This weekend estimated data on boxofficemojo showing that jumanji is going to make $50 million, which is around 35% higher than last weekend. Normally there is a small drop from 1st weekend to 2nd weekend. But this film is doing the opposite? 

I have not heard about it, neither seen it. what are the reasons for its success? and is it really doing above expectations?

Billion?

I've seen it and thought it was fun entertainment. I'm pleasantly surprised to see it do as well as it has in the Box Office. I didn't expect it that's for sure.

According to Box Office Mojo, it’s only a couple million behind Star Wars this weekend. Worldwide, it’s made over $322 million in less than 2 weeks. Not bad at all.

The week between Xmas and New Years is the best of the year. Nearly every movie is up or has a smaller than usual drop because people are out of work/school. Jumanji did do very well though.Its final domestic gross might be close to 300 million which would be fantastic.

I hope it does well, took the family to see it and it was pretty entertaining.

If it helps steal some thunder from TLJ, I'm all for it.

I was so put off from the trailer, is it better than it looks?

It will be pretty impressive if a film starting with a ~30 million ends at ~300 million

Actually it did more than 320m worldwide in 12 days since the count of the week was made public not long ago. Probably around the time of your post. 500m is already a given to be reached in 2 weeks or so. Whether it can reach 600m, could still be possible. And on a 90m budget, 50 marketing, Sony keeping half of the gross it probably will make over a 100m in pure profit, not to forget income from any merchandise and home media down the line. Also besides all of this its a very fun movie on its own.