I don't know which subtropic area you are relocating to, but my son has been to Belize and other countries in the local vicinity on mission work and he says many of the cows there appear to be Jerseys. I know the dairy where my first cows came from have shipped cows to Puerto Rico and Guatemala and they were Jerseys. Jerseys are supposed to be pretty heat tolerant. It gets pretty hot here, sometimes over 100 with near 100% humidity, but generally 90's with high humidity for most of the summer. We notice that milk production slows down some because our herd spends a significant amount of time cooling off and not grazing, which is expected, wish I could give them A/C but that's not reasonable.
If it were me, I would try and identify what kind of cows are already being milked where you are going and see how they are faring. Ask how long they are milking, try some of the milk. Areas like I think you are moving can pose interesting opportunities to milking and cheese making. My son tells me the locals sell their milk right after filtering and what is not sold is made immediately into a cheese (not sure what kind or how) because electricity there is hit and miss lots of times and so refrigeration is not reliable. Most of all, I wish you good luck, it takes a pioneering spirit to give up all you know to start over someplace very different. (I would consider settling in a little before getting a cow, they like routine and it can be hard to establish immediately after moving, just from personal experience.)