Hurricane Center: Beware of the Storm Surge

During a hurricane, storm surge is one of the greatest threats to life and land, yet many people don’t understand the dire warnings from forecasters to get out of its way. So this season, they hope to offer easy-to-understand, color-coded maps and change the way they talk to the public.

Simply put, storm surge is the abnormal rise of sea water. Predicting it is far more complicated, and so is explaining it, as forecasters at the National Hurricane Center discovered, again, during a review of Superstorm Sandy.

“Scientists by their very nature use very sophisticated language, technical language,” said Jamie Rhome, leader of the hurricane center’s storm surge team. “It turns out that nobody else understands what we’re talking about. So once we figured that out, we started using more plain language.”

Forecasts during Sandy were exceptionally accurate, but often confusing. Perhaps because so many things contribute to storm surge: intensity, pressure, forward speed, size, where it makes landfall and other factors.

Most people believe storm surge is a wall of water, similar to a tsunami, but it’s actually just sea water being pushed toward the shore by winds. It can happen quickly and move miles inland, flooding areas not accustomed to being inundated with sea water.

Large death tolls have been blamed storm surge. At least 1,500 people died during Hurricane Katrina either directly or indirectly because of storm surge, the hurricane center said.

To better explain the danger, forecasters talked to focus groups consisting of local and state officials, law enforcement and hospital associations and other people from Maine to New Orleans. One thing they found out is that when they talk about storm surge, they should say “height” instead of “depth” when explaining how water levels might change.

“We were using ‘depth,’ thinking this was very clear. It turns out that nobody else does,” Rhome said. “They’re waiting for height, how high it is, and I would never have guessed in a million years that one word – one word – makes a difference in how people interpret something.”

Forecasters also will try to stress that the storm surge isn’t just from the ocean and can come from other bodies of water such as sounds, bays and lakes, sometimes well inland.

The hurricane center also plans to show people where to expect storm surge with high-resolution, color-coded maps, much like a radar map on the local news showing rain and severe weather. If forecasters can’t post the maps on the hurricane center’s website this storm season, which begins June 1, the plan is to have the maps ready in 2014.

The storm season is expected to be a busy one, with federal forecasters on Thursday predicting 13 to 20 named Atlantic storms, seven to 11 of which will strengthen to hurricanes. Three to six of those are forecast to become major hurricanes.

A National Oceanic and Atmospheric Administration evaluation of the weather service’s performance during Sandy also recommended increasing the number of storm surge forecasters at the hurricane center, and providing potential storm surge hazards at least 48 hours before the onset of tropical storm or gale-force winds.

Miami-Dade Emergency Management Director Curt Sommerhoff said his priority is getting the public to understand that the county’s evacuation zones are based on storm surge, not hurricane winds.

New data from the hurricane center’s storm surge models prompted the county to redraw its storm surge planning zones to include inland areas along canals and rivers that previously weren’t identified as being at risk for storm surge.

“That’s the new message, the surge danger well inland, well in from the coast,” Sommerhoff said.

Separate storm surge warnings, similar to current tropical storm or hurricane warnings, will be rolled out in 2015.

The hurricane center dropped estimates for storm surge and inland flooding from its wind scale three years ago because the predictions often didn’t match what actually happened. For example, Hurricane Ike was a Category 2 with winds of at least 96 mph when it hit the Texas coast in 2008, but its storm surges was much greater than a typical Category 2 storm.

“Storm surges can behave so differently from storm to storm that you can’t just apply a single number or use a scale like you can with the wind. That’s been tough, trying to get people to understand that every storm is different,” Robbie Berg, a hurricane specialist who has taken the lead on social science at the hurricane center.

Berg said Hurricane Irene didn’t produce the storm surge in 2011 that some expected, and the following year, many people were surprised by Sandy’s extreme tides and flooding.

Still, the advisories for Sandy were dramatically improved from the ones for Ike, explaining storm surge in layman’s terms and easy-to-read bullet points instead of long pages of jargon that required meteorologists and emergency officials to make their own calculations.

The progress may seem subtle, but Berg believes it’s helping emergency managers make better decisions about whether to order evacuations.

“For as bad as Sandy was, it almost makes you wonder what would have happened had we not made some of these changes since Ike,” Berg said. “I would hope that because of these new changes, they’re more educated and they’re more prepared to make those evacuation decisions when needed.”