Are Hurricanes and Typhoons Less of a Threat?It should be clear by now that there is a lot of year-to-year variability in the number, location, and strength of Hurricanes and Typhoons. Typhoons are hurricanes that are west of dateline. There are the hurricanes in the Atlantic Basin and Caribbean and also
off the west coast of mainly Mexico which typically move NNW. Typhoons form in the more western Pacific. The Pacific Hurricanes have their own names, different from that form East of Central America extending to the Eastern Atlantic. Since these generally move out to the Pacific and die, they most often directly impact the Baja and not the United States directly. And Typhoons use yet another pool of names. Actually there are six separate basins, each with their own set of names. So if you want something named after you, your odds go up.
The damage potential of a hurricane or typhoon is proportional to the square or cube of the wind field. Minor hurricanes, although more numerous, do not do nearly as much damage as a major hurricane is capable of doing. Keep in mind that a building does not have to be totally destroyed to be “totaled”. If something like 50% of the building is destroyed, it is a total loss.
Two different measures (maybe more) are used to describe the damage potential or strength of a hurricane (or typhoon). One is the Hurricane Severity Index (HSI) and another is the Accumulated Cyclone Energy (ACE). And no doubt there could be more.
The HSI defines the strength and destructive potential of a storm. This index, in the aggregate, includes all storms, not just hurricanes. The principal feature of this storm is that the size of the storm may be as important as its peak wind speed. Points are given (1-25) for the size and another set form (1-25) for intensity. So a storm is categorized as a score between 1 and 50. This includes all storms from tropical storms through hurricanes and typhoons.
A better know and more widely quoted index is the ACE index. It is used by NOAA. It is computed by taking the wind speed for all tropical storms and hurricanes and summing the square the maximum speed (in knots) and doing this every six hours. That addresses the maximum wind speed and duration. For convenience the result is divided by 10,000. The units are then 104 kn2 . The contribution of storms in the Atlantic Basin to the Global total of is shown in the accompanying figure in light grey, where as the global total is shown in dark grey. You can see the Atlantic Basin is a little lower that it has been for much of the past several decades, but it is normal when compared to all years. Yet the Global ACE value is lower that normal. The trends do not support some of the scenarios put forth by Global Warming enthusiasts.
Both of these indexes show great annual variability. ACE values ranging from near zero to 250 the focus of HSI is on characterizing individual storms, rather than climatology.
In recent years, pacific activity has picked up. Even so, there has been an overall apparent decrease in the numbers of global storms particularly in the Atlantic basin.