When is rainy season in Malaysia?

Monsoon season is around June in Tokyo and wet typhoons come in September.

(I informed myself some more using http://www.durianpalace.com)

The Thai fruit might be alright as the fruit is supposed to ripen off the tree... once the Thai Durians start showing any cracks in the membrane casing they're already over-ripe. I'll use my nose, shake the fruit and listen for some movement, expect the fruit to feel light for its size (the opposite to coconuts), check for cracks and holes, and look carefully at the stem (which should be thick, healthy looking and emit a clear sweet sap - just as figs do - milkiness is a no-no).