When should I visit the south coast?
The south and west coast are usually strongest from roughly December to March, when many travellers plan Hiriketiya, Weligama, Mirissa, Galle, and safari add-ons.

Sri Lanka is not a one-season island. Match your month to the right coast, safari area, and pace of trip.
The south and west coast are usually strongest from roughly December to March, when many travellers plan Hiriketiya, Weligama, Mirissa, Galle, and safari add-ons.
For Yala and Udawalawe, dry periods can improve visibility around water and open ground. Still, a good operator should advise based on current conditions, not only a generic month chart.
Yes. Off-peak trips can be excellent if the itinerary is built around the better coast, flexible days, and realistic weather expectations.