I am there every March - this year we went in Mid March instead of the first week and noticed a difference.
First week sometimes brings in chilly weather, especially at night! One year the high was only in the 60's, and the lows were very low. However I've been there in March when the high's were in the 70's too. It's very hit or miss. Just 2 weeks later this year, and it was in the 80's the entire week. That could easily happen the first week too.