Model simulation for the medicane while offshore Friday. (wxcharts.eu)

A “medicane” is set to threaten coastlines along the Mediterranean Sea over coming days, and Greece appears to be among the main targets.

While medicanes are not technically hurricanes, despite the similar nomenclature, they are cyclones that can deliver hurricane-strength impacts, and they do tend to develop some tropical characteristics. Medicanes are fairly infrequent, with only a dozen forming between 1982 and 2003. But as we’re likely to see in the days ahead, significant medicanes do occasionally spin up, and when that happens, they can leave a mark.

In coming days, an organized area of low pressure is expected to form to the south of the heel of Italy. As soon as Friday, the cyclone may be flirting with low-end Category 1 equivalence, stirring up waves in the Ionian Sea and packing 75 mph gusts or even greater.

Strong southerly winds are set to pile water up against west-facing coastlines in the storm’s path. This should trigger a storm surge of 2 to 3 feet. Hardest-hit areas are likely to include southern Albania and the Greek Isles, where 3 to 5 inches of rain is expected. The storm will weaken as it interacts with shore by Sunday, probably while also dousing Athens with heavy downpours and tropical stormlike conditions.


The European weather model forecast for early Saturday shows a 'medicane' off the coast of Greece. (weathermodels.com)

Because the Mediterranean is a small basin bounded by landmasses, medicanes have a limited amount of time and energy they can feed off.

Medicanes tend to be small systems — at most 200 miles across — and have much shorter life spans than their big-ocean cousins. While some medicanes have been able to stick around for a few days, like a 90-hour beast in September 1983, they tend to only show tropical characteristics for hours rather than days. Most of the time, these hybrid storms are more akin to a nor’easter that we see in winter along the East Coast.

Ordinary hurricanes form over ocean surfaces warmer than 79 degrees. It’s these lukewarm seas that fuel a juicy atmosphere and can blossom up a storm in no time. But in the Mediterranean, the waters are cooler. In fact, medicanes have happened over seas as chilly as 57! Based on this fact alone, it is easy to see these curious tempests are different from hurricanes, and they derive their energy in a different way.

Further, hurricanes and tropical cyclones are “warm-core” systems. That means the storm feeds off vertical instability, and sustains itself by drawing in warm, humid air.

Medicanes are more typically cold-core based. Like other mid-latitude storms, they start off when an atmospheric disturbance, commonly known as vorticity, rotates around a dip in the jet stream. This is typically associated with cold air aloft. That frigid air in the center sinks and settles to the ground, drawing more air in to fill the void. Nor’easters, snowstorms and most other continental disturbances are other examples of cold-core systems.

Under the right circumstances these cold-core pockets of vorticity can encounter warmer waters over the Mediterranean. In the absence of harsh winds tearing the fledgling area of rotation apart, it can develop from the bottom up. In some cases, a medicane can develop a warm core and take on some mischievous tropical traits.

Like a hurricane, the stronger medicanes are typically symmetrical. That’s something you don’t tend to see with a cold-core system. And likewise, they can have calm and clear eyes. That’s rare in anything but a hurricane.

Regardless of the technicalities, medicanes aren’t something to mess with. On Sept. 26, 2006, a medicane buffeted the Italian port city of Salerno with 89 mph winds as the air pressure dropped to 986 millibars. One particularly memorable event in September of 1969 punished areas from Tunisia to Algeria, where more than 600 people died in the wake of devastating flooding fed by the storm. Over a quarter million were also left homeless by that event.

More destructive medicanes may be in the offing thanks to climate change. Although studies have suggested they may become slightly less frequent, those that do form have a shot at being significantly stronger thanks to warmer waters.