transient
TRAN-zee-untadjMeaning lasting only a short time; staying only briefly
Memory hook TRAIN-sient: a TRAIN passing through. The express train roars through the mountain valley, toots once and is gone. Its visit is transient: here for a moment, then away.
The transient storm soaked the picnic and moved on within ten minutes.
In context Most of the town’s summer crowd is transient: visitors arrive in June, rent a cottage for a week or two and are gone by September.
Similar temporary, passing, brief, short-lived
Opposite permanent, lasting, enduring
From Latin transire, “to go across, to pass by”: trans (across) + ire (to go).