Severe flash floods in Mallorca

By Mária Putsay (Hungarian Meteorological Service), Ivan Smiljanic (SCISYS) and Sancha Lancaster (Pactum)

As the severe storm systems crossed the island more than 230 mm of rain fell in the area of Sant Llorenç in just two hours, according to the Spanish weather service AEMET. The resulting flash floods were reported to have been the most serious floods to hit Spain in the past 25 years. At least 10 people were reported to have died.

The weather situation is seen in the Meteosat-11 Airmass RGB image (Figure 1) and the animation, 9 October 09:55 UTC–10 Oct 02:40 UTC (Figure 2). The heavy rain was caused by an upper level low situated over the Iberian Peninsula and west of the Mediterranean Sea.

As seen from the animation, below the stationary upper level low several intense convective storms formed and developed during the daytime hours.

The evaluation of the convective systems can be followed more closely on the HRV Cloud RGB imagery (Figure 3). Several cells formed, developed and propagated (some from a different direction to main flow, so-called 'left-movers') over the island.

On the satellite imagery several factors indicated the possible severity of the storms:

• Cold U and cold ring shapes on the infrared imagery.
• Intense overshooting tops, gravity waves and above-anvil cirrus plume
• Presence of small ice crystals on the cloud tops.

The cold U and cold ring shapes can be clearly seen in the IR10.8 imagery, see the Meteosat-11 IR10.8 image at 17:40 UTC (Figure 4).

Confirmation of the severity of the systems also comes via the following precipitation products: the MPEF Multisensor Precipitation Estimate (MPE) and the NWCSAF Convective Rainfall Rate (CRR) product (Figure 5).

Both products suggested very intense rain events associated with observed system, where MPE in particular depicted some very localised areas of intense rainfall rates (more than 35mm/h).