On a macro level there are 2 main seasons when trade winds are either predominantly from the Northeast (NE Monsoon) or from the Southwest (SW Monsoon). However, individual cruising regions have different weather. Please see below for more details.
Andaman Sea Weather (Mergui, Phuket, Langkawi)
The best time for a yacht charter in Phuket and the Andaman Sea region is during the dry season, between December and April. The region has a moderate temperature all through the year within the range of 23°C to 31°C. It has a tropical climate. There are no severe climate conditions except for tropical storms and rains in late summers and monsoons. The monsoons (May to August) and post-monsoons (September to November) are accompanied by medium to heavy rain falls.
Komodo & Flores Weather (Lesser Sunda Region)
The area due east from Bali is the Komodo – Flores region and is best visited by yacht between the months of April and October. In general Indonesia has two yearly seasons of monsoon winds: the southeast monsoon (dry) and the northwest monsoon (rain). The dry season usually runs from the end of April to the end of September and the rainy season from November to March. The exception to this pattern is the Raja Ampat/Banda region where seasons are reversed (more rain falls between May and September).
Bali’s weather follows the normal Indonesian pattern of a dry season from May to September and a rainy season from November to March. Bali weather is typical of the tropics, where the sun rises around 6am and sets at 6pm most of the year. In general temperatures vary between 25°C and 30°C, and the humidity between 65% and 85%.
Komodo National Park has the driest climates of Indonesia. Komodo National Park has little or no rainfall for approximately 7 months of the year (between April and October). Most of the annual rainfall of between 800mm and 1000mm will come between the months of November to March. Mean daily temperatures in the dry season from May to October are around 30°C.
In Komodo the highest annual temperature in the park is 43 °C, the minimum is 17 °C. November is the hottest month of the year. The highest humidity is in February at 86%. The lowest humidity is in October at 75%.