The storm system that pounded the Northeastern US last week has wandered out in to the mid Atlantic, and over the weekend became detached enough from surrounding fronts and weather, and tropical enough, for the National Hurricane Center to start tracking it as a tropical system. It’s definitely a fish storm; here’s the impact swath:
If you look at the above swath map you’ll notice something weird: although there are tropical storm markers, there is no wind swath for most of the track. The reason is that while the winds were above tropical storm strength, the modeling system recognized it wasn’t really tropical – it was a nor’easter in characteristics. Even now it’s somewhat marginal, but does technically meet the criteria to be a tropical system.
This is another example of a storm that in the past more than likely would not have been named or tracked. Changes in the criteria that NHC uses for when to start advisories, combined with the tremendous improvements in sensor systems the last 20 years, means that it is likely that at least six, and as many as eight or nine of the 21 storms this year would not have been counted prior to 2000 (and certainly not prior to 1980). This presents a real challenge for those trying to figure out how the Earth’s atmosphere is changing. In a 2009 paper in the Journal of Climate, researchers from NHC and NOAA show that there has been an obvious bias in “short duration” storms (those with lifetimes less than two days) due to observational bias. They state …
In particular, frequency of hurricanes and major hurricanes, duration of TCs, length of season, peak intensity, and integrated TC measures [like Accumulated Cyclone Energy (ACE) and Power Dissipation Index (PDI)] should not be used directly from HURDAT for climate variability and change studies without consideration of, or quantitatively accounting for, how observational network alterations are affecting these statistics. In general, the subsampling of TCs back in time will artificially introduce increases in all of these parameters with time.
The situation since this paper was written has become even more pronounced, with post-Sandy changes in how advisories are issued. Unfortunately, there are those who use data and warning issues like this to dismiss concerns over global warming, just as there are those who point to the inflated tropical cyclone counts as evidence of a crisis. As I ranted earlier, there is a balance between understanding the limitations of the modeling and historical data, and understanding that in fact humans have changed the chemistry of the atmosphere and surface of the Earth, changing our weather and climate. It’s an artificial conflict fueled by politics to say it has to be one or the other, and the choices aren’t simply “do nothing and keep exploiting the Earth’s resources” or “radically reshape our society while exploiting different resources”.
But being sensible has nothing to do with politics … 😦