Hurricanes are categorised in order to quickly convey their destructive potential. Bigger storms do more damage.
Traditionally hurricanes have been categorised using the maximum sustained wind speed, using the Saffir Simpson Scale:
The National Hurricane Centre still uses this scale, and you will still see hurricanes declared using this number system in the news.
The problems with wind speed
However there are several problems with this:
- Firstly the maximum sustained wind speed in a hurricane is often an estimate; it's not often reliably measured.
- Damage from hurricanes is caused by rain and flood or storm surge, not just the speed of the wind. By categorising hurricanes only using wind speed, we fail to take into account any of these factors.
Why is this a problem? Well some hurricanes can be very large and do lots of damage, but have low wind speeds.
A larger hurricane usually has a bigger storm surge, brings more rainfall and may have more embedded tornadoes. A larger storm is also more likely to bring damaging hazards to larger population centers.
Scientists recently published their findings that pressure was a better estimator of the damage caused by a hurricane.
The lower the pressure of a hurricane, the larger it will be and the more destruction it will bring.
Pressure can also be measured much more accurately than wind speed within a hurricane. These scientists proposed the National Hurricane Centre change their system. However they have to date resisted.
We use the system that is proposed by these scientists. We describe them using names in order to avoid confusion:
|Yokahu Category||Equivalent National Hurricane Center Category||Pressure||Expected Impact|
Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.
Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.
Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be unavailable for several days to weeks after the storm passes.
|Very High||4||945-926 mbar||
Well-built framed homes can sustain severe damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
|Extreme||5||925 mbar or less||
A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.
Over 90% of the time our scale matches the National Hurricane Centre scale. eg if they declare a Category 4 it will be a Very High Hurricane, 9 times out of 10.
10% of times the categories may differ eg a Category 4 may be upgraded to an Extreme or downgraded to a High by our system.
However we believe this system is better for you.
Why is this better for me?
Hurricane Categories are there to guide you on the danger and damage that can be caused by a storm. We analysed every storm advisory where pressure and wind speeds were available (every advisory for every hurricane since 1979). What we found was that using our categories we had a much better grouping of physical hurricane size of a hurricane. This then showed a stronger link to damage.
What this means for you is that you are more likely to receive the money you need, when you need it, after a storm with our system than if we relied upon the National Hurricane Center's categories. There will be examples of large hurricanes with low wind speeds which cause damage/loss to you similar to Hurricane Sandy in 2012 (that later became Superstorm Sandy). This was a Category 1 hurricane before landfall in New York, however it caused huge amounts of damage. Using our system this type of storm would be classified as Very High (the 2nd highest level). It this type of event were to occur again, then you would receive a larger payment from us than if we used the old system.