The National Hurricane Center took the next step towards creating separate hurricane storm surge warning messages on Thursday, releasing an example of new color storm surge watch and warning maps to be used on an experimental basis in the 2015 hurricane season.
The new maps will be used to highlight areas along the Gulf and Atlantic coasts of the United States that have a significant risk of life-threatening inundation by storm surge from a tropical depression, storm or hurricane.
The new maps still may not include areas within the newly completed New Orleans area hurricane surge levee system, unless the storms are predicted to be large enough to overtop the levees.
The map will use the color red to show areas where a storm surge warning will be in effect, indicating there is a danger of life-threatening flooding from rising water moving inland from the shoreline, generally within 36 hours. Yellow will be used for areas where life-threatening flooding is possible, generally within 48 hours.
The maps will urge those in the marked areas to follow evacuation and other instructions from local officials.
The threat of surge flooding often covers different coastal areas than the threat of hurricane wind damage, which has led to confusion among the public about what areas are at risk. Surge flooding can also impact at different times from hurricane winds.
Beginning with 2014's Hurricane Arthur, the NHC began issuing a separate "Potential Storm Surge Flooding Map" that shows areas where rising water from storm surges and accompanying tides can occur and how high above ground that water could be, based on the latest NHC forecast and its likely errors.
The new maps for the 2015 season will become part of a comprehensive program of surge watch and warning messages that will be consolidated with the center's watches and warnings for winds in 2016. When complete, the new process will merge inland and coastal warning information from both threats into a single message. After a year of testing, the new storm surge warning system is expected to become fully operational in 2017.
Jamie Rhome, leader of the NHC's storm surge unit, said Thursday that his staff will send initial watch and warning maps to local National Weather Service offices to assure that local geography is properly represented when final versions are released.
"For Louisiana, we would push a proposed warning to the local office, and they would edit the warning and send it back, based on their local expertise and knowledge," Rhome said.
Frank Revitte, warning coordination meteorologist with the weather service's Slidell office, said the new surge maps will help the public and local emergency management officials better identify areas that might need to be evacuated.
"If people can visualize their particular area is in the storm surge warning, that will really help communicate the risk they face," Revitte said.
The new maps may not show flood risk inside the New Orleans area hurricane surge levee system, unless a storm is expected to overtop the levees. That's because information about rainfall-related water heights inside the levee system is limited, and often is only collected by the Army Corps of Engineers or local levee authorities, and not by the National Weather Service, Revitte said.
"There are certainly storms that produce a lot of rainfall, and there will be challenges keeping up with that," he said.