Interesting. I wonder if this would necessitate a Sardinian or other intermediates: "Italian" was certainly not a language when this word arrived, even though it us cited as the source language for the Castilian

word. Even still, Arabic > Catalán/Occitan > Sardinian(?) > Italian (Neapolitan?) > Spanish... ¡Cuántas vueltas ha dado esta palabra!
Well, my mentioning the influence was a general aspect. I don't think that, regarding the word, this has been the journey of the word, because it is an old word in Tuscan too.
Following Corominas:
Even if
jaloque appears in the DRAE, after reading about it, it is clear to me that it is not Castilian, but Aragonese. The attestation for
xaloque/jaloque is late and mainly in writings from the Crown of Aragon or territories influenced by it, and its use in modern Spanish is rare (Castilian sailors used 'sureste' for the wind).
In other words, the version of the word in Spanish is the
siroco loanword.
Xaloque is Aragonese, taken from the Catalan
xaloc, where the word exists already in the first Chronicles (James I, 1270s) and in Llull (1280s).
In Occitan,
(e)issalot would come from Catalan
eixaloc, while
eissiroc, in Provence, would rather come from Italian.
Scilocco in Italian (that is, in Tuscan) is as old as
xaloc in Catalan. Scirocco apparently can be found in Dante.
In Arabic, shalûq for the SE wind can be found in a text from 1365, but it must have been seen as a foreign word, as no medieval Arabic authors used it. Nowadays, shloq in the Maghreb and shalûk in Egypt are used, and hesitation in the vowels seems to point to the word being taken from a Romance source. But even if the Arabic word comes from Romance, the Romance word itself must have come in turn from Arabic too, most likely from
shurûq 'sunrise', Southern European sailors understanding it as the East. Once in Iberia, it wouldn't be the East as in North Africa, but logically the South-East.
Colin's etymology, deriving SALÚC- from Latin SAL, with the meaning of 'salty wind, wind from the sea', is unacceptable by Corominas, since there's no such -UC- suffix, the Ú wouldn't explain the Romance o's, and semantically it wouldn't fit the use in parts of Italy.
My personal impression is that there could have been two branches, depending on the origin of the Mediterranean sailors: the Catalan one (Crown of Aragon) or 'shalok' one, and the North Italian one (including Tuscany) or 'shirok' one, both coming from Arabic shuruq. And from those two branches the rest would have come, most languages taking it from the Italian scirocco.