NOAA - Cyclonic Storms Hit Peak Intensity Closer To Poles - Shift +/- 35 Miles Per Decade
In a recent study led by Dr. James Kossin from the NOAA National Climatic Data Center, researchers discovered that cyclones are reaching their maximum intensity farther towards the poles than before. On average, these storm systems have been peaking in intensity towards the north and south poles at a rate of 53 and 62 kilometres (33 and 39 miles) per decade respectively. The researchers unexpectedly came upon this while they were studying something else: the upper-atmosphere temperatures above tropical cyclones.
"The poleward migration of the tropical cyclones was something we stumbled on..." Kosin said. "We kept seeing a trend that we couldn't explain unless the storms themselves were migrating away from the deep tropics. This did surprise us at first, but after looking at how the environment has been changing over the past few decades, it makes good physical sense."
Part of this environmental change has to do with the deep tropics becoming increasingly hostile to cyclone formation, while its expanding edges turn into benign grounds for them.
Two of the factors that determine cyclone generation are vertical wind shear and potential intensity. Essentially, vertical wind shear disrupts the formation of storm clouds, while potential intensity describes the maximum strength a storm can reach in a specific area. In the deep tropics vertical wind shear has become more pronounced while potential intensity has dropped, with the opposite happening in the subtropics.
EDIT
http://news.mongabay.com/2014/0924-hong-tropical-cyclones-on-the-move.html
