Why a hurricane's 'cone of uncertainty' matters even for those who live outside of it

The cone of uncertainty.

The good news is thatbecause forecasts of hurricane trackscontinue to improve and become more accurate, the cone of uncertainty has been shrinking with each new hurricane season.

However, a smaller forecast cone also means we need to be sure we understand what the cone is and what it represents when a hurricane is tracking into our region.

What is the cone of uncertainty?

The National Hurricane Centre (NHC)says the cone represents the probable track of the centreof a hurricaneand is formed by enclosing the area swept out by a set of circles along the forecast track (at 12, 24, 36 hours, etc).

"The size of each circle is set so that two-thirds of historical official forecast errors over a five-year sample fall within the circle," the centre says.

There are some important takeaways there. Most notably,the cone represents where the centre of the storm might track, and it isbased on how good or how bad the NHC forecast has been over the past fiveyears.

So if we base this year's cone on NHC forecasts over the previous fiveyears, the centre of the storm can be expected to remain within the cone of uncertainty roughly 60 to 70 per centof the time.

One of the most important things to remember when looking at a projection track and cone is that a hurricane is not a point.

Even if the forecast track is accurate and the centre of storm remains within the cone of uncertainty, impacts can be experienced well outside of the cone. Hurricanes, tropical storms and even post-tropical storms can be large systems and the cone does not take into account the size of the storm.

On this side of the border, the Canadian Hurricane Centre (CHC) has also added the cone of uncertainty to its official track maps in recent years.

You may also notice on the CHC hurricane track mapthat some storm tracks are in red and some are in blue. The difference here is that when the CHC issues bulletins on a storm, it will appear in blue, while storms being tracked only by the NHC are in red.