In spoken English, [w] can occur as a transition between /uo͞oueuo͞oueuo͞oue/ and other vowels. For example, the word hour can be pronounced with the diphthong /ɑʊowowɑʊowowɑʊowow/ and may be followed by the vowel /ɚûrurɚûrurɚûrur/. In this combination, new hearing cuers may notice a [w] sound occuring between these two vowels. This consonant cound is referred to as instrusive [w]. It is, however, not a consonant phoneme. It is simply a transitional sound between the vowels. One should not cue the word hour using handshape 6.
Instrusive [w] is generally shown with brackets which indicate that the sound is phonetic. This is different than the phoneme /w/, which is written between slashes.
Understanding the difference between phonetic [w] and phonemic /w/ can be abstract and difficult to grasp. An easy approach for instructors to help students discriminate the difference is to ask them simply to take it out and see if the word changes. If one attempts to remove the [w] sound from hour, flower, power, sour, or Jewish, they will find that the sound comes back on its own. The [w] cannot be taken out of these words without inserting an unnatural pause between the two vowels that surround the transition. However, taking the /w/ out of words like quit, quite, and quick will change the words to kit, kite, and kick. This change helps cuers to see that the 'w sound' in a word like quit is fundamentally different from a word like sour.