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Extreme Water Levels
8545240 Philadelphia, PA

At this location, the tidal range has increased significantly over the period of record. The monthly extreme high water levels include a Mean High Water (MHW) trend of 4.41 millimeters/year
with a 95% confidence interval of +/- 0.24 millimeters/year based on monthly MHW data from 1900 to 2011 which is equivalent to a change of 1.45 feet in 100 years. The monthly extreme low water levels include a Mean Low Water (MLW) trend of 0.95 millimeters/year
with a 95% confidence interval of +/- 0.23 millimeters/year based on monthly MLW data from 1900 to 2011 which is equivalent to a change of 0.31 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
(Different station number for older data recorded at this location)
Highest Extremes 10/11/1903 8/24/1933 3/21/1936 11/25/1950 10/15/1954 8/13/1955 10/17/1955 3/8/1962 6/30/1973 2/26/1979
Highest Extremes 10/25/1980 4/17/2011 10/30/2012 12/21/2012
Lowest Extremes 3/8/1932 1/26/1939 1/25/1945 12/2/1946 1/6/1959 12/31/1962 3/8/1986 11/21/1989

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

A listing of the Top Ten Highest Water Levels at 110 long-term stations is also available as a table in meters or a table in feet above MHHW. No adjustment has been made for the rates of sea level rise or fall at each station. Therefore, stations with falling sea level trends are likely to have most of their Top Ten values near the beginning of their periods of record. An inferred level indicates that missing data at the peak water level were filled in. A high water mark is a physical mark near the station that can indicate the maximum elevation of a storm event. For some stations, older data recorded at a particular location may be stored in our database under a different station ID number.

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Extreme Water Levels - Philadelphia, PA - NOAA Tides & Currents

Revised: 08/08/2018
NOAA / National Ocean Service
Web site owner: Center for Operational Oceanographic Products and Services