Cantonese written in Vietnamese script

This is an attempt to write Cantonese phonemically making use of the Vietnamese script (quốc ngữ). Notice that we are not trying to follow the Vietnamese orthography, but only trying to make use of the rich vowel diacritics which happen to meet the need of the Cantonese vowel system.

Initials
Initials (or onsets) are initial consonants of possible syllables. The following is the inventory for Standard Cantonese as represented in the proposed script followed by IPA:

Finals
Finals (or rimes) are the remaining part of the syllable after the initial is taken off. There are two kinds of finals in Cantonese, depending on vowel length. The following chart lists all possible finals in Standard Cantonese as represented IPA according to traditional analysis: Syllabic nasals:

Although that analysis can reduce the number of vowel phonemes to eight, as all vowels beside - show complementory distribution, it is difficult to explain why the allophones become short vowels. It should also be noticed that the vowel in and  is actually more open than the English counterpart, much closer to. The vowel in and  is also closer to. We therefore adopt an alternative point of view, that there are in fact seven long vowels and three short vowels in Standard Cantonese, and there are three constrasting long-short vowel pairs. The following chart list that view along with the proposed script.

For the syllabic nasals, since we do not have unicode symbols that provide enough tone marks on "m" amd "ŋ", we tenatively use the vowel that is left "ă" to mark the "null vowel". So the syllable nasals are:

mă and ŋă

Tones
Standard Cantonese has nine tones in six distinct tone contours.

Vietnamese script allows six tones, five diactics plus one unmarked tone. The follow table shows their tone names, tone contours and correspondence to the Chinese tone system according to James Campbell :

Obviously, we had to follow to view to merge the three Cantonese ru tones to other tones of the same tone contours to make the system work. We also found following the traditional corresponding to Chinese tones couter-intuitive for certain tones, for example, "á" may not be a good choice for the Cantonese yin qu (33) tone. So we aim at matching tone contours and shape of the diacritics to make them easier to remember. This is our proposal:

Samples
Guóŋdỗŋwá (Cantonese), Hỡŋgóŋ (Hong Kong), Guóŋzẫu (Guangzhou)

Nẻi gẫmyật yẩu mỏu cỗt guo gãi? (你今日有冇出過街？) (Have you gone out today?)