(By the way, "tropical cyclone" is a blanket term that refers to tropical depressions, tropical storms, and hurricanes.)
![]() |
| A "cone of uncertainty" for Hurricane Irma (left) and Hurricane Harvey (right). Both cones are from 2017 and are therefore identical to each other in their construction. |
The size of the cone is fixed for every forecast of every storm during an entire hurricane season, but the size slowly evolves from year to year. If the storm is moving quickly, the cone will appear more elongated and if the storm is moving slowly, the cone will appear more compact... but it's the exact same cone. The examples shown above are from Irma (left) and Harvey (right); both storms occurred in 2017, so both cones are identical in their construction.
The cone is updated each year prior to the start of hurricane season, and it usually shrinks each year. Overall, hurricane track forecasts are gradually improving, meaning that in general, there is less uncertainty where a storm will track now than there was a couple decades ago.
The cone is updated each year prior to the start of hurricane season, and it usually shrinks each year. Overall, hurricane track forecasts are gradually improving, meaning that in general, there is less uncertainty where a storm will track now than there was a couple decades ago.
The map below shows a sample satellite image with the new 2026 cone overlaid on the 2015 and 2004 cones for comparison. In 2026, the cone is the smallest it has ever been at days 2-4 and then tied for the smallest at 1 and 5 days! The largest improvement over last year's cone is at the 2-day lead time, with a 7.4% reduction in size.
So just how is the size updated each year? The National Hurricane Center uses its own track forecast errors over the previous five years to calculate a circle at each "lead time" (1 day, 2 days, ... 5 days). The size of that circle is designed to enclose the position of the storm's center with 2/3 probability, meaning that there's historically a 1/3 chance the storm will track outside the circle at that time. Lines connecting the various circles complete the shape of the cone. [Note that the 2026 cone size is thus determined from track errors during the 2021-2025 seasons.]
This next chart shows the evolution of the cone's size at each forecast day -- it's clear that progress is slowing and perhaps has reached a limit at some forecast lead times.
Improvements are getting increasingly challenging to achieve because there can never be a perfect forecast of a chaotic system like the atmosphere. We call this a "limit of predictability", and there will come a time when we reach it and meaningful improvements can no longer be made. Some would argue we are very close to that limit. It's critical to understand that forecasts evolve and there is always some amount of uncertainty in them.
Since the cone is so widely used yet sometimes misunderstood, here are some key refreshers:
- The cone does not tell you anything about where impacts will be experienced. It is NOT a "cone of concern"! Even for a perfect down-the-middle track forecast, impacts such as strong wind, heavy rain, storm surge, and tornadoes will extend beyond the cone. Cone graphics on the NHC website include some of the relevant watches and warnings, as shown in the examples at the top of the post. Given its positive reception during the past couple of years, tropical storm and hurricane watches and warnings will be displayed inland too, not just on the coast (see this example from Milton 2024).
- The cone does not tell you anything about the size of the storm. Regardless of how strong they are, hurricanes come in a wide range of sizes. Back in 2017, NHC added the latest observed size of the wind field to its cone graphics to help illustrate this (see the Irma and Harvey examples above... the orange and red shading indicates the extent of tropical storm and hurricane-force winds at the time the forecast was issued).
- The cone does not tell you anything about the actual uncertainty associated with the forecast. Since the size of the cone is fixed, it cannot become more narrow or broad to accommodate a more or less predictable environment.
- Nothing magically happens at the edge of the cone. If a hurricane is approaching and you are scrutinizing each new forecast to see if you are inside the cone or not, you are missing the point of it. It is arbitrarily chosen to be the 67% historical probability threshold... a 75% probability cone would be larger, and a 50% probability cone would be smaller. Again, it is NOT a "cone of concern"... there is no such thing.
- If you use the cone graphics from NHC, there is some information about intensity provided. At each forecast point, there is a letter written inside the black dot corresponding to a general intensity range: D (tropical depression), S (tropical storm), H (hurricane (Category 1-2)), and M (major hurricane (Category 3+)). But keep in mind that there is uncertainty associated with the intensity forecasts too!
To create the next figure, I simply averaged five years of intensity errors together such that the values listed for 2026 are based on the NHC's intensity errors during the 2021-2025 seasons (and 2025 used 2020-2024, and so on). This five-year averaging helps to mimic the smooth trends of the track forecast cone, but it is not a 2/3 probability like the track cone. Although not quite as convincing as track, one could make the case that we are nearing the limit of predictability for intensity at several lead times too.
Next, using a made-up five-day intensity forecast and the average error values for 2026, I created the following chart. This is what an intensity forecast cone could look like; a hypothetical intensity forecast is shown with the red line and the "cone of uncertainty" is the light red shading surrounding the forecast.
Anyone who lives on or near a hurricane-prone coast is undoubtedly familiar with the track forecast cone or "cone of uncertainty" which has been produced by the 
















.png)









