Our kids have been super excited since yesterday afternoon that school has been canceled for today. Waking up this morning and looking around they were a bit surprised to see that it seemed to be neither blowing nor even raining outside. That got us into a good conversation about why Sandy is a dangerous storm for New York City. In the Northern hemisphere hurricanes rotate counter clockwise due to the Coriolis force. With the center of the storm supposed to be passing South of us, that means we have very strong onshore winds. These winds essentially push the ocean towards the city.
So the real danger for New York City are not the wind nor the rain but the storm surge. Think of it like the ocean rising up. As that higher sea water level is forced into the narrow harbor it rises even more (same volume of water but less area, so greater height). Now to get a sense of just how much water this storm is moving take a look at these tidal surge predictions which show probabilities for 6 feet or more above normal tide levels:
As you can see there is a 40-50% chance of this happening later today around Manhattan. If you want to play around with the surge levels, you can play around with this terrifying surge predictor created by NOAA.
Now you have to keep in mind that this is surge above normal tide. To make matters worse, tonight is a full moon and we are expecting a high high tide to begin with. If you have been to various parts of the waterfront at high tide you know that we don’t have a lot of room to spare. If the surge gets above that we will have flooding. How much? We won’t know until it actually happens, but right now the models don’t look very reassuring. We have taken our car out of the underground parking garage and put it in a parking lot and we have also started to clear out our basement.
If you want to watch the swell rising you don’t even need to leave your house. As long as you have power and Internet, you can check out the live data from the New York Harbor buoys here (the Harbor Entrance, about 15 miles out) and here (in the Harbor, right off the Battery). You can also see more at this handy NOAA Sandy Quick Look page that pulls a bunch of buoy data together and shows plots of normal predicted tide versus actually observed water levels. Also shown in each chart is a purple line labeled HAT, which stands for Highest Astronomical Tide. It’s the highest water level that has been observed in the absence of a storm. As you can see we will be very much above that.
Good luck to all of us here in New York and along the shore.
Update: This is the Hudson already breaching its banks near the Standard Hotel (picture taken by Fred)