People who once had little to fear from tropical storms and hurricanes may have something new to worry about. It looks like powerful storms are heading further out of the tropics now. A new study shows that powerful tropical cyclones could be heading further north or south in the future as the climate changes.
The study from the Massachusetts Institute of Technology and the National Oceanic and Atmospheric Administration (NOAA) shows that the “peak range” for tropical storms is getting wider. Jim Kossin, a scientist with NOAA’s National Climate Data Center says the tropical storms are moving north at a rate consistent with the expansion of the tropics. This expansion, he noted, seems to be influencing environmental factors that in turn influence tropical storms and driving the poleward migration of tropical storms.
To reach this conclusion, scientists analyzed international data for 1982 through 2012 from NOAA’s National Climate Data Center. They used the location of peak intensity of cyclones as an indicator, rather than storm duration, which brings up the question of when a storm becomes a tropical storm.
Tropical storms have been peaking further north and south, shifting at 35 miles per decade over the past 30 years. The shift was a little more dramatic in the Northern Hemisphere, at 38 miles per decade compared to 33 miles per decade in the Southern Hemisphere. The results of the NOAA study were published this week in Nature.
The tropics are also moving outward from the equator, in a climate sense at least. This could become an issue for areas not used to dealing with hurricanes and tropical storms, because as tropical conditions expand, the area vulnerable to powerful storms. The movement of the tropics might explain how tropical storms are able to move further north and south as the climate changes.
Scientists state that more research is needed before the mechanism can identified. A general warming of the oceans could be involved. Water temperatures of 82 to 86 degrees Fahrenheit are ideal for tropical cyclones. Another theory suggests that migration of the trade winds could be the cause.
The shift in peak intensities might be bad news for southerly latitudes. But countries in the north, in higher latitudes may be at less risk from strong storms. The Philippines, in the northern part of the tropics might be in less danger, while the risk could increase for Japan and South Korea.
The amount of shift varies further with the ocean. Patterns don’t seem to have shifted in the Atlantic. Scientists did find substantial migration in the northern and southern parts of the Pacific and in the Indian Ocean.
The latitudes where the storms reach their peak intensity seems to increasing in most places, said MIT professor Kerry Emanuel, who co-authored the paper. The trend is statistically significant too. While the scientists are still investigating the mechanisms behind this trend, it is consistent with a warming client.
Emanuel also says the trend may be connected with the poleward expansion of the Hadley circulation, a global wind pattern.
Changing wind patterns and general warming of the planet could both be driving tropical cyclones to reach peak intensity further outside the tropics, in effect driving tropical storms further north and south of the tropics. This phenomenon is not happening uniformly across the globe, so some parts of the planet are at greater risk from powerful storms, while other areas might be somewhat safer.
By Chester Davis
Daily News Digest