General about Mediterranean weather
According to general tourist-clichés the Mediterranean would be an area of eternal sunshine separated only by days of endless rain.
Those clichés are pretty much nonsense. During the summer-months it will be pretty much like that, but the winter brings enduring rain. The notorious north winds Mistral, Meltemi and Bora may rise the whole year and kill the laziness aboard in a rush. If the sea turns white within an hour, the way to the next crowded harbour may turn out to become a long one, maybe too far. A momentum of danger is the relatively small amount of sea-space. Often it is impossible to outrun a storm, without running into Léger wall.
Even antique displays of ships show: The boats get either rowed or sailed with ruffed sails. Actually in the long-term view the Mediterranean is one of the stormiest and most dangerous waters of the northern hemisphere. Many experienced Yachties or Regatta-Sailors count the sailing-areas of the Golf de Lyon or the area of West-Corsica to Sardinia as one of the most dangerous worldwide. To be precise the Mediterranean isn't well suited for sailing at all. Let's not cheat ourselves, we rather go there because of the sun, the mild climate, the culture and the well maintained infrastructure.
Basically the Mediterranean weather is split in two half's during the course of the year. In summertime the Azores-High uses to drive a wedge in the very far western Mediterranean and to spread a hot low over Turkey or Iraq. This basic constellation with little to no weather change may be interrupted by light winds from the west or north by storms with gale-power (Mistral, Bora, Meltemi). These irregularities usually do not last for long. In general it is sunny with soft and recognisable rise of the temperature, the atmospheric pressure and the wind in the course of the day, which means off-shore-winds in the afternoon and on-shore- or slack-wind during night. That's why it is no use to leave the harbour. The early hours are the nicer ones at land anyway, where as out at sea it is still lull and dull.
During winter there is a different constellation: The Azores-High gives in to some lows, that may rotate for days and drop huge amounts of rain, sometimes in connection with thunderstorms. Nearly the whole rainfall goes done during the winter-months. Of course it is sometimes possible to celebrate Christmas in Malaga with 25ºC on the thermometer. The weather-change usually comes within days like the monsoon. This rainy weather often stays for a longer period of time, when it got the hold of it. Usually this happens in the western Mediterranean in the end of October, in the eastern part this happens a little later. This humid weather with relatively high temperatures leads to a lot unpleasance aboard, because the interior is covered with humidity. This could easily be managed by a strong heating or air-condition, but it is neither cold nor are heating's installed on a common charter-yacht.
During Autumn and Spring, the transition, the weather may go crazy in the Mediterranean. This is the time of the year where storms and other weather-phenomena's like Libeccio or Scirocco are the most likely.