In the past couple of days, it recorded 15-20degrees Celsius (59-68 degrees Fahrenheit) during the daytime in central Tokyo area. It feels warmer than typical spring weather in Tokyo. This temperature is the same as average of end of April to early May.
Average temperature in March in Tokyo is high of 13 degrees Celsius,(55 degrees Fahrenheit), and low of 5 degrees Celsius(41 degrees Fahrenheit).
You might need a light weight jacket, but globes and a hat are not necessary this year. Or you may not need a jacket! If you stay outside for a long time, just in case you might be better to have a jacket.
However, we sometimes experience snow in March in Tokyo so please check weather when you go out this season. We had snow 1day in 2014, 2015 and 2016. No snow in March 2013 and 2017.
Have fun in Tokyo!