Seems odd that those islands would be moving south when the overall motion of the Pacific plate is north-west.

In fact, that statement is at odds with the GPS measurements I see at:

http://sideshow.jpl.nasa.gov/post/series.html

GUAX (south end Guadalupe Island)
lat +25.290mm/yr +-0.972
lon -47.146mm/yr +-0.884

Comparing to SNI1 on San Nicholas Island here off SoCal...
lat +23.713mm/yr +-0.134
lon -42.204mm/yr +-0.114

That Guadalupe is moving faster NW than San Nicholas is probably explained by San Nicholas being closer to the plate boundary to the east than Guadalupe is. Further out in the Pacific, Honolulu is also moving north-west, but much faster than either of the other two locations:

HNLC
lat +34.626 mm/yr +-0.089
lon -62.561 mm/yr +-0.095

Brian