Medicane Qendresa hits Malta and Sicily

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A Medicane (MEDIterranean hurriCANE) or Tropical-Like Cyclone (TLC) brought severe weather to parts of the Mediterranean in early November.

Medicane Qendresa hits Malta and Sicily
Date & Time
07 November 2014 03:00 UTC– 08 November 12:00 UTC
Satellites
Meteosat-10, Metop-A & B, Suomi-NPP
Instruments
SEVIRI, AVHRR, VIIRS, ASCAT
Channels/Products
Day-Night Band, Airmass RGB, HRV, ASCAT Winds, Water Vapour

By Jochen Kerkmann and Mark Higgins (EUMETSAT), Sancha Lancaster (Pactum), Hans-Peter Roesli (Switzerland), Eleftheria Tsiniari (Hellenic National Meteorological Service) and Dr Michael Sachweh

On 7 November the storm first hit Lampedusa on the island of Linosa, then Malta (at around 16.30 UTC) and then the eastern coast of Sicily before it disappeared to the east.

Gusts of 135 km/h were recorded at Lampedusa in Linosa and up to 154 km/h in Malta. Airport and ferry operations were suspended and many areas were left without power, as the storm caused damage across the three countries.

The system can be clearly seen on the a Day-Night-Band image (750 m resolution) in B/W with yellow hues of IR11.45 (band I5 at 375 m resolution) from cold-white to warm-yellowish — high cloud appears white, lower cloud and artificial light is yellowish (Figure 1, above right, click to expand, Download full resolution VIIRS image). The scene is well lit by the full moon.

The Airmass RGB animation, Met-10, 07 November 03:00 UTC–08 November 12:00 UTC (MP4, 8 MB), shows the birth of the medicane out of cut-off low and its progress across the Mediterranean. It also shows the deceleration of the rotation after the TLC hit the Catania coast.

Earlier in the week the heavy rains from the deep trough, at the origin of the cut-off, had caused Lago Maggiore in the Alps to overflow.

A branch of a polar jet stream over south western Europe headed sharply towards the south, starting to meander over Tunisia. In the Water Vapour (WV 6.2 µm) images from 6 November 18:00 UTC–8 November 00:00 UTC (Figures 2–7) the location of the jet stream is identified as a strong gradient from high to low humidity (dark stripes).

  • Met-10 Water Vapour
    Figure 2

    Met-10 Water Vapour, 6 Nov 18:00 UTC

  • Met-10 Water Vapour
    Figure 3

    Met-10 Water Vapour, 7 Nov 00:00 UTC

  • Met-10 Water Vapour
    Figure 4

    Met-10 Water Vapour, 7 Nov 06:00 UTC

  • Met-10 Water Vapour
    Figure 5

    Met-10 Water Vapour, 7 Nov 12:00 UTC

  • Met-10 Water Vapour
    Figure 6

    Met-10 Water Vapour, 7 Nov 18:00 UTC

  • Met-10 Water Vapour
    Figure 7

    Met-10 Water Vapour, 8 Nov 00:00 UTC

Water vapour imagery clearly shows the stratospheric air extruded well downwards into the troposphere indicative of strong cyclogenesis. The sequence of WV images also reveal the main stages of this development. Noteworthy features can be seen, such as baroclinic leaf, a comma head and the cloud hook (Figures 2 & 3).

Figure 8
 
Figure 8: Met-10 Airmass RGB, 7 Nov 12:00 UTC

After 12:00 UTC, the characteristic dry swirl pattern is evident (Figures 5–7), indicating that the cyclone was entering the occluded phase of its life cycle.

A scalloped pattern is clearly visible along the dark WV stripe, indicating a maximum of cyclonic shear vorticity (Figures 3 & 4 – yellow arrow).

The position of the jetstream can also be seen in the Airmass RGB image, 7 November 12:00 UTC (Figure 8) where there is a colour difference (red changes to purple – black arrows).

Figure 9 shows the storm seen from Metop-B on 07 November at 08:25 UTC. The images are the 0.6 micron channel from AVHRR and the winds are taken from ASCAT 12.5 km coastal wind product. The winds are approximately hour mean winds, showing the gross speed and direction — gusts will have been much stronger. Areas with wind greater than 74 km/h (40 knots) are shown in brown and red.

Image comparison
Metop-B AVHRR, 07 November 2014, 08:25 UTC Metop-B AVHRR with 12.5 km ASCAT winds overlay, 07 November 2014, 08:25 UTC
Figure 9: Comparison of Metop-B AVHRR images of the medicane, with and without ASCAT winds.

The animated gif of Meteosat-10 HRV imagery, from 07:00–11.45 UTC (Figure 10), shows the storm over Lampedusa.

Gif

 
Figure 10: Met-10 HRV imagery, 7 Nov 07:00–11:45 UTC
Full resolution image 10:00 UTC

Development of marine conditions using ASCAT observations

The region to the south of the low pressure centre is a region of strong pressure gradient, with resulting strong winds. The wind field near the surface can be captured by the Advanced Scatterometer (ASCAT) instruments on board the Metop satellites.

Figure 11: Metop-B ASCAT winds, 07 Nov, 08:37 UTC
Figure 12: Metop-A ASCAT winds, 07 Nov, 09:25 UTC

A close examination of the wind direction retrieved from ASCAT Metop-B (Figure 11) showed a defined vortex with maximum speed of more 50 kt (92 km/h).

Figure 13
 
Figure 13: Metop-B ASCAT winds, 07 Nov, 19:56 UTC

According to Figure 11 the centre of the system was located east of the coasts of Tunisia at about 08:37 UTC. The winds exceeded 50 kt locally to the south and southwest of the low where the wind flow converged.

We have similar vector winds observations from ASCAT on Metop-A at 09:25 UTC (Figure 12).

At about 18:00 (19:56 UTC), as the low pressure system had moved eastwards, west northwest winds of 40–45 kt maxima value were observed in the area of interest (Figure 13).

The tropical-like cyclone of 7 November 2014 seems to have been a notably severe one, with gradient wind strengths up to 75 kt over the island of Lampendusa (ICAO index LICD). This value of wind speed coincides with the data retrieved from ASCAT at the same time.

Strong winds produced high waves of about 3 m or more. The highest waves were located right of the track of the cyclone, at the “danger semicircle” as was expected.

Observations of both wave and swell height show that a wave height of 6 ft (about 3 m of total wave height) in the area between Sicily and Malta at 02:00 UTC, seem in good agreement with the model forecast.

According to the Extreme Forecast Index (EFI) values, the marine situation seems to have been unusual and dangerous, and could have been expected to generate strong swells.

Taking into account the fact that the model wave height fields showed a wave maximum area exceeding the threshold values warnings, it would be expected that warnings would be issued. Indeed, Greece, who is responsible for the provision of marine bulletins for the eastern Mediterranean Sea and Black Sea, issued a strong gale warning for Boot, Sidra Melita and Gabes.

The intensity of the wind field was quite well forecast: the cyclone lost its strength after landfall (Figure 14) at about 02:00 UTC on 8 November, and began to weaken rapidly, as seen from the Metop-B ASCAT winds on 8 November at 08:16 UTC (Figure 15).

Figure 14: SNPP Day-Night Band (DNB), 08 Nov, 01:43 UTC
Figure 15: Metop-A ASCAT winds, 08 Nov, 08:16 UTC

The models did well in forecasting the location of the storm center, the drop and timing of mean sea level pressure and the significant wave height.

The strong winds near the centre of the storm, were not well described in the models because of the rapid deepening of the cyclone.

Satellites as weather observing tools seem to offer a new dimension in the field of marine meteorology improving markedly forecasting ability.

Addendum by Dr Michael Sachweh

MSG — Rapid Scans

RGB

 
Meteosat-9 RGB, 7 November 12:00 UTC (source: RGB images created by MeteoGroup)
Download animation, 7 November 06:45 UTC–8 November 08:13 UTC (MP4, 34 MB)
Watch the animation on YouTube

The RGB animation shows the development of Medicane Qendresa as seen by Meteosat-9 5-minute rapid scans, from the birth in the area of Pantelleria to its dissipation in the area east of Sicily.

The standard RGB using the HRV and the IR10.8 channels is shown (i.e. RGB HRV-HRV-IR10.8).

In the night the images look bluish as the HRV images (which are put on the red and green beams) are not available at night. From 17:15 UTC to 05:00 UTC the images are only available at 15-min frequency, thus the imagery judders slightly during the night hours.

Dissipation of the storm

The land contact of Qendresa over eastern Sicily (overnight 7–8 November) caused a reduction of the energy, moisture and fluxes from the warm sea surface, and also led to an unbalance of the system both of which probably contributed to the quick dissipation on 8 November. Storms of this kind are very sensitive to rotational asymmetries.

Strong winds in Catania

It is interesting to note that, during the passage of Qendresa, Catania recorded very strong N to NE winds. This could be a barrier effect, from Mount Etna, which enhanced the winds on the left side of the vortex (a funnelling effect).

This northerly funnel might be the reason why the system, after hitting Sicily, moved back to the south. It would be interesting to simulate this case with high-resolution NWP models.

Radar

 
Rainfall radar, 8 November 02:00–06:00 UTC

Radar/Precipitation

As previously stated, Qendresa caused heavy precipitation in Malta and Sicily.

On 8 November, more than 100 mm in 24 hours were recorded in the Catania and Ragusa Provinces.

The animated GIF of the radar (source: Protezione Civile, Italy) nicely shows the eye as the storm passed along the east coast of Sicily, revealing the tropical storm nature of Qendresa.

Ground observations

Because of its track hitting several synop stations, Qendresa offered perfect ground truth observations of a Medicane (e.g. the pressure funnel recorded on the Island of Linosa, Italy).

Graphic width=

 
Pressure funnel recording at Bugibba, Malta
Download full resolution

The recording at Bugibba, in the north-west of Malta, perfectly shows the structure of a tropical storm:

  1. The eye-wall with average winds of 111 km/h and gusts up to 154 km/h.
  2. 15 minutes later, the eye of the storm (see pressure funnel) with totally calm conditions (no wind) with a remarkable pressure of 978.6 hPa.
  3. The second eye wall with about 50 km/h winds.

Topografic effects may have increased the wind (first eye wall) or reduced the wind (second eye wall), as the wind recording is not symmetric, unlike the pressure recording.

This photograph shows the damage north of Catania (Giardini-Naxos) from Cosimo Manitta.

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