Medicane season 2016

The 2016 season is upon us! I unofficially take September as the first month of the medicane season, and this will last all the way through until January. So far the month has been unremarkable (and September usually sees the highest frequency of tropical like systems) with one exception which I will talk about. Below is a copy of the description from last year. Please enjoy.


Please comment (can be done anonymously) with any suggestions to improve these entries. It would be great to get some discussion going on an unofficial medicane record.

Since there is no official monitoring of the tropical storm like cyclones in the Mediterranean, here is an unofficial record with some amateur comments. Names are chosen randomly and alphabetically. The medicane season would probably start in September and end in January. Once again I emphasize I am an amateur, and there is nothing official about these thoughts below.

The designations I will use are

           Inspec: Disturbance with the potential to develop into a tropical system 

Medistorm: Maximum sustained wind-sp0eeds below 39mph (equivalent to tropical depression)

Medicane: Maximun sustained wind-speeds between 39mph and 74mph (equivalent to tropical storm)


Major Medicane: Maximun sustained wind-speeds above 74mph (equivalent to cat1 hurricane)


Inspecs will be documented as they occur, but will not form part of this summary. I can make no promises that these storms are tropical-like, as I have limited means to do so. In the tropics the weakest tropical cyclone (tropical depression) simply needs to show closed circulation and deepening. For the Mediterranean this is inadequate because there is no guaranteed a cyclone is tropical-like, further baroclinically fueled storms are every bit as capable of producing strong winds (if not more so) than tropical-like systems. The difficult part is separating the mid-latitude storms from the tropical like systems. The following criteria will be taken into account:

1) Whether or not the cyclone has a warm core: cyclone phase diagrams from the following source are especially useful: moe.met.fsu.edu/cyclonephase/

2) Evidence of lack of frontal systems. Cloud patterns associated with cold, warm and occluded fronts strongly oppose a tropical like nature. However occluded fronts may sometimes, unfortunately, mimic tropical like cloud patterns

3) Characteristic features, especially eye-wall and eye.

4) Absence of significant lightning, lightning implies strong vertical motion; in cyclones we would expect more horizontal motion. This might be a useful way to distinguish organised thunderstorms from cyclones.

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Medicane (Subtropical storm) Stephanie

Duration: (September 15 - September 16th)
Maximum sustained wind-speed (estimated): 50mph
Minimun pressure: 999mb

Background   

To begin with I feel I have to justify including this storm here since it technically didn't occur in the Mediterranean. Some useful background context first of all: I feel that the mediterainian 'basin' has three sub basins; the west (generally easy of Italy), the east (east of Italy), and the black sea. Medicanes may form in all three of these subbasins but more than 90%  form in the west, and black sea 'medicanes' are exceptionally rare. The formation of this storm encourages me to add a 4th subbasin, the bay of Biscay which has the lowest frequency of tropical like systems. My justification for this is as follows: the system was very similar to medicanes forming in waters with a SST of 23 degrees centigrade (highly typical of medicanes which only require SSTs of 15C, yet highly atypical of atlantic tropical storms), it formed during the peak of the medicane season and during meterological conditions that are characteristic of medicanes (such as very cold 500hpa temperatures). I think given that this storm fits the characturistics of a medicane to a tee, it is not unreasonable to call it one and by extension include the bay of Biscay as a sub basin.   

Nomenclature

I usually name my own medistorms/medicanes unless a name has already been assigned. I'm not sure subtropical storm Stephanie is official although it was being floated by some official sounding sources. As with medicanes the stronger storms may attract more attention (keeping in mind medicanes are not monitored officially by anyone), and I do not wish to cause any further confusion by using my own name. As such I am taking the name  Subtropical storm Stephanie for this storm but am also using my own 'Medicane' identifier; I personally believe that althrough subtropical storm may be a better descriptor than 'tropical storm', medicanes are in themselves a unique breed of storms and I think this descriptor works even better.

History and development

Medicane subtropical storm Stephanie started out life as a extratropical depression which formed over the bay of Biscay on a trailing cold front on the 13th September. The large warm sector of this depression  was dominated by exceptionally warm south easterly winds (which actually brought record warmth to south east England). By early on the 14th the depression had matured and filled out a little, sitting over NE france. The frontal system had started to occlude with the cold front moving in a NErly direction over the continent, the warm front stagnated over Irelandand Scotland. Meanwhile the low moved back out to sea and started to deepen. Significant vertical advection occurred ahead of the cold front and thunderstorms broke out widely across southern parts of France. During the early hours of the 15th the main frontal system started to become decoupled from the low level circulation of the system (see sequence below), indicating perhaps the beginning of tropical-like development

Sat 24 images with fronts overlayed by myself. Note the frontal system becoming increasingly decoupled from the LP. Normal midlatitude depressions have associated frontal systems, however for this system these frontal boundries become less well defined and unrelated to the low pressure centre.

Even as early as 8UTC convective activity was evident SW of the low pressure centre. By 11UTC there is some evidence of convection both west and south of the low pressure centre. Tropical like intensification rapidally occurs by 12UTC , with a very swift transition to a warm core symmetrical system and the development of an eyewall. It reaches its peak strength just an hour later with a clear well defined circular eye and what looks like a feeder band to the NW. From this point onwards there is a slow decline in the storm's strength, however it does not undergo extratropical transition; the storm remains tropical like. Stephanie makes landfall in spain (basque region) at 17UTC bringing rain and gusty winds but moving lethargically. Stephanie only begins to decline rapidaly at 20UTC when the LP centre itself moves over land. From then on the decline is rapid; as the mountainous terrain quickly destroys what is remaining of Stephanie. Stephanie is completely absorbed by 6UTC on the 16th.

Track of Stephanie in 6 hr intervals starting at 13UTC

In total Stephanie was a tropical like system from 12UTC on the 15th to 1UTC on the 16th (although its a bit arbitrary deciding when Stephanie becomes and ceases to be a tropical like system). The very short life span is another characteristic feature of medicanes; it is very rare for a medicane to be tropical-like for more than 24 hours. I think this further justifies including this system.

Concluding thoughts

The first medicane of the 2016 season didn't even occur in the meditaranian sea, but because she possessed so many features typical of a medicane I think it is justified to include her. Either way a beautiful system that would be a shame to ignore.