By Jane Sutton
MIAMI (Reuters) - Friday marks the end of an Atlantic-Caribbean hurricane season where the greatest devastation was caused by water rather than wind, U.S. National Hurricane Center Director Rick Knabb said.
Accordingly, the center is ramping up efforts to develop new warnings that better convey the threat from the deadly storm surge pushed ashore by monsters like Sandy, which slammed the U.S. Northeast in October.
"We've been working toward a new storm surge warning for a few years now," Knabb told Reuters in an interview at the hurricane center in Miami. "And Debby, Isaac and Sandy show us how much we really need to hit the accelerator on getting that storm surge warning out the door."
Debbie, Isaac and Sandy were three of the four storms that hit the United States during the 2012 season.
Starting with a meeting next week, the forecasters will review their warning systems and speed up development of a separate warning system for storm surge in hopes of having an experimental version ready to test in the next couple of years, Knabb said.
It will include a high-resolution graphic showing how high the surge would grow and how far inland it would reach at various times. Storm surge rarely correlates neatly with wind strength, Knabb said.
"Hurricane-force winds and storm surge doesn't always occur in the same places or at the same times when a storm approaches," he said. "Where the storm surge occurs is very dependent upon details of the coastline and the elevations and all that."
The United States is increasingly at risk from storm surge. Much of its densely populated Atlantic and Gulf coastlines lie less than 10 feet above sea level, and the seas are gradually rising as the Earth warms and ice caps and glaciers melt.
At the same time, the population in the hurricane region is growing rapidly. From 1990-2008, population density increased by 32 percent in Gulf coastal counties, 17 percent in Atlantic coastal counties, and 16 percent in Hawaii, according to the 2010 Census.
Much of the nation's commerce also depends on seaports and the transit systems that link to them.
Improving the storm surge warning system not only could help tailor evacuation orders as a storm approaches, it could help homeowners, business owners and governments know where and how to fortify before the next season comes.
"We can't hope that it doesn't happen again ... because it will. It's just a matter of when, not if," Knabb said.
Superstorm Sandy highlighted the need for more flexible warnings and greater focus on storm surge.
After killing 69 people on a rampage through the Caribbean, Sandy hit the densely populated northeastern United States in October, killing at least 131 more people and causing an estimated $71.3 billion of damage in New York and New Jersey.
It leveled entire beach towns, flooded subways and tunnels, paralyzed the nation's financial capital and knocked out power to 8.5 million customers in 21 states.
The behemoth storm was more than 900 miles wide as it churned northward up the Atlantic. It approached New Jersey as a hurricane, a spiraling system that draws energy from warm seas and has its strongest winds around the center.
Just offshore, it morphed into an extra-tropical "Nor'easter," a colder storm that draws energy from the atmosphere and spreads the strongest winds over a broader area. That did not lessen the danger.
"The ocean was churned up over a long period of time by this massive wind field. Tropical or not, we knew the storm surge hazard was going to be significant," said Knabb, who had warned for days that Sandy would push a surge of seawater up to 11 feet high over parts of New York and New Jersey.
"That's what did most of the damage in Sandy," he said. "We had a huge area impacted by storm surge and waves and most of that area did not get hurricane-force winds."
The hurricane center worked closely with local government officials who ordered evacuations in low-lying areas, and waged an intense media campaign to get the warnings out.
But since Sandy was not expected to be a hurricane or tropical storm at landfall, it didn't fit neatly into the hurricane center's standard package of warnings and graphics that focus on wind.
Hurricane watches and warnings, which are issued by local governments on the advice of forecasters, are based on expectations for strong winds within 36 to 48 hours.
The forecasters did not want hurricane warnings issued only to have them taken down when Sandy made its anticipated transition to an extra-tropical storm near the shore. They feared that would create a false impression that the danger was over just when it was greatest.
"It would have really caused a lot of confusion for a lot of people trying to make decisions and evacuate," Knabb said.
Another option - "faking it" and pretending it was still a hurricane when it wasn't - would have been an obvious deception, Knabb said.
"We do need to have some credibility and call it like we see it," he said.
Instead, the hurricane center continued to issue advisories in the regular format and through its regular distribution system, stressing the storm surge danger and referring people to their local Weather Service office for specific flood projections.
In all, the 2012 season brought 19 tropical storms, 10 of which strengthened into hurricanes.
That made it a busier-than-average year that topped the seasonal forecasts issued in the spring by government and private meteorologists.
But none of the storms that hit the United States this year were "major" hurricanes on the Saffir-Simpson scale that ranks them into five categories according to their wind strength. Most were not even hurricanes, which are tropical cyclones with sustained winds of at least 74 miles per hour.
Beryl was a tropical storm when it swirled ashore in Florida and soaked the southeastern United States in May, before the season officially began. Debby was also a tropical storm when it dumped 2 feet of rain over northern Florida in June, sending thousands fleeing from rapidly rising rivers.
Tropical Storm Isaac delayed the start of the Republican National Convention when it brushed by Tampa, Florida. It strengthened into a hurricane that flooded the Mississippi and Louisiana coasts and put New Orleans' refurbished levees to the test.
Despite storm surges that topped 12 feet, the elaborate defenses built to protect the city after the 2005 Hurricane Katrina disaster withstood the onslaught.
(Reporting by Jane Sutton; Editing by Vicki Allen)