Summer in the Netherlands!
What is warm weather is discussable (depending on what you are used to) but temperatures between 25 and 30 degrees might be uncomfortable for many people.
Here some tips to cope better: it is important that you prevent dehydration and overheating. During exercise your body temperature can be higher: drink plenty of fluids and limit physical exertion in the afternoon if this affects you. Protect yourself from the sun with sunscreen and a cap or a hat. Especially for the elderly and young children it is important to take the heat into account.