HURRICANE SANDY SOME OBSERVATIONS. J. Richard Weggel, Ph.D., P.E., D.CE

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1 HURRICANE SANDY SOME OBSERVATIONS J. Richard Weggel, Ph.D., P.E., D.CE Rainfall The US Geological Survey (USGS) operates a number of recording precipitation gauges in New Jersey. The data from these gauges are not archived but are available for a period of time following their recording. The New Jersey State Meteorologist operates similar stations. Figure 1 presents the cumulative rainfall records at 6 USGS precipitation gauges in New Jersey during Hurricane Sandy. The total rainfall at Cape May and Atlantic City exceeded 8 inches during the hurricane. Figure 2 compares the rainfall at Cape May and Atlantic City with rainfall statistics for the Cape May peninsula. The 24-hour rainfall depth at these two locations was about 7.5 inches which would give a return period of about 80 years; equivalently, it would have a probability of 1/80 = 125 (1.25%) of occurring in any one year. Other, non-recording gauges on the Cape May peninsula recorded greater 24-hour rainfall depths with at least one gauge at Wildwood Crest reporting more than 11 inches on the two days, 29 and 30 October Such depths exceed the 100-year event. Figure 3 presents the same information as Figure 2 but in a different way. Shown on the figure are the rainfall depths at Wildwood Crest for 30 October at 8.7 inches and the two-day depth of 11.7 inches. The duration of the 11.7-inch depth is likely longer than 24 hours. The 8.7-inch depth is the 200 year event while the 11.7 inch depth, if it fell within 24 hours, would exceed the 2000 year event. "SANDY" RAINFALL NEW JERSEY CUMULATIVE RAINFALL DEPTH (inches) CAPE MAY, NJ ATLANTIC CITY, NJ BARNEGAT LIGHT, NJ SHAMONG, NJ LAKEWOOD, NJ POINT PLEASANT, NJ TIME (hours after noon, 28 October 2012) Figure 1 Cumulative 24-hour Rainfall at 6 New Jersey Gauges (unverified USGS data) 1

2 DEPTH-DURATION-FREQUENCY DATA - SOUTHERN NEW JERSEY yr 7 6 CAPE MAY, NJ ATLANTIC CITY, NJ 50 yr 25 yr 10 yr DEPTH (inches) yr 2 yr 1 yr DURATION (minutes) Figure 2 Comparison of Hurricane Sandy Rainfall at Cape May and Atlantic City with Rainfall Statistics for the Cape May Peninsula. RAINFALL FREQUENCY CAPE MAY COUNTY, NJ HOUR DURATION 12 HOUR DURATION 6 HOUR DURATION TotalRainfall at Wildwood Crest, NJ 29 & 30 October 2012 = 11.7 inches, 3 HOUR DURATION RAINFALL DEPTH (inches) 1 2 HOUR DURATION 1 HOUR DURATION 1/2 HOUR DURATION Total Rainfall at Wildwood Crest, NJ 30 October RETURN PERIOD (years) Figure 3 Cape May County Rainfall Statistics showing Rainfall at Wildwood Crest during Hurricane Sandy 2

3 New Jersey and New York Atlantic Ocean and Long Island Sound Water Levels The National Ocean and Atmospheric Administration s National Ocean Survey makes tide predictions for numerous locations around the world. They also operate water level recording gauges at a number of sites in New Jersey and New York. Specifically, recording gauges are located at Cape May, Atlantic City, Sandy Hook in New Jersey and at The Battery and Kings Point in New York. Data from these gauges were downloaded following Hurricane Sandy. The figures below are from the above listed stations. Shown on the figures are the predicted astronomical tide due to the attraction of the moon and sun (blue line) and the measured water levels during the hurricane (red line). The surge level or storm tide is the difference between the measured water level and the predicted level (green line). Notable is the timing between the maximum surge and the high astronomical tide. At Cape May the two are nearly out of phase with the maximum surge occurring near low tide. At Atlantic City the maximum surge still does not coincide with the maximum astronomical tide; however, at Sandy Hook and The Battery, the maximum surge and high tide are coincidental leading to a maximum water level which reached 14 feet above mean lower low water (MLLW) at The Battery. (Note that data for measured water levels at Sandy Hook is missing after the peak high tide.) 1 OCEAN WATER LEVELS AT CAPE MAY, NJ HURRICANE "SANDY" Figure 4 Hurricane Sandy Water Levels at Cape May, New Jersey 3

4 OCEAN WATER LEVELS AT ATLANTIC CITY, NJ HURRICANE "SANDY" 1 Figure 5 Hurricane Sandy Water Levels at Atlantic City, New Jersey 1 OCEAN WATER LEVELS AT SANDY HOOK, NJ HURRICANE "SANDY" 1 1 Figure 6 Hurricane Sandy Water Levels at Sandy Hook, New Jersey 4

5 OCEAN WATER LEVELS AT THE BATTERY, NY HURRICANE "SANDY" Figure 7 Hurricane Sandy Water Levels at The Battery, New York. 1 LONG ISLAND SOUND WATER LEVELS AT KINGS POINT, NY HURRICANE "SANDY" Figure 7 Hurricane Sandy Water Levels at Kings Point, New York. 5