Slide 14 of 29
This is a cross section along 18N, traversing the axis of the tropical wave. Note that this wave is confined to the lower atmosphere, generally below 700 hPa. The axis is positively tilted, to nearly vertically stacked, as it extends from 18N 40W at 1000 hPa to 18N 43W at 700 hPa.. Which is from east-to-west with height.