The Earth’s north magnetic pole is slowly moving towards Russia, and Tampa airport had to readjust.

http://www.aolnews.com/2011/01/07/magnetic-north-pole-shift-affects-tampa-airport/

Nat Geo explains why this is happening:  http://news.nationalgeographic.com/news/2009/12/091224-north-pole-magnetic-russia-earth-core.html