http://www.wunderground.com/blog/JeffMasters/comment.html?entrynum=1059&tstamp=200809When hurricanes collide
I'm getting this question a lot--can hurricane collide to form a super hurricane? No, hurricanes cannot collide to make a bigger hurricane. When hurricanes get within about 900 miles of each, they begin to interact. There are three possible outcomes:
1) The larger storm will destroy the smaller one. The larger storm's upper-level outflow will bring hostile wind shear over the smaller storm, and the larger storm may steal the smaller storm's moisture. This occurred in 2005, when Hurricane Wilma destroyed Tropical Storm Alpha over Hispaniola.
2) Both hurricanes will compete for the same energy, resulting in weakening of both storms.
3) The storms will rotate around a common center of rotation (the Fujiwhara Effect), before going on their separate ways. Hurricane Humberto and Hurricane Iris took part in a brief Fujiwara interaction in 1995. Iris then began interacting with a third storm, Tropical Storm Karen, which orbited and later merged with the more intense Iris.
Sometimes, a recurving hurricane will leave behind an enhanced trough of low pressure that will act to help recurve the storm behind it along the same path. This is possible this week with Ike and Hanna.