When a hurricane threatens land, one of the most familiar images you’ll see on weather maps is the “cone of uncertainty.” This cone shows the probable path of the storm’s center based on forecast models, and it widens over time to account for the increasing margin of error or “uncertainty.”

However, it’s important to note that the widening isn't based on the uncertainty of that particular storm, but rather the historical margin of error over the last five years. Therefore, the cone “encloses the area where the center of the storm is forecast to be approximately 60-70% of the time over the next five days,” according to NOAA.

Each circle’s size is set so that two-thirds of historical official forecast errors over the last five years would fall within it.

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The narrow end of the cone marks the storm’s current location, while the widening shape shows where the center could be several days into the future, typically up to five days out.

It’s important to remember that the cone does not show where impacts will occur. Hazards like heavy rain, flooding, storm surge, and tornadoes often extend far outside the cone. In fact, dangerous conditions can affect areas hundreds of miles from the center line. The cone only represents where the eye of the storm might travel, not where the damage will happen.

The reason the cone expands over time is that forecasting a hurricane’s exact path becomes more difficult the farther out you go. Small differences in atmospheric conditions like wind shear, ocean temperatures, or the position of nearby weather systems can alter a storm’s trajectory. That’s why forecasters urge people to prepare for impacts even if they live outside the cone.

Jennifer Gray is a weather and climate writer for weather.com. She has been covering some of the world's biggest weather and climate stories for the last two decades.