Meteotsunami resulting from the propagation of synoptic-scale weather systems

From time to time in conditions of light swell and balmy weather, long waves of up to I m in height and several minutes period occur on the eastern seaboard of New Zealand. These waves are an insidious threat to navigation because they cause set-down in vessels navigating to berth, thus reducing their under-keel clearance. The events are strongly correlated with low-pressure systems that emerge from the tropics and propagate southwards 1000 km or more to the east of New Zealand. The speed of propagation of the weather systems is generally of the order of 20 km/h, which is well below the long wave speed of 800 km/h, but is close to the group velocity of swell waves in deep water. (C) 2009 Elsevier Ltd. All rights reserved.