Either condensation from warm/code air exchange through the meter to panel nipple or the meter hub or weatherhead is leaking. Not irreparable, but well worth documenting.
You should really be sealing any raceway that passes from inside to outside. People usually get away with it but you do have the possibility of drawing moisture in from outside to condense or cold air that condenses the moisture on the inside, depending on season.
This is covered in 300.7
**300.7 Raceways Exposed to Different Temperatures.
(A) Sealing. **Where portions of a cable, raceway, or sleeve
are known to be subjected to different temperatures and
where condensation is known to be a problem, as in cold
storage areas of buildings or where passing from the interior
to the exterior of a building, the raceway or sleeve shall
be filled with an approved material to prevent the circulation
of warm air to a colder section of the raceway or
sleeve. An explosionproof seal shall not be required for this
purpose.
This effect is also why a perfectly sealed (all water tight pipe joints) underground raceway will eventually collect water. Thermal cycling pulls moisture in and it condenses in the cool ground.
You should probably be using duct seal in them too if you wanted it dry but nobody does. You need wet location wiring anyway.