Weather News

'Medicane' bearing down on Greece

Ben Domensino, Friday September 28, 2018 - 14:14 AEST

An intense low pressure system being referred to as a 'Medicane' will cause severe weather in parts of southern Europe this weekend.

Unusually warm water in the Mediterranean Sea and a pool of cold uppler-level air are combining to fuel the development of the intense low pressure system today.

The term 'Medicane' is a portmanteau combining the words Mediterranean and hurricane. However, while this system is similar to a hurricane in some ways, it's not quite the same.

Hurricanes, which are the same as tropical cyclones and typhoons, gain their strength when warm and moisture-laden air evaporates from the ocean and forms towering masses of clouds around their core. These systems are referred to as 'warm-core lows' because they are driven by the presence of warm air at their core.

Another common type of intense low pressure system, called a 'extratropical cyclone', derives its energy from the interaction of cold air near its core with warm, moisture laden air in the surrounding environment. These systems typically occur outside the tropics in a part of our planet called the mid latitudes, where cold polar air clashes with warmer subtropical air. Extra-tropical cyclones are referred to as 'cold-core lows' because they are driven by the presence of cold air at their core. In Australia, East Coast Lows are an example of these cold core extratropical cyclones.

If a cold-core extratropical low spends enough time over warm water, the incursion of warm and moist air at the surface can cause it to partially transition into a warm-core system in its lower levels, while still showing cold-core characteristics in the upper levels. This hybrid system is called as a subtropical low.

The Mediterranean low pressure system, or 'Medicane', is a subtropical cyclone that is gaining strength from both the unusually warm water of the Mediterranean Sea and the strong temperature gradient between the warm Mediterranean and cold air a few kilometres above it.

Sea surface temperatures are currently sitting at around 26-28 degrees Celsius in some parts of the Mediterranean Sea, which is more than a degree above average for this time of year and warm enough to support tropical cyclone activity.

This intense low pressure system could cause heavy rain, thunderstorms and gale force winds in southern Greece on Saturday, before affecting western Turkey on Sunday.

- Weatherzone

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