*The Accumulated Cyclone Energy (ACE) Index is calculated by summing the squares of the estimated 6-hourly maximum sustained wind speed in knots (Vmax2) for all periods in which the tropical cyclone is a tropical storm or greater intensity (sustained winds of 34 kt or greater). Note that the official NOAA definition of the ACE Index does not include those periods when the system is characterized as sub-tropical. However, we are including this information to allow for comparison between individual cyclones across all basins, many of which contain records which inadequately distinguish between tropical and subtropical cyclones. For a complete description of the ACE Index see Bell and Chelliah (2006), Journal of Climate (19) 590-612. |
The Saffir-Simpson Scale for Tropical Cyclones |
Category | Miles Per Hour (mph) | Knots (kt) | Kilometers Per Hour (km hr-1) |
Tropical Storm (TS) |
39-73 | 34-63 | 63-118 |
Cat 1 |
74-95 | 64-82 | 119-153 |
Cat 2 |
96-110 | 83-95 | 154-177 |
Cat 3 |
111-130 | 96-113 | 178-209 |
Cat 4 |
131-155 | 114-135 | 210-249 |
Cat 5 |
156 or greater | 136 or greater | 250 or greater |