The Mesoscale Convective System
If one analyzes the convective activity around the island one can identify the formation of an organized convective system at 6-7 UTC to the southwest of the island (Figure 8). This system (that included individual cells as referred above) moved towards the island, being over land between 10 and 12:30 UTC and dissipating after 13 UTC. Therefore, from the 6 to 7 hours of its activity, 2.5 h happened over Madeira Island.
Figure 8: Cloud type product from meteosat 9 on 20/06/2010, from 06:00 to 14:00 UTC (every hour).
Regarding the extension of the system, the area of cloud top temperature below -35°C extends for around 350 km in the axis of maximum extent (Figure 9). This fits the criteria for a mesoscale convective system (MCS) which, for oval-like systems, sets a threshold of 200 km for the maximum extension of the area with cloud top temperature below -32°C (eg, AEMET, 1999). Despite there is no known climatology of MCS over this region of the North Atlantic, the time length of this system is in line with the 5.5 hours duration that Morel and Senesi (2002) found for an average MCS detected by satellite in Europe.
Figure 9: Meteosat 9 Infrared 10.8 on 20/02/2010 at 11 UTC, overlaid with two-end arrow for MCS extension.