Wednesday, September 9, 2015

50-year Anniversary of Hurricane Betsy's Louisiana Storm Surge

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Hurricane Betsy struck South Louisiana 50 years ago today. Betsy made landfall south of New Orleans, near Grand Isle. As Betsy was tracking to the northwest, much of Southeast Louisiana, including St. Bernard and Plaqumines parishes, the New Orleans metro area, and all of Lake Pontchartrain, stayed on the “strong” side of the storm.

Hurricane Betsy inflicted intense winds and high storm surge on Southeast Louisiana. Betsy's storm surge flooded much of eastern and southeastern metro New Orleans.
Image: Wikipedia Commons

Betsy made landfall in the hours before midnight as a category-3 hurricane with maximum sustained winds of approximately 120 mph.  However, just several hours before landfall, Betsy was a category-4 hurricane, near the threshold of category-5, with maximum sustained of 155 mph (Atlantic Oceanographic and Meteorological Laboratory 2014).  Betsy’s intense pre-landfall winds were one reason the storm produced such high storm surge levels in South Louisiana, as storm surge heights correlate better with pre-landfall hurricane winds than wind speeds at landfall (Needham and Keim 2014).

Betsy’s highest storm tide (storm surge + tides) reached 15.7 feet above Mean Sea Level (MSL) at Bohemia- East Landside, in South Louisiana (U.S. Army Corps of Engineers 1965). This observation came from the near the levee on the east side of the Mississippi River, in Plaquemines Parish, about 30 miles upriver from the mouth of the Mississippi.

 Betsy's storm surge in Louisiana peaked at 15.7 ft above Mean Sea Level at Bohemia, in Plaquemine's Parish.

Betsy’s storm surge inundated much of eastern and southeastern metro New Orleans. This flooding unfortunately inflicted both loss of life and tremendous financial losses. Betsy inflicted 75 fatalities (not all in SE Louisiana), and $1.42 billion in property loss (Blake et al. 2011). This made Betsy the first hurricane to produced more than $1 billion in financial losses (Blake et al. 2011).

ADCIRC run of Betsy's peak storm tide levels in South Louisiana. Note the several distinct pockets of water levels exceeding 10 ft (3 m), visible to the east of the Mississippi River levee, in the eastern portion of New Orleans, and in the western portion of Lake Pontchartrain. Also note the drastic difference in surge heights to E and W of MS River.
Image courtesy of J. Westerink, see: http://www3.nd.edu/~adcirc/betsy.htm

Although storm surge flooding in New Orleans caused the biggest impact and attracted the most media attention, Betsy actually inundated much of Southeast Louisiana with a storm tide ranging from 12-16 ft. The map below, which depicts storm surge and storm tide heights, as well as Betsy’s hourly track and intensity, depicts many “red” water levels in the region. In this map, red symbols depict storm surge or storm tide heights between 12-16 ft.

Hurricane Betsy hourly track, intensity and storm surge/ storm tide observation map.
Image courtesy: Hal Needham (SCIPP/ SURGEDAT)

Many people are surprised to learn that Betsy produced the highest storm tide on record near Frenier, on the southwest coast of Lake Pontchartrain. Betsy’s 13.1-ft storm tide at Bonne Carre (a few miles from Frenier) was the highest hurricane-induced water level ever recorded near that location. The 1915 Hurricane produced a 13-ft storm tide near Frenier (Rank #2), but Hurricane Katrina’s storm tide was only 5.58 ft above NAVD88, which is ranked #9 for that location. These data are provided courtesy of the SURGEDAT project, which has compiled a history of 27 high water marks that have been observed at Frenier since 1900.

Betsy generated the highest recorded storm tide level near Frenier, Louisiana. Note that Hurricane Katrina generated the ninth-highest storm tide level in this location.
Image: Hal Needham

This may surprise us, as Frenier is situated on Lake Pontchartrain, and not far from New Orleans, which was devastated from Katrina. This is further proof that storm surge is a very localized phenomenon. While Katrina generated a massive storm surge east of the Mississippi River, in Mississippi Sound, and to the east and north of New Orleans, the wind setup in Lake Pontchartrain did not support a prolonged, intense wind from the east, which is needed to pile up a lot of surge near Frenier.

Both Hurricane Betsy and the 1915 Hurricane produced prolong, intense winds blowing from east to west over Lake Pontchartrain, enabling these storms to generate higher surge levels than Katrina in places like Frenier and near Lake Maurepas.

 Frenier is located on the southwest shore of Lake Pontchartrain. This location requires the strongest hurricane winds to blow from the east or northeast to pile up large storm surges. This happened in Betsy (1965) and during an unnamed hurricane (1915). This did not happen so efficiently during Katrina (2005), keeping storm tide levels < 6 ft (1.83m).

Anecdotal stories from Hurricane Betsy are common in South Louisiana, as Betsy was the measuring stick by which people compared other storms, until Katrina.

A woman who installed a glass elevator on her home near Boothville, Louisiana, once told me that Betsy, Camille and Katrina floated her home from its foundation, but she has rebuilt each time.

 Betsy revealed the vulnerability of communities in eastern and southeastern metro New Orleans to storm surge flooding. This photo was provided by a website that archived the storm damage in Chalmette, St. Bernard Parish.
Image: http://chalmettecoc.org/images/betsy/phpslideshow.php?directory=.&currentPic=0.

My father-in-law tells a story about how he saw the eye of Hurricane Betsy pass over Port Allen, in the early hours of September 10, 1965. Port Allen is just across the river from Baton Rouge, where I work.

But my favorite story comes from Malcolm Moreau, a seasoned weather observer, who has been taking daily rainfall observations for more than 50 years. “Ole Moe” and I worked together in the Southern Regional Climate Center (SRCC) for the past four years, until he retired this summer, less than two months before turning 80 years old. Moe tells the story of how he was working at the National Weather “Bureau” (before it was called the National Weather Service) office in New Orleans the night that Betsy made landfall. Unfortunately, there were problems with some of the equipment on the roof of the building, and Moe was chosen to go on the roof for a maintenance job at the height of the storm! He still recounts how his coworkers tied a rope to him and held him fast from the stairwell, so he wouldn’t blow away!

Betsy stories abound in Louisiana because many eyewitnesses are still alive to recount the tales from this storm, unlike major hurricanes that struck Louisiana in 1893 and 1915. Also, Betsy generated a massive storm surge that produced the highest water levels on record in many places until Hurricane Katrina. It truly became the measuring stick for storm surge potential in Southeast Louisiana for decades, as it produced observed water levels from which the New Orleans metro area tried to protect itself for a long period of time.

REFERENCES:
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Atlantic Oceanographic & Meteorological Laboratory, 2014: Chronological list of all hurricanes:1851-2014. Funded by the National Oceanic and Atmospheric Administration. Link:http://www.aoml.noaa.gov/hrd/hurdat/All_U.S._Hurricanes.html.

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Blake, E.S., C.W. Landsea, and E.J. Gibney, 2011: The Deadliest, Costliest, and Most Intense United States Tropical Cyclones from 1851 to 2010 (And Other Frequently Requested Hurricane Facts), NOAA Technical Memorandum NWS NHC-6, available on the Web at: http://www.nhc.noaa.gov/pdf/nws-nhc-6.pdf.
Needham, H.F., and B.D. Keim, 2014: Correlating Storm Surge Heights with Tropical Cyclone Winds at and before Landfall, Earth Interactions, 18, 1-26.

U.S. Army Corps of Engineers, 1965: Report on Hurricane Betsy, 8-11 September, 1965. New Orleans District Office.

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