A couple of years ago, I had our WNYC engineers use a plotter to print out this huge evacuation map PDF. Seemed like a good thing for the disaster-planning file. Just in case.
Then, back in June of this year, I was browsing the NYC DataMine (like you do), and realized New York City had posted a shapefile for the colored zones on that map.
UPDATE (Feb. 11, 2012): NYC has nicely revamped the DataMine since the summer Irene struck -- even mapping geographic files like this right in the browser. But it's actually tricker to find the shapefiles now. Here's the hurricane zones dataset. Click "About" and scroll down to "Attachments" for the .zip file containing the shapefiles. Or just use this shortcut.
I knew I could use the shapefile to make a zoomable Google map -- which would be a heckuvalot easier to use than the PDF. So I imported the shapefile into a Google fusion table. (It's super easy to do; check out this step-by-step guide.) Next, I added that table as a layer in a Google Map and tacked on an address finder I'd developed for WNYC's census maps.
Then I tucked the code away on my computer. Just in case.
Fast-forward to Thursday morning, as Irene approached. On the subway in to work, I polished the map and added a color key. It was up on WNYC.org by midmorning, long before the Mayor ordered an evacuation of Zone A.
When the order was announced, I used another fusion table to add evacuation center locations, updating that list with info from New York City's Chief Digital Officer Rachel Sterne. (The dots are gone now, since the sites are closed.)
I'm not at liberty to reveal traffic numbers, but the site where we host our maps received, um, a lot more views than it usually does. By orders of magnitude. Huge props to the WNYC.org digital team for keeping the servers alive.