Use of existential it ...
In some American vernacular dialects, particularly in the South (including the Appalachian and Ozark mountains), speakers may pronounce it as hit in stressed positions, especially at the beginning of a sentence, as in Hit's cold out here! This pronunciation is called a relic dialect feature because it represents the retention of an older English form. In fact, hit is the original form of the third person singular neuter pronoun and thus can be traced to the beginnings of the Old English period (c. 4491100). Read more here.
The information is very interesting.
1. Historically there has been competition between 'there' and 'it' for the subject position in existential constructions. Evidently, 'there' has won.
2. There are some dialects where 'it' is still used in existential sentences. But as is known, dialects are outside the language normative usage.
3. If we deny the impersonal meaning of 'it' in sentences like 'It is raining', on the basis of the assumption that 'it' = weather (The weather is raining), we will have to deny its existential meaning in this sentence as well, regard 'it' as a personal pronoun in this sentence, and the sentence itself to convey a classifying meaning ('the' with 'weather' is another argument for it).
4. By the way, there are some existential patterns in present-day English where 'there' and 'it' overlap. 'There is no use doing smth' / 'It is no use doing smth'.