Tasmania on January

Hi,
Me and a friend of mine will visit Tasmania around 12th of January.
What weather conditions should we prepare for?
According to this wikipedia page http://en.wikipedia.org/wiki/Climate_of_Tasmania
it's going to be around 20C during the day and around 10C at night.
What should we expect at the Overland track is going to colder?
What kind of sleeping bag should we bring? (will -4C comfort temperature bag will suit for Tasmania at this time of the year? Is it too hot?)
Any additional tips and hints are welcomed
Thanks
Slava (Tel Aviv, Israel)
Me and a friend of mine will visit Tasmania around 12th of January.
What weather conditions should we prepare for?
According to this wikipedia page http://en.wikipedia.org/wiki/Climate_of_Tasmania
it's going to be around 20C during the day and around 10C at night.
What should we expect at the Overland track is going to colder?
What kind of sleeping bag should we bring? (will -4C comfort temperature bag will suit for Tasmania at this time of the year? Is it too hot?)
Any additional tips and hints are welcomed
Thanks
Slava (Tel Aviv, Israel)