Let's start with Dorian's vertical structure. One critical change is how vertically coherent Dorian's vortex has become, as seen below.
Correspondingly the low-level vortex migrates to the northeast.
Yesterday's 06z GFS run had a shallow vortex, & its steering was impacted by the low-level Caribbean trade winds (925-700-hPa) into #Hispaniola.
![](https://pbs.twimg.com/media/EDDhrQgU4AE1joi.jpg)
![](https://pbs.twimg.com/media/EDDhr3aVAAAncqs.jpg)
My hypothesis is that yesterday's center reformation further north helped couple it with the mid-level center.
This was not fcasted before the center reformation. Even after reformation, the track heading shifted more poleward, possibly due to the deeper vortex feeling deeper layer steering.
![](https://pbs.twimg.com/media/EDDhsnPUcAA08rJ.jpg)
This ridge is critical to Dorian's track after Puerto Rico.
![](https://pbs.twimg.com/media/EDDhtWfUUAEkXiZ.jpg)
Fin.