As in any hot climate ,after the sun goes down it does FEEL CHILLY. Some years ago my wife & I spent a wedding aniversary in a hotel in the desert in tunisia.Went for camel ride into the desert around 5.30 pm before going to hotel for the night. By bedtime we were both freezing cold & could not bare to touch each other.ON OUR ANIVERSARY which is on 11th February which is well before you visit

Yes, but,.......
It is a lot colder in the desert at night than in a town, the sand does not hold the heat for long so it gets cold a lot quicker.
You will want long sleeves though if you are walking outside. I'll be going on 23rd April, to Djerba, and I'll expect to be comfortably warm in the day, and yes cooler, but not cold, in the evenings.
Look here;
http://www.weatheronline.co.uk/Tunisia/Tunis.htm
click on the town nearest to where you are staying and you'll get a pretty good idea of the differences.
Kevin

We've been towards the end of May and it's been lovely and hot then but not too hot like it gets in July/August. Can cloud over a bit some days but we've never had much rain. Not sure how different the beginning of May is. It does cool down at night but it's still nice and warm

Vikki

Sorry, didn't make it clear, my long sleeves comment applies to the evenings not the daytime.

im going the first week ive not been before but been to other country about the same kind of weather

i just normally throw in a pashmina and hubby wheres a t shirt under a shirt, not as cold as it would be here