My favourite time of year to visit the beach is actually the Winter. You can't beat Southwold on a cold, crisp and sunny day. After the end of September, you can let your dogs off the lead so they can have fun too.
Since it is so quiet, it's also a perfect time to take in the beach huts in all their glory. It's hard to pick a favourite, but I actually like the smaller and less posh ones!
Park at Gun Hill which is the Walberswick end of Southwold, and you may be able to get one of the free spaces if it's quiet otherwise there's a pay and display there too. You can start the walk with a coffee at the Gun Hill cafe, walk up to The Harbour at Walberswick for lunch and the perhaps a drink at the Sail Loft before home!