This is a pretty far cry from "each consonant and vowel in each word has its own meaning". Going by the handbook, the example word of diction is 57% meaningful symbols and 43% meaningless ones. The word called for by the encoding system, diti, is in fact nonexistent, but you're free to supply whatever other letters you feel like until you've formed an English word.

The example I asked about, the dew-point indicator left, is much worse, with -- as far as I can tell -- 25% letters with independent meaning and 75% letters without a meaning of their own. The handbook notes that dew-point indicators are not part of the system, and instead a lookup table is supplied which must be memorized. The linked document does not appear to include that table, though, so it's hard to characterize the dew-point indicators.

I did appreciate the note that temperatures are to be reported modulo 100 degrees, but "the intelligence of the translators will prevent any error arising".

I'm not sure why the dewpoint indicators had to be arbitrary, rather than using the same scheme. Maybe it was a way of providing some robustness because fields could occupy variable numbers of words, so an identifiable dew-point word would help to mark a specific field in the report.

My mistake. Pages 20-30 are all blank; I figured that was the end of the document.