Hurricane Ian’s ‘cone of uncertainty’ and what it may mean for the Philly region

Hurricane Ian has made its potentially catastrophic landfall in southwest Florida with estimated top winds of 150 mph, and understandably, its fearful symmetry and frightening progress across western Cuba and through the warm waters of the Caribbean understandably have been centers of national attention.

“This is a worst-case scenario for southwestern Florida,” said Bryan Norcross, veteran hurricane specialist with Fox Weather. By 4 p.m. Wednesday, it had moved inland to near Cape Coral, about 10 miles south of Fort Myers, with winds up to 145 mph, the National Hurricane Center said.

» READ MORE: Hurricane Ian makes landfall in southwest Florida as a Category 4 storm

But above and beyond the immediate drama, meteorologists were monitoring upper-air systems thousands of miles away from Ian’s center — including one that has affected the Philadelphia region — for clues about the future of what almost certainly is going to be the season’s most-destructive tropical storm to date.

The hurricane center’s “cone of uncertainty” has predictably wobbled with each forecast update. That’s because it is anything but a cone of certainty, says Joel Cline, tropical program coordinator for the National Weather Service, and a major reason why nine western Florida counties were under mandatory evacuation orders Tuesday.

Ian, said Norcross, is a classic case study of “why we have the cone.”

» READ MORE: So much for those concerns about the absence of hurricanes

On average based on five years of data, the hurricane center says, the 24-hour forecast track is off by 39 miles. That’s a huge difference on a populated coast: Consider that monster Hurricane Andrew in 1992 came within about 10 miles of making a direct hit on downtown Miami.

Ian ended up making landfall perhaps 90 miles south of the Tampa Bay area.

Computer models and their human interpreters were conflicted about what would happen during the next several days.

» READ MORE: The pre-season outlooks were bullish on a busy hurricane season

The average error for a five-day forecast is 200 miles. On Sunday morning, the forecast track took the center to the Florida Panhandle. That is something to keep in mind as what is left of Ian is forecast to make a run at the Mid-Atlantic region during the weekend, and forecasters say it could have impacts in the Philadelphia region, particularly at the Jersey Shore.

Ian, which began as a seedling near Trinidad, sailed along the coast of Venezuela and then turned north toward Cuba, Cline said. The winds circulated around high pressure, or heavier air, centered in the North Atlantic. Since they travel clockwise around the center, they blow from the east-to-west to the south of the center — the trade winds — and from the south-to-north on the west side.

Thus, Ian’s right turn, which was a turn for the worse for western Cuba, where it will be days before the level of damage is calculated.

Ian since has been captured by additional south-to-north winds generated by a sprawling area of low pressure to the west, a system tied to the recent cold fronts that have passed through the Philly region, he said.

Unfortunately for forecast purposes, the steering winds have been languid.

And it’s not as though Ian is on automatic pilot: Its own newly gained powers are affecting its motion.

“All this mass of water, essentially, whether it be in clouds or rain or whatever, has got some momentum and inertia built up with it,” Cline said. “It can’t turn quick. It’s like turning a big battleship.”

Between the upper-level winds and the storm itself, “There’s a lot of interplay,” said Cline.

The farther out in time, the more problematic the forecast, which is why that cone balloons. The cone depicts only the possible ranges for the path of the center — not the impacts, and flooding rains can develop hundreds of miles from a storm’s center.

It’s likely that post-landfall, the cone will take on quite a different look. Encounters with land are game-changers for hurricanes. Not only do they get cut off from their warm-water fuel supply, they leave what is essentially a frictionless surface to get roughed up by the irregularities in the terrain.

For the next few days at least, we can count on a 100% chance of ambiguity, says Matthew Brudy, meteorologist with the National Weather Service Office in Mount Holly, with possibilities ranging from partly cloudy to outright nasty.

The weather service says the impacts likely would hold off until at least the weekend, depending on what happens after it rips through Florida.

Five days out the cone of uncertainty on the hurricane center’s map resembles a helium balloon. It has the center of Ian’s remnants near the North Carolina, Virginia, and Tennessee borders. “It’s going to cause issues up the coast,” said Norcross, with some rain getting into the Philadelphia region during the weekend.

A flood watch might be needed for parts of Delaware and South Jersey, the weather service says, and while how much for Philly is an open question, “It isn’t going to be Ida,” Norcross said.

Said Brudy, “there’s no reason to throw off the alarms,” said Brudy. At least not yet.

» READ MORE: Remembering Ida, a hurricane name that won't be repeated

In the short term, unless the forecasts go awry seriously, the name “Ian” appears destined for retirement, a distinction reserved for the most-deadly and damaging tropical storms, which are removed from the list that recycles every six years.

Since the alphabetical naming system began in 1953, 13 “I” storm names — including Ida, in 2021 — have been retired. No other letter comes close.