As many as 15 district administrations, including Chennai, have declared a holiday for schools and colleges on Monday.
The weather department has forecast heavy to very heavy rains over Tamil Nadu and neighbouring Puducherry till Tuesday.
According to the department, the low pressure may concentrate into a depression by Monday, while the landfall time can be estimated later on Monday.
In many areas, fallen trees disrupted vehicular traffic.
Civic officials pressed into service high-powered pumps to remove water from subways and inundated residential areas.
Anna University has postponed all exams slated during November 16-18 due to the rain.