitting land. Another key component in determining the impact of storm surge is the tide level at the time the surge makes land. Storm surge at low tide may only be similar to a high tide. However a simultaneous high tide and surge may result in an extremely high water level.

There are various other factors which determine the severity of a storm surge including bathymetry (topography of the sea bed), coastline shape and the size and speed of the storm.

The impact of storm surge is generally measured as the difference between the predicted tide level and the actual tide level. Tide gauges will tend to be located in Ports and key coastal settlements. Storm surge prediction during a storm event is used in the US to warn citizens of danger and other countries such as Japan have Tsunami warning systems in place.

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Asked:
2013-12-06 16:56:23 +0000
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Last updated:
Dec 09 '13