What would you like to know about the weather in Malaysia?
Set just to the north of the equator, Malaysia enjoys a tropical monsoon climate. It's pretty much hot and humid with a bit of rain throughout the year. Even in the middle of dry season don't be surprised to get a sudden, often very heavy downpour, but it's likely to be gone as quickly as it arrived.
Split between Peninsular Malaysia and Sabah and Sarawak (on Borneo), each area remains under the sway of the southwest and northeast monsoons, while a transitional period between the two delivers less rainy conditions. It's worth noting that Malaysia sees a fair amount of rain year round and it's not at all unusual to see a heavy downpour in the middle of what would be considered "dry season", so the wet season often seems to just be a slightly wetter dry season. The exception to this is the east coast of the peninsula, which sees considerably wetter conditions during the northeast monsoon.
The southwest monsoon runs from roughly May to October, while the northeast runs from November to March. Adding to the mix is typhoon season in the Western Pacific from April to November, which can see inclement weather hitting Sabah and Sarawak at random intervals.
When the southwest monsoon hits from May to October, it brings rain to the lowlands on the west coast of the peninsula and particularly the southwest coast between the capital of Kuala Lumpur and Melaka. To the northern end of the west coast of the peninsula, around Penang and Langkawi, the rain can be especially heavy in September and October.
While the west coast is getting heavy rain, the east coast of the peninsula is bathed in sunshine and dry weather. This changes however when the northeast monsoon blows in between November and March, bringing with it torrential rain and often flooding along the east coast of the peninsula. At this time most resorts on the islands along the east coast of the Malaysian peninsula close up till the rains ease.
Sabah and Sarawak are affected slightly differently. As with the east coast of the peninsula, the northeast monsoon brings with it extremely heavy rain, delivering over half of Sarawak's rainfall for the entire year. While the entire period from October to March is, well, damp, January in particular is a very wet time in both Sabah and Sarawak. The region is less affected by the southwest monsoon but they still see a fair amount of rain through the rest of the year.
There is no "right" time to visit Malaysia. As with Singapore, visitors to Malaysia should expect some rain whenever they go.
There are however certain areas that are particularly wet at times and best avoided then. The eastern coast of Peninsular Malaysia is best avoided during the northeast monsoon from November to March. This is the case partly because it will be heaving with rain a lot of the time and there may be flash floods, but also because most, if not all the accommodation on the Perhentian Islands, along with the other east coast islands, will be closed due to bad weather and rough seas.
Sticking with the peninsula, the northern part of the west coast of Peninsular Malaysia (Penang and Langkawi) can get quite a bit of rain in September and October. This is less of an issue in Penang, where a rainstorm is just a good excuse to eat more, than in Langkawi where visibility for diving is badly affected.
Another area best avoided is Sabah and Sarawak in January when the rain, even by Borneo standards, is torrential.
The best time to visit the east coast of the peninsula is from April or May to October, when you can expect calm waters and clear blue skies (most of the time).