A day after Tropical Storm Elsa formed just east of the Caribbean Sea, the storm’s projected path was extended to include South Florida and Tampa Bay into the “cone of uncertainty” on Friday.
Here’s everything you need to know about “the cone” and what it means.
The cone is created by the National Hurricane Center after a tropical disturbance reaches tropical storm or hurricane strength. Its goal is simple: Alert residents to the potential path of an incoming storm up to five days in advance.
The cone always begins at the latest known position of the storm’s center. Then, the cone extends as far as meteorologists expect it will travel over the course of five days, with 12-hour intervals time stamping the estimated time of arrival.
While the cone appears to be self-explanatory, scientists at the National Hurricane Center say its exact meaning is often misunderstood.
“Even though this graphic is very popular, we’ve also found that it is misunderstood and is used for ways it was never meant for,” said Robbie Burr, a scientist with the National Hurricane Center.
The most common misconception, according to Burr, is that the size of the cone reflects the size of the storm. That’s not the case.
The size of the cone is used as the best estimate of where the storm’s center will be at a given time. This means that hurricane conditions often occur well outside the cone of uncertainty. Burr said that residents should not use the cone to decide whether to evacuate or not.
The size of the cone used by the National Hurricane Center varies from year to year depending on how good — or bad — the forecasts have been in the last five years.
So, just how accurate has the cone been lately?
The storm’s center stays within the cone of uncertainty in two of every three forecasts, according to the National Hurricane Center. Updated cones are released every three hours once a storm reaches tropical storm strength.
The cone is broken into two parts: A three-day forecast and a five-day forecast, which are designated by different backgrounds within the cone.
The cone also contains information about what forecasters expect the storm to be at a given time. A “D” means a tropical depression is expected at that time, an “S” means a tropical storm and an “H” means a hurricane is expected. In the rare case a major hurricane of Category 3 or higher is expected, it will be given the designation “M.”
While it is a useful visual for residents, Burr said residents to rely on their local emergency management officials to receive guidance on what action — if any — they should take.
“Probably the most important point is that a hurricane is not just a point,” Burr said. “Impacts from the storm often occur well outside the cone and it’s important to consult other forecast graphics when preparing for a storm.”
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