WEATHER BLOG: Evolution of hurricane forecast cones

National Hurricane Center forecasters issue forecast cones for tropical cyclones. These cones have improved considerably since their inception.

The 2022 Atlantic hurricane season has been relatively quiet, especially since we expect above-average tropical activity this season. After a period of tropical inactivity, the arrival of Invest 97-L last weekend marked the awakening of the Atlantic. It should be mentioned that we are currently one month away from the peak of hurricane season.

Invest 97-L’s chances of development have diminished over the past day, making it unlikely to become a named storm and get a forecast cone.

Forecast cones are synonymous with hurricane season. You know what they look like, but do you know how see at their?

A forecast cone indicates probable trace of the center of a tropical cyclone. Since the size of the storm is not taken into account, impacts can extend beyond the cone. These impacts can include strong winds, heavy rain, storm surge, flooding, tornadoes – basically what you find between the eyewall and the rain bands.

Forecast cones are created by circles placed along the forecast path. These circles are based on the last five years of forecast errors. The size of each circle is such that two-thirds of these forecast errors fall within the circle. Longer-range forecasts have higher error, which is why the forecast cone’s probability circles – and therefore, the forecast cone – get larger farther from the storm.

Three days later, the NHC error (circle of probability) is 100 miles. This means that the 72 hour forecast cone is 100 miles in diameter. At five days, the error is 200 miles.

The first forecast cones were issued in 1970, and they were only out for three days. More than 30 years later, they have been expanded to include the fourth and fifth days.

Forecast cones have improved dramatically over time – and not just due to extended lead times. In the 1970s, the average three-day track error was about 375 miles. Over the past two years, the average track error for the same period has decreased to 75 miles.

Here’s a better visualization: let’s compare hurricanes Rita (2005) and Laura (2020). Both made landfall in western Louisiana. Here’s what their forecast cones looked like 48 hours before landing. You can see how much the forecast has improved over the past 15 years alone, as shown by the narrower cone for Laura.

These improvements are all due to advances in technology and weather observations. And, they’ll only get better over time – keeping us safer in the process.

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