Not sure what the verdict should be on "when" or how helpful this info would be because I am unsure whether it "dumps" in Bandon or if it is just a steady drizzle most of the day, but anyways . . .
The range of monthly temps for Bandon is not that huge - 54/38 in Jan - 64/49 in June - up to 68/50 in August/Sept and back down to 54/38 for Dec.
The precip is where you get a pretty big range:
Jan, Nov, Dec - Over 9 inches per mo
Feb, March - 7 to 8 inches per mo
April, May, Oct - 3 to 5 inches per mo
June, July, August, Sept - Under 2 inches per mo
Does this align with experience people have had at Bandon at different times of year?