In the summer, tropical storms (aka "tropical depressions") build off the coast of Baja Mexico. A good sized one can generate a killer south swell for all us swell-starved summer surf bums. Of course the storm's intensity, duration, and location determines how far the swell travels. At the first sign of a tropical depression check the swell at Pacific Beach (in south San Diego) and Swami's and watch it grow. With any luck, the swell will make it to the south facing beaches of Santa Cruz!
For those of you who pray for surf, just remember that while big storms mean big waves for us here in the north, it also means destruction for the people of Baja, Mexico. So hope for safety and surf :-)