ELECTIONATE OCTOBER 30, 2012
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Anyone who ever attempted to plan around a five day weather forecast knows that long-range forecasts are accompanied by considerable uncertainty, and hurricane forecasts are no exception. Tropical cyclones routinely defy intensity forecasts and occasionally veer off of their projected paths, often by enough to leave residents placed under warning to wonder what the fuss was about. But Hurricane Sandy was a decisive win for the meteorologists and their computer models. Not only did the models correctly project Sandy's strength and path, they predicted an unprecedented storm--just about the highest accomplishment in forecasting.
Both Sandy's path and its sources of strength were highly unusual. Hurricanes typically draw their strength from warm tropical waters and are often pushed out to sea when they move north and encounter the prevailing westerly winds of the mid-latitudes. With Sandy initially moving into the Atlantic ahead of a cold front, hundreds of storms worth of precedent would dispose a forecaster to believe that the storm would have rapidly decayed encountered wind shear and moved over the colder waters of the northern Atlantic.
But while cold waters and strong upper-level winds usually combine to weaken tropical cyclones, Sandy actually intensified as it interacted with the same forces that usually destroy hurricane. A deep trough of low pressure and the subtropical jet-stream created enough wind shear to rip apart just about any other hurricane, but wound up creating enough baroclinic energy and upper level divergence to sustain and even intensify the cyclone despite colder waters and a hostile environment. Not only would this process transform Sandy from a typical, tightly wound tropical cyclone into a massive hybrid storm of unprecedented size and strength, but an unusual area of high pressure would prevent Sandy from moving out to sea and actually force Sandy back to the east and over the United States.
Despite the odds, it was as early as last Tuesday when the European model showed Sandy transforming into an extraordinarily intense hybrid storm and making landfall in the mid-Atlantic. Back then, Sandy was a small and utterly conventional tropical cyclone off the northern coast of Venezuela. Yet the European model peered 144 hours into the future and offered this prediction:
I actually laughed out-loud when I first saw this counter-intuitive forecast. Six day forecasts just aren't accurate and they occasionally produce far-fetched results. But over the next few days and before Sandy began to transform into the monster storm that would ultimately engulf the northeastern quadrant of the country, the other computer models joined one-by-one until the only disagreement was the exact location of landfall.
The models correctly anticipated an unprecedented storm with startling precision, nailing the storm's unusual path, strength, and character well in advanced. As predicted, Sandy transformed into a hybrid storm of unprecedented size and intensity, with tropical storm force winds stretching over 1,000 miles across, making it the largest tropical cyclone in the history of the Atlantic. While meteorologists often get a bad rap, they deserve credit for forecasting a historic storm well in advance.
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12 comments
I realize that no one particular weather event can be attributed to climate change, but the increasing frequency of highly unusual, even unprecedented events, well beyond the bounds of what can be statistically described as typical or normal, does add weight to the notion that climate change is indeed having a big impact. In the present case I've heard virtually no mention of climate change, & how it may be a factor with respect to Sandy. Almost as if commentators are being extra-special careful to avoid making the connection, as careful as the candidates were in the debates to avoid mentioning climate change. Why?
- Haole45
October 30, 2012 at 11:37am
Haole45 -- I'm starting to see that discussion trickle up, but have been surprised as well that it hasn't gotten more play. I wonder if the same social forces at play in the election are also suppressing this discussion... That said, an awful lot of people are paying attention right now and are asking the question, "why was this storm so much worse than anything we've seen before?", which is a good starting point for the climate change discussion, now that the storm is a reality (as opposed to a possibility)
- hairdan
October 30, 2012 at 12:52pm
One very important part of this story is that we are finally approaching the point where we have enough data and enough number crunching power to get these things right with reasonable frequency and certainty. Those of us in the tech industry who work with very large data sets and models are experiencing a sea change in our ability to see into the future. For fields like weather and climate and clinical medicine, this is going to be a huge revolution in how computing affects our lives. (And as a moderately snide aside, it will be a revolution that matters a whole hell of a lot more to our quality of life than the oft-hyped mobile revolution of apps that feed our always connectivity habit).
- IowaBeauty
October 30, 2012 at 12:59pm
To an extent, however, it's not something we've never seen before -- the 1938 New England storm was deadlier. But it is something not seen since 1991. It difficult for a non-expert to assess the windows of time in which these storms appear, e.g. 38, 91, 2012.
- ironyroad
October 30, 2012 at 1:43pm
To be clear, I believe the science about climate change, but, as Haole said, you can't trace any particular storm or attribute of a storm to climate change. Climate change affects probabilities, and there was a probability that this storm could have occurred just as it has even in the absence of greenhouse gases due to human activity. Along the same lines, is there really an "increasing frequency of highly unusual, even unprecedented events, well beyond the bounds of what can be statistically described as typical or normal", or is that a perception based on our human limitations with respect to time and, perhaps, our expectations of what should happen due to climate change? In fact, the models of the affects of climate change on storms are somewhat mixed and contradictory. On the other hand, if unsophisticated (science-wise) people who have doubted climate change are now willing to consider that it exists, so much the better for us all.
- mrheckman
October 30, 2012 at 1:48pm
Iowa, one of the local TV meteorologists here in the Raleigh area loves to show predictions from several models, one from the local university (NC State, tailored for NC weather prediction), one from NOAA and one from Europe (he never says exactly which "European models" he's referencing). This guy is a bit different than most TV weather guys in that he seems more empirically driven, with his forecasts being a meteorology lesson quite often, as if you're in a class more than just a typical TV forecast. The European models have been eerie in being accurate way more than the US models from what I've noticed, with this latest storm being nailed last week in it's ferocity and track way before than the US models. I've noticed with these large storms the Euro model he references is right more often than the US models, that it seems to skew towards more ferocity of these big events and calls it sooner by days than the US models. The data and simulation models seem to be here now, I'm just not sure how much those models are used when reported to the US public.
- tmmats
October 30, 2012 at 1:53pm
ironyroad, true, but the 1938 storm was not quite the same sort of hybrid as Sandy. When you're standing in the midst of the devastation that doesn't matter, but there are some technical differences between the two. For the most part serious weather geeks go places like Weather Underground to get as much model information as possible. Aside from occasional Weather Channel bits I've not seen a lot of advanced model talk like you describe, tnmats, except occasionally when I lived in south Florida.
- cspencef
October 30, 2012 at 3:04pm
Kudos to NOAA, regardless of whose model was best. It was the Hurricane of 1938 that gave credibility to making weather forecasting more scientific. There was a young forecaster in DC who was silenced by his crusty supervisors at the infant Weather Service, who did not want to even pass on the forecast to New York City. The youngster factored in the unusually warm coastal water temperatures to forecast an unusual acceleration in speed of travel (that one was moving at 50 mph!).
- K2K
October 30, 2012 at 3:51pm
Spence, this TV station's forecasts aren't the typical from what I've seen in the past. Often they're like short science lessons. They often cite multiple models in forecasts of big weather events. Here's a blog post from one of the station's staff from last week: http://www.wral.com/the-s-storm-forms-/11690406/ Their chief meteorologist mentioned this model divergence the same night during his broadcast and spent bit of time on the subject.
- tmmats
October 30, 2012 at 3:55pm
K2K, you better care who's model is being used. If NOAA doesn't have the funding, something the GOP would slash, their predictions will become less reliable as global climate patterns shift. We suffer for it since the emphasis from research done overseas will have much emphasis on climatic models for the US.
- tmmats
October 30, 2012 at 3:59pm
Argh, need to proofread better. Make that "will NOT have much emphasis on climatic models for the US"
- tmmats
October 30, 2012 at 4:17pm
"Along the same lines, is there really an "increasing frequency of highly unusual, even unprecedented events, well beyond the bounds of what can be statistically described as typical or normal", or is that a perception based on our human limitations with respect to time and, perhaps, our expectations of what should happen due to climate change?" The truth is that for events that have an expected mean time between occurances measured in multiple decades to a century, for any give region, we don't have enough data and won't for some time. There just aren't enough datapoints to distinguish a random cluster from a forced cluster. We have to settle for "this occurance is consistent with what we'd expect to see with increasing frequency if global warming is occuring and acting as expected."
- IowaBeauty
October 31, 2012 at 4:41pm