New England Hurricanes, the forecast every time

12 11 2012

Kevin Anchukaitis

Let me start my first post here at Strange Weather by thanking Julien for the opportunity to join him here at his blog. I’ve been studiously preparing by listening to lots of Tom Waits albums, and although I hadn’t intended for my first post to be about hurricanes in the northeastern United States, some strange weather intervened.

I’m a recent arrival to the Massachusetts coast and now a scientist at the Woods Hole Oceanographic Institution, after spending the previous several years in New York City. While Superstorm Sandy, née Hurricane Sandy, was still several days from landfall in New Jersey, though, the region’s history of deadly hurricanes was already in the front of my mind. In August of 1991 Hurricane Bob scored a direct hit on Falmouth on Cape Cod in Massachusetts — my new home. At barbeques and gatherings this summer, my immediate neighbors were telling their stories of Bob’s “furious” landfall, the wind, the snapping trees, the storm surge, the flooding — and the long aftermath without power. So as Sandy lined up for her run at New England at the end of October, I admit I was somewhat nervously eyeing the tall but spindly locust trees near my house.

New England is not without a reason to keep one eye on the tropics in the late summer and autumn. Besides Bob, the New England Hurricane of 1938, the Great Atlantic Hurricane of 1944, Hurricane Carol in 1954, and Hurricane Donna in 1960. Wikipedia has a list of New England hurricanes. In 1821, a hurricane passed directly over New York City, resulting in 13 feet of storm surge and causing the East River to flow across lower Manhattan south of Canal Street. Yet another reason to be wary about hurricanes in New England lies in the mud and sand of the coastal marshes up and down the New England coast, several of which are disconcertingly within walking distance of my new home. These environments preserve a long record of storm activity in coastal New England going back hundreds or thousands of years.

Jeff Donnelly is a colleague of mine at Woods Hole Oceanographic Institution and one of the world’s experts in paleotempestology (Andrew Alden has a nice write-up on this science, here) — the study of past major storm activity from geological or biological evidence. Jeff uses sediments in coastal environments like marshes to identify and date past storms, but others have also used stable isotopes in tree rings, corals, and cave deposits, as well as historical records.

Marsh sediments from across New England tell a story of past hurricane strikes in the region, some clearly quite large. These environments record the passage of strong storms in the overwash deposits of sand that flood over their barrier with the sea during high waves and storm surges. Shore Drive in Falmouth is just such a barrier, and Sandy demonstrated quite clearly what an overwash deposit on its way to a backbarrier marsh looks like.

In a 2001 paper in the journal Geology, Jeff Donnelly and colleagues used multiple sediment cores extracted from a backbarrier march at Whale Beach, New Jersey, located between Ocean City and Sea Isle City, just to the south of Atlantic City, and close to where Hurricane Sandy made landfall, to reconstruct a history of beach overwash. They found deposits of sand associated with a 1962 nor’easter and another strong storm which they believed was the 1821 Hurricane. They dated a third deposit, thicker than the 1821 sand layer and probably related to an intense hurricane, to between 1278 and 1438 CE. In their article they note that the Whale Beach record suggests an annual landfall probability of 0.3%.

In a 2004 paper in Marine Geology, Donnelly and his team again looked at overwash deposits in New Jersey, this time from Brigantine, just to the north of Atlantic City. Here again they identified a layer of sand in the backbarrier marsh likely corresponding to the 1821 hurricane. They also dated large sand layers to the period between 550 – 1400 CE, which might correspond with the 13th or 14th century event identified at Whale Beach.

Donnelly et al. 2004, Marine Geology

Original caption from Donnelly et al. 2004, Figure 7: Cross-section of Transect 2 at Brigantine. ( p ) Location of radiocarbon-dated samples (see Table 1). Horizontal axis begins at the barrier/marsh boundary. The vertical datum is the elevation of the barrier/marsh interface (approximately mean highest high water).

Further to the east, in another 2001 paper Donnelly and his team used sediment cores from Succotash Marsh (near the fabulous Matunuck Oyster Bar near Point Judith in Rhode Island) to date hurricane strikes to known events in 1938 and 1954, as well as 1815 and the 1630s. Two other overwash deposits were dated to 1295-1407 and 1404-1446 CE. Donnelly and coauthors concluded that “at least seven hurricanes of intensity sufficient to produce storm surge capable of overtopping the barrier beach at Succotash Marsh have made landfall in southern New England in the past 700 yr”

One more, closer to home: In 2009, Anni Madsen and her coauthors (including Donnelly) published dates on hurricane deposits in Little Sippewissett Marsh in Falmouth, Cape Cod, Massachusetts, using optically stimulated luminescence (OSL) dating. This particular core shows a number of overwash deposits over the last 600 years, including probably Hurricane Bob and the 1976 Groundhog Day storm, but is also indicative of some of the difficulties and uncertainties in using backbarrier marshes to reconstruct hurricane strikes: Little Sippewissett Marsh doesn’t have sand layers that obviously date to recorded storms in 1938, 1944, 1954, 1815 and 1635, which include some of the largest to hit this region. Uncertainties arise from, amongst other things: a single core may not record all the storms at a site, storms themselves alter the height of the barrier and inlet channels, dating of events comes with analytical and depositional uncertainty, and in New England strong storms could be hurricanes or nor’easters.

Madsen et al. 2009, Geomorphology

Location of Little Sippewissett March, showing 19th and 20th century storm tracks across the region, from Madsen et al., A chronology of hurricane landfalls at Little Sippewissett Marsh, Massachusetts, USA, using optical dating, Geomorphology 109 (2009) 36–45, 2009

On Dot Earth, Andy Revkin has pointed toward his articles on Donnelly’s Caribbean research, as well as a 2002 paper by Anders Noren on millennium-scale storminess in the northeastern United States.

Bringing us back to Sandy, what does the history and geology of New England hurricanes tell us? There is evidence from all along the coast that powerful storms do occasionally make landfall in the region. The evidence from Whale Beach in New Jersey, near to where Sandy came ashore, records the very strong 1821 hurricane as well as another likely event in the 13th or 14th century. Other strong storms have hit the New England coast at other times in the past millennium. A 2002 article from the Woods Hole Oceanographic Institution quotes Donnelly:

“Most people have short memories,” says Donnelly. In fact, it is estimated that three-quarters of the population of the northeastern US has never experienced a hurricane. Donnelly’s research provides evidence to be heeded. “The geologic record shows that these great events do occur,” he says. “We need to make people aware that it can happen again. We’ve got to have better evacuation plans and we need to equip people to react to a big storm.”

I’m so far agnostic on the precise influence of human-caused climate changes on the track and characteristics of Sandy. The process of sorting out the influence of natural variability from the human-influence on this particular storm has just begun. As Justin Gillis notes in the New York Times Green Blog:

Some [climate scientists] are already offering preliminary speculations, true, but a detailed understanding of the anatomy and causes of the storm will take months, at least. In past major climate events, like the Russian heat wave and Pakistani floods of 2010, thorough analysis has taken years — and still failed to produce unanimity about the causes.

The influence of rising sea levels, particularly along the east coast of North America, no doubt has to be factored into understanding current and future storm surges. But what the geological and historical record indicate is that even in the absence of a human-influence on the strength, track, or magnitude of tropical storms, we would still need to be prepared for destructive coastal storms to strike areas of high population and considerable infrastructure. Paleoclimatology — in this case, paleotempestology — nearly always provides us with evidence of an even greater range and diversity of behavior of the climate system then we’ve witnessed over the relatively short period of instrumental observations, and gives an idea of some of the events — droughts, floods, and storms — that we need to keep in mind when figuring out how to build resilient communities.

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6 responses

27 11 2012
Brian Dodge

“Bringing us back to Sandy, what does the history and geology of New England hurricanes tell us? There is evidence from all along the coast that powerful storms do occasionally make landfall in the region. ”

How many of them had the center of the storm within 200 miles of Jamaica? How many had left curving tracks, because of a blocking high, associated with a record Arctic ice minimum? (google jennifer francis Rossby waves arctic)

“I’m so far agnostic on the precise influence of human-caused climate changes on the track and characteristics of Sandy. ”

Human fossil fuel CO2 emissions have driven the atmospheric levels from 280ppmv to 390+ppmv. This has increased atmospheric temperatures, increased SST’s, increased humidity/latent heat in the atmosphere, and melted snow/ice thereby altering the spatial and temporal distribution of solar energy gain. The forcing from the additional greenhouse gases is ~1.75 W/m^2, or ~ 9e14 watts total. Weather systems such as Sandy are the culmination of a chain of chaotic events, turbulent transfers of energy among radiative, conductive, convective, mass flow, and latent heat pathways. The path taken is exquisitely sensitive to initial conditions and perturbations as the weather evolves – the “butterfly effect”. A single butterfly can generate ~9e-2 watts, so AGW forcing is the equivalent of 10^16(ten million billion) butterflies.

How is it possible that all those equivalent butterflies human emissions created didn’t cause Sandy, and one real natural butterfly flapping its wings in Brazil is responsible?

27 11 2012
El Niño

Dear Brian,
the butterfly effect is a moniker for “sensitivity to initial conditions”, first discovered in a simplified model of atmospheric convection by Ed Lorenz in 1963. In weather terms it means that two initially close states (which differ only by a proverbial flap of a butterfly’s wings) may eventually diverge far apart (just like skiers dropping their wallets at the same approximate point at the top of the mountain might have to go pick them up at very different points downslope).

CO2 emissions, however, are not initial conditions, they are boundary conditions for the atmosphere. A productive analogy is that of “weather on steroids“, popularized by Jerry Meehl, Tony Broccoli and others. You wouldn’t be able to tell that a player is on steroids if they hit one homerun. But if they only do 5 in their average season, and all of a sudden they do 20, then you can suspect that something fishy is going on.
So it goes with hurricanes: one storm cannot be blamed on global warming ; only their statistics can. So far, quality hurricane observations don’t go back far enough for people to be absolutely confident that their intensity is trending upwards as clearly as, say, temperature and a host of other climate variables.

That’s why (careful) climate scientists are hesitant to blame Sandy on climate change. But I agree with you that the dynamical conditions (including the Jet stream diverting its path towards land) were highly unusual. We simply can’t exclude that this could have happened on our planet two centuries ago with far less CO2 in the air.
HTH,
Julien

28 11 2012
Brian Dodge

My point is that whenever you choose the initial condition to propagate weather forward (a day ago, a week ago, a year ago), those conditions are different, by much more than a single butterfly flap, because of additional anthropogenic CO2 forcing than they would have been otherwise. Suppose we have a weather model and global measurements accurate enough to start on September 16 and faithfully reproduce the weather through Sandy’s landfall on October 29. If you run that model starting with 5 million instead of 3.4 million km2 of arctic sea ice, or with sea surface/water column temperatures in the Atlantic 1 degree cooler, you are not going to get hurricane Sandy.

The results of a model, or the actual weather conditions, at every iteration or instant are initial conditions for the next moment and all future moments of the evolution of weather(and ultimately climate), real or modelled. If you took the model conditions each day, and duplicated them for a second simultaneous run, then duplicated each model on every successive day, after 10 days you would have 1024 identical models. If you perturbed each duplicate by a “butterfly flap”, they would all differ by a small amount at 10 days – and widely after a year. We have only one real weather model, and it is being perturbed every day by ~10e16 human generated virtual butterflies.

How many hurricanes have a central barometric pressure less than 945 millibar? 1/10? 1/100? (Depends on SST)
How many hurricanes make landfall within 100 miles of Sandy’s? 1/10? 1/100?
How many hurricanes have tropical force winds >500 miles from the center? 1/10? 1/100? (depends on SST, humidity, and Rossby wave dynamics)
How many hurricane paths have a left hook? 1/10? 1/100? (Rossby dynamics, again)

What’s the probability that Sandy was a random event(1/10000, 1/1e6?) unrelated to warmer oceans, higher air temperatures, higher humidity, slower and larger Rossby waves – all observed consequences of global warming? Slim to damned close to none.

29 11 2012
El Niño

Hello Brian,

whenever you choose the initial condition to propagate weather forward (a day ago, a week ago, a year ago), those conditions are different, by much more than a single butterfly flap, because of additional anthropogenic CO2 forcing than they would have been otherwise.

Different from ? Are we comparing this year to the last one, 10 years ago, or 1850?

Suppose we have a weather model and global measurements accurate enough to start on September 16 and faithfully reproduce the weather through Sandy’s landfall on October 29. If you run that model starting with 5 million instead of 3.4 million km2 of arctic sea ice, or with sea surface/water column temperatures in the Atlantic 1 degree cooler, you are not going to get hurricane Sandy.

I’m not sure what you are basing this reasoning on.
Every hurricane is different, so simulating one exactly like Sandy would be impossible unless we had perfect models and perfect observations (we don’t).
The link to climate change is possible, but one storm won’t do it:
http://engineering.columbia.edu/columbia-engineering-atmospheric-expert-weighs-hurricane-sandy

What’s the probability that Sandy was a random event(1/10000, 1/1e6?) unrelated to warmer oceans, higher air temperatures, higher humidity, slower and larger Rossby waves – all observed consequences of global warming? Slim to damned close to none.

It’s a great thing to think probabilistically. Now, how did you compute those probabilities?

1 12 2012
Brian Dodge

“Different from ? Are we comparing this year to the last one, 10 years ago, or 1850?”
Yes. Take your pick; human fossil CO2 emissions, and other human land use changes have been perturbing the weather since the advent of agriculture. Land clearing changes the balance of stored carbon, changes the amount, timing, and intensity of runoff; irrigation changes the amount, timing, and spatial distribution of evapotranspiration (and rainfall). Some of those human caused changes simply move energy already in the system around, just like butterflies, or ENSO. Increases in GHGs increase the solar energy retained in the system, and push the weather in one direction – warmer, less ice, higher humidity, lower tropical/polar gradient. Higher temperatures and melting ice are signals that have unequivocally emerged from the noise. One mistake Judith Curry makes is conflating uncertainty in “how much” with “which direction”; the question isn’t whether the Arctic will become ice free, but when. The uncertainty now isn’t whether low Arctic sea ice will cause larger, slower Rossby waves and blocking highs which will push storms ashore in the Northeast, but how often – “when” has already been answered – Oct 29.

“…simulating one exactly like Sandy would be impossible unless we had perfect models and perfect observations (we don’t).”
The models we do have are good enough to show the butterfly effect, and better models won’t make it go away. My presumption was WHAT IF we have an (imperfect) model and observations, imperfect but still good enough to predict Sandy a month and a half prior; a model this good would show that the perturbations in water temperature and Arctic sea ice due to AGW made Sandy what it was, and if those observed perturbations hadn’t happened, Sandy wouldn’t have occurred. Arguing that the increase in retained energy from GHGs magically got sequestered somewhere, and some other internal variable source of energy melted the sea ice and warmed the Atlantic is as silly as the argument that human fossil fuel CO2 emissions disappear magically and an unknown source proportionately adds “natural” CO2 to the atmosphere.

“….one storm won’t do it:”
And one bad roll of the dice won’t prove they’re loaded either. But if you know the weight, dimensions, center of gravity, and have film of the dice rolling to snake eyes, you know. And we don’t have just one storm – we have the storm track, diameter, water temperatures, evolution of central pressure, characteristics of adjacent ridges and troughs, observations of changes in Rossby waves because of sea ice melt, increased humidity from AGW, and a bunch of other 3,4,5 sigma events which are becoming 2,3,4 sigma events.

“…how did you compute those probabilities?”
I looked for storms with similar unusual tracks like Sandy that started or made landfall near Sandy’s at http://csc.noaa.gov/hurricanes/#, and came up with 1-3 (depending on parameters) in >120 storms. There are 5-10 tropical Atlantic cyclones per year since 1900, e.g. 500 to 1000 storms. I’ve seen a lot of expert comment along the lines of “unusually low barometric pressure for a storm with no eye” and “unprecedented storm diameter”; nobody’s saying “this happens all the time”, so my SWAG is that the probabilities of those characteristics I listed are small, smaller than 1 in 10, probably nearer 1 in 100. Allowing for Dunning-Kruger and confirmation bias on my part leads to a generous probability of 1 in 10 for each, or 1 in 10000 aggregate – but maybe this was a one in a million storm absent AGW effects.

3 12 2012
El Niño

Speculation is your absolute right, my friend, though most people choose to exercise it with less vehemence. With more rigorous approaches comes the privilege to assert your point without yelling it.
It is entirely possible that Sandy was a one in a 10,000 storms, but your argument does little to convince a healthily skeptic reader that it is the case. You are, however, perfectly entitled to that opinion.
Over and out,
J.E.G

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