Below are my notes for visiting Croatia. These travel tips, such as the best time to visit Croatia are obtained from a variety of sources including some of the following: my first hand observations, personal conversations, magazines, newspapers, websites, books and so forth. Whenever I hear something that interests me about Croatia, I jot it down here. Hope this comes in handy.
Best Time to Visit Croatia
Short Answer: May through September
Long Answer: It really depends what you are looking for. Mid-May through September should give you good weather to swim (warmer as the summer season goes on), boat and explore. However, if you are looking for nightlife, then July and August are best. If you are looking for swimming and boating without as much of the crowds, September is great. October the water temperatures can still be warm. If you want to explore without people, May is also great.
Apart from the coastline, Zagreb will be cold in the winter, with snow, and warm in the summer, with passing thunderstorms.
Miscellaneous Travel Tips for Croatia
Besides the obvious draws like the very touristy Dubrovnik and the bustling Split, look into Rovinj and Pula. Also, the islands should be explored.
You might be able to get to Rovinj from Venice via ferry. In Rovinj, you should try malvazija, a white wine local to the Istrian peninsula in northern Croatia. Check out Figarola Island for wild beaches. Also nice is Golden Cape Forest Park south of the old town. Blitz is an art festival held in September.
The Jadrolinija ferry is a nice, if perhaps slower, way to travel between Dubrovnik, through the islands and up to Split (and beyond).