Fall on both sides of the island
Fall can be a rewarding time to watch migration, but the useful plan is a place and enough time—not a list of birds you are promised to see. The Birding & Nature Center's FAQ identifies fall migration as an active birding period. Start there on day one, walk at the pace that suits you and ask staff what has actually been observed recently. Binoculars help, but curiosity is enough.
Day one: Laguna Madre habitat
Use the morning for the Birding & Nature Center. Admission, hours and programs can change, so check its current visitor information. If you want a shorter free bayside walk on another day, the Laguna Madre Nature Trail is a separate public trail, not an entrance to the center.
Day two: a Gulf beach, conditions permitting
Andy Bowie Park gives the second day a Gulf-side focus. Fall weather can still be hot, windy or stormy, so decide on swimming only after reading the current National Weather Service forecast and surf forecast. Check the county park for current access arrangements before setting out.
Move the beach stop rather than forcing it into poor conditions. For a wet or stormy day, compare rainy-day activities and verify which parts are actually indoors.