Source

The storm developed off the US northeast coast on 2^nd January 1991 and moved northeastwards towards the UK crossing Scotland. The central pressure dropped to a minimum of approximately 946 mbar as the storm approached the UK on 5^th January (Irish Meteorological Service, 1991). By midnight, the storm was over the northeast of Scotland and the central pressure was 959 mbar. The storm then moved off over the North Sea, crossing Norway (Harwood, 2012). A strong southerly gale developed ahead of the storm and affected Ireland, southern Scotland, England, and Wales. Maximum 10-minute average wind speeds at 14 weather stations around the UK ranged from 37 to 54 knots [19–28 m/s] with gusts of 63 to 83 knots [32–43 m/s]. In Ireland (near Connemara), average 10-minute wind speeds of 60 knots [31 m/s] with gusts of up to 90 knots [46 m/s] were recorded.

The storm generated skew surges of over 1 m in the Irish sea and between 0.5 m and 1 m in the southern North Sea. Water levels exceeded the 1 in 5 year return level at two sites, both in the Irish Sea; the high water levels there were thus fairly localized. The highest return period water level was at Portpatrick and was 1 in 134 years. At Millport the water level had a return period of 1 in 81 years. The highest skew surge was at Millport and was 1.31 m (Hickey, 1997).

Waves of 30 m in height were recorded off the UK west coast and computer models suggested significant wave heights of up to 15 m on 5^th January.

Pathway

The stormy conditions during this event caused overtopping of defences in many locations around the UK, most notably in the Firth of Clyde.

Receptor and Consequence

This event is noted for causing extensive and costly damage to parts of the western and southern coasts, from Starthclyde to Sussex as sea defences were overwhelmed (Met Office, 1991). In Scotland, the Helensburgh waterfront was completely submerged and some streets flooded to a level of up to 1 m. In Millport, the sea front and promenade were flooded, and 50 m of the promenade was washed away, and many streets were covered by up to 0.35 m of water. There was extensive damage to coastal defences at Ardrossan, Helensburgh and Millport and sand dune erosion at Androssan (Hickey, 1997). There was severe coastal flooding in the Firth of Clyde totaling £7 million in damages (Kaya et al., 2005); with Rothesay, Dumbarton Central, and Dumbarton East suffering a total of £4.6 million in damages (Mcnair, 1998). This storm resulted in the commissioning of the Clyde Estuary Flood Warning system, operated by the Scottish Environment Protection Agency (SEPA) since 2001 (Kaya et al., 2005).

Gusts brought down trees and power lines, and thousands of homes were without power in Ireland and southwest England (The Canberra Times, 1991). Thirty fatalities were attributed to the storm, in the UK, Ireland and Germany (Munich RE, 2012). This included a couple walking on the beach in Brighton who were swept away. Undine was one of the costliest winter storms of the 1990’s, with estimated damages of £545 million (The Telegraph, 2014).

Summary Table

*No known sources of information available