California tends to get above average winter rainfall mainly during "moderate-plus" or strong El Nino events. Southern California is more likely to get this rainfall surplus than northern California, but in the very strongest events all of the state is likely to get it. But not all moderate events bring such rains. Note that 1986-87, 1987-88, and 1963-64 did not, and 1991-92 (a fairly strong event) only gave good rains to southernmost California. It's really impossible to predict when much of the California coast will get soaked. And this year, we still don't know for sure whether the event will be strong (>1.5C above average for at least one 3-month period in Nino3.4 region) or only high moderate. It currently looks promising, with last week's average (using OISST, not the official ERSSTv4) up to 1.4. As for summer effects, we are even less sure of any effect in California, and see little evidence of anything systematic. I don't often deal with data prior to 1950, so can't quicklly check out the eastern Pacific tropical cyclone behavior in the late 1930s that you speak of. I do hope something will break the drought in the western US, and California in particular could benefit from the El Nino, especially in the later part of the winter (Jan to Mar).