For many locales across the United States, the last week of July is the hottest time of the year (i.e., the highest normal maximum temperature). And given the prolonged heat over much of the country this summer, just the idea that there is cooler weather ahead may be a reason to rejoice.
But a few locations, especially along the immediate West Coast, have a delayed peak. For example, while on average, Sacramento has its warmest day of the year on July 20th, San Jose waits until August 29th and it's not until September 24th that San Francisco reaches its maximum. The largest moderating factor is the adjacent cool water of the eastern Pacific along with the weakening and southward shifting of the Pacific High.
Full-size versions of the California and United States maps (below) can be downloaded from https://ggweather.com/warmest_cal.jpg and https://ggweather.com/warmest_us.jpg. Tabular US Daily Normals are available at: https://ggweather.com/normals/daily91.htm.
Jan Null, CCM
Certified Consulting Meteorologist
Golden Gate Weather Services