what part of NM were you from? If you're from the Northern half, with higher elevation, it *might* be temporary elevation sickness in reverse. I live in ABQ and find going down to sea level very hard for a while, but then I acclimate.
If I were you, I might look into an allergy test or something similar, to see if he's allergic to the new surroundings.
When I hike or climb up to a higher altitude I will get a migraine... or if I take a plane up to a higher altitude I get a migraine... but, if I stay at that altitude then I adjust... It usually only happens because of the change in altitude for me.
Climate can for sure be a migraine trigger though!! I get terrible migraines in some climates and hardly any migraines in some climates. The climate I live in is particularly terrible for my migraines.. my mom keeps suggesting that I move as a solution to my migraines... we live in a place where it rains a lot and the pressure changes a lot... and pressure changes are a known trigger. Does the pressure change a lot in your climate? Apparently "a decrease of 0.7 kPa (kilopascal) or more" is a known trigger for aches and pains according to my local weather network. Also does the dewpoint change a lot? Apparently "an increase of 5 degrees Celsius or more" can be a trigger for aches and pains according to my local weather network. What about humidity, does that change a lot? According to my local weather network, "an increase of 20%" of humidity can be a trigger. And what about daily changes in temperature? My local weather network says daily "decreases of 5 degrees Celsius or more" can trigger aches and pains.
Hope that helps!
There is another possibility too that I just thought of...
although there are noted differences in the number of migraines people get depending on the part of the world they live in (highest in north america, lowest in asia)... usually the stats are about the same no matter where you live in the US, as in.. there isn't really a statistical meaningful difference. But, that doesn't mean that there aren't differences... it is just that they don't think those differences mean anything important or are related to geography because the differences aren't large enough... when looking at data like that, the data is usually only meaningful if there are large enough discrepancies between the sets of numbers (so in this case, between the amount of migraines people get depending on what state they live in). For men who have migraines living in different areas in the US, the largest discrepancy is about 4%.
Still, with that said... you moved to an area in the US that has the highest percentage of migraines among males at 9.2% of the population of East South Central America. Where you were living before, Mountain region, the male population with migraines is only 6.4%.
Anyway... why it appears that there are small increases in the population of those with migraines depending on geographical location within America is unknown and the fact that the discrepancies between regions is so small implies that there are no real variations between regions.
Still, I thought I'd offer this up as a possibility since you did happen to move to East South Central America... although it's likely just an interesting coincidence.
Last summer when I went from my mountain home in NE GA to sea level in Seattle WA I got a terrible migraine. Could the flying to seattle and leaving the mountains all in the same day trigger a migraine?