Wii U will need to have a really great December to sell more software than PS Vita this year.
Current gap is quite big, and this gap wasn't shortened in July, a month that was supposed to be big for Wii U (Pikmin 3, New Super Luigi U, Nintendo Land + Wiimote). Furthermore, these games don't seem to have typical Nintendo strong legs, Pikmin 3 will get to 250.000 and New Super Luigi U has probably eaten into New Super Mario Bros. U sales.
So far, there is only one game that will do good numbers which is The Legend of Zelda: The Wind Waker HD. And by good numbers I mean 200.000 - 300.000 units max. The rest with the exception of The Wonderful 101 will be lucky to sell a few thousand units each one. So we will already be in November and the gap will probably be as big as today or even bigger (I haven't checked the list of upcoming PS Vita releases).
Best case scenario for Wii U during late November and December would be Super Mario 3D World, Wii Fit U, Wii Party U, Mario & Sonic at the Sochi 2014 Olympic Winter Game and Donkey Kong Country: Tropical Freeze. Well, if all these games are released Wii U at least stands a legitimate chance to sell more software than PS Vita. So far only Super Mario 3D World, Wii Fit U and Wii Party U are slated for 2013.