WRAL WeatherCenter Blog

We were in a party where the question arose: Can hurricanes spawn hurricanes? Also, willl Hanna be able to draft Gustav? Finally, have 2 hurrianes ever merged to become one? Thank you kindly!

Posted September 13, 2008

MIKE MOSS SAYS:       Pam,     On your first question, if you mean can a new hurricane spin off of an existing hurricane, that isn't a process that I'm familiar with ever having had happen. On the other hand, a decayed hurricane remnant can potentially re-develop as a new or revived system days later. For instance, in 2004 the extratropical remnants of Hurricane Ivan reached the northeastern U.S., then split into an upper-level disturbance that sped away through New England while the low-level circulation tracked southward off the east coast and re-developed into a tropical storm as it turned west across Florida. We've also seen this occur a few times with eastern Pacific storms that have weakened and then re-developed over the Atlantic side of Central America and vice versa, and also with occasional storms that dissipate over the Atlantic due to unfavorable wind shear or cool ocean waters, only to redevelop later under more favorable conditions.

Hurricanes don't really "draft" one another, if you're thinking in terms of auto, bicycle, or mid-distance track & field races. In fact, it can be bad for a storm to follow along the same path as a previous storm too closely, in part because the first storm often churns up the ocean surface in a way that brings cooler water to the top, thus limiting the available heat energy to be drawn upon by the second storm.

As for the question about merging, when two tropical cyclones close within about 900 miles, they sometimes exhibit something called the Fujiwhara effect, which involves the two systems beginning to "dance" around one another, effectively orbiting a common centerpoint, and somtimes interfering with the organization (low level inflow, upper level outflow, etc) of each other. Rarely, a stronger storm may heavily disrupt the organization of a weaker one, with the less intense system eventually absorbed into the circulation of the other. An example of this occurred in 1995 when Hurricane Iris was approached by Tropical Storm Karen. Following a brief Fujiwhara interaction, Karen was absorbed into Iris on September 3rd.


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