Advertisement
If you have a new account but can't post, please email Niamh on [email protected] for help to verify your email address. Thanks :)
New AMA with a US police officer (he's back!). You can ask your questions here

Mediterranean strong depressions

  • 24-09-2011 10:57pm
    #1
    Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    I choose the word 'depression' out of confusion as to what they are supposed to be called.

    I'm talking about the storms that form in the Western Med as regular depressions before sometimes attempting to form a warm core and ditch it's associated fronts. The sea temperature required for them seems to be lower than a tropical storm and they seem to occur January-August, often forming off the coast of Libya before heading east.

    What exactly are they? Simply powerful depressions? Subtropical storms? "Tropical" storms? "Polar" lows? Some form of hybrid?


    January 1982

    medssss1982.jpg


    January 1995

    medssss1995jan.jpg


    October 1996

    medssss1996oct.jpg


«1

Comments

  • Registered Users Posts: 1,279 ✭✭✭ snowstreams


    They sure do look like hurricanes alright. They must be something related to polar lows. Especially the ones that occur during January etc.
    There can be some air masses with very cold upper temperatures that come down over the eastern med. They must feed the tropical characteristics of the lows.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    Just for the fun of it I'm going to put this low pressure area, currently forecast to come north off Libya, up for small potential of forming something interesting eventually to the SE of Italy for the 9th/10th. Cue bog standard low pressure :D


    libyalow.png


  • Closed Accounts Posts: 5,150 ✭✭✭ Deep Easterly


    Nice analysis of a similar depression in the Med on the 26th September 2006:

    http://www.mmm.ucar.edu/people/rotunno/files/weather.pdf

    As Snowstreams says, they are basically a Mediterranean version of a Polar Low .

    This satellite image was taken earlier that morning before the cyclonic feature developed fully off the SE coast of Italy:

    177218.JPG

    Fax analysis for 0000 UTC - 27th Sept 2006:
    177220.JPG

    shows that the mesoscale depression formed in a cold sector, similar to Polar Low features in the North Atlantic*

    EDIT: *Actually, that is not strictly true in this case. A further look at the DWD analysis charts shows that this mesoscale feature developed more or less along the actual surface cold front rather than behind it which would make its formation less Polar Low like, although the feature did seem to separate itself from the front and into the cooler sector as it matured later in the day. (open to contradiction)

    2 metre temp analysis for 6z:
    177223.gif
    shows a tongue of very warm air being drawn up from N Africa ahead of the front which no doubt helped to feed energy into the developing low. The small scale low developed more or less along the 15c isotherm along the south coast (Italy) which is roughly where the cold front lay around that time.


  • Closed Accounts Posts: 4,279 Su Campu


    Here's an ASCAT windmap for the area from 04:36 UTC that morning, several hours before the peak, showing some 50 knot vectors over the sea.

    WMBas158.png


  • Closed Accounts Posts: 5,150 ✭✭✭ Deep Easterly


    Here's a nice on the spot daily run down on the 'TMS' (Tropical-like Mediterranean Storm) that developed in the western Med between the 5th-7th this month, with a detailed discussion on both the sub & broader-scale synoptic processes involved in its formation:

    http://translate.google.com/translate?sl=auto&tl=en&js=n&prev=_t&hl=en&ie=UTF-8&layout=2&eotf=1&u=http%3A%2F%2Fwww.keraunos.org%2Ftropical-like-mediterranean-storm-novembre-2011.htm

    European satellite animation for period 4th to 8th November. One big factor in triggering off this particular storm is the deeply cool and very unstable mP air mass that spilled into the western Med on the 4th & 5th:

    animation_it.gif
    Image: AeMet.is



    Some further reading on these unusual storms:

    http://www.eumetsat.int/Home/Main/Publications/Conference_and_Workshop_Proceedings/groups/cps/documents/document/pdf_conf_p50_s8_05_luque_v.pdf

    ABSTRACT:
    "Tropical-like storms in the Mediterranean Sea with a clear eye surrounded by an axisymmetric cloud structure are quite unusual. Almost one case per year on average is identified in satellite images in all the Mediterranean basin. These storms, once generated over the sea, can affect islands and continental coastal lands. Although, documented tropical-like cyclones have not usually achieved hurricane intensity, their potential for damage is high due to the densely populated Mediterranean coastal regions."



    ftp://texmex.mit.edu/pub/emanuel/PAPERS/Fita_etal_2007.pdf

    ABSTRACT:
    "Tropical-like Mediterranean storms grow and evolve from a combination of deep convection and typical mid-latitude baroclinic processes. The axisymmetric cloud-resolving model assumes a homogeneous atmosphere. This assumed background atmosphere is also temporally invariant during the period of simulation. Spatial homogeneous and temporal invariant assumptions are inappropriate in the Mediterranean basin"


    Basically, while structurally similar to Tropical Stroms, due to the conditions that allow TMS's to form. they can be classed no more that 'Sub-Tropical Storms', which is fair enough I suppose, since the Mediterranean is not in the tropics.. :cool:


    An excellent site listing numerous case studies of TMS's with satellite and synoptic charts and animations as well! :) (more excellent links listed in both of the above papers)

    http://www.uib.es/depart/dfs/meteorologia/METEOROLOGIA/MEDICANES/


  • Advertisement
  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    Some decent looking convection building south of the Balearics at this time. Any chance of development? I don't recall any plunge of colder air down to the area though in the last few days that might have otherwise fueled this low to something stronger?

    http://www.sat24.com/sp


  • Closed Accounts Posts: 4,279 Su Campu


    That activity is the usual type of convection that occurs when an upper low is near or over Iberia. There is actually warm air advection of the Med at the moment, so a different setup altogether. The thunderstorms are being generated by upper features.


  • Closed Accounts Posts: 4,279 Su Campu


    In fact, ESTOFEX explain quite nicely what's going on there today. A good chance of waterspouts over much of the Med.
    Storm Forecast
    Valid: Mon 21 Nov 2011 06:00 to Tue 22 Nov 2011 06:00 UTC
    Issued: Mon 21 Nov 2011 05:29
    Forecaster: VAN DER VELDE
    A level 1 was issued for eastern Spain and Balearic islands mainly for excessive convective precipitation.
    A level 1 was issued for Sardinia and Sicily mainly for severe convective wind gusts, large hail and possibly a tornado.

    SYNOPSIS
    A low pressure area has now installed itself in the western Mediterranean with increased amounts of CAPE. The mid level potential vorticity maximum which entered Africa will start digging into the southern Mediterranean during the afternoon and develop a cold/dry front subsequently moving over Sardinia and Sicily. The Balearic islands will be near the almost stationary occlusion with where models trigger quite a lot of precipitation.

    DISCUSSION

    ...eastern Spain...
    The region south of Valencia will see most orographic moisture lifting as the low level wind direction turns from easterly to more northerly directions. As has already been the case during the night, persistent storms should continue there for some more hours and cause locally excessive rain sums. Storm motion should remain very weak.

    ...Sardinia and Sicily...

    GFS and HiRLAM disagree on the areal distribution of vertical wind shear and helicity, but are quite in agreement on the amount of CAPE (800-1500 J/kg). While shear is around 15 m/s over a deep layer, SREH can reach 300 m2/s2, most sure over Sicily. Both models agree on a band of >22 m/s mean winds between 1-3 km AGL over Sardinia. A linear convective system with severe wind gusts is a likely scenario. Embedded supercells could also create large hail and perhaps a tornado
    Waterspouts are likely to be observed here and there over a large section of the western Mediterranean.

    HiRLAM Precipitation
    hir_prec_sw15.png


  • Closed Accounts Posts: 4,279 Su Campu


    Widespread thunderstorms, some with hail, are occuring in Sardinia and Tunisia this evening. A ship is reporting 38 knot winds and squall just off the north coast of Tunisia.

    201111211800_e2_40N010E_Sg.gif

    Latest radar from Sardinia.

    PZE1132520053G.001.gif


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    http://www.estofex.org/cgi-bin/polygon/showforecast.cgi?text=yes&fcstfile=2012090406_201209022206_2_stormforecast.xml

    Italy, Corsica, Sardinia potentially under threat from strong winds and extreme rainfall. Be interesting to see if a 'medicane' occurs with this system.


  • Advertisement
  • Closed Accounts Posts: 4,279 Su Campu


    This is from Lightning Wizard's (Estofex) Facebook page, when they were getting excited about this system in Saturday's Hirlam run.

    It seems to be a bit of a downgrade on latest runs but nevertheless a lot of rain for Sardinia, Corsica and much of central and northern Italy.

    315074_441140712596122_1118198672_n.jpg


  • Closed Accounts Posts: 5,150 ✭✭✭ Deep Easterly


    Some scattered but intense looking storms over parts of Italy right now.

    http://www.sat24.com/en/it

    (click on 'Lightning' option at bottom right hand of satellite image for sferic data)


  • Closed Accounts Posts: 4,279 Su Campu


    The 12Z 0.05° Hirlam shows a distinct warm-core system forming in the Tyrhennian Sea tomorrow and affecting much of the coastal areas of central Italy, eastern Corsica and northeastern Sardinia. Instantaneous contraction map shows fluid trapping and banding around an eye-like centre, generating humungous rain rates.

    hir_icon10_sw33.png

    hir_prec_sw33.png


    Theta-e charts also show it as a warm-core system, so it would tick the boxes of a sub-tropical storm-like system, with the wind field a little displaced from the centre.

    12090421_0312.gif

    Upslope rainfall enhancement on the high terrain of Corsica and central Italy is going to cause some real problems of flash-flooding.


  • Registered Users Posts: 845 tylercollins




  • Closed Accounts Posts: 4,279 Su Campu


    Estofex have an interesting discussion on it this morning. It reads like something out of the NHC!


    Side note:

    Since yesterday, a well structured cold-core low looped cyclonically atop Corsica and is currently situated roughly at 40°30' N and 8-9° E, featuring an E-W elongated center. Also, mid-tropospheric vortex built downwards and 19Z ASCAT scan featured a 15-20 kt surface depression just to the NW of Sardinia which moved east/southeastwards since then. A 30-35 kt surface wind maximum along its northern/western fringe is not correlated with the organizing surface circulation but exists rather due to a channeled gradient flow. Just before landfall over N-Sardinia, DMC increased in strength and organization next to the center but decreased markedly after landfall. An increase in DMC was noted along the northern/northeastern fringe due to increasing LL convergence.

    During the start of the forecast period, the depression's center should emerge off of Sardinia into the N-Tyrrhenian Sea and therefore further to the north than most models indicated 24 h ago. However, due to the asymmetric and elongated circulation center and movement atop the rough orography of Sardinia, uncertainties still exist if the center may reform a bit more to the south. Anyhow, this motion brings the depression's center atop an anticyclonic eddy with SSTs of 27-28 °C / positive SST anomalies of 2-3 K and good heat content. As the cyclonic vortex is not yet vertically stacked, some slow eastward motion is still expected with a more or less quasi-stationary motion over the far NE Tyrrhenian Sea during the end of the forecast. At that time, SSTs decrease by roughly 3K. Despite a gradual warming trend of the mid-/upper level vortex and an increase of the geopotential heights as a response of the more zonal flow pattern over N-Europe, background environment remains supportive of a temporarily confined core modification. DLS is already weak and continues to weaken with some weak upper divergence forecast.

    A lot depends on the final track of the depression, but confidence increases that a subtropical cyclone may evolve between Sardinia and C-Italy during the forecast. Still a few high resolution models indicate moderate to rapid intensification and is was noted that overall model tendency approached the shallow warm core phase in FSU phase diagrams. Surrounding sounding data also confirm a decrease of the dry slot strength and ongoing moistening, so overall environmental conditions seem supportive for strengthening/organization. An intensity forecast is hard to create due to

    a) proximity to the islands/Italy
    b) potential infiltration of more stable stratified, rain cooled air from N-C Italy during the forecast
    c) uncertainty how strong/persisting convergence and DMC east of Corsica may affect the development of the depression's center and attendant banding structure

    Especially in case of the depression's motion atop the warm eddy, we would not rule out a ST 2.5 classification, which would equal 35-40 kt . In any case, the feature will be closely monitored during the following 24 hours.

    The latest runs now show it moving southwards through the Tyrhennian Sea tonight, which would keep it over warmer SSTs and possibly allow it to strengthen more. Interesting to watch.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    Thought I'd resurrect the thread. Close it if I'm wrong to but...

    Models picking up on a possible "Medicane" come Friday potentially affecting Italy and Greece. Might be another event of interest to people.


  • Moderators, Science, Health & Environment Moderators Posts: 15,171 Mod ✭✭✭✭ Gonzo


    Fuengirola and the general Malaga region, had a terrible rain storm depression early December last year, I remember some business's in the local area who were ruined and closed down due to severe flooding. There was a similar storm back in 1989 in the same area which resulted in millions spent on fixing the promenade and flood prevention.

    Let's hope the same area doesn't have a repeat this year, they can do without another red alert storm this year.

    http://www.theolivepress.es/spain-news/2016/12/04/flash-floods-leave-costa-del-sol-underwater-in-worst-rain-since-1989/


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    Area of interest between Greece and Italy a couple of hours ago. It's not expected to be one of the stronger medicanes if it develops those tropical like characteristics but could bring more flooding to an already sodden Greece.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    http://www.severe-weather.eu/mcd/a-possible-formation-of-medicane-in-the-tyrhenian-sea-on-thursday-sept-20th/

    "Medicane" season has arrived.

    Possible development 'somewhere' in the Tyrrhenian sea picked up by some models.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    A more traditional cyclone has formed in the area of interest with strong convection towards its centre. Conditions are favourable for the development of a "Medicane" within this circulation. It is expected to brush eastern Sardinia before moving towards Tunisia though is currently near still in position. Several inches of rain in a short period of time possible in Eastern Sardinia. Though it's predicted to travel to Tunisia previous storms in this location have been known to dupe forecasters and travel eastward.

    https://twitter.com/twitter/statuses/1042683823559987200


  • Advertisement
  • Registered Users Posts: 200 ✭✭ Awaaf


    This is an interesting thread and with a lot of people travelling in the region all year round, it is of more than academic interest. I wonder however would the thread title lead to it being overlooked especially as the thread is likely to disappear before reappearing periodically. Might the word "medicane" be useful in the title? Maybe in brackets as an addition? Just a thought!


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    The disturbance failed to gain a characteristic Medicane eye formation. It travelled South to Tunisia as forecast and is currently dropping heavy rain in the north of the country


    1145.jpg

    .


  • Registered Users Posts: 8,191 ✭✭✭ Gaoth Laidir


    It did have a very warm core but the max winds were displaced from the centre. I'd say it would be classified more of a subtropical cyclone.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    Four people confirmed dead from the effects of the storm in NE Tunisia. The coastal city of Nabeul was one of the worst hit with 8 inches of rain falling in a 24 hour period. That's the equivalent of 6 months of average yearly rainfall in the region.



  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    New area of interest in the triangle between Italy Libya and Greece. A tropical like system appears on several models. Orginally it was aiming towards the Greek islands but some want to take it westwards towards Italy. 3 days away its make-up, direction and strength are up in the air.

    DoAyUS8VsAEW6eA?format=jpg&name=small


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    International forecasters and media seem to have picked up on this storm given its severe potential. This might be useful for any unsuspecting late getaway Irish holidayers in the region.

    The GFS has given up on moving the disturbance into Italy. Most models have it head in that NW direction before turning east. They seem to be trending toward a more southerly track pushing the focus from the Greek mainland to Crete in particular.

    Gales and heavy rain have already been affecting many areas of Greece in recent days. Local authorities who have closed schools as a result of this have decided to keep them closed as the development of this storm brings potential for deterioration of conditions.

    Wind speeds and rainfall remain uncertain but both, particularly rainfall, could become extremely dangerous with several inches likely across a wide area where the storm passes and higher amounts again locally.

    Beyond the area of Crete models currently show the now weakening disturbance travelling towards SW Turkey.


  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    All eyes to the Sirte Gulf north of Libya. A non tropical cyclone has begun to form. This will likely transition in the coming hours.

    aiYduzJ_d.jpg?maxwidth=640&shape=thumb&fidelity=medium


  • Registered Users Posts: 12,554 ✭✭✭✭ sryanbruen


    Weather and climate site - https://www.ukandirelandclimate.com/ (advised to view on PC, not optimised for mobile)

    Photography site - https://www.sryanbruenphoto.com/



  • Registered Users Posts: 10,402 ✭✭✭✭ dsmythy


    The storm as it arrived in SW Greece this weekend

    6034073


  • Advertisement
  • Registered Users Posts: 19,554 ✭✭✭✭ Rikand


    Is there another one out there off the coast of italy - the european weather forecast on rte had a brief mention of something something


Advertisement