Langkawi is a beautiful group of 99 islands off Malaysia, a family holiday alternative to island destinations like Phuket and Pattaya. It is a tropical rainforest through and through, hence the best time to visit this place is the dry season, that is from January - March. With no rain during this time and sunshine for long hours, you are bound to bask in warm climes. 

This is the heavy tourist season, from January - March where the sun is merciful and rains almost non-existent. The season actually begins from October through November and goes well on until April. With average temperatures around 34°C, this is the perfect time to visit Langkawi. But since it is the tourist season, expect higher rates on almost everything.

April - August is the mid season, with infrequent rainfall, cloudy skies and the occasional thunderstorm. Showers are torrential and happen around late afternoon, temperatures cool to about 30°C. But often because Ramadan falls in one of these months, most hosts and shopkeepers fast all day, leave work for prayers and are eager to go home. It might not be the best time if you are a first time visitor as you will miss a lot of exploring and shopping. 

September - October is the main monsoon here. Avoidable at best even though it rains for only two hours a day. If you like some rain and relative cool (temperatures are about 27°C) then this is the time to visit. You will get to see the lush, wet greens and a fertile land all around. But the ocean waters may get choppy sometimes and restrict water sports.