The United States Postal Service (USPS) has been delivering mail for over 200 years (and recently, losing a lot of money doing it). Their motto, which apparently is not their official motto at all (just branded all over their NYC postal building) is well known: “Neither snow nor rain nor heat nor gloom of night stays these couriers from the swift completion of their appointed rounds”. Notably missing from this statement is “hurricane”, “superstorm”, or “storm hybrid” – Hurricane Sandy showed that it is not possible to deliver mail when a good portion of your city is underwater.
Last Friday the Atlantic tropical season officially ended. There isn’t a switch that gets turned off that prevents tropical cyclones from developing after November 30; in fact, we have seen storms form into January as recently as 2005. Nevertheless it is beneficial to designate a tropical cyclone season; it gets people’s attention and does have some scientific merit. The great majority of storms do form between June 1 and November 30, and storms that do form outside those times rarely affect the U.S.
Of course in other parts of the world the tropical cyclone seasons may be just beginning. The conditions that allow for their formation in the northern hemisphere late summer/early autumn (warm ocean waters, favorable atmospheric conditions) are just now setting up as the season turns toward summer in the southern hemisphere. In the tropical western Pacific, where more tropical cyclones form than any other basin, conditions are so favorable that storms can form year round.
For Americans, the 2012 tropical cyclone season will be remembered by one name – Sandy. But it was quite an active season as well, with 19 storms becoming strong enough to earn a name. This movie shows many of these storms:
Of those 19, only a handful were directly sampled with reconnaissance aircraft; for the rest, as well as storms in every other part of the world, their intensity were estimated primarily from the Dvorak technique. Cyclone Center citizen scientists use a similar technique to classify historical tropical cyclones – one day Hurricane Sandy will be one of those that users will classify.
We launched the project back in September and it’s had more than 100,000 classifications so far. Cyclone Center is one of the most challenging projects ever built by the Zooniverse, but with each classification you’re contributing to our knowledge of tropical storms.
So far the Cyclone Center community has analyzed more than 500 storms as they raced across the globe. The weather data used on the site comes from 30 years of satellite images and so many memorable storms are being closely inspected by volunteers on the site each day: Katrina (2005), Andrew(1992) and Gilbert (1988) amongst them.
Interestingly, this is the 7th consecutive season that the U.S. was not impacted by a major (Category 3 or higher) hurricane – hard to believe after going through a storm like Sandy which technically may not have even been a hurricane as she came ashore. As storms continue to become stronger in a warmer climate and societal impacts become more severe, it will be more difficult for mail carriers to make their appointed rounds…assuming mail delivery isn’t cut to 1 day a week by then anyway.
- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville - this blog is part of the 2012 Zooniverse Advent Calendar.
During election season I will occasionally tune in to a few of the news networks to get my 10 minute dose of partisan noise. As Hurricane Sandy churned in the Atlantic and aimed herself at the New Jersey coast, I happened to come across a show that featured an economist and a political analyst discussing the nuances of tropical cyclones and climate change. I don’t recall exactly what was said, but it went something like this:
Economist: Sandy is huge! Why isn’t anyone talking about climate change?
Analyst [very eager to break in to the conversation]: “Yes! Look at Sandy – an ‘S’ storm! When was the last time we’ve had an ‘S’ storm in the Atlantic? Usually we only make it to the H’s, or I’s, or K’s. Look at 1992 – the ‘A’ storm that year didn’t form until mid-August!”
Now I’m sure both of these gentlemen are very bright people and I have a lot of respect for the analyst (when he talks about politics), but having them discuss hurricanes and climate is like me commentating on a grandmaster chess match – I know how the pieces move but that’s only 10% of the battle.
There was nothing particularly unusual about Sandy in the beginning – we have seen plenty of hurricanes form in the deep tropics in October, and she moved and behaved in a pretty typical fashion. Nor has there been anything outright weird about the 2012 hurricane season in the Atlantic Ocean. Before the season, every documented seasonal forecast of the number of named storms was above the long-term average, and the season has played out accordingly (even exceeding expectations in many cases).
But a season is usually remembered by one or two storms, and Sandy has made 2012 quite historic. Weather forecast models accurately predicted days in advance that Sandy would have a major impact on the northeast United States. And judging by the images and stories coming out of New Jersey, New York, and surrounding states, Sandy lived up to expectations.
As with any major storm or weather event, the inevitable question is asked: “Did climate change cause/enhance this?” Although a definitive answer is elusive (we don’t have a big enough laboratory to create a “warming free” experiment), we can make a reasonable assessment about some of the factors that probably played a role.
Individual storms such as Sandy respond to the instantaneous ocean and atmosphere environment they find themselves in – or in a way, weather. Climate is the palette, not the paint; it sets the scene for the actors to do their part. So what was Sandy’s “scene”?
We know that the world’s oceans are warming – warm water means more energy is available for the hurricane. We know that sea levels are rising, leading to larger hurricane storm surges. And we know that coastal development continues to expose millions of people to storms like Sandy.
Most climate scientists believe that we are in for stronger hurricanes in a warmer world and that we are already seeing a move toward this new era. But our data are just not good enough to know for sure if tropical cyclones have already been becoming stronger. Almost all tropical cyclones, even in recent years, are not measured directly; and even when they are, we can only measure small samples of these vast storms at any one time. This is a big reason why there are conflicting accounts on recent tropical cyclone trends.
Cyclone Center was created to help resolve these questions. By having the public analyze 30+ years of tropical cyclone images, we will provide meteorologists with new data that can be used to reconcile differences in individual storms, as well as long-term trends.
And by the way, the last year with an ‘S’ storm in the Atlantic was 2011. And that ‘A’ storm in August of 1992, one of only six named storms that year? Hurricane Andrew, a category-5 storm that devastated South Florida. To those residents affected by Andrew and Sandy, climate change is a secondary concern.
- Chris Hennon is part of the Cyclone Center Science Team and Associate Professor of Atmospheric Sciences at the University of North Carolina at Asheville
Hurricane Sandy and her merger with a strong autumn storm system are making history along the U.S. eastern seaboard. But for a time earlier in her life, Sandy provided a bit of mystery to forecasters – showing why what you see in a satellite picture is not always what you get at the ground.
Shown below are three infrared images of Sandy as she was approaching Cuba from October 24-25.
In the absence of observations, meteorologists perform the Dvorak technique to determine the maximum wind strength, or intensity; Cyclone Center uses a modified version of this technique to analyze historical tropical cyclones. The expert who put these images together said that he would assign a minimum intensity of 115 kt. for all three of these times. That would have made Sandy a Category-4 hurricane on the Saffir-Simpson scale, capable of catastrophic damage. An automated Dvorak technique produced a similar intensity, and official intensity estimates from the U.S. National Hurricane Center and the U.S. Satellite Analysis Branch were also over 100 kt.
That may have been the end of the story if it were not for one key piece of additional information – data from “Hurricane Hunter” aircraft that were sampling the storm at the same times these images were taken. They determined that the surface winds were about 75-80 kt, at least 20 kt. lower than the Dvorak estimates. So what’s going on here?
This instance illustrates some of the challenges that forecasters and analysts have when trying to determine the strongest winds in a tropical cyclone. In cases where a tropical cyclone intensifies rapidly, as here, the cloud pattern typically leads the surface wind increase. So an analyst using the Dvorak technique may get an instantaneous wind value that may be much higher than the actual surface wind speed (which hasn’t had time to increase yet). Because of this, the Dvorak technique takes into account the storm’s recent intensity and does not allow storm to “jump” too high from one time to another.
Even when we have aircraft data, it is impossible for 1 or 2 planes to sample the entire storm. So it is quite likely that the point in the eyewall with the maximum winds does not get observed, especially in cases when the wind field is changing rapidly.
In Sandy’s case – a dangerous tropical cyclone close to populated areas – observations from inside the storm have provided forecasters with a pretty good idea about the wind speeds. But imagine a storm like Sandy swirling out in the middle of the Pacific, thousands of kilometers from civilization, with only satellite pictures and data available for estimating her strength. It is pretty easy to see how we don’t always get the intensity right. In fact, we don’t even know what the “right” intensity is! But from a scientific perspective, these storms are just as important as the ones that ravage our coastlines. By having an accurate account of their strength, we may, for instance, be able to determine how tropical cyclones worldwide have been reacting to our changing climate.
And that is the whole point of Cyclone Center – to have all of you provide us with your analysis of storms, so that we can determine not only the “best” intensity, but also get an idea about how certain we can be about it.