Thanks for your response.

Since only a portion of your hydrangea is affected and presumably rather localized, I suspect that what is happening is something called “sun scald” or also termed “leaf scorch”.  We have had several questions such as yours from gardeners in the Twin Cities area involving a variety of different shrubs with the same issue.  This condition is typically seen during periods of dry, windy weather, low rainfall, and high temperatures with bright sunshine. Under such conditions, hydrangea roots are unable to supply sufficient water to the foliage to replace what is lost by transpiration from the leaves.  Hydrangea need a steady supply of water to maintain themselves, including their blossoms.  If they do not have this available to them, browning of various parts of the plant will occur.  In most cases unless your hydrangea is unhealthy to begin with, which is unlikely given its overall appearance,  there is no cause for serious concern.

See the following for further information and possible remedial actions:

https://www.hyanniscountrygarden.com/hydrangea-flowers-turning-brown/

https://homeguides.sfgate.com/dry-brown-leaves-hydrangea-69182.html

https://www.hyanniscountrygarden.com/hydrangea-flowers-turning-brown/

https://homeguides.sfgate.com/keep-hydrangea-leaves-burning-full-sun-36097.html

https://www.hyanniscountrygarden.com/why-did-my-hydrangea-flowers-turn-brown/

For immediate purposes, I would suggest that you just remove the browning blooms and leaves and dispose of them accordingly.  I feel quite confident that as our days shorten and cool, you will see less and less of this on your hydrangea.

Good Luck!!