What season sleeping bag needed for Madagascar?

Going to Madagascar travelling for a month from mid-July to mid-August this year. Unsure as of temperature?? Camping all month, will be visiting Ranomafana NP, Isalo NP and then spending some time at Tulear, amongst visiting a couple of other places around and about these areas. Currently have a between1&2 season sleeping bag and both a silk and a fleece liner.. which to take?? will sleeping bag plus either liner be warm enough or am i better to get a thicker sleeping bag?? have heard it will be nippy during the nights, but surely the temperature can't fall that low can it?!!