A few days before your flight, look at
Wind Map - Britain and then click on the arrow that shows forecast winds for Gatwick (or anywhere else in the SE). A table appears showing forecasts for that site several days ahead, including wind direction and strength.
Do it every day as it gets closer.
The balloon people will tell you roughly what wind strength would make it too high to allow your flight and need it to be deferred.
Hope this helps.
Chris N.