|Basin||Current YTD||Normal YTD||% of Normal YTD||Yearly Climo*||2020**|
|Western N Pacific||184.735||291||63%||298||149|
|Eastern + Cent N Pac||95.94||136||70%||132||77|
*Yearly climatology from historical 1991-2020 Tropical cyclone best track datasets
**Preliminary values from real-time ATCF advisories and will become final when best-tracks are available from JTWC and NHC after post-season analysis Small differences have been found in previous years between real-time and best-track ACE.
Southern Hemisphere Year-To-Date represents October 2020 - May 2021 activity.
|Tropical cyclone accumulated cyclone energy (ACE) has exhibited strikingly large global interannual variability during the past 40-years. In the pentad since 2006, Northern Hemisphere and global tropical cyclone ACE has decreased dramatically to the lowest levels since the late 1970s. Additionally, the frequency of tropical cyclones has reached a historical low. Here evidence is presented demonstrating that considerable variability in tropical cyclone ACE is associated with the evolution of the character of observed large-scale climate mechanisms including the El Nino Southern Oscillation and Pacific Decadal Oscillation. In contrast to record quiet North Pacific tropical cyclone activity in 2010, the North Atlantic basin remained very active by contributing almost one-third of the overall calendar year global ACE.|
|Figure: Global Hurricane Frequency (all & major) -- 12-month running sums. The top time series is the number of global tropical cyclones that reached at least hurricane-force (maximum lifetime wind speed exceeds 64-knots). The bottom time series is the number of global tropical cyclones that reached major hurricane strength (96-knots+). Adapted from Maue (2011) GRL.|
Last 50-years+ of Global and Northern Hemisphere Accumulated Cyclone Energy: 24 month running sums. Note that the year indicated represents the value of ACE
through the previous 24-months for the Northern Hemisphere (bottom line/gray boxes) and the entire global (top line/blue boxes). The area in between represents the Southern Hemisphere total
|Figure: Last 50-years+ of Global Tropical Storm and Hurricane frequency -- 12-month running sums. The top time series is the number of TCs that reach at least tropical storm strength (maximum lifetime wind speed exceeds 34-knots). The bottom time series is the number of hurricane strength (64-knots+) TCs.|
|Figure: Last 4-decades of Global Tropical Storm and Hurricane Accumulated Cyclone Energy -- Annual totals. The Southern Hemisphere tropical cyclone season occurs from July-June each calendar year. The graph is constructed such that SH annual value for July 2014 - July 2015 is positioned in 2015.|