By Thomas P.

During the winter period, over the Mediterranean basin, several low pressure systems are formed, that result in volatile and bad weather patterns, which are made even worse by the influence of this season's low temperatures.In contrast, during the summer, the distribution of the pressure systems in the Mediterranean is very different, smoother and relatively stable.

Meltemi

The eastern Mediterranean and the Aegean Sea - as our area of interest – are almost permanently under the influence of two barometric systems.
A high pressure system (High) formed over the continental Europe and a low pressure system (Low) formed in the southeastern Mediterranean, over Cyprus and the Middle East.

Meltemi

meltemi

These two barometric systems are almost firmly in place during the summer and their strength and location are barely changing.

So, the winds blowing in the Aegean Sea throughout the whole warm period have an almost fixed direction in every area of concern and a certain range of intensity, which essentially depends only on the combination of those two barometric systems.

These winds are the well-known 'Etesian winds' (named by the Aristotle himself and means "winds prevailing every year") also known as 'Meltemia', and as mentioned above, they are the result only of the combination of these two permanent barometric systems that are installed during the summer in the Eastern Mediterranean basin.

They are not considered to be sudden and unforeseen gusts of winds, but very stable and predictable in their intensity and direction over time and space in large scale.
In more detail, the actual distance and the depth/strength of the centers of those two barometric systems, that either close-in or move-apart from each other slightly, affects the intensity and direction of the prevailing winds in every area.
So, only by the analysis of the surface atmospheric pressure of the Aegean area, measuring the location and strength of the two barometric systems, we can easily find the intensity and direction of the winds in general.

Schematically, it is a rather simple, arch-like path, starting from the Dardanelles Strait in the Northeast part of the Aegean, continuing along the coasts of Turkey, and finally finishing its course in the Southeast Aegean in Rhodes and Kastelorizo islands.

Meltemi (Etesians)

In a general rule, these winds are of northeast directions in the north Aegean, northward direction in the central and eastern Aegean and of Northwestern directions in the southeastern Aegean Sea.

Since the effect of the wind in theory is the result of the difference of the pressure from one area to another (called the pressure gradient), the intensity of the Meltemi winds, depends on two main factors:

  • The distance between the centers of the two barometric systems.
    The closer their isobars are getting, the pressure gradient increases (same pressure difference divided by a smaller distance), hence the wind gains in force.
  • The difference in pressure of the centers of the two barometric systems.
    When the pressure difference between them is increasing, either because the Low is very deep or because the High is very strong, or even worse when both cases apply, then the pressure gradient is also increasing, and in result the wind force rises in analogy.

 

So, the continuous but limited movement of both pressure systems, and the also limited fluctuation of their barometric intensity, results in the changes in the force of the winds. In example, if we see winds' intensity of 7 or 8 in the Beaufort scale, this means that: both the distance between the two barometric systems is small and the pressure difference is significant, resulting in this level of wind force.

Meltemi (Etesians)

Then why there are so many fluctuations and variance in the direction and strength of the surface winds in every place? Why, don't we see only stable and absolutely predictable winds with a sole, specific direction, creating evenly formed ripples and waves, without any unpredictable or severe weather and sea state?

The answer is simple: the Aegean Sea is not an open sea without any obstacles. On the contrary, it has countless islands islets and rocks, forming every kind and size of straits, blocks and tunnels between them.
All this perplexed topography and distinct morphological configuration and orientation of every geographical position is a real labyrinth, and the wind is forced to move through it!


It has to go over smaller land slopes or move around the big land formations or steep slopes, to slow down by the friction because of them and then run faster thru tunneling areas (the Bernoulli Effect), and so on...More so, the air mass carried by the wind also faces changes in air temperature, due to the varying sun position or angle and the diversity of heating between land and water. All these are resulting in variations in its humidity, condensation, temperature and density.

Meltemi (Etesians)

This whole procedure results in the creation of turbulence, disrupting the smoothness of the winds, changing them significantly from one location to another and leading to the development of messy ripples and conflicting waves from multiple directions, and in essence, the harsh and often inaccessible seas, we have to confront from time to time.
And the real problem is that all this turbulence makes the small scale, locally accurate prediction of the winds and waves, almost impossible.
As a fair result, the Aegean Sea is considered to be one of the toughest to navigate seas, not because of its easy to predict wind gradient in large scales, but mainly due to the immense complexity of its topography.

In a rule of thumb, when the winds are strong, we must definitely avoid narrow straits and tunneling areas between land formations that cause the winds to be compressed in order to pass, and violently increase their force and the wave height.

For navigators

  • Our travel destinations options may seem countless in the Aegean Sea and promising of magical moments, yet we must always keep in mind of the dangers hiding behind every beautiful scenery.
  • The selection of a plotted course must be made very carefully, taking into serious consideration all the local wind directions, tricky straits and hazardous passages.
  • During almost the entire summer period, the average intensity of the winds during daylight is in the scale of 6 plus Beaufort, reaching a maximum in noon hours and decreasing again late in the afternoon.
  • So, one rule of thumb here is to try and navigate at very early morning hours, before the winds gain in force.
  • When travelling in the southern sides of islands with tall land formations, stay far from the shores since the gusty, sudden winds that descend from the mountains can be really scary and make your trip a real hell.
  • When setting your anchor for an overnight stay, in the southern bays and gulfs of the islands, always try to be as close to the shore as possible, and only by using two different ropes, attached by two very stable points.
  • Also, don't get tricked by the calmness of the sea during the day, because the gusty winds that may burst after midnight, are coming down at you with such fearsome intensity that may put you into serious trouble.
  • Don't be fooled by the small distances on a map.
    Even a relatively short, 15 mile course with strong gusty winds and troubled seas can make it seem like it will never end...

And always keep in mind...
The Aegean Sea is a tricky place to navigate!

...keep Ribbing!

 

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