Question

when the malabar coast is receiving heavy rainfall in july ,the tamil nadu coast is comparitively dry

Answer 1

Hey friend,

Malabar coast is on the western coastline of India whereas Coromandel (Tamil Nadu) coast is on the eastern coastline of India.
In June-July, the south west monsoon winds blow from the sea to the Indian landmass. These winds get divided into two-Arabian sea branch and Bay of Bengal branch.

The Arabian sea branch when blows over the landmass is obstructed by the western ghats causing heavy rainfall on the windward side of the ghats (where Malabar coast lies). Whereas, the Bay of Bengal branch is not obstructed by the Eastern Ghats, instead it goes parallel to the ghats leaving the eastern coastal area (where Coromandel coast lies) comparatively dry.