Accumulated Cyclone Energy (ACE) values on our site are not official values. The values on our site are calculated from best track data and not advisory data. This index is calculated by summing the squares of each estimated 6-hourly maximum sustained wind speed, in knots, for all periods in which the tropical cyclone is a tropical storm or greater in intensity (sustained winds of 34 kts or greater). For best track files where the level of development for each storm position is noted we do not include any period where the storm was subtropical or either extratropical or post-tropical in the main value, but we do provide additional values that include this information as long as the wind speed was at least 34 knots. If the level of tropical cyclone development is later adjusted to a tropical storm or higher in the best track file for positions where the storm had not yet been upgraded to a named storm at the time, then these positions are also included in the calculation for this index, even if the name listed at the time is still the depression number or invest.