concur. i don't ever remember the last time rain was an issue in socal in october.
smoke from the multiple fires due to the santa ana winds that also bring low low humidity and the heat? that's a consistent issue in october (and the first half of november) in socal.
all that said, october is my fave month to ride in socal. were i doing your tour, i'd aim for the middle of october.
if you're starting from san francisco, then you can handle what la will throw at you along the coast in terms of traffic. once through malibu, dedicated coastal/beach bike path/mup from santa monica
(north of santa monica pier area) all the way to redondo beach (small slow/dismount area at redondo beach pier two miles north of path terminus). very (southern) end of said bike path is pretty steep
but it's only a 60 yard walk uphill...or you can double back about a third of a mile and ride up an easier ramp to the cliffside street and continue southwards. bike paths/mups allow you to bypass much
of the la auto traffic from santa monica to redondo beach, then again from long beach to newport beach. that's roughly 45 miles of flattish, easy, safe coastal riding w/o any or minimal auto presence.
visually ugliest part will be the 10 miles or so from just north of the vincent thomas bridge in san pedro to long beach just past the 710 freeway. lots of big rig traffic on this
short stretch but streets are wide. biggest issue on this segment is actually road debris. the newport beach/corona del mar/laguna beach gauntlet (some quiet spots during) is probably your biggest safety challenge thru the socal portion. if you stay on highway one/pch, you will need to take the lane several times in likely (depending on your timing) heavy bursts of traffic at times.
if you're truly heading to san diego, you'll need to take the 5 freeway south for approx 8 miles from the las pulgas rd onramp to the town of oceanside to bypass marine corps base camp pendleton.
shoulder is wide and the pavement is good but the problem is the volume/speed of adjacent traffic along with dodging occasional (mostly shredded tires and assorted auto) debris.
a couple workarounds to this eight-mile freeway stretch...
1. you currently possess military clearance to enter/navigate the base
2. you possess and can produce the yearlong (free) pass procured from the base visitor center at the (unfortunately) southern end of the base. takes approx 10-15 mins to get in person with proper id.
3. you catch either the amtrak or metrolink train from the san clemente station (closest stop to the base on the north end) and take said train to oceanside. short ride. amtrak will necessitate
registering your bicycle on their website (can't do it on the amrtrak app yet) when purchasing a ticket. metrolink is the regional train system which is more affordable and you don't need to pre-register
bringing your bike aboard but may not have a convenient arrival/departure time for you.
last ten miles into san diego (south of the ucsd area) can be really complicated or very easy...depending on exactly where you want to go. some of the obvious north/south straight lines
have lots of traffic or really harsh/difficult intersections.