late-summer greeting card
A seasonal greeting card sent from around August 8 (the start of autumn on the traditional calendar) through early September, inquiring after the recipient's health during the lingering summer heat. Often sent in reply to a 暑中見舞い or as a follow-up when one missed the midsummer greeting period.
See also: 残暑
After the Obon holiday, let's send out late-summer greeting cards.
In a late-summer greeting card, you add words expressing concern for the recipient's health.