There are a ton of weather terms that might be easy to confuse including hurricanes, tropical depressions, and tropical storms, and tropical disturbances. Here’s the difference.
Tropical disturbance forms over waters of at least (80F). It is an area of organized thunderstorm activity 100 - 300 miles in diameter which maintains its identity for 24 hours or more, and it’s in the lower levels of the atmosphere (surface). If the disturbance acquires a spin, and winds of at least 30 mph. It is now called a tropical depression.
Tropical depressions form when a low-pressure area is accompanied by thunderstorms that produce maximum winds below 39 mph.
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Tropical Storms usually develop from a tropical depression, once the depression’s winds reach between 39 and 73 mph. They also must follow a cyclone pattern to become a storm. At this point, the storm will also receive a name. By this time, the system tends to be better organized and its winds and convection are closer to its center. Water temperatures under the system are usually above 80 degrees Fahrenheit.
Subtropical storms are similar to tropical storms as they can develop over tropical or subtropical waters with a temperature of at least 70 degree. They also have a closed circulation, but the difference is its organization. Usually, their maximum winds occur well far from its center (at more than 60 nautical miles from it) and tend to be messy, meaning not symmetric. Its rains are usually shifted to the side.
If a storm’s maximum sustained winds exceed 74 mph, then it becomes a hurricane.
Hurricanes are further rated into five categories based on their wind speed:
Category 1: 74-95 mph
Category 2: 96-110 mph
Category 3: 111-129 mph
Category 4: 130-156 mph
Category 5: above 157 mph
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