Cyclones are violent tropical storms that form over tropical waters and involve the circulation of warm and cool air masses. They can cause heavy rain, flooding, and strong winds that damage homes and infrastructure. Countries most affected by cyclones include Bangladesh, India, Thailand, Malaysia, Indonesia, and Sri Lanka due to their locations near the Indian Ocean. Pakistan has experienced two major cyclones, the first in 1948 that killed over 1,000 people and the second in 1999 that caused damage but no deaths in Karachi.