NOAA: Tropical Cyclone ‘Maximum Intensity’ Is Shifting Toward Poles

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Typhoon Usagi

In this infrared satellite image, Typhoon Usagi (2013) bears down on Hong Kong as it intensifies to a Category-5 storm. CREDIT: NOAA via Climate Central

A NOAA-led study finds “the location where tropical cyclones reach maximum intensity has been shifting toward the poles” at roughly 35 miles per decade. This roughly one-half a degree of latitude shift per decade for tropical cyclones (hurricanes and typhoons) was seen in both the northern and southern hemispheres.

NOAA’s news release quotes the lead author Jim Kossin:

“The rate at which tropical cyclones are moving toward the poles is consistent with the observed rates of tropical expansion,” explains Kossin. “The expansion of the tropics appears to be influencing the environmental factors that control tropical cyclone formation and intensification, which is apparently driving their migration toward the poles.”

The expansion of the tropics has been observed independently from the poleward migration of tropical cyclones, but both phenomena show similar variability and trends, strengthening the idea that the two phenomena are linked. Scientists have attributed the expansion of the tropics in part to human-caused increases of greenhouse gases, stratospheric ozone depletion, and increases in atmospheric pollution.

For more on how manmade pollutants appear to be driving tropical belt expansion, see here.

Kossin summarizes his findings this way: “The tropics are becoming less hospitable to tropical cyclones and the higher latitudes are becoming less hostile.” On the one hand, it’d be good for the tropics to be become less vulnerable to the most devastating hurricanes.

On the other hand, the concern is that “coastal populations and infrastructure poleward of the tropics may experience increased risk. With their devastating winds and flooding, tropical cyclones can especially endanger coastal cities not adequately prepared for them.” Another problem is that tropical regions that “depend on cyclones’ rainfall to help replenish water resources may be at risk for lower water availability as the storms migrate away from them.”

The good news for Americans is “there is no evidence that the peak intensity of Atlantic hurricanes has migrated poleward in the past 30 years.” The bad news is that the Atlantic “has been, as we know, behaving differently than the other basins” — it’s the “only basin with clear trends in the intensity and duration of hurricanes.”

In a later post I will examine the expansion of the subtropics in more detail because it has many other potentially severe consequences for humanity, such as Dust-Bowlification.