Medicane over Ionian Sea causes storms in Italy and Greece

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Tropical storm-like cyclone causing storms, severe wind and high seas over Ionian Sea.

Date & Time
16 September 2020 00:00 UTC–18 September 21:00 UTC
Satellites
Meteosat-11, Metop-A, B & C
Instruments
SEVIRI, AVHRR, ASCAT
Channels/Products
Infrared Channel, Water Vapour, AVHRR Clouds RGB, HRV + IR10.8 Sandwich Product, Sea Surface Temperature, Precipitation

By Vesa Nietosvaara and Natasa Strelec Mahovic (EUMETSAT), Ildiko Szenyan (OMSZ) and Aida Alvera Azcarate (University of Liège)

A Mediterranean tropical-like cyclone, also referred to as a Medicane or a Mediterranean hurricane, named 'Ianos' by the Hellenic National Meteorological Service, started to develop over the Mediterranean Sea on 14 September, just off North African shores.

The general synoptic environment was characterised by an upper level low over the Mediterranean, where additional synoptic forcing was ensured by the 300 hPa jet-stream bringing dry air (black in water vapour image) with high vorticity values from the upper levels to the system (see Figure 1).

Figure 1
 
Figure 1: Left: Meteosat-11 IR10.8, 14 September 09:00 UTC, with 500 hPa absolute topography (blue) and Mean Sea Level Pressure (black) overlaid. Right: Meteosat-11 WV6.2, 14 September 18:00 UTC, with 300 hPa wind barbs overlaid
 

By 16 September the cyclone had intensified and strong winds developed surrounding its centre. Figure 2 shows the winds measured by the ASCAT (scatterometer) instrument on the Metop satellites, indicating wind speeds over 90 km/h (25 m/s) around the cyclone.

Figure 2
 
Figure 2: Metop ASCAT winds: a) Metop-A on 15 September, 19:25 UTC, b) Metop-C on 16 September, 08:13 UTC, c) Metop-B on 16 September, 20:19 UTC, d) Metop-C on 17 September, 19:11 UTC. Source: NESDIS
 

By early 17 September the cyclone had moved closer to the Italian coast over the Ionian Sea, with advancement of strong quasi-stationary rain bands reaching the southern shores of the Calabria region, and causing locally high precipitation amounts (Figure 3).


Figure 3: Meteosat-11 IR 10.8 Enhanced image loop, 16 September, 00:00 UTC–18 September, 11:00 UTC.

The cyclone's centre had an eye-like structure in the morning of 17 September. The Metop-B image on 17 September at 08:40 UTC (Figure 4) shows a well defined vortex centre with surrounding rain bands in the north. The rainband over Calabria is clearly visible.

Figure 4
 
Figure 4: Metop-B AVHRR Cloud RGB image (0.63 µm, 0.865 µm and 10.8 µm), 17 September 08:40 UTC
 

Later that day the cyclone's centre moved slowly towards the east, approaching west coast of Greece. The Greek Meteorological Service issued red warnings for parts of Greece for 17 and 18 September, in particular for high precipitation and lightning, and orange warnings for the wind (Figure 5).

Figure 5
 
Figure 5: Meteoalarm warnings issued by the Hellenic National Meteorological Service for 18 September
 

The whole episode took five to six days. The sequence of various development stages is shown in the Sandwich product (High Resolution Visible imagery overlaid by IR10.8 cloud top temperature information) (Figure 6). The development started within an unstable air mass, with several individual convective clusters between Sicily and the North African coast, during 13 and 14 September. On 15 September the vortex started to develop, and on 16 September it rapidly intensified, developing a clear tropical-like cyclone appearance. Finally the mature Medicane moved over the Ionian Sea to the Greek coast during 17 and 18 September.


Figure 6: Meteosat-11 Sandwich product (High Resolution Visible image overlaid with IR10.8 temperature) 13-18 September. Credit: Hungarian Meteorological Service.

During the evening of 17 September Medicane Ianos made landfall on the Greek islands and the west coasts of Greece. The Ionian Sea islands of Zakynthos, Kefalonia and Ithaca were all badly hit. Wind speeds of up to 100 km/h were reported.

On 18 September the storm travelled across mainland of Greece. Heavy precipitation and flash flooding, caused by convective storms developing within the Medicane, occurred in many places. Intensive precipitation occurred on the islands in the night and early morning.

The near-real time precipitation product H03B, generated by IR images from the SEVIRI instrument 'calibrated' by precipitation measurements from microwave satellite sensors on polar-orbiting satellites, is shown in Figure 7.


Figure 7: Near-real time precipitation product H03B (IR + MW measurements) loop, 18 September 00:00–21:00 UTC.

Later in the day a convective storm embedded into the Medicane cloud-band, causing persistent heavy precipitation over central and eastern parts of Greece. In the towns of Lamia and Karpenissi the flooding led to people being trapped by their houses and vehicles. Due to damage to the railway line, the train connection between Athens and Thessaloniki was disrupted. Hundreds of people had to be rescued from flooded buildings, especially in the region north of Athens. At least three people were reported to have been killed by the storm.

Tropical storms, including Medicanes, rely on warm underlying water to release heat into the upper atmosphere and create rotating winds. Warmer water supplies more energy, which can result in increased intensity of the storm. Therefore, it can be assumed that a major contributing factor in the development process and the intensification of Medicane Ianos, was the warm surface of the sea near where it initiated.

Figure 8 shows the Sea Surface Temperature on 12 September, before the formation of the storm and on 18 September, after the storm has passed over the sea. The L3 multi-sensor product (on the left of Figure 8) is built from bias-corrected L3 mono-sensor products at the resolution 0.02 degrees, with the following hierarchy of the datasets used: Metop-B AVHRR, SEVIRI, SLSTR, SNPP VIIRS, AVHRRL-19, AVHRRL-18, AQUA MODIS-A, TERRA MODIS, AMSR2. Missing data was reconstructed using DINEOF resulting in the right-hand image. With the storm developing and moving over the Ionian Sea, the sea surface was getting cooler. After the Medicane left, the sea surface was almost 5 deg cooler than before the storm.

Figure 8
 
Figure 8: Multi-sensor sea surface temperature (left) and SST reconstructed using DINEOF (right) for 12 September 2020 (top panel) and 18 September 2020 (bottom panel). Credit: University of Liège.
 

The photographs in Figure 9 show the ground-to-ground and cloud-to-cloud lightning caused by the Medicane in the early hours of 17 September.

Figure 9
 
Figure 9: Lightning strikes off the Calabrian coast in the early hours of 17 September. Credit: Caterina Mazzuca
 
 
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