1.   A third factor in the hurricane equation is the behavior of stratospheric winds that circle the globe at the equator.

2.   Aided by westerly stratospheric winds, they became the seeds of hurricanes.

3.   Stratospheric winds, which change direction every few years, are expected to go on blowing from the west, which produces hurricanes.

4.   The team has only about a week left before the stratospheric winds they hope to ride around the world change direction until December next year.