height of summer; hottest part of summer
Refers to the peak of summer, typically the hottest period around late July to August. Often used in weather reports, seasonal greetings, or literary descriptions.
In the height of summer, you can't get by without air conditioning.
As we reach the peak of summer, intense heat continues day after day.
A set phrase combining 夏 (summer) with the possessive particle の and 盛り (peak, height). The reading さかり for 盛り is standard for 'peak' or 'prime'.