Hala-Bala receives on average 2.7 m of rain annually, in some years (e.g. 2001) almost 5 m, most of it in the south-east monsoon of October to January when it can rain for days and nights on end. But there are frequent afternoon thunderstorms, even in the 'dry' season of February to May, and especially during the south-west monsoon of June-September. The climate is always warm and humid, coolest during the monsoon and hottest during the dry season, but the interior of the forest remains mild and damp throughout. Leeches are most abundant after rain, and ticks after drought, but mosquitoes are relatively few and mainly diurnal.