Wind speed tells you how strong a hurricane is. Size tells you how much it can do. This page adds size to the record: the radii of gale-, storm- and hurricane-force winds, the radius of maximum wind and the outer closed isobar from NHC's extended best track. From those it builds 2-D surface wind fields for every six-hourly fix, which give integrated kinetic energy (IKE), power dissipation (PD) and wind swaths for every storm since 1988. It also asks whether tropical cyclones are getting bigger.
Each panel shows one size measure, year by year: the mean over all six-hourly fixes of tropical or subtropical storms at tropical-storm strength or stronger. It is a mean because NHC reports radii in 5–10 nm steps, which makes yearly medians too coarse to show a trend. Lines are Theil–Sen trends, fitted separately to the full record and to 2004 onward, when NHC began best-tracking the wind radii after each season. Red means growing, blue means shrinking, and grey means the trend is not significant (Mann–Kendall p ≥ 0.05).
ACE depends only on peak wind. IKE counts all the kinetic energy in the ≥34-kt wind field, so a large Category 1 can carry more than a compact Category 4. The ratio of the two shows how much of a season's energy comes from size rather than peak intensity.
A calendar year is an arbitrary cut, and in the southern hemisphere it falls in the middle of the season. A running sum has no boundary at all — every point is a full year, or two, of activity ending in that month — so the hemispheres can be added together honestly and a busy season reads as a plateau instead of being split across two bars. This is the treatment the global ACE curve has always had, applied to integrated kinetic energy and power dissipation.
share of six-hourly fixes, by quadrant-mean R34 (nm)
fixes per cell (shading); median R34 at each intensity (line)
median R34 (nm) · median RMW of hurricanes (dashed)
median R34 (nm) by month
median R34 (nm) by day since reaching 34 kt