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Don't Panic -- But Prepare. Sandy Looks Like The Real Deal.

[NOTE: For my latest updates on Hurricane Sandy, follow me on Twitter. You may also want to read my thoughts on potential election impacts from Hurricane Sandy. Additionally, I did radio interviews today for WCBS 880 AM in New York (listen here), KFAB 1110 AM in Omaha (listen here) and WBAL 1090 AM in Baltimore (no archive link yet).]


Above: The impending clash of titans -- a strong trough of low pressure (a.k.a. cold front) that would probably have produced a powerful Nor'easter even if no hurricane were present, and Hurricane Sandy, which is expected to join forces with the trough to create an epic storm of historic proportions.

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"The more data I see, the more I think we're going to be talking about this storm for decades."

That's what meteorologist Nate Johnson said last night on the WeatherBrains live show about Hurricane Sandy. It's a sentiment I keep seeing expressed again and again, in various forms, by pretty much everyone with pertinent meteorological knowledge. Not just serial alarmists, but everyone. (That includes plenty of AGW skeptics, for what it's worth. This isn't a global warming hypestorm. This is, potentially, a truly historic weather event, regardless of your stance on climate change.)

When you look at the data -- at the best information presently available -- you just can't escape the conclusion that Sandy appears increasingly likely to be an unprecedented and extremely serious storm, as the Capital Weather Gang writes:

With computer models locked in on the eventuality of a punishing blow for East Coast from Hurricane Sandy (with the latest model runs favoring the northern mid-Atlantic), analyses suggest this storm may be unlike anything the region has ever experienced.

Model simulations have consistently simulated minimum pressures below 950 mb, which would be the lowest on record in many areas.

"Below 950 mb" is an understatement. Last night, a run of the HWRF model forecast an impossible-seeming 922-millibar storm at landfall (see below). That was Hurricane Andrew's intensity when it hit Florida in 1992! The GFS and Euro models have also shown very low pressures in various models runs. Realistically, the models are probably overstating things a bit -- Sandy probably won't get quite that intense (and even if it did, its winds wouldn't be anywhere near Andrew-like levels, because it will have a much, much wider and more diffuse circulation -- in other words, gale- and hurricane-force winds over a huge area, but no central area of Category 3, 4 or 5 type winds) -- but when the models are ranging from the 920s and 930s to more "reasonable" values in the 940s and 950s, you can't help but take the storm seriously. The "perfect storm" was only 972mb! Anything below 960mb is pretty epic and historic.


It isn't just the barometric pressure that has folks alarmed, of course. So many of the potential tracks would bring devastating coastal flooding. The official NHC track could be calamitous for Delaware Bay. The latest GFS model could bring devastating flooding to the shores of Long Island Sound. And of course there is the New York Harbor nightmare. Or, Washington, D.C., the Delmarva and Chesapeake Bay could be crushed. Or the New Jersey shore could. It's important to emphasize that we don't know exactly where Sandy will go, and won't for a while yet. But at this point, it's hard to find a reasonably likely track that wouldn't be a serious disaster for someone, in a region that's so heavily populated.

Moreover, because Sandy is so huge, its impact will be widespread and long-lasting. North and east of the landfall point, its relentless onshore winds will pile up a storm surge over a wide area through multiple tide cycles -- making each successive high tide higher than the previous one. With astronomical high tide on Monday, this is a particularly big problem. AccuWeather meteorologist Mike Smith (an AGW skeptic and non-alarmist) writes on his blog: "Based on some media coverage I'm seeing, the threat of flooding in coastal areas is being underplayed. Especially, if you live ten feet or lower above sea level, you need to be prepared to evacuate should the order be given." I completely agree with that statement.

While we're on the topic of ocean flooding, models suggest Sandy will stir up the ocean to an almost unbelievable extent, with offshore waves that are, well, just huge:


And then there's the potential rainfall... and snowfall!

Rainfall_Days_1-5 A6HdTl-CQAA1K_u

(The total rainfall would actually be greater than the graphic at left shows, because that's only a 5-day forecast, going through Wednesday morning, when the storm is forecast to be inland over Pennsylvania, still dumping lots of rain.)

I'm picking up some skepticism of all this "hype" from commenters and on Twitter, by folks who say this is "just" a Category 1 hurricane or "just" a big Nor'easter, and the media is jumping the gun again, like they did with Irene and various other storms. (Actually, Irene arguably lived up to much of the hype, but I'll leave that argument for another day.) This sort of critique, which is often more rote media criticism than actual storm-specific analysis, routinely fails to recognize that weather forecasting is an inherently uncertain probabilistic enterprise -- meaning most worst-case scenarios, warned of days in advance, don't happen; if we wait to discuss them until they're likely or certain to happen, it's too late to prepare -- so you have to judge the validity of "hype" contemporaneously, not with the benefit of hindsight. And, given that fact, the "overhype" critique is particularly misguided and wrong-headed in the present situation. The currently available data suggests, almost unanimously, that the universe of realistic scenarios for Sandy ranges from "bad" to "very, very bad." The moment that data shifts, and starts suggesting a lower probability of disaster, I'll let you know, just as I did with Irene and Isaac when the data shifted toward more favorable outcomes in those cases. But right now, that's just not what the data says.

Some folks -- local TV news departments probably being among the worst offenders -- will always hype every semi-serious storm, and even more folks (including national cable news writ large) routinely fail to walk back previously-justified hype when the data changes, or events on the ground prove the data wrong. But those of us who take our roles seriously only hype those storms that deserve it, and tamp down the hype when conditions change such that the storm no longer deserves it. Right now, this storm deserves it.

It's also critically important to remember yesterday's quote from meteorologist Brad Panovich: "Don’t let the Category of the storm or whether it’s 'just' a Nor’easter dictate your response. Your personal memories of previous storms are no use in this unique situation."

Why, you may ask, is it so unique? Why is all of this happening? Why is a Category 1 hurricane so potentially devastating? The Capital Weather Gang gives the most succinct answer I've seen:

[T]he clash of the cold blast from the continental U.S. and the massive surge of warm, moist air from Hurricane Sandy will cause the storm to explode and the pressure to crash.

This is highly unusual for a variety of reasons, about which, more after the jump.