Factors, II: Small scale, quasitropical cyclone over the Balearics.
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A small, quasi-tropical cyclone occurred on 12 September 1996 over the Western
Mediterranean. Intense convective activity over the region during this period produced a tornado outbreak (6) in the Balearic Islands and torrential precipitation with severe flooding over eastern mainland Spain (600 mm/24h), and over the Balearics (100 mm/24 h in Mallorca, 170 in Ibiza). Serious damages from winds were reported as the quasi-tropical cyclone crossed Mallorca with wind speeds exceeding 35 m/s (126 km/h). All operational NWP models under-predicted cyclone intensity and wind strength.
The synoptic setting of the event can be seen on slide 1, with the 'parent' or main cyclone prior to the event located east of the Balearics. This 'parent' cyclone favored intense northeasterly winds with cold advection between the Balearics and the spanish coast favouring latent heat fluxes and evaporation rates. Slide 2 shows an intense core of potential vorticity at upper levels upstream of the surface cyclone. That, together with the low level temperature field, confirms that baroclinic instability was a key factor at the initial stages of the event .
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| Synoptic overview for 9/september/1996 at 00 UTC. Left: Sea Level Pressure + temperature at 1000 hpa . Right: 500 hpa geopotential + temperature. Taken from Homar et al. (2003). |
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| Potential vorticity at 300 hpa for 9/september/1996 at 00 UTC. |
