The period June to September is referred to as the 'Southwest Monsoon' period. Southwest Monsoon period is the principal rainy season for the Indian subcontinent.  This is the summer monsoon period where the southwest monsoon holds away over the country.  The whole country receives nearly 75% of  its rainfall during this period.                    

                                Southwest monsoon sets in over the extreme southwestern tip of the peninsula by the end of May. The onset of Monsoon is charecterised by a sudden spurt of rainfall activity.  It progresses inland in stages and covers the entire  country by the middle of July.
                                    It starts retrieving from the extreme northwest by the beginning of September, progressively  receeding southwards.  
                                Out of the thirtysix (36)  meteorological sub divisions of the country , Coastal Karnataka receives the heighest area weighted rainfall of about 297 cms during the season. Other subdivisions of the state also receives considerable rainfall in this period.
                                 Subdivision consisting of Kerala and Lakshadweep receives about --%  of its  annual rainfall during SW Monsoon.
                                  Tamil Nadu is considered as a rain shadow region as it lies on the eastern (leaward side) side of western ghats   The total annual rainfall is maximum over the southmost part of the state.  In this period the state receives only 32% of its annual rainfall.
                                  The  highest mean point rainfall  of about 837 cms occurs over Mausingram in Meghalaya where as the lowest of about 5.2 cms occurs over Pamban in Tamilnadu.
                                   Chirapunji in Meghalaya recorded 156.3 cms of rainfall on 16th June  1995. This is World's highest recorded rainfall in a day.