Forget Hurricane Andrew. Irma could be the new Big One.

One day after Hurricane Andrew tore its demolition-derby path east to west across Miami-Dade, Hugh Willoughby drove from his damaged South Miami house to a Home Depot by Mall of the Americas near Doral. Street lights were working, so there was power. He bought roofing supplies and was soon atop his home nailing on new shingles.

But if the far-larger Hurricane Irma rakes a possible course from south to north along the county’s spine, Willoughby — an atmospheric scientist — fears things won’t be so simple this time.

In that worst-case scenario — still very much an “if” at the end of the day Friday — Irma brings substantial and extensive damage to Miami-Dade on a scale that might make Andrew pale by comparison, he said. That’s like having Andrew’s fearsome but compact hurricane wind field, and the destruction it wrought, extend across most of the length and breadth of the county.

“The worst case is pretty bad,” Willoughby, a professor at Florida International University and Andrew expert, said. “The scary thing is, we may have more widespread damage. We are talking winds much like the damage in Andrew, only more widespread.”

To be sure, Irma’s track remained highly uncertain, and forecasters say its course would not become clear until virtually the last hour Saturday. With a jog in the storm’s path either to the east or west, Miami-Dade could experience another strong but lesser storm like 2005’s Hurricane Wilma, perhaps. But it would not in that case be a cataclysmic Andrew writ large.

But that nightmare possibility is what’s kept Willoughby and millions of anxious South Floridians glued to the National Hurricane Center’s forecasts and predictive models for the better part of a week. Anyone who believes Miami-Dade experienced the worst a hurricane can deliver 25 years ago better think again, he and others say. South Florida’s vaunted subtropical climate is perfectly capable of delivering far worse.

“My experience with these storms coming out of the south is that a lot of times they get here weaker and pass offshore,” Willoughby added. “Most of the time it’s not as bad as your worst imaginings. But sometimes it can be a lot worse.”

If Irma’s center runs west of I-95 but parallel to it, South Florida could wake Monday to an Andrewesque aftermath: untold thousands of homes and structures damaged, many severely, by wind. Public infrastructure knocked out. Power out, possibly for weeks. Stores and banks out of commission. Trees wiped out. Blocked roads at nearly every turn.

If it hugs the Miami-Dade shoreline, Irma might also push mind-boggling amounts of seawater onto shore as it plows north, inundating miles of thickly populated urban and suburban neighborhoods in the county’s most valuable stretch of real estate, and the backbone of its vital tourism and banking industries, in unprecedented fashion.

Just as disturbing is the fair-to-good chance that Irma could proceed north through Florida on a couple of different possible tracks: just along the inside of, or just off, its densely populated shoreline. Or right up the center of the state. Either course would knock the entire state back on its heels.

That in turn raises the sobering possibility that help for victims in Miami-Dade would be markedly slow to arrive — even slower than after Andrew, when authorities were caught unprepared for the severity of damage. In 2017, state and federal emergency management officials are dramatically readier to respond.

But, noted Republican U.S. Senator Marco Rubio, highways might be unavailable for out-of-state recovery aid to make its way south to Miami, at least until Irma moves on to Georgia. And in that case, Rubio said, there could be further delays because some of the federal assistance is “pre-positioned” in … Georgia.

“One of the things that concerns us is that it could overwhelm the capacity of the [emergency response] system,” Rubio said Thursday in a briefing at the Miami-Dade Emergency Operations Center.

And it’s not just a question of funding from the Federal Emergency Management Agency, already stretched thin by Hurricane Harvey in Houston, the senator said. What if there aren’t enough nurses or doctors to care for the sick or hurt?

In a subsequent interview, Rubio predicted it could take a day and half just to get help close enough to Miami to begin distributing supplies.

“I’m not sure there is anywhere to go in Florida that doesn’t put you in a significant problem situation,” he said, adding that several friends told him they were headed to Orlando. “Well, I’m not sure it’s going to be a lot better in Orlando.”

The potential for nearly unprecedented damage in Miami-Dade has rattled many, especially those who experienced the ravages of Andrew at close hand.

Veteran Homestead tree and vegetable farmer John Alger, who suffered heavy losses in Andrew, said a strike on South Miami-Dade by Irma could be even more calamitous now given the dramatic increase in population and residential and commercial development that’s occurred since 1992.

“Even a glancing blow from this will be very tough,” Alger said. “This is Andrew but much, much bigger. Remember, back then, south of Campbell Drive the population density was low. Not anymore.”

And, like Rubio and Willoughby, Alger worries assistance to south Miami-Dade won’t come quickly enough — and that even those able to get out to help themselves won’t find much open anywhere close.

“After Andrew, in our neighborhood we had curfews and military at every intersection. But you could drive to the Keys and have dinner the next day,” he said. “We had plenty of help coming from just 35 miles north or south of us.”

The problem with Irma, Willoughby said, begins with its size. Its hurricane-strength winds stretch 70 miles from its center. That’s wider than Miami-Dade is by a considerable length, so if the storm even comes close it could sweep much of the county with hurricane-strength force. Forecasters on Friday fully expected it would make landfall in South Florida as a strong hurricane, possibly a major hurricane at Cat 3 or above — regardless of its precise course.

Andrew, by comparison, came ashore at Naranja in south Miami-Dade as a Category 5 storm but was so compressed that heavy damage was concentrated between Florida City and Kendall Drive, which roughly marked the path taken by the north edge of its eyewall. That’s the fiercest portion of a storm, Willoughby said.

“Andrew was a really small, really intense storm,” he said.

Immediately north of Kendall Drive, wind speeds, and the resulting damage, diminished significantly, Willoughby said. At his home off Sunset Drive in South Miami, Andrew’s windspeed was around 115 mph, a still-major Cat 3 but well below a Cat 5’s 157-mph minimum. That’s important because even small-sounding differences in windspeed and direction can make a big difference in how buildings fare in a hurricane.

“After Andrew, you could almost go by street as to what the damage was,” he said.

Willoughby and his neighbors lost shingles and roof felt, and his own roof was down to bare wood decking in places, Willoughby recalls. But the house, which he said is built well, otherwise held up fine.

That would probably not be the case in Irma, which, if some forecast tracks hold true, would roll its extensive eyewall pretty much directly over his house, he said. If the storm, whose hurricane-force winds extend 70 miles from its center, tracks to the west of the shoreline, damage would be especially pronounced. That’s because much of the county from Homestead through downtown Miami and the densely populated northeast suburbs would be exposed to the worst of Irma’s winds, those to the right or “dirty” side of the storm.

“If the right side comes up through over the city, our houses really aren’t built for that,” Willoughby said. Homes built under toughened post-Andrew building codes should fare better than most.

“That building code is pretty good. There will be a lot of newer houses that will get beat up but stand. But even houses that did fairly well in Andrew will be challenged,” he added.

The one potential amelerioating factor: If Irma makes landfall around Key Largo and wends its way north with at least some of its circulation over land, its windspeed could slow considerably, Willoughby said. That might spare areas farther north along its course from the most dangerous wind intensities.

But the extent of damage at that county-wide scale would not only prolong recovery and rebuilding time, it could also potentially deal a potent and long-lasting blow to property values and the county’s overall economy, experts say.

As Irma headed on a western course for Cuba, the concerns for Rubio were more immediate. And there are many. Will enough TSA agents be able to leave their homes to reopen airports? Will seniors still get Social Security funds if banks remain closed and power out? Will emergency responders will be able to get to the elderly and homeless who may be unable to heed evacuation warnings.

“There’s a lot, and you’ve got to think in terms of this worst case” Rubio said. “I don’t think there’s ever been a storm like this, that is coming literally at the center of the state. … Is there a precedent for four major metropolitan areas getting struck by a major hurricane in a 24-hour period in one state?

“I don’t necessarily believe that a contingency of this nature has ever been foreseen. I’m not panicking — but it’s a lot to worry about.”