You have said that this is a brand new electrical panel. It is possible that your main breaker is a little fancier than what most of us are familiar with. I have read a number of threads recently about arc-fault protection being required on new electrical work, which could easily trip during a storm. You may also have overvoltage or undervoltage protection, surge protection, or ground fault protection built in to the panel. Before you pay an electrician to make a service call, Google the brand and model of your panel or main breaker to see if it may have one of these features.
Branch circuits, if you say individual circuit breakers most people will follow your meaning.
Do you happen to know what make your breaker (or panel) is? If it’s a new panel it might very well be a thermomagnetic breaker which could be tripped by lightning strikes it there were any in the area, or a fault on the line side. The power company would usually be aware of those if they occurred. Some new breakers are out of calibration as well, I’ve never seen it but I know other electricians who have encountered it. That’s a rare problem though as far as I know.
Since this is basically a simple mechanical device (barring some weird breaker) there aren’t many avenues to investigate. It’s a new panel so you’ve either got a bad ground, faulty breaker, or it was struck by lightening. You can test for a bad breaker by throwing every item in the house on to see if you can trip it. If it trips and none of the other breakers trip then you have something wrong with the main breaker.
Looks like a case of the hoo-has