For a full account of the events surrounding the fire sermon, you have to look in the vinaya pitaka. An old translation of the complete account is here.
The closest he comes to "thundering" is when he defeats the naga:
3. Then the Blessed One entered the room where the fire was kept, made himself a couch of grass, and sat down cross-legged, keeping the body erect and surrounding himself with watchfulness of mind2. And the Nâga saw that the Blessed One had entered; when he saw that, he became annoyed, and irritated, and sent forth a cloud of smoke. Then the Blessed One thought: 'What if I were to leave intact the skin, and hide, and flesh, and ligaments, and bones, p. 120 and marrow of this Nâga; but were to conquer the fire, which he will send forth, by my fire.'
4. And the Blessed One effected the appropriate exercise of miraculous power and sent forth a cloud of smoke. Then the Nâga, who could not master his rage1, sent forth flames. And the Blessed One, converting his body into fire2, sent forth flames. When they both shone forth with their flames, the fire room looked as if it were burning and blazing, as if it were all in flames. And the Gatilas, surrounding the fire room, said: 'Truly, the countenance of the great Samana is beautiful, but the Nâga will do harm to him3.'
5. That night having elapsed, the Blessed One, leaving intact the skin and hide and flesh and ligaments and bones and marrow of that Nâga, and conquering the Nâga's fire by his fire, threw him into his alms-bowl, and showed him to the Gatila Uruvelâ Kassapa (saying), 'Here you see the Nâga, Kassapa; his fire has been conquered by my fire.' Then the Gatila Uruvelâ Kassapa thought: 'Truly the great Samana possesses high magical powers and great faculties, in that he is able to conquer by his fire the fire of that savage Nâga king, who is possessed of magical power, that dreadfully venomous serpent. He is not, however, holy (arahâ) as I am.'
Pretty clear that there wasn't actually any affectation on the Buddha's part. The word "threw" is a mistranslation; it would better be "placed".
The closest he gets to actual disturbance is when he finally confronts Uruvela Kassapa:
17. Then the Blessed One thought: 'This foolish man will still for a long time think thus: "Truly the great Samana possesses high magical powers and great faculties; he is not, however, holy like me." What if I were to move the mind of this Gatila (in order to show him my superiority).'
And the Blessed One said to the Gatila Uruvelâ Kassapa: 'You are not holy (arahâ), Kassapa, nor have you entered the path of Arahatship, nor do you walk in such a practice as will lead you to Arahatship. or to entering the path of Arahatship.'
Pretty tame, but then that's to be expected; he was, after all, a fully enlightened Buddha. There are a couple of examples I can think of where does affect an emotional disposition to get his point across, if only in the words he chooses:
- His words to Vakkali, who spent all his time staring at the Buddha's majesty:
But in spite of the Teacher’s admonition, Vakkali could not let the Teacher get out of his sight or leave the Teacher’s presence. Finally the Teacher thought to himself, “Unless this monk receives a shock, he will never come to understand.” Now the season of the rains was at hand, and the Teacher desired to enter upon residence. So on the day appointed to enter upon residence, the Teacher went to Rājagaha, turning Vakkali away with the words, “Go back, Vakkali.” So for the space of three months Vakkali was unable to be with the Teacher and kept saying to himself, “The Teacher speaks to me no more.” Finally he said to himself, “What is the use of my living any longer? I will throw myself headlong from the top of a mountain.” And with this thought in mind, he climbed to the top of Mount Vulture Peak.
-- Dhp-A 381 (Burlingame, trans)
The English here is poor; apehi means "Go away!", or even "Get lost!", so it was a bit like a slap in the face to the poor deluded man.
- His words to Devadatta, when he challenged the Buddha to enforce his five extreme rules:
'I would not give over the Bhikkhu-samgha, Devadatta, even to Sâriputta and Moggallâna. How much less, then, to so vile and evil-living a person as you.'
The actual Pali of this one is actually closer to "lick-spittle", as per the footnote:
In the text read khavassa khelâpakassa. On the first word, compare V, 2, 8. For the second the Dhammapada commentator (Fausböll, p. 143) reads, as does the Sinhalese MS. in our passage, khelâsika. Buddhaghosa, explaining it, says, 'In this passage (we should recollect) that those who obtain the requisites (of a Bhikkhu) by an evil mode of life are said by the Noble Ones to be like unto spittle. The Blessed One calls him khelâpaka (to ex-press that) he eats, (that is, 'gains a living) in sin like that.' (For the Pâli, see the edition of the text, p. 323, where the comma after khelasadisâ should be before it.)