Meteorological conditions associated with major storm surge events at New York City
Katherine Rojowsky, Stony Brook University, Stony Brook, NY; and B. A. Colle and F. Bounaiuto
A large fraction of the New York/ New Jersey metropolitan region is less than 5 m above sea level; therefore, much of the area is vulnerable to coastal flooding during tropical and cool season storms. In order to improve the forecasting of these events, more understanding is needed of the atmospheric conditions that favor storm surges around New York City (NYC). Many of these flooding events are clearly attached to extratropical and tropical storms, although the exact position, track, and strength of the cyclones as well as the wind direction and speeds that favor flooding have not been quantified for these surge events. A threshold of 0.6 m and 1.0 m above Mean High Water (MHW) was used to denote minor and moderate flooding at the Battery, NY (south side of Manhattan) given the thresholds used by the National Weather Service at this site. This resulted in 170 cases of minor events and 29 cases of moderate events since 1968. The NCEP reanalysis (before 1979) and Regional Reanalysis (>1979) was used to track the cyclone positions and the composite analysis of the synoptic evolution. The winds and JFK airport were used to investigate the local wind evolution from 48 h before to 24-h after the time of peak surge. The climatological distribution of number of surge events was also analyzed back to 1958.
There is a lot of interannual variability in minor surge events at NYC, ranging from 0 to 14 events per year. The number of moderate surge events also vary, with the most active period in the last 50 years in the 1990s (16 events) as opposed to only 5 events during the 1980s. Storm surges are greatest on average during the cool season, with a peak in December and January given the active storm track. During the time of maximum surge, the average cyclone position is over southern New Jersey, which favors easterly flow toward the NYC area from the Atlantic. However, there is a relatively large spread in cyclone positions for individual cases. The tracking of many individual cyclone events suggest that flooding can occur for a variety storm tracks ranging from the classical nor-easter track along the East Coast to inland and offshore tracks. For stronger surge events, the tracks tend to be more along the coast. The winds at JFK veer from an average northwesterly direction -48 h before the surge event to a northeasterly at the time of maximum surge. The average winds peak near the time of maximum surge at ~14 m s-1 (~10 m s-1) for the weak and moderate surge events. The presentation will also compare the differences between the tropical and extratropical storm tracks and conditions that favor surge events.
Joint Session 2, Observations/Studies of High—Impact Weather in Urban Regions
Tuesday, 13 January 2009, 1:30 PM-3:00 PM, Room 124A
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