[temporary note: With Irene approaching our area, I'll mention that it has shown some weakening instead of strengthening on Friday, so it extremely unlikely to have a similar strength or impact to the Hurricane of 1821. Check the latest updates at http://SeaAndSkyNY.com%5D
Hurricane Irene is approaching the Bahamas, and models suggest it is likely to hit the U.S. Southeastern coast somewhere around the Carolinas. The forecast storm track and intensity is similar to the most destructive storm to have hit NYC in the past 500 years, the “1821 Norfolk and Long Island Hurricane“, that caused a 13-foot storm surge which inundated large low-lying tracts of NYC. Moreover, it could arrive in the area around the day of spring tide (next Wednesday), potentially adding a few more feet to the surge. There remains a great deal of uncertainty with the storm so far off, but this should definitely be on our radar.
Surprisingly, the Norfolk storm is believed to have had its eye over land for much of it’s final few days preceding NYC landfall, just inside the North Carolina, Delmarva, and New Jersey coasts. However, this coastline contains a great deal of warm surface water in bays and estuaries, so can still help supply fuel to support a hurricane.
Evacuation of 1-2 million people in low-lying NYC neighborhoods deemed vulnerable to a 15-foot storm surge would require advance notice of two days … so some difficult choices would have to be considered this coming weekend if the storm hits North Carolina and appears on track to maintain hurricane strength and approach our shores around Tuesday [note that a newer forecast suggests Sunday]. An excellent simulation of the city’s response to such an event is available from the NYC Office of Emergency Management (follow the link, then drag the red timeline bar to see the progression to Day 0, the day of landfall).
The likelihood of Irene striking the Southeastern U.S. Coast is moderately high, but the NHC’s forecast discussion makes clear that “IT IS IMPORTANT TO REMIND USERS NOT TO FOCUS ON THE EXACT FORECAST TRACK…ESPECIALLY AT DAYS 4 AND 5 (or beyond) … SINCE THE MOST RECENT 5-YEAR AVERAGE ERRORS AT THOSE FORECAST TIMES ARE 200 AND 250 MILES… RESPECTIVELY.”
My interpretation is that the likelihood of Irene striking near NYC as a hurricane is still low, below one-in-ten. This is because there is still a week of travel between us and the storm. There is plenty of time for it to diverge inland or out to sea, or for it to weaken due to tracking over land, cold water, or due to wind shear. Let’s hope it veers eastward of its forecast track and stays out in the Atlantic with no continental landfall whatsoever. At the minimum, this storm will provide a real-time test of early hurricane preparedness plans…