Other contributors have said "The most powerful storm it is a large swirling low pressure system that forms over the?" is the same question as "What is a large swirling low pressure system that forms over tropical waters?" If you believe that these are not asking the same thing and should be answered differently, click here
What is a large swirling low pressure system that forms over tropical waters?
A storm system called a 'Tropical Depression' also known as a 'Hurricane' if it forms over the Atlantic, a 'Cyclone' if it forms over the Indian Ocean and a 'Typhoon' if it forms over the Pacific.