When Hurricanes Go Extratropical
In a recent post, I recounted the unusual redevelopment of the remnants of Tropical Storm Erin over Oklahoma in August 2007, a few days after it had made landfall along the Texas coast. This inland "ghost" of Erin did not fit the criteria of any traditional storm type -- tropical, extratropical or subtropical -- according to the National Hurricane Center.
While not the case with Erin, at least not officially, about 25 percent of all hurricanes and typhoons moving northward of 30-40 degrees north latitude do become extratropical storms, in some cases larger and stronger than the original storm, through a redevelopment process known as extratropical transition.
Extratropical is a fancy name for the kind of storm that we are all used to -- the typical storm that moves across the United States with a cold front and warm front extending outward from a low-pressure center.
Keep reading for more on storms that go extratropical. Also, see our full forecast through the weekend and beyond.
Relative to tropical systems, extratropical storms are different in structure, size, and in the physical processes that govern their development and motion. For example, tropical storms and hurricanes have centers that are warmer than the surrounding air, no fronts, and winds that are strongest near the ground. Extratropical storms, on the other hand, have centers that are colder than the surrounding air, fronts, and winds that are strongest high up in the atmosphere.
The classic example of a storm going from tropical to extratropical is Hurricane Hazel, which in 1954 transformed into an extratropical cyclone that behaved much like a Nor'easter after crossing the coast near the North Carolina/South Carolina border. The extratropical version of Hazel produced sustained winds of 78 mph in D.C., and wind gusts to 112 mph in New York City -- over 200 miles from the storm's center. That remains the highest wind speed on record for the Big Apple.
Indeed, hurricane-force winds were maintained even after Hazel's remnants had moved 600 miles inland. Had Hazel tracked a bit further east and approached New York just west of the city, the unique configuration of the shoreline might have resulted in a surge of waters into New York harbor that could have inundated much of the city, a NASA/Columbia University study showed.
Extratropical storms that were once tropical in nature often produce heavy rainfall and widespread floods over a much broader expanse than the parent storm (minus the coastal flooding from storm surge). With Hazel, heavy rains of up to 11 inches occurred as far north as Toronto, Canada, where 81 people were killed and entire neighborhoods were washed away.
Hurricanes in the west Pacific (actually, they're called typhoons there) transform into extratropical storms more frequently than do Atlantic-born hurricanes. I can hear you thinking, "So what, that doesn't affect me." Wrong! Oh, yes it does! While the impacts of Hazel were felt directly and immediately over much of the eastern U.S., seemingly far-removed events occurring in the west Pacific can often affect the weather locally within a week.
This is not a "believe-it-or-not" wonder. It's a natural phenomenon that is not well understood or predicted. Curious? Stay tuned for more in a future post.
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