Hurricane Milton is barreling toward Florida as a catastrophic storm projected to hit the Tampa area, but where it will actually make landfall is still unknown, and slight shifts in track could spell disaster.

Milton was a Category 4 storm on Wednesday, forecast to make landfall overnight with life-threatening winds and storm surge. Exactly how much will depend on where it hits. If it arrives south of Tampa Bay, "reverse" storm surge could suck it dry. But just a short 10- to 20-mile jaunt north, and storm surge will overwhelm the densely populated area.

The Tampa Bay area, home to about 3.5 million people, is the nation's most vulnerable metro area to storm surge. On its current track, Milton is forecast to push 8 to 12 feet of seawater onto the shore, the "highest storm surge forecast ever explicitly issued by the National Hurricane Center for Tampa Bay," according to Michael Lowry, a hurricane specialist at WPLG Local 10 in Miami.

"Storm surge is historically the single deadliest hazard of a hurricane, responsible for more than half of all hurricane-related deaths over the past 50 years, and is the primary reason evacuations are issued ahead of hurricanes," Lowry said.

Milton's path is difficult to predict with certainty, said Rick Davis, a meteorologist with the National Weather Service in Tampa Bay. The National Hurricane Center said early Wednesday that people are "urged not to focus on the exact landfall point." Even 12 hours ahead of landfall, the margin of error is about 25 miles, which could make a big difference, Davis said.

"We would like to emphasize that Milton's exact landfall location is not possible to predict even at this time, particularly if the hurricane wobbles during the day and into this evening," the hurricane center said in Wednesday's 11 a.m. discussion.

How the point of landfall changes Milton's impacts

While much of Florida is expected to face devastating winds and flooding rainfall, Milton's worst wind and surge impacts will be near where the center of the hurricane comes ashore.

By late Wednesday morning, the Hurricane Center forecasted landfall south of Tampa Bay. But in the previous 24 hours, that forecast bounced north and south, and could continue to do so.

"That is going to be a big difference on storm surge conditions in the Tampa Bay area," Davis said. "If it just moves another 10 or 20 miles, then all that surge will be materialized in Tampa Bay."

Storm surge forecasts are very sensitive to the storm's exact track, and "the risk of devastating storm surge still exists across much of the west-central and southwest coast of Florida given the size of the storm and the uncertainties in exactly where landfall will occur," the Hurricane Center said.

Davis said Milton's winds will be stronger than expected on its north side, which is usually the weak side of a storm. So regardless of where the center of the storm roars ashore, extreme winds are going to be felt across the region.

Why is it so hard to predict the storm path?

Weather is hard to predict in general. But a massive hurricane at this point in the season brings unique challenges to forecasters trying to determine just where Milton will hit.

The steering currents, or the winds that are guiding Milton, are highly influenced by changes in the jet stream, Davis said. That's because of how late in the season Milton formed. Earlier in the summer, steering comes from a high pressure ridge, not the jet stream, he said.

"Any little ripple in the jet stream can push the storm in one direction or lift it in another direction. So it's very chaotic." Davis said.

At about 24 hours from landfall, the average error at is about 40 miles. By 12 hours, it's about 25 miles. So even though the forecasted track puts landfall at just south of Tampa Bay, people aren't out of the woods, because they could still experience the full impact of storm surge and winds, Davis said.

"It's weather. It's chaos. There's inherently uncertainty in the weather," Davis said.

Contributing: Doyle Rice and Dinah Voyles Pulver, USA TODAY