Well Tamriel is about 2000 miles North to South and the warmer climates are to the South which suggests the Equator of Nirn passes through the bottom third of Tamriel. And there is a small continent to the south called Pyandonea. http://www.imperial-library.info/maps/minibigmaproadslore31gv.jpg
Yep, heard about Pyandonea and how Maormer live their, but can't it be possible that Pyandonea marks the equator.