Planning for the weather is a good way to make your trip to Mostar relaxing and enjoyable, especially when you’re splurging. The hottest months are usually August and July, with an average temperature of 21°C, while the coldest months are January and February, with an average of 5°C. The rainiest months in Mostar are November, December, October and January, with each month seeing an average of 211 mm of rainfall.