Comentario sobre Exodo 9:34

ויוסף לחטוא, up until now he had not been a deliberate sinner, not having acknowledged that what he had been doing had been sinful. Now, after having acknowledged this, reneging constituted a deliberately committed sin. This is why the Torah now describes Pharaoh as a deliberate sinner.

וירא פרעה כי חדל המטר, Pharaoh saw that the rain had stopped, etc. The Torah mentions this to show that Pharaoh's repentance already evaporated; he continued to sin almost immediately. When the Torah reports him as ויוסף לחטא, "he continued to sin," this does not refer to his continuing on his previous path; it means that Pharaoh added additional sins to the ones he had committed already. He now made a commitment not to release the Israelites under any terms and conditions.

וירא פרעה כי חדל המטר והברד והקולות, “when Pharaoh saw that the rain, the hail, and the thunder had ceased, etc.” Note that in the previous verse the Torah had described the cessation of the plague as occurring in a different sequence of steps, i.e. 1) thunder, 2) hail; 3) rain. The latter was described as being arrested in mid-air. The sound of Moses’ prayer resulted in the sound of thunder ceasing, the spreading out of his hands resulted in the hail and rain stopping to fall. Pharaoh’s perception of the sequence of these events was different, however. He first noticed that the rain and the hail had stopped. Only later did he realize that also the thunder had ceased.