"Medicane" hits the western Med

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  • MODIS image of the "Medicane" labelled Tropical Storm 01M by NOAA, 11:10 UTC November 9, 2011. Image: NASA.

    Eumetsat satellite image of the October 1996 "Medicane".

    The January 1995 storm. Image: NOAA

  • "Medicane" hits the western Med
    10.11.2011 16:56

     

    Anybody who flew to the Côte d'Azur or Provence this week for some autumn sunshine might have been sorely disappointed.

    An intense low pressure system developed in the western Mediterranean and became slow moving west of Corsica, dumping some torrential rainfall and generating fierce winds.

    This late in autumn the weather does tend to turn in the Mediterranean, and only a couple of weeks ago Greece and Turkey were suffering heavy rain and gales.

    This particular depression, though, was an odd one. As it developed, meteorologists watched satellite animations that showed it assuming the sort shape associated with tropical cyclones, even suggestive of a central “eye”.

    Before we get too carried away, the sea surface temperature in the Mediterranean is not high enough to create or sustain a hurricane. Near Corsica, the western Mediterranean has been at about 20 degrees Celsius this week, and hurricanes require water at close to 27 degrees beneath them.

    However, the storm exhibited sufficient tropical characteristics for NOAA in the US to grant it tropical storm status through its National Environmental Satellite, Data and Information Service (NESDIS). An advisory on Monday 7th November called it 01M (the M standing for Mediterranean), the first such ever issued for the Mediterranean.

    Winds were above storm force with heavy thunderstorms breaking out, similar in intensity to those in the tropics, and there was some coastal flooding. The department of Var, north of Toulon, recorded over 400mm of rain in four days, and a gust of 95mph hit PorquerollesIsland just offshore south of the city on Tuesday 8th November. Just ESE of Toulon, 129mm of rain fell on Ile du Levant on Tuesday alone, and there was a gust of 92mph.

    The relatively high sea temperature was overlain by cold air aloft, with temperatures of -20 degrees C at 5000 to 6000m. That difference of 40 degrees meant a very unstable airmass, ideal for the formation of such storms and for very deep convection to be sustained.


    Heavy seas at the French Riviera at least proved a boon to surfers.

    Similar Mediterranean storms are uncommon but not by any means unknown, and are given the rather playful portmanteau name “Medicane”: that is, “Medi-terranean Hurri-cane”.

    Two of the more recent occurrences were in 1995 and 1996. In January 1995 there was a similar formation southeast of Sicily, and in October 1996 one over the Tyrrhenian Sea, both of which had very distinct central “eyes”.

    The 1995 storm could arguably be called a proper hurricane – although strictly not because of the insufficient warmth of the sea – because it had sustained winds, not gusts, of around 90mph.

    These were measured by a German research vessel which - fortunately or unfortunately depending on your viewpoint – got caught up in it. Highly appropriately the ship was called the “Meteor”.

    By: Stephen Davenport