Joseph:
I don't know what types of weather records might be available for Mexico, especially for the year you specified - 1793. However, it seems to me that military reports for that time period would include weather reports. I don't know where such military reports would be archived, but my guess would be that they are in the national archive of Mexico in DF or in Spain.
I googled < weather records mexico > and one of the sites I came across was for the "Instituto de Geografia, UNAM". Try these sites - they don't have what you asked about, but there is some other cool information:
http://indy2.igeograf.unam.mx/instituto/index.html
http://indy2.igeograf.unam.mx/instituto/publicaciones/atlas_nacional.htm
http://indy2.igeograf.unam.mx/instituto/publicaciones/atlas_con.html#Hi…
(I didn't check the Links section of Nuestros Ranchos to see if they are already posted.)
Have a good weekend.
Natalie in VA
Weather records
Addendum:
I googled: WEATHER RECORDS MEXICO
Sorry to have left that notation out of message --- that's what happens when one does not proof-read one's messages ... : 0
ncc in VA