We haven't even gotten around to posting our traditional end-of-May/beginning-of-the-hurricane-season look at the various forecasts for the Jun1 - November 30 season. Maybe next week.
From Yale Climate Connections, July 21:
It’s been one of the least active years on record for tropical cyclones in the Northern Hemisphere. That could change soon.
lash floods have been front and center in this month’s U.S. weather picture, while tropical cyclones have been mostly lying low, as we discussed in our July 18 Eye on the Storm post. The year’s fourth named storm of the Atlantic season has only low odds of developing this week from a bubbling disturbance in the tropical Atlantic, and it looks unlikely to become a serious threat to land even if it does get organized.
It’s not just the Atlantic that’s been quiet. Each of the four basins of the Northern Hemisphere that generate tropical cyclones — the Atlantic, Northeast Pacific, Northwest Pacific, and North Indian Oceans — is now running below average on accumulated cyclone energy, or ACE, a function of peak wind speeds and storm longevity. For the hemisphere as a whole, the total ACE to date is the third-lowest in records dating back more than half a century.
year from January 1 through July 21, 1971-2025. (Image credit: Data courtesy Colorado State University)
The graph above shows Northern Hemisphere ACE for each year from January 1 through July 21, starting with 1971, the first year of reliable data from the Northeast Pacific. The ACE to date of 45.5 is only about 41% of the climatological average for the period 1991-2020. The only years with lower ACE at this point were 1977 (23.0) and 1998 (39.1).
The table below, from the Real-Time Global Tropical Cyclone Activity page maintained by Colorado State University, shows how each basin on Earth is faring on various measures of tropical cyclone activity. The Northern Hemisphere hasn’t been slack in producing named storms: the total of 16 thus far is actually at the year-to-date average. It’s just that the systems that do develop haven’t been surviving long or intensifying much. The cumulative longevity of each named storm (or “named storm days” in the table below) is only about two-thirds of average. As for hurricane-strength systems — which are called typhoons in the Northwest Pacific and severe cyclonic storms in the North Indian Ocean — their cumulative longevity is a mere 27% of average.
Figure 2. Summary global and regional statistics for tropical cyclones in 2025 as of July 21. (Image credit: CSU)
....MUCH MORESurprising at it may seem, given how active the Atlantic has been over the past 30 years, the total number of tropical cyclones on Earth hasn’t increased in recent decades, although the strongest hurricanes, typhoons, and cyclones are getting more intense on average.
In its 2021 assessment, the Intergovernmental Panel on Climate Change concluded that these trends are liable to continue:
- “the proportion of Category 4-5 TCs [tropical cyclones] will very likely increase globally with warming”
- “it is likely that … the global frequency of TCs over all categories will decrease or remain unchanged”
Though they’re in a minority, a few researchers have found evidence in high-resolution modeling for a potential global increase in tropical cyclone numbers, including Kerry Emanuel of the Massachusetts Institute of Technology.
Looking region by region at 2025 thus far....
Regarding ACE, a repost from June 8, 2021:
2021 Accumulated Cyclone Energy
It is such a crude measure of the energy expended by hurricanes, cyclones and typhoons but it is the best we have. I mean ideally we would compute the energy in every invest/tropical disturbance, tropical storm, cyclone on up through the supertyphoons of the Pacific. But we can't.
The numbers are so crazy big that they become almost meaningless. The energy required to get and keep the big ones spinning is best measured in petaoules of the heat required for that task and the heat required to lift the water that falls as rain.*
So instead we use ACE.
From Climatlas:
2021 Accumulated Cyclone Energy [ACE]
| Basin | Current YTD | Normal YTD | % of Normal YTD | Yearly Climo* | 2020** |
|---|---|---|---|---|---|
| Northern Hemisphere | 63.2600 | 41 | 154% | 568 | 436 |
| Western N Pacific | 46.0225 | 30 | 153% | 302 | 149 |
| Eastern + Cent N Pac | 2.2475 | 3 | 74% | 138 | 77 |
| North Atlantic | 1.13 | 0 | % | 104 | 183 |
| North Indian | 13.86 | 6 | 231% | 18 | 26 |
| Southern Hemisphere | 184.005 | N/A | N/A | 212 | 144 |
| Global | 207.4920 | 213 | 97% | 765 | 584 |
**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.
....MUCH MORE
*From NOAA:
How Much Energy does a Hurricane Produce?The energy released from a hurricane can be explained in two ways: the total amount of energy released by the condensation of water droplets (latent heat), or the amount of kinetic energy generated to maintain the strong, swirling winds of a hurricane. The vast majority of the latent heat released is used to drive the convection of a storm, but the total energy released from condensation is 200 times the world-wide electrical generating capacity, or 6.0 x 1014 watts per day.
If you measure the total kinetic energy instead, it comes out to about 1.5 x 1012 watts per day, or ½ of the world-wide electrical generating capacity. It would seem that although wind energy seems to be the most obvious energetic process, it is actually the latent release of heat that feeds a hurricane’s momentum.
To Calculate:
-
Method 1 – Total energy released through cloud/rain formation: An
average hurricane produces 1.5 cm/day (0.6 inches/day) of rain inside a
circle of radius 665 km (360 n.mi) (Gray 1981). (More rain falls in the
inner portion of hurricane around the eyewall, less in the outer
rainbands.) Converting this to a volume of rain gives 2.1 x 1016 cm3/day. A cubic cm of rain weighs 1 gm. Using the latent heat of condensation, this amount of rain produced gives5.2 x 1019 Joules/day or
6.0 x 1014 Watts. -
Method 2 – Total kinetic energy (wind energy) generated: For a
mature hurricane, the amount of kinetic energy generated is equal to
that being dissipated due to friction. The dissipation rate per unit
area is air density times the drag coefficient times the windspeed cubed
(See Emanuel 1999 for details). One could either integrate a typical
wind profile over a range of radii from the hurricane’s center to the
outer radius encompassing the storm, or assume an average windspeed for
the inner core of the hurricane. Doing the latter and using 40 m/s (90
mph) winds on a scale of radius 60 km (40 n.mi.), gets a wind
dissipation rate (wind generation rate) of1.3 x 1017 Joules
1.5 x 1012Watts.
Reference: Emanuel, K. A., (1999): “The power of a hurricane: An example of reckless driving on the information superhighway” Weather, 54, 107-108
There are some good energy comparisons on the web. I know Vaclav Smil did some calculations of all the hydrocarbon energy ever used by humans and got to 5.3 yottajoules (YJ — 24 zeros) for coal and 4 YJ for oil. I'll dig it up before the first landfall
And a note on the historical distribution of storms across the season:
The official hurricane season for the Atlantic Basin (the Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico) is from 1 June to 30 November. As seen in the graph above, the peak of the season is from mid-August to late October. However, deadly hurricanes can occur anytime in the hurricane season.
