A tropical cyclone is a large storm that forms over warm ocean water and has high winds and heavy rain. They are one of nature’s most powerful storms. The ingredients needed for a storm to form are:
- Warm ocean water - sea surface temperatures at least 80°F extending at least 50 meters deep, that’s why hurricanes weaken over land or cold water.
- Atmospheric instability - The surrounding air must be warm and moist, allowing it to rise rapidly and form heavy storm clouds and thunderstorms.
- Coriolis effect - the Earth's rotation must provide a rotational spin, which means the system must develop at least 5 degrees latitude.
- Low vertical wind shear - Winds high and low in the atmosphere must blow at similar speeds and directions.
- Mid-level moisture - High relative humidity in the middle troposphere is necessary to sustain thunderstorm growth.
- A starting weather trigger - such as a tropical wave or cluster of thunderstorms, is needed to begin the low-pressure circulation.