On Sunday, just days from the tenth anniversary of the 9/11 terrorist attack, water from Irene floods the World Trade Center site, which is being redeveloped. Irene's storm surge pushed some 3.5 additional feet (110 centimeters) of water into New York Harbor earlier in the day.
Irene's astronomically inopportune timing exacerbated storm surges in parts of the East Coast.
During new and full moons, the sun, Earth, and the moon are arranged in a straight line, with the sun and moon intensifying each other's gravitational pull on Earth. The result is more severe tidal fluctuations—low tides are lower than usual, but more to the point, high tides are higher.
Due to these so-called spring tides ("spring" in the sense of jumping), any town that sees the hurricane pass by during one of the two daily high tides is especially in danger of heavy flooding due to storm surges.