Hi Sap,
start from the end:-
3). if it is sunny during the day, ambient temperature on the beach could waver between 30 deg. C to 36 deg.C. Not too long exposure to sun, as it increases risk of skin cancer;
2). very much dependent on your own body temperature. Temperatures at night, where there has been no rain at all during the day is around 26-28 deg.C. Temperatures drops slightly by 0.5-1 deg C when it rains heavily with winds. Not sure how thick your woolens are? Even in the evenings, during official functions, it is not unusual for people to wear a jacket/blazer. Majority of dining areas in langkawi are non-airconditioned.
1). Weather pattern been rather difficult to predict these days, with El Nino, and recently two typhoon that luckily had been downgraded to storm, which hit the Philippines, then moving to Vietnam--if you have those foldable poncho that does not take up too much space in your luggage, you could bring it along--Be Prepared, right(?), but will be a bonus if during your stay, it is rain free days.
langkawi also experienced isolated showers, in that one part of Langkawi could be raining, but another part is rain free.
Hope you could catch some Yuletide spirits in some hotels in Langkawi.
Oh yes, thought, to advise you if you are not aware, recently it appears that Malaysian Governement is disallowing VOAs for people arriving from Chennai. Is this news properly disseminated in India?