How would we have known how many Atlantic tropical storms there were in the 1930s?Rise and fall of barometric pressure at a distance by multiple (reporting) stations (incl. ships at sea); observation of the sky for tell-tale circular out-flow cloud patterns.
Just a (heavily-influenced by history, knowledge of meteorology and earth-science SWAG) guess on my part.
/sarc
I guess the reporting stations at sea would have had to be ships. I don’t know how many ships would have been in the tropical storm zone continuously.
Seriously, I doubt that there was much reliable info on the storms. I recall that in the 1950s it was big news to have airplanes enter these storms to record pressures and wind speeds.