In the Aegean Sea, it sure is different
You know the dramatic beginnings of a storm. At a distance you see heavy dark blue clouds, approaching at high speed. And then the wind of the storm engulfs you, often accompanied by torrents of rain. Then the rain may cease, but the clouds are still there, racing over the sky at breakneck speed. The force of the wind is awesome, waves are building up.
If you happen to be in the Aegean Sea (Aigaíon pélagos in Greek, Ege Deniz in Turkish), be it at sea in a boat or on a nice beach on some Greek island or on the Turkish coast, you can completely forget most of that -- the blueish-black clouds, the downpour. Because the Mediterranean sun is shining as brightly as ever, there is no cloud in sight.
Tempest without a warning
But what you can’t possibly forget are the terrible tempestuous winds that suddenly start blowing, at up to 7-8 Beaufort (14-21 m/s). They were certainly not there in the morning, but now the storm has appeared from nowhere, without any warning. It is almost blowing you away, paying no heed to the intense glare of the hot sun and the absence of clouds.
What now has suddenly struck you is the vicious meltemi (in Greek, meltem in Turkish), a strong tempestuous northerly wind that strikes out of a beautifully undisturbed blue sky, without any warning-signs in advance. I remember a meltemi on the Greek island of Chios, just off the Turkish coast, not far from the city of Izmir (Smyrna). Everything not permanently anchored or arch-welded to something solid blew away -- beach parasols, blankets, babies. Vacationers had to take cover in the taverns, drowning their windward troubles in ouzo.
The meltemi is a seasonal or etesian (from Greek etos, annual) atmospheric calamity that was already described by Aristotle and Theophrastus. The trouble with the meltemi is not so much that it is a tempest-like strong wind (it seldom exceeds Force 8), but that it strikes without warning, from a clear sky. You sail lazily out in your dinghy on a hot summer afternoon, dressed in next to nothing and --WHOOSH -- suddenly you find yourself shipwrecked, in a most pitiful state.
Fierce struggle between an H and an L
The atmospheric conditions leading to the meltemi are twofold: a high pressure area (H) over the Balkans and a low pressure area (L) over Asia Minor.
Between the (H) and the (L) strong winds develop, blowing southward through the Aegean Sea with its multitude of islands -- Thasos, Lemnos, Skyros, Lesbos Chios, Samos, the Dodecanese Islands, just to mention a few -- and not to speak of the Peloponnesian and Turkish coasts. Because in summertime these pressure areas consist of very dry air, so no clouds can develop to alert you beforehand.
The Skyscraper Effect
In between islands the meltemi can be additionally accelerated. This is a phenomenon well known to Manhattans as the “skyscraper effect” -- even moderate winds will be funnelled into uncomfortable tempests by high-rise buildings.
Hold on to your medals!
The meltemi is etesian, i.e. it occurs in the summer period from May to September, when the weather conditions are right for forming a dry (H) area over the the Balkans and an equally dry (L) area over mainland Turkey. It generally blows in the afternoon, but some meltemi storms can blow for several days, day and night. Some of the 49er sailing crews in the 2004 Athens Olympics were overtaken by a meltemi, which foiled some of the contestants medal hopes. So if you are sailing in summertime among the Greek islands -- be prepared!