This is the annual look at seawater levels at the NOAA Sewells Point water level gauge.
Caution -
- There are many nuances to this data and interpretations of it.
- Do not make decisions based on the information here
- Contact me if you plan to use the information presented here.
- The average annual water level for the whole year 2019 was the highest since 1928.
- Hours of nuisance flooding was 5th highest since 1928.
- The monthly average water level was highest on record in January, May, August, and October. It was the third-highest in July.
- By 2050 floods that used to happen every 12 years will happen every year.
Hours per year of nuisance flooding
First, the iconic plot of hours of nuisance flooding per year.
Nuisance flooding is a value determined by the National Weather Service in collaboration with regional emergency managers. It is 0.53 meters (1.7 feet) above Mean Higher High Water: the horizontal black line in the lower panel.
The upper panel shows:
1. There are occasional years with abnormally high hours of flooding. These are typical during a major hurricane or northeasters with long durations in the area.
2. There is a slow, steady increase from about 2005.
3. Based on this plot we can expect at least 40 to 50 hours of nuisance flooding per year in the coming years.
The lower panel shows
The lower panel shows the hourly water level since 1927. Since it is hourly you can see the twice-daily range in tides of about 1.5 meters or 3 feet. You can also see the occasional higher values well above 1 meter when hurricanes and northeasters pass our region.
Because of sea-level rise, the water levels are slowly increasing. The solid line is the nuisance flooding value of 0.53 m. You can see how the daily tides are slowly reaching more often into the nuisance flooding value. This is why we have more flooding.
Note - the hours of flooding are calculated assuming that any water level point above 0.53 m represents one hour of flooding. Thus, even if the water level was above 0.53 meters for one minute (unlikely) we count it as one hour.
Hourly Plot for the whole record for 2019
This is a plot of the water level measured every hour so you see the tidal range of a few feet and the variability month to month.
You can see that the water level can change over weeks to months. Changes in the ocean, wind fields and passage of hurricanes and northeasters cause these longer-term changes. The extreme values in September through December were caused by hurricanes and northeasters.
Average Monthly Water Levels
The above plot shows the average monthly water level for each month since 1928. The heavy line is the 2019 data. The monthly water levels for 2019 were in the top four for the entire record.
Ranking of months
This table shows the 10 highest months (highest to 10th highest). 2019 was in the first place 4 times, 3rd place once, 4th 4 times and 6th 2 times.
January 2019 2016 1998 2005 2010 2017 1996 2011 1993 2013
February 1998 2005 2010 1999 1983 2019 2016 2013 1993 1973
March 2010 2018 2013 2019 2014 1983 2011 1987 2016 2012
April 2010 2018 2013 2019 2014 1983 2011 1987 2016 2012
May 2019 2017 2005 1998 2011 2016 2008 2014 2006 2012
June 2018 2009 2012 2019 2014 2011 2016 1997 2017 2005
July 1975 2018 2019 2017 2015 2012 2009 2005 2011 2016
August 2019 2017 2014 2011 2010 1995 2013 2015 1998 2018
September 2018 2017 2016 2019 2015 2009 2003 2014 2011 2006
October 2019 2015 2016 2013 2004 2009 2005 2018 2012 2002
November 1928 1931 1936 1933 1934 1941 1929 1930 1943 1940
December 2018 2009 2012 2014 1996 2019 2015 2010 2011 2016
Average Monthly Water Level Movie
Now we show an animation of the monthly water level values from 1928 through 2019
Yearly Average
In 2019 the average water level was the highest since records began in 1928.
Ranking of years: 2019, 2018 2016 2010 2017 2014 2012 2009 2011 2005
Floods 1.5 feet above MHHW occur every 12 years now on average. In 2050, when water levels are predicted to be higher by 1.5 feet flooding will occur every year.
Trends
The figure above is directly from the NOAA website. The linear trend is about 4.7 mm per year or 1.54 feet per century. Note that the most careful analysis of these records strongly suggest that the rate is not linear.
The Sea Level Rise Report Cards produced at the Virginia Institute of Marine Science are an excellent source of information on acceleration rates and the causes of sea-level rise.
I urge you to go to that site for more information on projected rise rates.
They calculate the current linear rate at 5.33 mm/year and the acceleration rate as 0.13 mm/year. Note that both numbers are slightly higher than last year.
