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As Hurricane Florence tracks toward East Coast, Philadelphia should take a deep breath

Philadelphia area residents should not be on high-alert yet — but they should be alert, weather experts say.

Florence's projected winds.
Florence's projected winds.Read moreNational Hurricane Center

Hurricanes aren't quite as unpredictable as human behavior. But it's a close call.

It's a certainty that this will be a frightful week along the North and South Carolina coasts, where officials already have ordered evacuations, and in Maryland, which has declared a state of emergency. The National Hurricane Center says it might issue hurricane watches there as early as Tuesday morning.

But as menacing as Hurricane Florence might appear on satellite and radar images — and this is going to be a protracted drama all week — ultimately far-larger weather systems will determine its course, and it still has hundreds of miles of ocean and atmospheric chaos to navigate before it approaches land.

While it had regrown into a Category 4 hurricane with peak winds of 140 mph late Monday, the hurricane center said, Florence still was better than 1,500 miles east-southeast of Cape Fear, N.C.

All of which means it is too soon to have an idea of what Florence will mean for the southeast, never mind the rain-soaked Philadelphia region.

"Give it two days from now," said Dave Dombek, a meteorologist with AccuWeather Inc. "At that point we're going to have a good consensus of the models."

Meteorologists and the computers they consult for guidance were reasonably confident Monday that Florence would crash into the Carolina coast before the end of the workweek, probably late Thursday night, and its remnants would mean heavy rains inland during the weekend.

Despite the uncertainty, it would not hurt for people around here to assemble emergency kits and prepare for potential power outages, said Chris Slocum, a Colorado State University hurricane specialist and Downingtown native. But at this point, he said, "the impacts are so far out that's a wait-and-see."

No matter where Florence makes landfall, it is likely to incite storm waves off the Jersey and Delaware coasts and perhaps more coastal flooding. Inland, tropical-storm-force winds and heavy rains would be the most significant threats, particularly west of Philadelphia.

This year's record rainfall, enhanced by downpours in recent weeks, adds to the threat, since "that area is saturated," Slocum said. Trees, which are adapted to prevailing winds from the west, are especially vulnerable to strong winds from the east, he said. It's possible that whatever is left of Florence could generate such winds. Slocum noted that the remnants of Hurricane Isabel in 2003 stirred up several hours of powerful winds from the east that caused hundreds of thousands of power outages at a time when the soils weren't nearly as soaked as they are now.

The post-landfall fate of Florence and its remnants is far more uncertain than its path across the Atlantic. And that path is by no means a certainty, even though track forecasts have improved markedly in recent years.

Slocum noted that if Florence makes it all the way to the East Coast, it would be an anomaly. Of 24 major hurricanes in the past that had occupied Florence's position as of Monday afternoon, 21 failed to reach the coast. The U.S. models have been hinting at Florence's curving back into the Atlantic, Slocum said, while the European models haven taken dead aim at the coast. The hurricane center track has consistently targeted the coast.

Florence has been riding the east-to-west winds on the southern flank of the same high-pressure system over the Atlantic that delivered record heat last week, forcing Philadelphia schools to send kids home early.

In terms of size, that steering high-pressure system is 20 to 30 times larger than Florence, said Slocum.

Winds circulate clockwise around high centers, and those easterly winds to the south of the center have caused Florence to pick up some speed, the hurricane center said.

But a new high pressure system building over the Great Lakes might slow it down later in the week. Plus, Florence could encounter wind shear as it approaches the coast, Dombek said, and that would weaken it.

Where a hurricane makes landfall can make all the difference in impacts. Slocum said. Take last year's Hurricane Irma, which caused close to $53 billion in damages, according to ICAT, the insurance catastrophe-modeling service. As devastating as it was for Florida, it would have been far costlier and perhaps deadlier had it tracked farther west and made landfall near Tampa, rather than Naples.

As for Florence, said Dombek, "There's always those chances that it does something weird as it gets near the coast."