The forecast cone and why it’s often misunderstood

Delayed evacuations in Lee County during Hurricane Ian bring the issue front and center

Responders from the de Moya Group survey damage to the bridge leading to Pine Island, to start building temporary access to the island in the aftermath of Hurricane Ian in Matlacha, Fla., Sunday, Oct. 2, 2022. The only bridge to the island is heavily damaged so it can only be reached by boat or air. (AP Photo/Gerald Herbert) (Gerald Herbert, Copyright 2022 The Associated Press. All rights reserved.)

By now, you’ve seen some of the haunting images coming out of Florida in the wake of Hurricane Ian.

The destruction is jaw-dropping when you look at the before and after satellite pictures.

Now, as the death toll grows, so too does the finger-pointing. Should something had been done differently?

The reactions are becoming increasingly political. The epicenter of the frustrations are in Lee County, where the majority of deaths from Ian occurred.

County officials are getting criticized for not evacuating residents in vulnerable areas sooner. The counter to that argument is that the hurricane “took a turn” and caught some people by surprise. Even with evacuations, according to Lee County officials, people opted not to leave because they didn’t expect it to be that bad.

While most of Lee County was within the forecast cone over a 5-day period and the surge forecast warranted some evacuations, it wasn’t until a day before, as Ian passed over Cuba, that hurricane warnings were extended south to include the southwestern stretch of the Florida coast.

There was a significant gap between the opinions of computer models until about 36 hours out.

Many times, models come into agreement sooner than this, but that disagreement is taken into account by the forecast cone. Ian proved to be more difficult than most when it came to nailing down the features that directed the storm.

Graphics belong to the National Weather Service (GIF created by KSAT) (Copyright 2022 by KSAT - All rights reserved.)

With all that said, the lack of urgency for some in Lee County was likely a communications error and a result of how our brains work.

When we look at forecast cones, our mind wants to shoot down the middle and think this must be where the highest of odds of landfall will be. That’s not necessarily how it works.

These are designed so that you have between a 60 to 70 percent chance of the storm’s eye staying within its boundaries. That means there’s still a one-in-three chance it moves outside the cone. It’s also important to remember that even if you aren’t in the cone, effects can extend hundreds of miles beyond those boundaries.

Hurricane forecasting has improved dramatically over the years. The graph below shows how, over time, forecast error, when it comes to the track, has consistently gotten better.

Forecasting intensity has also improved. In general, the National Hurricane Center does a phenomenal job at forecasting.

Over the last several decades, forecasting hurricanes have improved dramatically.

County officials also have a tough job. If they evacuate large populations and the effects are minimal, they’ll likely face harsh criticism.

This occurred during Hurricane Rita in Houston. Likewise, like in the case of Ian, if they aren’t proactive enough, lives may be on the line.

When it comes to communications, it may be more prudent to focus on individual impacts for areas, like storm surge and flooding, instead of the cone being front and center. Further education on how the cone works by meteorologists would likely be helpful, too.

Read more like this on the Whatever the Weather page.


About the Author:

Justin Horne is a meteorologist and reporter for KSAT 12 News. When severe weather rolls through, Justin will hop in the KSAT 12 Storm Chaser to safely bring you the latest weather conditions from across South Texas. On top of delivering an accurate forecast, Justin often reports on one of his favorite topics: Texas history.