From a sailor's point of view, the Saronic Gulf and the eastern coast of Peloponnese compose an area with mild weather conditions. In mid summer, July and August, the northern, strong winds, also known as the 'meltemi', might prevail. This is the only case when the weather becomes predictable: stable wind direction through out day and night, small waves, since in the Saronic there is always a shore at the North and bright sky. In other words, the Saronic offers ideal sailing conditions, unless the meltemi gets too strong, 7 beauforts or more and sailing becomes very hard. This is not often. What is more common, in July and August, is to experience wonderful sailing with 4-5 beauforts, with minor impact from waves, even when sailing upwind. And it is so refreshing!
The Saronic Gulf is ideal for yacht chartering and sailing for its mild weather conditions, especially for those who are interest to enjoy happy sailing!
Note that geography defines the weather conditions: The shore of Attica covers the Saronic Gulf from the North. Similarly, the peninsula of Argos covers the Eastern coast of Peloponnese. So, when the meltemi blows, the area does not allow big waves to be created, while the northern winds remain strong. It is a major advantage compared to the Cyclades islands, to avoid big waves when sailing...
As noted, however, not all days are gifted with stable, northern winds. As a matter of fact, in other summer months as well as the whole year, wind conditions can never be predicted. South winds are common, up to 5 beauforts. The same stands for western or eastern winds alike, but these are rather rare and less strong. With strong south winds, the waves are more annoying, as they have travelled bigger distances. Western winds come from the land so there is no hard effect while eastern winds are very rare.
Most islands provide good shelter to all wind directions. Aegina, Poros, Spetses have bays that are well protected from the northern wind, where sailors enjoy relaxing days and nights despite the wind force. The same stands for nearly all wind directions! There is always a safe bay or port nearby to anchor when things get rough. The strait of Poros also offers protection from all wind directions. The same stands for the islet of Dhokos, further south and near the island of Hydra. The port of Porto Heli at the coast of the mainland offers full shelter and heading south, so does the port of Gerakas although sailing into this fantastic bay needs high caution. Farther south, Monemvasia which is a unique destination, has a safe marina, but it is so small that it's possible not to have free spots in the high season (July, August).
Finally, temperature is so comfortable that people sail through out the year (maybe except for January / February). The season extends from May to full October. There is a small possibility for rain in May and June while autumn has been dry and quite warm in the last years.