Storm Surge

Unique identifier / Notation

MH0027

Synonyms

Not identified.

A storm surge reflects the difference between the actual water level under the influence of a meteorological disturbance (storm tide) and the level which would have occurred in the absence of the meteorological disturbance (i.e., astronomical tide) (WMO, 2008, 2011, 2017).

Primary reference(s)

WMO, 2008. Technical Regulations, Volume III: Hydrology, WMO No. 49. World Meteorological Organization (WMO). Accessed 26 November 2019.

WMO, 2011. Guide to Storm Surge Forecasting, WMO No. 1076. World Meteorological Organization (WMO). Accessed 12 August 2020.

WMO, 2017. Regional Association IV – Hurricane Operational Plan for North America, Central America and the Caribbean, WMO-No. 1163. World Meteorological Organization (WMO). Accessed 26 November 2019.

Additional scientific description

A storm surge is the rise in seawater level caused solely by a storm. It is the abnormal rise in seawater level during a storm, measured as the height of the water above the normal predicted astronomical tide. The surge is caused primarily by a storm’s winds pushing water onshore. The amplitude of the storm surge at any given location depends on the orientation of the coastline with the storm track, the intensity, size, and speed of the storm, and the local bathymetry (NOAA, 2019a).

This is illustrated in the graphic below (NOAA, 2019a). A storm tide is the water level that results from the combination of the storm surge and the normal (astronomical) tide. A 3-metre (9.8 feet) storm surge on top of a high tide that is 2 metres (6.6 feet) above the mean sea level will produce a storm tide that is 5 metres (16.4 feet) above mean sea level. Storm surge should not be confused with storm tide. This rise in water level can cause extreme flooding in coastal areas, resulting from storm tides reaching up to 6 meters (20 feet) or more in some cases (NOAA, 2019b).

An illustration showing the difference in storm surges and storm tides — Storm surge vs. storm tide (NOAA, 2019.)

Metrics and numeric limits

Not available.

Key relevant UN convention / multilateral treaty

Not available.

Examples of drivers, outcomes and risk management

On top of a storm tide are pounding waves generated by the powerful winds. The area of seawater flooding may extend along the coast for over 100 km, with water pushing several kilometres inland if the land is low lying. The combined effects of the storm tide and surface waves can destroy buildings, wash away roads and run ships aground (Australian Government, 2020).

Examples of National Alerting Parameters include storm surge warning issued in Canada (Government of Canada, 2019) and an Advisory for storm surge watch/warning issued by the World Meteorological Organization (WMO, 2017).