Forecast India
The ECMWF model over the subcontinent. Surface fields at 0.1° — about 11 km — and eleven pressure levels alongside them, out to fifteen days.
The four homogeneous regions
IMD monitors the monsoon on these four, and on the country as a whole. Every rainfall figure in a seasonal bulletin is issued for one of them.
Northwest India
The plains and hills from the Thar to the Karakoram. Monsoon arrives last and leaves first, and winter rain here comes from western disturbances rather than from the monsoon at all.
Central India
The core monsoon zone. Most of the season's rain falls from depressions that form over the head of the Bay of Bengal and track west-northwest across the peninsula.
South Peninsula
Where the monsoon makes landfall, and the one part of India with a second rainy season — the northeast monsoon of October to December, which is the main one for Tamil Nadu.
East and Northeast India
The wettest ground in the country. The Meghalaya plateau forces the Bay branch of the monsoon straight up, and Mawsynram and Cherrapunji record some of the highest annual rainfall on Earth.
All thirty-six states and union territories
The thirty-six IMD meteorological subdivisions
The units the monsoon is actually measured in. These are not the states — some split one, some merge several, and some cross a state line.