Thursday, March 24, 2016

Why Palm Beach County Residents May be Unprepared for Storm Surge Flooding

On September 17, 1947, a category-4 hurricane struck southeast Florida, generating an 11-foot storm surge at Palm Beach (Barnes 2007). The sea water at Palm Beach on that date reached the highest recorded level, even topping a 9.8-foot storm tide generated by the "Lake Okeechobee Hurricane" of 1928 (Harris 1963). Both of these storms generated high enough storm surges to inflict substantial damage along the coast.



The 1947 Hurricane smashed the coastline of Palm Beach County with a powerful storm surge. This photograph of the Seacrest Hotel in Delray Beach was taken at the northwest corner of Ocean Boulevard and Atlantic Avenue. Image Courtesy: Florida Memory: State Library & Archives of Florida (https://www.floridamemory.com/items/show/38352).


In fact, since 1926, five hurricanes have generated coastal floods at least 7 ft high in Palm Beach County; this level was reached in 1926, 1949 and 1965, and exceeded by hurricanes in 1928 and 1947. However, all of these events occurred more than 50 years ago, as the area has enjoyed an absence of large storm surges over the past five decades. Why is this?

The absence of large storm surges in this region during recent decades partly has to do with climate and partly has to do with luck, randomness, chance or fortune (pick your favorite term).



Time series of storm surges near Palm Beach/ West Palm Beach from 1880- present. Larger chart available on Palm Beach/ West Palm Beach U-Surge page at: http://www.u-surge.net/palm-beach-west-palm-beach.html.

Climatologically, hurricane activity in South Florida was suppressed from around 1968-1994 due to a negative phase in a climate teleconnection called the Atlantic Multidecadal Oscillation (AMO). Climatic teleconnections are links between weather or pressure patterns and resulting weather phenomena, like hurricanes. El Nino is a familiar teleconnection.

The AMO relates to a temperature index of the Sea Surface Temperature (SST) in the Atlantic. When the AMO is in a positive (warm) phase, the SSTs are relatively high and hurricane activity generally increases. When the AMO is in a negative (cold) phase, however, SSTs are relatively low and hurricane activity generally decreases. The AMO was negative from around 1968-1994, meaning there was less activity in those years, followed by a more active period beginning around 1995 (
Kossin and Himont 2007). 




The AMO Index relates to average sea surface temperatures in the Atlantic Ocean. Negative phases, depicting colder than normal temperatures, occurred between 1900-1925 and approximately 1968-1994. These periods were preceded and followed by warm phases. Image: https://en.wikipedia.org/wiki/Atlantic_multidecadal_oscillation.


However, Hurricanes Hugo (1989) and Andrew (1992) were two major hurricanes that struck the Southeast U.S. during the AMO cold phase, which proves that these teleconnections relate to general correlation, but do not mean there will be an absence of powerful hurricanes.

Randomness also plays a role in hurricane impacts at a particular site, and Palm Beach has been a "lucky" location in recent decades, at least concerning hurricane storm surge.

​The 1990s saw Hurricanes Andrew (1992), Erin (1995) and Irene (1999) impact Southeast Florida, but none of these storms generated a substantial storm surge in Palm Beach County because of their their tracks and landfall locations. Hurricane Andrew inflicted catastrophic wind and surge damage in Miami-Dade County, as cat-5 winds and a 16.9 ft storm surge tore through areas south of Miami (Rappaport 1993). However, storm surge levels north of Fort Lauderdale were modest, and typically not even observed. Hurricane Erin made landfall well north of the area, near Cocoa Beach, so the strongest winds in Palm Beach County were blowing offshore. And Irene approached from the southwest, so the water it was pushing mostly impacted the Keys and Everglades.

In the 2000s, hurricanes continued to strike southeast Florida, inflicting the greatest damage on Palm Beach County in 2004. That September, Hurricanes Frances and Jeanne inflicted substantial wind damage on the county. However, since these storms made landfall near the county's northern border, the strongest winds in the area were blowing offshore and suppressing surge levels. Frances produced elevated water levels on the coast, with water levels at Lake Worth Pier reaching 6.3 ft above the NAVD88 datum (Wang and Manausa 2013). Within 10 miles of the Palm Beach/ West Palm Beach area, Jeanne produced a maximum surge of around 3.5 ft (National Weather Service 2010).



Hurricane Jeanne struck much of Palm Beach County with maximum sustained winds exceeding 70 mph, however, the strongest winds were blowing offshore since Jeanne made landfall north of the area. Due to this track, Palm Beach County experienced substantial wind damage but relatively little storm surge damage. (Note: wind damage was greater in Martin County, to the north. Image printed in Wang and Manausa (2005).

Several more hurricanes followed in 2005, and although storms like Katrina and Wilma generated substantial wind and rain, their track and intensity were not ideal for generating large storm surges near Palm Beach.

This lack of large surges over more than five decades may leave many residents of Palm Beach County unprepared for saltwater inundations in the future.

Massive population growth in this region will substantially increase storm surge impacts even if future storm surges do not surpass the frequency or magnitude of surges in the past. From 1970 to 2014, Palm Beach County has grown by more than 400%, as the population increased from approximately 349,000 to 1,398,000 (U.S. Census 2014). That's an addition of more than one million people in 45 years.

This 2007 air photo depicts widespread suburban sprawl encroaching on a water-logged area of the northern Everglades in Palm Beach County. Massive population growth in recent decades places more people at risk from storm surge and sea-level rise. Image Courtesy Herald-Tribune Archive/ The New York Times.

Sea level rise has also increased the ocean level in recent decades, meaning a lower magnitude storm surge today could reach the same water levels reached in the 1960s, because the seawater has a head start. Unfortunately, many people along Florida's Atlantic coast may feel that sea level rise is an issue restricted to Miami-Dade and Broward counties, but will not affect Palm Beach County and points north.


Long story short, Palm Beach County is vulnerable to inundation from coastal flooding, but because of climatological factors and a bit of good luck, the area has avoided any substantial storm surges for more than 50 years. Many local residents are transplants who have never experienced a hurricane before, and long-timers likely think of hurricanes as wind events instead of storm surge events, given the history of the past five decades. We can only hope residents realize their luck will run out and salt water will once again inundate their coastal communities.




REFERENCES


Barnes, J., 2007: Florida’s Hurricane History, 3rd Edition, University of North Carolina Press, Chapel Hill, North Carolina, USA, 407 pp.



Harris, D.L., 1963. Characteristics of the Hurricane Storm Surge. United States Weather Bureau, Technical Paper No. 48. Available on the web at: http://www.csc.noaa.gov/hes/images/pdf/CHARACTERISTICS_STORM_SURGE.pdf.



Kossin, J.P., and D.J. Himont, 2007: A More General Framework for Understanding Atlantic Hurricane Variability and Trends. Bulletin of the American Meteorological Society, DOI: 10.1175/BAMS-88-11-1767.


National Weather Service, 2010: Hurricane Jean, Miami- South Florida Weather Forecast Office, Miami, Florida. Available on the Web at: http://www.srh.noaa.gov/mfl/?n=jeanne.



​Rappaport, E., 1993: Preliminary Report, Hurricane Andrew, 16-28 August, 1992. National Hurricane Center, Miami, Florida, USA. Link: http://www.nhc.noaa.gov/1992andrew.html.



U.S. Census, 2014: Census of Population and Housing. Link: http://www.census.gov/prod/www/decennial.html.



​Wang, R., and M. Manausa, 2005: Hurricane Jeanne, Characteristics and Storm Tide Evaluation, Draft Report. Submitted by Beaches and Shores Resource Center, Florida State University, 11 pp. Link: https://www.dep.state.fl.us/beaches/publications/pdf/tropical/2004/strmtide/jeanne.pdf.



​Wang, R., and M. Manausa, 2013: SBEACH High-Frequency Storm Erosion Model Study for Palm Beach County, Final Report. Submitted by Beaches and Shores Resource Center, Florida State University, 52 pp. Link: https://www.dep.state.fl.us/beaches/publications/SBEACH/sbeach-PalmBeach-FinalReport1.pdf.

2 comments: