All it took was about 7.6cm of rain in three hours to bring the US' largest mass transit system to its knees.
Subway tracks were swamped, buses were overwhelmed and commuter trains were held up for hours because of flooding on Wednesday. Some roads became waterways, and one woman was killed in a car accident during the storm.
The weather also created problems for the region's airports, where delays of up to an hour were reported, and thousands of people throughout the region lost electricity for part of the day.
Much of the mess had been mopped up by early yesterday, but the region still faced the possibility of more storms.
Wednesday's storm hit just before dawn. By rush hour, pumping stations became overwhelmed, and the subway system was virtually paralyzed. Bedlam resulted from too much rain, too fast; some suburban commuters spent half the day just getting to work. Crews worked feverishly to pump out the subways, but it took until the evening rush hour to get most of the system up to speed.
The washout marked the third time in seven months that the subways were disrupted by rain.
Metropolitan Transportation Authority (MTA) engineers were asked to report back to Governor Eliot Spitzer within 30 days with suggestions about how to deal with the flooding.
"One big rain, and it all falls apart," Ruby Russell, 64, said as she sat waiting on a train in Brooklyn on Wednesday morning. She had been trying to get to Manhattan for three hours.
The US National Weather Service said a tropical air mass dumped an extraordinary amount of rain in a short period of time. The most was recorded between 5am and 8am, with 6.4cm falling on Central Park and almost 8.9cm on Kennedy International Airport.
Public officials called for improvements to the drainage system after a similar rain-related shutdown in 1999, and the MTA made some changes after another round of paralyzing tunnel floods in 2004, when the remnants of Hurricane Frances washed out the subways for hours.
The National Weather Service said a tornado touched down several times in Staten Island and in Brooklyn, where winds downed trees, tore off roofs and wrapped signs around posts. At least 40 homes were damaged.
Tornadoes have hit New York City before, but not often.