Exceptional events of recent years

As shown in the previous section, time series reveal that in recent decades there has been a change in the wind climate in some regions of the world which has resulted in a higher windstorm hazard.

Besides the quantitative increase in the windstorm exposure in areas that were already known to be at risk, exceptional meteorological events have provided further indications that processes of change are taking place in the atmosphere.

Tropical cyclone in the Mediterranean in January 1995

Tropical cyclones in the Mediterranean — and especially in the winter half-year — are events that should not really happen at all given the common understanding of how they start. Nevertheless, on 14 January 1995 a cloud vortex began developing in the southern part of the Mediterranean with all the features of a typical Atlantic hurricane: cloud structure, central pressure (minimum of 988 hPa) and maximum wind speed (gusts exceeding 170 km/h) were very close to a Category 1 hurricane on the Saffir-Simpson Scale.

As there are few measured data from the centre of the cyclone, there is no way of saying with any scientific certainty whether the cyclone really had the internal convection structure of a tropical storm or whether the event was simply a particularly intense extratropical storm.

On the island of Sicily, precipitation depths of up to 514 mm in 48 hours and hurricane force winds caused severe property damage in some places. The storm then moved southwards to Libya, dissipating shortly after landfall in the Gulf of Sirte.

Typhoon Vamei: a tropical cyclone near the equator in December 2001

As a result of the very low level or complete lack of Coriolis force in equatorial ocean regions — strips of ocean north and south of the equator each some 300 km wide — they were long considered devoid of tropical cyclones.

In December 2001, this common doctrine was disproved by an event such as had not been seen in more than a hundred years. On 27 December 2001, Typhoon Vamei developed near Singapore with a rotation centre at 1.5°N. With a convective cloud vortex 200 km in diameter, the storm's impact zone extended into the latitudes south of the equator.

Direct measurements showed that the wind attained speeds of over 190 km/h in gusts. Most of the damage that was caused involved ships that were surprised by the unexpectedly high intensity of the storm.

Hurricane Catarina off the coast of Brazil in March 2004

In March 2004, a storm system developed off the coast of Brazil that bore the characteristic features of a tropical cyclone and grew in intensity to a full-blown Category 1 hurricane on the Saffir-Simpson Scale. This region had also been considered hurricane-free because of the low temperatures in the South Atlantic. The final meteorological evaluation of "Hurricane" Catarina and the analysis of its birth will keep scientists busy for quite some time to come.

Although an answer to the question of how this unusual windstorm came about has still to be found, there is no doubt about the extent of damage it caused: 40,000 damaged buildings (of a total of 125,000 buildings) in Catarina's landfall area and destruction in the agricultural sector to the tune of several tens of million US dollars.