The long rainy season is from March to May which brings heavy downpours at times during the day. The Short rainy season is from October to December and is only called "short" because of the duration not the amount of rain.

Even though they are called the rainy season, there are still wonderful sunny days during that time. It might open up a huge downpour while you zip around in your LandCruiser, but other than that you will be fine.

There also might be some discounts on air and hotel in those seasons.