Best
As a surfer, you should be aware that wave action peaks in winter (from November to April). This time of year, kite-surfing seems to be surpassed. Water visibility is regarded to be best in the calm month from June to August.
Avoid
Don't attempt an ascent of Fanispan in the height of the rainy season from May to September. Diving and snorkelling is virtually impossible between November and April because of windy climate and visibility drops.
Activities
In case you are seeking for outdoor activities, Vietnam may be the best choice. Although you have to leave your sun-lounger and make an effort but the feeling of experiencing those activities is really amazing.