Zansho omimai moshiagemasu (残暑お見舞い申し上げます)
This is the way to greet at this hot season.
Until yesterday it was "Shochu omimai moshiagemasu.(暑中お見舞い申し上げます)." The difference is "shochu" which means the middle of hot season and "zansho" which means "the late summer heat" though the heat itself is almost the same.
The reason of difference is today is risshu (立秋), the start of the fall on the calendar.
It is one of nijyushisekki (二十四節気), the 24 solar terms. The last one was taisho(大暑) on July 23, and the next one is shosho(処暑) on August 23.
The typhoon No.5 is gradually approaching. It rained at night but stopped. I hope it will pass without any problem.