How is Langkawi in the end of September? Rainy?
Might be rainy, might not. I have lived in Malaysia for over a year , it can be dry for about a fortnight then rain every day for an hour or so (like it is right now). It is very rare that you will get a whole day of rain, usually one or two hours then its back to sunshine ! Don't worry too much about the weather, even if it does rain its still really warm !