Hey, Dubrovnik in March is similar to Split, although you can get more sunny days in Dubrovnik and a bit warmer temperature, about 16c-17c, the biggest benefit is more sunny days compared to Split. 

Heres a general guide on what to expect in Croatia in March: Croatia in March Weather, Things to do and see & other tips for visiting Croatia in March

Weather in March in Dubrovnik is similar to Split but you get more sunny days, so when you visit you can explore alot around if its not raining. The weather is not stable so really depends if you have luck or not.

Here are best things you can do in Dubrovnik in March and generally, only thing you can exclude is swimming, but if its sunny weather you can try to sunbathe as under sun it will feel much warmer, in the evening you still need layering. 

16 Best Things to do in Dubrovnik, Croatia

Top 5 Day trips from Dubrovnik