Joel Cline

The three things that create a lot of rain are moisture, lift and instability [ in the atmosphere ]. We have two of these with tropical weather and the third is the lift — provided by the mountains in this case, on the slopes that are facing the oncoming winds directly — which is a very local effect — can create localized areas of heavier rain.

Instead of showing a single, definitive line of a track, the cone takes care of two-thirds of the possible track.