Missed this earlier. Depending upon your interests, I would head west towards Swanage and the coastal path as natural history abounds!
Take in the following:
Studland Bay Nature Reserve
Old Harry Rocks
Lulworth Cove
Durdle Door
Corfe Castle
Amazing coastline with ample evidence of pre-historic fossils and great scenery and wildlife - weather looks as though it may be reasonable to good too!