Severe flash floods in Mallorca

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Overnight 9/10 October 2018 severe storms caused devastating flash floods on the Spanish island of Mallorca.

Severe flash floods in Mallorca
Date & Time
09 October 2018 09:55 UTC–10 October 02:40 UTC
Satellites
Meteosat-11, Metop-A, Suomi-NPP, NOAA-19
Instruments
SEVIRI, AVHRR, VIIRS
Channels/Products
Airmass RGB, High Resolution Visible, Infrared, Sandwich Product, Day Microphysics RGB, Cloud Phase RGB, Severe Convection RGB, Cloud RGB, Multi-sensor Precipitation Estimate (MPE), NWC SAF Convective Rainfall Rate (CRR).

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, top right, click to expand) 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.


Figure 2: Meteosat-11 Airmass RGB animation, 9 October 09:55 UTC–10 Oct 02:40 UTC. Download animation (MP4, 4 MB).

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.


Figure 3: Meteosat-11 HRV Cloud RGB animation, 9 October 09:55 UTC–17:10 UTC. Download animation (MP4, 4 MB).
Figure 4
 
Figure 4: Meteosat-11 IR10.8, 9 Oct, 17:40 UTC

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 35 mm/h).

Precipitation Product comparison
Met-11 Water Vapour with MPE product Met-11 Water Vapour with NWCSAF CRR product
Figure 5: Meteosat-11 Water Vapour images with Multi-sensor Precipitation Estimate and NWC SAF Convective Rainfall Rate products.

Cloud top features are even better seen in the higher resolution images of the polar orbiting satellites.

At 12:24 UTC (before the heavy rain hit Mallorca) overshooting tops, cold-U shapes and an over-anvil ice plume could be seen on the 750 m spatial resolution NPP/VIIRS Sandwich image (Figure 6). At that time the storm systems were south-west of the island.

Figure 6
 
Figure 6: Suomi-NPP Sandwich product (VIS0.67/IR10.8 blended image), 09 October, 12:24 UTC.
 

The colour shades of the Suomi-NPP VIIRS Day Microphysics RGB (red-orange), Suomi-NPP VIIRS Cloud Phase RGB (bright cyan) and Metosat-11 SEVIRI Convection RGB (yellow) confirm the presence of small particles on the storm top (Figures 7, 8 and 9), associated with intense updraft activities.

Figure 7: Suomi-NPP, 09 October, 12:24 UTC
VIIRS Day Microphysics RGB (created with the NIR1.6 channel)
Figure 8: Suomi-NPP, 09 October, 12:24 UTC
VIIRS Cloud Phase RGB
Figure 9
 
Figure 9: Meteoesat-11 Severe Convection RGB, 09 October, 12:30 UTC
 

On the NOAA-19 AVHRR Sandwich image (Figure 10) and Cloud RGB (Figure 11) from 15:11 UTC, the systems which dropped 233 mm of rain in Colònia de Sant Pere, can be clearly seen over the island.

Figure 10: NOAA-19, 09 October, 15:11 UTC
AVHRR sandwich product (VIS0.63/IR10.8 blended image)
Figure 11: NOAA-19, 09 October, 15:11 UTC
AVHRR Cloud RGB

Five hours later, around 20:00 UTC, Metop-A IR10.8 image (Figure 12) shows that the more severe systems had moved towards the north-east, away from the island.

Figure 12
 
Figure 13: Metop-A IR10.8, 9 October, 20:01 UTC
 
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