Somewhere between 40-100K New Orleans (Katrina) residents moved to Houston.
In looking for the numbers I found two articles (actually several) that are vague on th numbers but both have interesting info on how the New Orleans evacuees were received in Houston. Mostly not well.
Before and after Katrina's Aug. 29 landfall as a strong Category 3 storm, more than 1 million people fled Louisiana and coastal Mississippi. As many as 250,000 landed in Houston - more than 27,000 of the most traumatized arriving at the Astrodome and other Houston shelters in a 500-bus caravan from the drowned Big Easy. By October 2005, approximately 100,000 evacuees temporarily had made Houston their home.
Today, perhaps heeding the oft-tendered advice of Katrina-era Mayor Bill White to "look forward, not backward," as many as 40,000, by some estimates, permanently have settled in the Houston metro area.
http://www.houstonchronicle.com/news/houston-texas/houston/article/Ten-years-later-Katrina-evacuees-now-part-of-6458412.php
Estimates vary, but of the 250,000-odd evacuees who arrived in Houston after the storm, up to 100,000 likely stayed permanently.
We call Houston New Orleans West, said Mtangulizi Sanyika, an academic who left New Orleans after his house flooded and ended up staying in Texas when his wife found a job at a hospital. Sanyika is chairman of the New Orleans Association of Houston, which is planning a series of commemorative events.
https://www.theguardian.com/us-news/2015/aug/25/new-orleans-west-houston-hurricane-katrina