Haiku started as something different, an opening (called a hokku) to a renga (a sequence of linked strophes with specific form). It's become a thing in itself, and it's become quite a misunderstood thing. The idea that haiku involves some 5/7/5 syllable count is based upon a misunderstanding. Haiku uses 5/7/5 morae in Japanese, and morae are not exactly syllables. Japanese morae/moras can be consonants in some contexts, for instance. So Kerouac had the right idea when he invented the short freeform American haiku, as well as the pop haiku.
To write something approximating a traditional haiku, you need a phrase and a fragment, with some attempt at a kireiji (cutting word) between them. A trad haiku isn't all one sentence, and it's not three fragments, it's in two parts. Anyway, haiku doesn't need the syllable count, doesn't use capitalisation or punctuation (though em dashes can approximate kireiji), doesn't need anything other than being a short, pithy, three-lined poem about direct, concrete observation, though some sort of twist in the meaning is useful. (These rigid, capitalised, 5/7/5 English haiku are just clunky.) It should never really be too abstract, should not include references to time, and ideally should include some reference to the season.