This is not as frivolous as it sounds. Last year the North African blogger who calls himself The Moor Next Door took the time and trouble to actually do spreadsheets and graphs of all Arab coups and attempted coups, and sure enough, he found a lot in the summertime: in fact, he found seven in July and five in August. These were by far the most except for the outlier November, which also had seven. (See his post here; a spreadsheet of coups here; and graphs of the data here.)
It does make you wonder. The Free Officers' coups in Egypt and Iraq are not alone: the Ba‘athist coup of July 17, 1968 was the key to the long rule of Saddam Hussein; in Syria, Husni Za‘im was overthrown in August 1949; in July 1963 a Nasserite counter-coup was put down bloodily; in Iraq Bakr Sidqi, who launched the first modern Arab coup in 1936, was assassinated in August 1937; a July 1971 coup in Sudan succeeded until Egyptian troops intervened to restore Ja‘far Numeiri; Sultan Qaboos of Oman deposed his father in July 1970; and so on. Mauritania, the only Arab country that still has coups these days, has had them (among others in other months) in July 1978, August 2005, and August 2008.But at the time, I was limiting myself to the Arab world. If we expand to the rest of the region, the "Operation Ajax" Anglo-American backed coup against Mohammed Mosaddeq in Iran in 1953 occurred on August 19. The 1960 coup in Turkey was on May 27 and the 1980 coup on September 12, nicely bracketing the summer.
And of course, returning to the Arab world, we have the Definitely-Not-a-Coup of June 30-July 3, 2013.
So I return to the earlier question, was it the heat, or what?