What are the conditions for a hurricane to form? Enumerate various categories of Hurricanes as per Saffir-Simpson hurricane scale.

A hurricane is a type of tropical cyclone storms, generally, begin as clusters of thunderstorms over tropical ocean waters.
Conditions for the formation of Hurricane:

1. High water temperature at least 26-27 Celsius
2. Relatively moist air Very warm surface temperatures
3. A continuous evaporation and condensation cycle
4. Air pressure difference between the surface and high altitude
5. Wind convergence 

Based on regions tropical cyclones are given various names for example in the Atlantic or Eastern Pacific such storms are hurricanes, In the western North Pacific, they are typhoons and in the South Pacific and the Indian Ocean, they are cyclones. The intensity of Hurricane is measured by Saffir-Simpson Scale. Based on wind velocity hurricanes are classified into following categories:

1. Category 1: wind 74-95 mph (119-153 km/h)
2. Category 2: winds 96-110 mph (154-177 km/h)
3. Category 3: 111-129 mph (178-208 km/h)
4. Category 4: 130-156 mph (209-251 km/h)
5. Category 5: exceeding 157 mph (252 km/h)

WMO maintains six separate zone wise lists of alphabetical names which are used in rotation and recycled every six years. If a cyclone is particularly deadly and costly, then those names are retired and are replaced by another name. The recent Hurricane Irma which devastated Caribbean islands was one of the most powerful hurricanes in history with a wind speed of 185m/h(approx 300 km/h).