Sea-level pressure variations tend to be small in the tropics, except during hurricanes. With the help of Tom Schroeder at the University of Hawaii, I have been able to confirm that these records have not been exceeded since 1971. On the United States mainland, the distinction of the least variability in sea-level pressure belongs to San Diego.
Winter brings occasional rains but few storms.
The chilly waters offshore weaken any tropical storms that might wander toward southern California from the west coast of Mexico or Baja, and the large, winter low-pressure systems of the North Pacific expend most of their energy north of San Diego.