Best time of the year to visit Penang: December-March

• December - March is the best months to visit Penang due to lower rainfall
• Try to avoid September-October, April-May, as these are the wetter month
• Temperature wise, honestly it doesn't change much all year round. Daily maximum temperature is around 31C any time of the year, and daily minimum is around 23C any time of the year. There's really no "winter" or "summer" here because of Penang's geographic location close to the equator
• There's also no such thing as busy season because Penang is not a major international tourist hub like Thailand (yet). There's always going to be a stream of tourists there but it doesn't change much by season

Penang Rain Fall by Month (source)

Penang Average Temperature by Month (source)