If you are on a sailing holiday in Malaysia then the weather plays an important part in your decision as to when to go, well the good news is that the whole of Malaysia has a classic equatorial climate with high temperatures and wet months throughout the year. Temperatures at sea level range from 21C to 32C and the annual rainfall varies from 2,000mm to 2,500mm.
The islands off the Western side of the Malay Peninsular, including Langkawi, are typically tropical, hot, sunny and humid with showers all year round, as per all tropical climates. This area of Malaysia is quite unaffected by the monsoon period, this is in part due to the moderate climate of the Andaman Sea and also that it is protected by the Indonesian island of Sumatra. However during September and October the showers do tend to be heavier, though it is still quite possible that during a 1 or 2 week holiday at this time of year you may only experience the occasional short tropical downpour, which often is a welcome relief from the humidity!
If you are planning on doing some diving whilst on your sailing holiday in Malaysia, then September/October are the best months to avoid, as the seas are heavier and therefore visibility is much poorer than at other times of the year.