flying In the RAIN. Safe or Unsafe.

Your flight may be delayed, but such delay will affect other flights and not yours alone.

Thunder storms contain high speed variable winds that are dangerous to aircrafts, your pilot knows this so he won't be flying you into a thunder storm.

Pilots won't take off if a thunder storm is directly on the departure path or if one is around the airport.

Pilots won't take off into heavy precipitation (heavy rains) even if there is no thunder storm involved.

Once your aircraft has gained altitude, heavy rains is not a big problem.

It is during take off and landing that a pilot needs to avoid the possibility of strong down drafts (movement of air downwards) which are associated with heavy rains.

There is nothing to bother much.
Your flight might only be delayed and you arrive late at your destination.

Relax, sit back and enjoy the flight.