I'm trying to understand the timing of Jacks along the beach and at the jetties (specifically PINS, Packery, Port A).

My impression is that they move offshore and/or south during winter, then come back sometime in the spring. Assuming good water conditions, are they available all summer, or do they move up towards Galveston, or is it just a sporadic sometimes they're around and sometimes they're not? Any rules?

I know it depends a lot on water conditions whether they'll be in close or not, but is there also seasonality to it?

They should be on the jetties year round.

They spawn offshore them move into the bay. A few are around all year but the main time for them is May to August. The big ones are closer September to November. They follow the bait. I've caught the biggest ones when the blue water is close to the jetties but you can run across the occasional one almost anytime.

They are there now and will be until the water gets cold. Most people in your neck of the woods drive down PINS looking for them in the surf. Look for birds working or bait getting busted on top and be ready to jump out and make a few cast before they are gone.