North-East Winds A-Blowin’

The big storm of 2012 (at least, we hope it’s the biggest we’ll see this year) is approaching the New York City area, and though no one can predict in detail how bad it will be and for whom, there’s no question that with so much energy to play with, post-tropical quasi-hurricane quasi-nor’easter Sandy (also called “Frankenstorm” in honor of the Halloween holiday) is going to hit some of us very hard in the northeastern United States.  Not that it will be a disaster everywhere in the region.  With hurricane Irene last year, some areas just had a bit of wind and rain, while others had tremendous flooding that wiped out towns and roads and houses and history… and a few dozen lives, too. It will likely be the same this time.

How unusual is this storm?  Several weather forecasters have been quoted as saying that their supercomputer-based forecasting tools, which predicted Sandy to strengthen and become a monster in size, were doing things they’d never previously seen them do.  Right now, all you have to do is look at the weather map — the fact that there are tropical force winds extending over several hundreds of miles, and at the fact that the pressure of the atmosphere at the core of this storm is around 946 millibars and falling — to know there’s a lot of energy in this system that has to go somewhere, and is going to be taken out on somebody.   Although this is a Category 1 hurricane in terms of its fastest winds, 946 millibars is what one expects for a strong Category 3 hurricane; 1000 is average atmospheric pressure, and the mid-800s is about as low as it ever gets.  By comparison, the great blizzard of 1993 had a central pressure of about 960 millibars.  The Perfect Storm of 1991 (also a nor’easter-hurricane hybrid, like Sandy) had a central pressure of 972 millibars.  Anyone who thinks Sandy isn’t a dangerous storm hasn’t read enough history.

I’m amazed at how often I hear New York City dwellers make fun of the weather prediction folks and the politicians for having advertised Irene as a dangerous storm, just because it turned out to be rather uneventful in the city proper.  This really involves a misunderstanding of the strengths and weaknesses of weather forecasting.  When the experts make predictions about weather, those predictions always come with the implicit caveat, one that everyone should be aware of, that weather prediction is neither an exact science nor a locally precise one.  It’s increasingly possible to predict general things for regions, such as that the weather in the northeast is going to become potentially very dangerous, that wind gusts will likely exceed 80 miles per hour in some places, and that it is likely that some locales in the northeast will suffer heavy damage.  But forecasters cannot reliably predict specific things for localities, such as whether the borough of Brooklyn will get 60 mile per hour winds and 3 inches of rain and a 5 foot storm surge — that’s more detailed than current scientific knowledge and technique permits.  Predictions with so much detail do get made — in fact you can look at the current prediction for New York City here — but one has to understand that such details are very uncertain, and are useful mainly for general guidance.  Fortunately, with somewhat more accuracy, it’s possible to predict the likely range of specific things: in particular, in this week’s storm, around Long Island and New York City the storm surge could perhaps be as bad as 11 feet, but is very unlikely to be worse than that.  The ability to predict a worst-case scenario saves many lives, by allowing policy-makers to focus on lives and property that are in the worst danger.

Forgotten in all the scorn that is heaped on those who predict the weather and often get the details wrong is how many lives weather forecasters save by getting the rough picture correct.  After all, they predicted that Irene would pass very close to the New York City area — and it did.  And here’s Sandy, whose potential to hit the northeast coast, as a very unusual westward-traveling (click here to see why) October hurricane, was first noted by the weather forecasters almost a week ago!  This forecast has become increasingly certain as days have gone by, and now all the forecasting methods agree that this will occur.  One must not lose sight of the fact that this achievement is astounding!

Consider that in 1938 a more powerful hurricane, sitting roughly where Sandy is now, suddenly and unexpectedly accelerated northward, and without warning blasted across Long Island and into the state of Rhode Island, with a massive storm surge and very strong winds that left over 500 people dead on what was expected to be a normal afternoon.  With modern methods of weather prediction, the potential for that northward lurch would surely have been known, and many of those lives would have been saved.

And without those modern methods, we would not have been known that today’s Hurricane Sandy would cease yesterday’s northeastward motion, and turn instead sharply to the northwest.  Instead of preparing last night with mandatory evacuations from low-lying areas, the shut-down of transportation systems, and cancellation of school in large sections of New York, Connecticut, New Jersey, Pennsylvania, Delaware and Maryland, we’d all be waking up in New York and its environs expecting a more or less ordinary rainy Monday morning, nonchalantly grabbing our umbrellas and putting raincoats on our kids — and we’d be completely unaware of the impending flood-tides and violent winds.

I can’t resist pointing out that for the lives saved today and tomorrow, we can thank investments in scientific research over the past century.  It is physics that provides the tools for our understanding of how weather works, and developments in physics underpin both the devices used to measure the weather and the computers used to predict it.  We should remember that advances in hurricane forecasting didn’t just fall from the sky, or blow in off the ocean in a strong wind.