MYRTLE BEACH Forget what you think you know about hurricane categories, wind speed and evacuations.

Two days before the start of the 2012 Atlantic hurricane season, area emergency officials are rolling out a dramatic change in storm coverage that includes much larger evacuation zones and earlier evacuation orders.

Lessons learned from the behavior of storms such as Katrina led Horry and Georgetown counties to be the first in the nation to undergo an evacuation study that took into account storm surge patterns and changes in population over the past two decades. Eventually all coastal counties in the state will follow suit.

Details of that study were made public Wednesday and Randy Webster, Horry County’s emergency management director, said it is the first comprehensive review since 1989’s Hurricane Hugo made landfall in the state.

“This is a significant change to how we’ve done the hurricane program in the last 20 years,” Webster said.

New technology, demographics

Using the latest technology, officials with the Federal Emergency Management Agency and the Army Corp of Engineers looked at all the issues that would result with a hurricane making impact in the state, the behavior of residents during a storm, the topography of the area and storm surge impacts and how long it would take to evacuate residents and tourists from the area, Webster said.

Since Hugo, Horry County’s population has gone from 144,000 in 1990 to 269,300 according to the 2010 census. Carolina Forest shot up 506 percent between 2000 and 2010.

Where once the Intracoastal Waterway served as a line of demarcation between coastal danger and inland safety, new storm surge models showed that areas of Horry and Georgetown counties that had never been under a mandatory evacuation order could be impacted by rising waters and should be evacuated, Webster said.

For example, population increases in communities that didn’t exist in 1989 such as Barefoot Resort and Carolina Forest, brought portions of those neighborhood under the new evacuation zone boundaries.

Residents living in Bucksport, the Waccamaw Neck and other inland areas away from the ocean, but near waterways such as the Waccamaw River and Intracoastal Waterway also are now in evacuation zones.

“The technology to map that surge has changed as well as our ability to see it,” Webster said. “It’s pretty significant in Georgetown and we see more impacts in Socastee, Carolina Forest and Forestbrook areas than ever before.”

Expanded boundaries and a population boom also means it will take longer to get visitors and residents out of the area. Just how much earlier will depend on the strength of the storm and whether it is expected to come ashore during prime tourist season, officials said.

Emergency officials have made the rounds over the past two months to meet with community leaders to give them an idea of what was ahead under the new NOAA models, known as SLOSH for Sea, Lake and overland Surges from Hurricanes. A key to the new emergency plan is what they call the “decoupling” of the hurricane category from the expected surge, which will now be the deciding factor in what zones will be evacuated.

“We have a better understanding of how storm surge may impact us and better models show how far inland surge will go if certain factors are present,” Webster said. “We’ve gone all these years and people were in harm’s way and we didn’t know it. I’m thankful we didn’t have that [worst-case scenario] storm.”

In the presentations, Webster cited some recent storms and the gaps between their official categories and their storm surge measurements. Hurricane Katrina made landfall as a Category 3 storm, but it had a storm surge of more than 25 feet; Ike, which was a Category 2 at landfall, drove a 12-foot surge. Florida’s Hurricane Charlie was a Category 4, but its storm surge was only 6 feet.

Evacuation orders

Under the zone system, the governor will no longer issue voluntary evacuation orders. Only a mandatory evacuation order will be issued by the governor, said Derrec Becker, spokesman for the S.C. Emergency Management Division.

Instead, officials will call for evacuations based on a formula that calculates the strength of the storm, the predicted storm surge and where it could make landfall.

“It has changed the way we’re going to look at the flooding situations when it comes to storm surge and inland flooding when it comes to the rivers,” said Sam Hodge, emergency management director for Georgetown County.

“Until now South Carolina has been one of the few remaining hurricane states to still issue two separate evacuations,” Becker said. “This enables all organizations on all levels to conserve as many resources as possible for when they will be needed most. . . .This update also enables us to coordinate regionally with neighboring states that will also be affected by the storm.”

Eventually, the technology will be used in every county susceptible to storm surge.

Informing residents

Emergency officials have updated their plans and county websites and urge residents to figure out which zone they live in and plan accordingly, so they are ready when a storm threatens, Webster said.

“They may never have experienced it because [1989’s Hurricane] Hugo was our last significant storm,” Webster said. “So they need to be ready now and get prepared now because the way we do things has changed.”

The flooding that followed Hurricane Floyd in 1999 was not caused by storm surge, but by rainfall that inundated areas upriver and then flowed downstream to overwhelm the Conway area around the Waccamaw River and tributaries.

To ensure residents are aware of what zone they’re living in and what actions they need to take before a storm threatens, officials are planning several community events, including StormFest from 9 a.m. to 2 p.m. June 9 at Inlet Square Mall in Murrells Inlet, Hodge said.

The free event will feature information about evacuation zones and allow residents to see the data used to develop the plans.

“With the new data that’s been made available to us, we have to plan for the worst case scenario. But keep in mind it is the worst case scenario,” Hodge said. “We’ll be letting them know which evacuation zone they’re going to be and what they need to do. We have some evacuation zones inside other evacuation zones.”

Getting the information out to residents is not the biggest challenge; Hodge said getting residents to heed the warnings is the larger task.

“Complacency is always our biggest challenge. The longer we go without that storm the greater the chance we’ll have one,” Hodge said. “With all the numbers saying it’s not going to be a record year is good, but keep in mind it only takes that one storm to affect Horry and Georgetown County.

“Everyone needs to sit down and know what evacuation zone they’re in and make sure they have their plans ready,” he said.

Contact TONYA ROOT at 444-1723.