Abstract
A climatological description (“climatology”) of storm surges and actual flooding (storm tide) events from 1959 to 2007 is presented for the New York City (NYC) harbor. The prevailing meteorological conditions associated with these surges are also highlighted. Two surge thresholds of 0.6–1.0 m and >1.0 m were used at the Battery, New York (south side of Manhattan in NYC), to identify minor and moderate events, respectively. The minor-surge threshold combined with a tide at or above mean high water (MHW) favors a coastal flood advisory for NYC, and the moderate surge above MHW leads to a coastal flood warning. The number of minor surges has decreased gradually during the last several decades at NYC while the number of minor (storm tide) flooding events has increased slightly given the gradual rise in sea level. There were no moderate flooding events at the Battery from 1997 to 2007, which is the quietest period during the last 50 yr. However, if sea level rises 12–50 cm during the next century, the number of moderate flooding events is likely to increase exponentially. Using cyclone tracking and compositing of the NCEP global reanalysis (before 1979) and regional reanalysis (after 1978) data, the mean synoptic evolution was obtained for the NYC surge events. There are a variety of storm tracks associated with minor surges, whereas moderate surges favor a cyclone tracking northward along the East Coast. The average surface winds at NYC veer from northwesterly at 48 h before the time of maximum surge to a persistent period of east-northeasterlies beginning about 24 h before the surge. There is a relatively large variance in wind directions and speeds around the time of maximum surge, thus suggesting the importance of other factors (fetch, storm duration and track, etc.).
INNOVATIVE DETERMINATION OF NEARSHORE FLOOD FREQUENCY
