Approximately two hours later at 10:05 am, Michaud observed at sea the "embrion of a waterspout" surrounded by "high plumes like sails pushed by the wind toward the surface" (a in Fig. 1). The structure narrowed and was later observed as a "column of fog" over land (b in Fig. 1).
At 11:52 am the confirmation of Michaud's prediction arrived, as his second son, now in charge with the observations, shouted: "Mon Pere, une trombe de mer superbe!" (Michaud 1801, p. 6). Fig. 2 shows the "superb" waterspout "passing majestically in front of Nice". The base of the waterspout, which was as the beginning "calm" was now "a veritable volcano crater" with parabolic jets of water emerging from the centre. As Michaud and his sons were watching this "extraordinary spectacle" hail (1-1.5 cm in diameter) begin to fall.
Soon after, a second waterspout begin to form and was observed initially only at the surface of the sea (a in Fig. 3). The vertical structure of the waterspout became apparent (c in Fig. 3) once the pendant structure from the cloud indicated as (b) in Fig. 3 moved over the sea surface structure.
The account of the waterspouts from 4 January together with some speculations regarding their formation were published by Michaud in Memoires de l'Academie de Turin in 1801. This account contains, to my knowledge, the first verified waterspout forecast for Europe. The article, which also contains a description of two waterspouts observed in 19 March 1789 Nice (Fig. 4) was translated to German an published in Annalen der Physik in 1801.
Michaud, 1801: Observations sur les trombes de mer vues de Nice en 1789, le 6 Janvier et le 19 Mars. Memoires de l' Acad. de Turin, Tome 6, p. 3–22. (via gallica.bnf.fr).