I am 48, male. I suffer from trigeminal neuralgia since 2001.600mg tegretol XR /day helps. But pain/frequency worsen during rainy season_ why?

Change in temp. ? Something similar occur with arthritic pains and cold temperature. May be rain changes in the environment loke humidity or even the local tempertaure triggering change in the autonomic or peripheral nervous system.
Trigger zones. About 50% of trigeminal neuralgia cases have "trigger areas" or "trigger zones", these are shock-like facial pain. Trigger zones are usually in the central face around the nose and lips. Attack of pain may be "triggered" by light touch during normal activities such as makeup application or an exposure to a cool breeze or cold water.
Common problem . Tn pain has multiple triggers including weather.