DISCUSSION: When one thinks of tropical cyclones, the initial thought directs to the tropical waters of the Pacific, Atlantic, and Indian oceans. In recent days, however, a tropical-like cyclone known informally over social media as a “medicane” (a connotation of Meditteranean hurricane) formed in the Meditteranean Sea and made landfall over southern Greece. This tropical-like cyclone delivered strong winds greater than 55 mph (80 kph) and significant precipitation to areas of southern Greece and Turkey over the weekend. While not necessarily rare, it is still an unusual event given the fact that the Meditteranean Sea is relatively drier compared to the more conducive tropical belt and waters are fairly shallow with various landmasses impeding significant development. So how did this cyclone form in an otherwise unusual region?
The development of this cyclone began from an anticyclonic wave-breaking event that occurred over northwestern Europe. As the upper-level trough over Europe began to break down, a potential vorticity (PV) streamer along the eastern flank of the trough moved south towards the Meditteranean Sea while a moisture plume was advected northward. The combination of these two features set a favorable environment for development. Enhanced PV interacted with the incoming moisture and existing convection induced baroclinic instability that led to the creation of a surface cyclone that was cut-off from the main PV streamer to the north. Sea surface temperatures around the cyclone ranged between 25-26 C which is consistent with maintaining tropical convection. However, the air aloft is much colder than what is observed with typical tropical systems, so the system has to rely on near-surface heat fluxes to help maintain convection surrounding the cyclone’s vortex. Data on September 28th from the SCATSAT-1 satellite revealed estimated surface winds of 30-40 kts (~35-45 mph), and satellite imagery indicated banding features that would resemble that of true tropical cyclones despite the fact that it is a different environment than that of the typical tropical cyclone. As the system completed its tropical transition, the system was advected eastward towards Greece under weak but present zonal (east-to-west) flow. The end result was localized flash flooding particularly in the Peloponnese islands and elevated wave heights leading to beach erosion, while the city of Kalamata experienced tropical-storm-force winds during landfall. While “medicanes” are indeed unusual, research conducted into understanding the processes involved with their formation is quite extensive. Several case studies have shown that other “medicanes” of the past were even more impressive in both strength and overall organization compared to this most recent case. In particular, a “medicane” from January 1995 serves as a reference for both researchers and forecasters alike in understanding the evolution of such a storm. While these “medicanes” can form once or twice in a year, it is their infrequent occurrence that does not warrant official tracking by any weather organization such as the National Hurricane Center. Still, witnessing a system like this develop only warrants more interests by both researchers and forecasters especially when the threat for landfall exists. To learn more about other high-impact weather events occurring across Europe, be sure to click here! © 2018 Meteorologist Brian Matilla
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DISCUSSION: Earlier on during the first half of August here in the Summer of 2018, parts of France felt the full force of several noteworthy severe weather events. During a couple of these rounds of severe weather, some locals got the opportunity to catch the full fury of some of these storms on camera. Therefore, in doing so, there is now an opportunity to break down and explain a good portion of what they physically witnessed. In looking at the footage attached above (which was provided courtesy of the Weer and Radar Facebook group), you can see how during the earlier part of the video clip there were particularly strong winds reaching the ground near the city of Forbach, France (which is located in far northern France and is practically located right on the border Germany and France).
The strong, gusty winds were which recorded towards the beginning of the footage were more than likely a product of a severe thunderstorm's main downdraft reaching the ground. A strong downdraft can often appear very much like those winds associated with a tropical cyclone at the point of landfall. This is due to the fact that rain-cooled air will often out from underneath the base of the thunderstorm and reaches the ground with substantial force. As a result of strong downdraft reaching and impacting the surface of the Earth, there are quite often found to be consequences such as downed trees, downed power lines, damaged homes and/or commercial businesses as a result flying debris or broken trees/tree limbs. Hence, regardless of the situation it is always imperative to respect the natural power associated with approaching severe thunderstorms when they do occur. Later on this severe thunderstorm footage, you also get a chance to see the periods of large hail and flash flooding which occurred in this same region with this round of severe weather. In starting off with hail stones, it is worth noting that once hail stones reach a critical size and weight, they are often quite damaging to nearly anything come into contact with during their descent towards the surface of the Earth. When larger hail stones are combined with periods of persistent, heavier rainfall this more often than not leads to major safety issues at the ground. This can often be further exacerbated by people trying to to risk travelling in the vicinity or even directly through flooded roadways which can lead to a further risk of unnecessary fatalities due to people and/or automotive vehicles being swept away in minutes or less. Thus, if you are ever faced with such a situation, always be sure to respect the natural power of severe thunderstorms and the natural hazards they are capable of producing. To learn more about other high-impact weather events occurring across Europe, be sure to click here! © 2018 Meteorologist Jordan Rabinowitz |
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