Figure 2. Tide gauge recordings of water levels in Portland Harbor from April 15th through 18th and shown in meters above the North American Vertical Datum (NAVD). The rhythmic rise and fall of the tides twice a day is shown as predicted by the National Oceanic and Atmospheric Administration (NOAA) in the lower blue line. The blue line shows a rise and fall (range) larger than the mean due to "spring tide" conditions forced by the gravitational pull of the moon and sun. These astronomically high tides were the largest of the year and coincided with the Patriots' Day Storm. The second tidal line (shown in red) is a plot of the data recorded at the Portland Tide Gauge (No. 8418150). The storm produced a surge (an extra elevation of the sea) driven by the wind and low barometer to levels of 0.7 meters (or 2.5 feet) above that predicted. The difference from the predicted tide and the storm tide is shown by the green line on the graph. It peaks between 10 and 11 a.m. on April 16, 2007 and remains elevated for 6 more high tides before the storm's influence abates. The surge seems to get slightly higher during flooding tides.
Last updated on June 7, 2007