In the published materials, Tolkien doesn’t say anything about the Adûnaic continuative present other than that it exists. It probably serves a function similar to the Quenya present tense: to describe an ongoing action in the present. There is general consensus in the literature that the two sentences on SD/251 are likely examples of the Adûnaic continuative present (VSH/26-27, AL/Adûnaic, LGtAG):

• narîka ’nBâri ’nAdûn yanâkhim “The Eagles of the Lords of the West are at hand [lit. are coming]”
• urîd yakalubim “The mountains lean over [lit. are falling]”

After removing the pronominal prefix ya- and the plural verb suffix -m, the base verb forms seem to be nakh- → nâkhi (biconsonantal) and kalab- → kalubi (triconsonantal). Based on this pattern, I would suggest the following conjugations for the continuative present tense:

Biconsonantal Verbs	Lengthen the stem vowel, then add an -i to the verb stem	nakh- “to come” → nâkhi “is coming” (SD/251)
Triconsonantal Verbs	Change the second vowel to u, then add an -i to the verb stem	kalab- “to fall” → kalubi “is falling” (SD/251)
Derived Verbs	Not enough information	?

There is only one continuative-present example each for biconsonantal and triconsonantal verbs, and none at all for derived verbs. Given the lack of examples, the above rules are quite speculative.

Other Theories

Carl Hostetter and Patrick Wynne suggested (VSH/27) that biconsonantal verbs form their continuative present with vowel-lengthening. Helge Fauskanger suggested (AL/Adûnaic) that it is formed by a-fortification instead: a → â, i → ê, u → ô, an idea also adopted in Thorsten Renk’s Adûnaic course (NBA/14). Our only example is a verb with the stem-vowel a, which would have the same result either way. I picked vowel-lengthening simply because it was an easier rule to apply and resembles present-tense formation in Quenya.

Andreas Moehn (LGtAG) was doubtful that kalubi is a conjugation of kalab- “to fall”. He suggested instead that it is a conjugation of a verb *kalub- “to lean”, and that the continuative present for triconsonantal verbs is marked simply by adding an -i to the stem. Again, given the lack of evidence, it is hard to say what the correct conjugation is.

Draft Verb Conjugations

There are no examples that are good candidates for the continuative-present in the earlier Adûnaic materials, so it is hard to guess how this tense might have been formed in the draft Adûnaic grammar.