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For now it seems Belgium will be spared from the worst weather coming out of France. Thunderstorms were initially predicted (possibly until morning) and in France (Calvados area) and off the Dutch coast whirlwinds were spotted. I'd advise people at TML keep tabs on the weather through a web service that offers satellite imagery.
Popular free apps here are Buienradar België (iOS and Android) or Buienalarm (iOS and Android), they offer radar imaging, but keep in mind only Buienalarm appears to offer an English user interface. You can also take a look at the Royal Meteorological Institute's website.
Like OP said, make sure your tents are secured properly and should the weather turn bad, practice common sense.