Machiavelli did not witnessed the event, since he was born in 1469, but he describes an event that had a strong impact and was keep alive in the memory of Tuscany . It is clear from Machiavelli's description that this event was at least a damaging wind event (tempesta di venti, which can be translated as windstorm). The use of the term turbine (whirlwind), which can be used to describe tornadoes (e.g., Boscovich 1749 ) and the description of the phenomena as "ora verso la terra scendendo, insieme si urtavano; e ora in giro con una velocità grandissima si movevano"  (translated as sometimes precipitated upon the earth, struggled, as it were, in mutual conflict, whirling in circles with intense velocity or sometimes as furiously towards the Earth, sometimes twisting round like a Cylinder ) indicates in my opinion the presence of a tornado or at least of a funnel cloud.
 Machiavelli, N., 1532: History Of Florence And Of The Affairs Of Italy From The Earliest Times To The Death Of Lorenzo The Magnificent. Commentator: Hugo Albert Rennert via http://www.gutenberg.org/
 Pedretti, C, 1973: Leonardo: A Study in Chronology and Style. University of California Press, 192 pp.
 Boscovich, R. G., 1749: Sopra il turbine che la notte tra gli XI, e XII giugno del MDCCXLIX danneggió una gran parte di Roma (Upon the Whirlwind that on the Night between the 11th and 12th of June 1749 Damaged a Large Part of Rome).Appresso Niccoló, é Marco Pagliarini, 231 pp.
 Machiavelli, N, 1532. Istorie Florentine.
 Machiavelli, N. 1891: The History of Florence From the translation of "The Works of the Famous Nicholas Machiavelli" published in 1675, edited by Sir Henry Morley, LL.D., London, Gerge Routledge and Sons, p. 319–321.
Machiavelli's portrait is by Santi di Tito (1536–1603) via wikipedia.org.