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.
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© 2018 Meteorologist Brian Matilla