Sea level rise increases storm surge damage
Of the six tide gauges with long-term periods of record along the west coast of Florida, Helene set an all-time high water record at three of them (Cedar Key, Clearwater Beach, and St. Petersburg) – in all three cases just before or just after midnight Thursday night – and came in second or third place behind Hurricane Ian of 2022 and Hurricane Irma of 2017 at the other two (Ft. Myers and Naples). Sea level rise made these records easier to set. Sea level rise since 1947 at the St. Petersburg, Fla., tide gauge has been about 3.09 mm per year, or about 0.3 meters (1.0 feet) if extrapolated to a 100-year period (Figure 1). A substantial portion of this sea level rise is the result of human-caused global warming; the global sea level rise since 1900 is estimated to be about 7.5 inches (0.19 meters). Most of this rise has occurred because of melting of glaciers and because water expands when heated. Over the past 10 years, sea level rise has accelerated along the Florida coast, and the rate has been about 7 mm per year (2.3 feet per century) at St. Petersburg. Changes in ocean circulation and wind patterns, with climate change a potential contributing factor, are thought to be the reason for the acceleration.
Six of St. Petersburg’s top-10 water levels since 1947 (highlighted in bold) have occurred since 2012. This is the kind of behavior one would expect to see in an era of climate change, since sea level rise makes it easier to set new high-water records. Here are the top ten water levels at St. Petersburg since 1947, as measured above mean higher high water, or MHHW:
- 6.31 feet, September 27, 2024, Hurricane Helene
- 4 feet, August 31, 1985, Hurricane Elena
- 3.8 feet, August 30, 2023, Hurricane Idalia
- 3.58 feet, October 8, 1996, Tropical Storm Josephine
- 3.52 feet, June 18, 1982, Subtropical Storm One
- 3.37 feet, November 12, 2020, Tropical Storm Eta
- 3.16 feet, December 17, 2023, Winter storm
- 2.74 feet, September 6, 2004, Hurricane Frances
- 2.91 feet, March 13, 1993, Storm of the Century
- 2.74 feet, June 25, 2012, Tropical Storm Debby
Here are the top seven water levels at Cedar Key since 1914 (above mean higher high water, or MHHW), again with records set since 2012 in bold:
1) 9.3 feet, September 27, 2024, Hurricane Helene
2) 6.84 feet, August 30, 2023, Hurricane Idalia
3) 5.98 feet, September 2, 2016, Hurricane Hermine
4) 5.41 feet, August 31, 1985, Hurricane Elena
5) 5.15 feet, October 8, 1996, Tropical Storm Josephine
6) 5.13 feet, March 13, 1993, Storm of the Century
7) 4.66 feet, August 5, 2024, Hurricane Debby
Here are the top six water levels at the Clearwater Beach tide gauge, on the Gulf of Mexico side of St. Petersburg, where records extend back to 1973:
1) 6.67 feet, September 26, 2024, Hurricane Helene
2) 4.02 feet, March 13, 1993, Storm of the Century
3) 3.58 feet, August 30, 2023, Hurricane Idalia
4) 3.32 feet, January 3, 1999, Winter storm
5) 3.17 feet, August 31, 1985, Hurricane Elena
6) 2.91 feet, October 8, 1996, Tropical Storm Josephine
Here are the top seven water levels at Naples since 1965 (above mean higher high water, or MHHW):
1) 6.18 feet, September 28, 2022, Hurricane Ian (gage failed before highest level was recorded)
2) 4.02 feet, September 10, 2017, Hurricane Irma
3) 4.01 feet, September 26, 2024, Hurricane Helene
4) 3.11 feet, August 4, 2024, Hurricane Debby (data from the new North Naples Bay station)
5) 3.11 feet, December 22, 1972, Winter storm
6) 3.08 feet, January 17, 2016, Winter storm
7) 3.02 feet, September 28, 2023, Hurricane Idalia
Helene brought the second-highest water level on record to Fort Myers, Florida, where accurate records go back to 1965. Here are their top seven water levels (above mean higher high water, or MHHW):
1) 7.26 feet, September 28, 2022, Hurricane Ian
2) 5.12 feet, September 27, 2024, Hurricane Helene
3) 3.41 feet, November 23, 1988, Tropical Storm Keith
4) 3.31 feet, September 14, 2001, Hurricane Gabrielle
5) 3.30 feet, June 18, 1982, Unnamed subtropical storm
6) 3.27 feet, August 4, 2024, Hurricane Debby
7) 3.2 feet, August 30, 2023, Hurricane Idalia
Note that there were multiple reports of inundations from 1960’s Hurricane Donna of eight to 12 feet in the Naples area and seven to 11 feet in the Fort Myers area.