Summer greetings are sent before the first day of autumn; after that they become late-summer greetings.
Usage
Rarely used on its own today. It lives in 暑中見舞い (a summer greeting card) and the set greeting 暑中お見舞い申し上げます.
Cultural note
Summer greetings are sent from the end of the rainy season until 立秋, the first day of autumn in the traditional calendar (around August 7). After that date the card becomes a 残暑見舞い, a greeting for the lingering heat.