Launch sites aren't chosen for the weather — Florida's is famously terrible. They're chosen by physics and geography: a free speed boost from the spinning Earth, an empty ocean to drop stages into, and a map of orbits each pad can reach.
The Earth gives you a running start
The planet is already spinning eastward, and everything on it moves with the ground — at the equator, about 465 meters per second, faster than the speed of sound. Launch eastward and that motion is free money: speed toward orbit you never have to burn fuel for. The closer to the equator, the bigger the gift, which is why Cape Canaveral sits at Florida's latitude 28.5° rather than in Maine, why Europe launches from French Guiana at 5° north, and why launching against the spin — westward — is so wasteful that almost nobody does it. Rule one of spaceports: go as far south as your country conveniently allows, and face east.
The ocean is the safety plan
Rule two: never fly over people you don't have to. A rocket climbing east from the Cape crosses thousands of kilometers of open Atlantic — which is where spent stages fall, and where a failing vehicle can be destroyed harmlessly. Every launch corridor is cleared of ships and aircraft, and every rocket carries a flight termination system — explosive charges, now usually commanded by onboard computers watching their own trajectory, that end the flight if it strays. This is also why polar-orbit missions leave from Vandenberg in California instead: fly south from there and the trajectory hugs the empty Pacific. The pad you launch from is chosen by the orbit you need — which is why the Station's 51.6° orbit, tilted to be reachable from Russia's launch sites too, shapes launches to this day.
Reading a scrub like an insider
Florida's storms make the Cape one of the lightning capitals of America, and the weather rules are strict and specific: no launching near towering anvil clouds (a rocket's exhaust plume can trigger a lightning strike — it happened to Apollo 12, twice, seconds after liftoff), limits on winds aloft, rules about cloud layers holding electric charge. So when tonight's launch scrubs with 'weather red', it's rarely rain — it's electricity. Add the instantaneous windows from the rendezvous lesson and you can now decode almost any delay on this site's schedule: the pad, the corridor, the clouds, and the clock are all just physics wearing a bureaucrat's vest.