I believe it depends in part on how strong the high pressure system is. Air moves clockwise around a high pressure system. A high pressure systen would tend to move a hurricane along its southern and western sides. I don't recall the location of high pressure systems during Katrina, but I do recall noticing clouds moving to the south in the area west of Louisiana which if resulting from high pressure would indicate it was west of La. There was also westward movement across Fl. which could indicate a high pressure system to its north.

Prior to Katrina a series of cold fronts had moved into the central plains and stalled there. One of them may have continued into Texas just prior to katrina hitting New Orleans.

I recall once reading that one of the "benefits" of hurricanes is that they can affect high pressure systems that tend to keep land temperatures and divert rainfall elsewhere.

there is a good site for following hurricanes at

http://www.wunderground.com/tropical/tracking/at200518_5day.html

the site includes a page that shows the results of various computer projections which are now coming closer to agreeing on a path that would indicate landfall roughly between Houston and San Antonio.