Kanto area

Need help to figure out, I want to travel around tokyo, kamakura, yokohama and nikko is JR pass worthy or I just used SUiCA ? my based is in tokyo, but i'm thinking to stay for 2 days in nikko. is there any pass I can used to go to nikko ?
Can someone tell me how cold it will be on late dec in Tokyo, kamakura , nikko and Yokohama because I'm from tropical country.will it be snowy in there ?

Thanks all,

I want to travel around tokyo, kamakura, yokohama and nikko is JR pass worthy or I just used SUiCA ?

The nationwide Japan Rail Pass does not pay off for short distance travel. You better use regular tickets or regional passes.

I personally would be using Suica for all your travel, except for the side trip to Nikko, for which I would consider a Nikko Free Pass:
http://www.japan-guide.com/e/e2358_002.html

Can someone tell me how cold it will be on late dec in Tokyo, kamakura , nikko and Yokohama because I'm from tropical country

Tokyo, Kamakura and Yokohama have almost the same weather, so I am only going to mention Tokyo. For Nikko I am going to mention temperatures that you can expect in the higher elevations of the national park. It should be a few degrees warmer in Nikko town center, where the shrines are located.

Average daytime highs in late December:
Tokyo: 11 degrees
Nikko:

Average nighttime lows in late December:
Tokyo: 1 degrees
Nikko: -7 degrees

There is a small chance of snow in Tokyo, and a big chance of snow in the higher elevations of Nikko.

Thanks Uji, you help alot.