Many thanks for the notes @chris, it makes a lot of sense! Somehow it hadn’t crossed my mind.
I have updated the component (20171128_Rainfall.gh (507.0 KB)) to incorporate the headers, but there is still something beyond my understanding - Although Ladybug’s header component and this one generate the same data, the Monthly Bar Chart doesn’t accept the output of the Rainfall component as a valid input. The error is:
Current document units is in Meters
Conversion to Meters will be applied = 1.000
Runtime error (TypeErrorException): unsupported operand type(s) for -: ‘str’ and ‘int’
Traceback:
line 299, in makeChartCrvs, “”
line 1135, in main, “”
line 1203, in script
So far, I have compared the data types coming out of both components, using print(type(Rainfall_mm[8])). All the items in both lists are equally strings so I can’t see any reason for it not to work. I guess it may have something to do with python data types - still a starter on that side. If someone has a hint on this, I should have it soon and make the pull request 
Regarding the GPM database from NOAA, it looks very accurate and complete. I guess that bringing that data into grasshopper would open a whole new set of capabilities - flooding simulations sounds a great use of this data. As much as I would like to embark on it, I’m still learning the basics of python and it seems a huge task to take on. In any case, I’m keen to keep exploring it and try to find some time push it forward (it is difficult to know to which extent) - Would it be better to open a Github topic for this?