Extreme Water Levels

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The monthly extreme water levels include a Mean Sea Level (MSL) trend of 1.98 millimeters/year with a 95% confidence interval of +/- 1.15 millimeters/year based on monthly MSL data from 1972 to 2006 which is equivalent to a change of 0.65 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 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.


Highest and lowest extremes which exceeded the 10% annual exceedance probability levels
Highest Extremes 1/15/1974 12/15/1977 12/16/1982 1/27/1983 12/9/1987
Lowest Extremes 12/12/1985 12/12/1989 12/24/1999 11/26/2007 1/12/2009

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

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Extreme Water Levels - Port Townsend, WA - NOAA Tides & Currents