How do you spell the exclamation that rhymes with the word "woe"? Is it woah or whoa? The correct spelling in the United States is whoa, but when words are primarily transmitted orally, spelling often varies. This is part of a complete episode.
It is not only being misspelled in personal emails, I have been seeing it misspelled in movie subtitles, in lyrics on You Tube, etc. It has been driving me crazy, too. The word "whoa," has been around forever. It's what you say to stop a horse. It has always been spelled, "WHOA." Now it seems the misspelling has found its way into general usage. What else will we start misspelling, simply because we are lazy and ignorant? It seems to me that it all has to do with the dumbing-down of America.
Actually, "Whoa" and "Woah" are separated in common usage only by about a decade, and both have been commonly used since the middle 1800s. Both are variants of "woa", around since the 1840s. "Woa" itself is a variant of "Wo" from the late 1700s, deriving from the interjection (not pronoun) "Who", which has been around since the middle 1400s. "Whoa" predates "Woah" by about ten years. But, (perhaps) interestingly, it depends on which English speaking country you live in as to which is considered "standard". "Woah" is the favored spelling in the UK, while both spellings are in common use in the US. Both are correct, so use whichever you like. Or, if you want to get REALLY "correct" (and by that I mean ridiculously anal retentive), just go back to "Wo". Apparently that's when the "dumbing down" started.
What are your sources for all that, Brian? I find no evidence at all in corpora or dictionaries that "woah" is the favored spelling in the UK. Also, you're confusing historical forms with modern forms, which is not really what the whoa vs. woah debate is about.
To elaborate: although the OED correctly lists those older forms as being the progenitors of the modern ones, they're not the same words, exactly, and to suggest that the older forms are somehow more correct is a form of etymological fallacy.
This discussion is about the modern standardized spelling of "whoa" vs. "woah." The evidence shows that "woah" is rare (here's a for-what-it's-worth Google Ngrams comparison http://goo.gl/XjXO1), almost never appears in professionally edited texts, and is rarely included as a variant spelling in any non-historical English dictionary (I do see it in one edition of a Collins dictionary).
An updated for-what-it's-worth, including Whoa and Woah with uppercase w's. With those in the mix, "whoa" is clearly far above woah in number of occurrences.
I believe it goes like so: Cowboys say "whoa", city people say "woah".