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 Sea Level Trend
 Table in mm/yr

 Sea Level Trend
 Table in feet/century

 Main Page Extreme Water Levels

Extreme Water Levels
8418150 Portland, Maine


The monthly extreme water levels include a Mean Sea Level (MSL) trend of 1.82 millimeters/year
with a 95% confidence interval of +/- 0.17 millimeters/year based on monthly MSL data
from 1912 to 2006 which is equivalent to a change of 0.60 feet in 100 years.

The plots show the monthly highest and lowest water levels with the 1%, 10%, 50%, and 99% annual exceedance probability levels in red, orange, green, and blue. The plotted values are in meters relative to the National Tidal Datum Epoch (1983-2001) Mean Higher High Water (MHHW) or Mean Lower Low Water (MLLW) datums established by CO-OPS (1 foot = 0.3 meters). On average, the 1% level (red) will be exceeded in only one year per century, the 10% level (orange) will be exceeded in ten years per century, and the 50% level (green) will be exceeded in fifty years per century. The 99% level (blue) will be exceeded in all but one year per century, although it could be exceeded more than once in other years.

probability curves
versus return period
Seasonal variation
of exceedance
probability levels
Tidal datums and
exceedance probability levels
relative to mean sea level

Highest and lowest extremes which exceeded the 10% annual exceedance probability levels
Highest Extremes 3/4/1931 4/21/1940 11/30/1944 11/20/1945 4/7/1958 12/29/1959 2/19/1972 3/16/1976 1/9/1978 2/7/1978
Highest Extremes 1/28/1979 1/2/1987 12/4/1990 4/16/2007
Lowest Extremes 12/11/1919 4/23/1936 1/7/1943 11/30/1955 12/30/1963 12/10/1977 3/16/1980 1/2/1999 12/12/2000 2/11/2001
Lowest Extremes 2/28/2002

NOAA's Continental US Daily Weather Maps: 1871-2002 September 2002-Present

Frequently Asked Questions:

What is Sea Level?
Why does Sea Level change over time?
What does Sea Level have to do with Climate?
What is Exceedance Probability Statistics?

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