FIG 9. Portrayal of climatological vertical profiles of zonal-wind conditions in the tropical ( 10°- 15°N) western Atlantic and eastern Caribbean basin from late August to early October (curve a) and of easterly QBO conditions (curve c). The dashed line shows the favorable tropospheric zonal-wind deviation from climatology and westerly phase QBO conditions that are required for the most active TC seasons. Curves c and d illustrate the east- and west-phase QBO conditions in the stratosphere [Adapted from Gray ( 1990)].