Swahili stress with two vowels in a row, how does it work?

Question

I'm uncertain how stress works with two vowels in a row,
so I used a regex to grab some words out of a small learner's-dictionary,
and then make the two possible stress-patterns after each entry,
marking them "1" and "2".

I separated things into:

- "long" verbs [I think]
- "long" non-verbs
- "short" verbs
- "short" non-verbs

For the "long" words,
I think stress should always be pattern "1"?

For the "short" words,
I think stress should always be pattern "1"?
Because they're two syllables still, right? Not one?

If there are any exceptions,
are they isolated one-offs that the learner should just memorize?
Or are there any, like, secondary rules?

Is stress ever affected by adding prefixes?
Any verb/non-verb differences?

Also,
what would be the difference between word-pairs like:

endelea

vs (hypothetical):

endeleya

or:

bomoa

vs (hypothetical):

bomowa

?

word-list:

# "long" verbs                                      
                    -ambia                              to tell to
                                    a-MBI-a         1
                                    A-mbia          2
                    -amkia                              to greet
                                    a-MKI-a         1
                                    A-mkia          2
                    -andaa                              to prepare
                                    a-NDA-a         1
                                    A-ndaa          2
                    -angalia                            to look at/pay attention; watch
                                    a-nga-LI-a      1
                                    a-NGA-lia       2
                    -bomoa                              to demolish
                                    bo-MO-a         1
                                    BO-moa          2
                    -chagua                             to choose
                                    cha-GU-a        1
                                    CHA-gua         2
                    -chukua                             to take
                                    chu-KU-a        1
                                    CHU-kua         2
                    -dharau                             to disdain; disregard
                                    dha-RA-u        1
                                    DHA-rau         2
                    -elezea                             to explain to sb.
                                    e-le-ZE-a       1
                                    e-LE-zea        2
                    -endelea                            to continue (state)/progress, develop (state), keep (doing)
                                    e-nde-LE-a      1
                                    e-NDE-lea       2
                    -enea                               to spread (state)/extend over (state)
                                    e-NE-a          1
                                    E-nea           2
                    -fungua                             to open
                                    fu-NGU-a        1
                                    FU-ngua         2
                    -ingia                              to enter
                                    i-NGI-a         1
                                    I-ngia          2
                    -jisikia                            to feel better
                                    ji-si-KI-a      1
                                    ji-SI-kia       2
                    -kataa                              to refuse
                                    ka-TA-a         1
                                    KA-taa          2
                    -kimbia                             to run/run away
                                    ki-MBI-a        1
                                    KI-mbia         2
                    -komboa                             to liberate
                                    ko-MBO-a        1
                                    KO-mboa         2
                    -letea                              to bring to someone
                                    le-TE-a         1
                                    LE-tea          2
                    -nunua                              to buy
                                    nu-NU-a         1
                                    NU-nua          2
                    -ongea                              to converse
                                    o-NGE-a         1
                                    O-ngea          2
                    -patia                              to give to/pass to sb.
                                    pa-TI-a         1
                                    PA-tia          2
                    -pindua                             to overturn sth.
                                    pi-NDU-a        1
                                    PI-ndua         2
                    -pungua                             to decrease (state)
                                    pu-NGU-a        1
                                    PU-ngua         2
                    -sahau                              to forget
                                    sa-HA-u         1
                                    SA-hau          2
                    -saidia                             to help
                                    sa-i-DI-a       1
                                    sa-I-dia        2
                    -salimia                            to greet
                                    sa-li-MI-a      1
                                    sa-LI-mia       2
                    -shangaa                            to be astonished
                                    sha-NGA-a       1
                                    SHA-ngaa        2
                    -shughulikia                        to look after/attend to
                                    shu-ghu-li-KI-a 1
                                    shu-ghu-LI-kia  2
                    -sikia                              to hear
                                    si-KI-a         1
                                    SI-kia          2
                    -sinzia                             to sleep/asleep ( fall/be –)
                                    si-NZI-a        1
                                    SI-nzia         2
                    -sumbua                             to annoy/bother
                                    su-MBU-a        1
                                    SU-mbua         2
                    -tegemea                            to rely on
                                    te-ge-ME-a      1
                                    te-GE-mea       2
                    -tembea                             to walk
                                    te-MBE-a        1
                                    TE-mbea         2
                    -tembelea                           to visit
                                    te-mbe-LE-a     1
                                    te-MBE-lea      2
                    -teua                               to designate/select
                                    te-U-a          1
                                    TE-ua           2
                    -tumia                              to use
                                    tu-MI-a         1
                                    TU-mia          2
                    -umia                               to suffer (be in pain)/hurt (be/get)
                                    u-MI-a          1
                                    U-mia           2
                    -vutia                              to attract
                                    vu-TI-a         1
                                    VU-tia          2
                    -zoea                               to get/be accustomed
                                    zo-E-a          1
                                    ZO-ea           2
                    -zuia                               to restrain
                                    zu-I-a          1
                                    ZU-ia           2
                    -pokea                              receive
                                    po-KE-a         1
                                    PO-kea          2
                    -potea                              lost (get/be)
                                    po-TE-a         1
                                    PO-tea          2
                    -tulia                              calm (be); calm down (state)
                                    tu-LI-a         1
                                    TU-lia          2
                    -ugua                               ill (be); sick (be)
                                    u-GU-a          1
                                    U-gua           2
# "long" non-verbs                                  
                    eneo                                region; area
                                    e-NE-o          1
                                    E-neo           2
                    kioo                                mirror
                                    ki-O-o          1
                                    KI-oo           2
                    uzio                                fence
                                    u-ZI-o          1
                                    U-zio           2
                    adui                                enemy
                                    a-DU-i          1
                                    A-dui           2
                    rais                                president
                                    ra-I-s          1
                                    RA-is           2
                    barua                               letter (message)
                                    ba-RU-a         1
                                    BA-rua          2
                    familia                             family
                                    fa-mi-LI-a      1
                                    fa-MI-lia       2
                    Ijumaa                              Friday
                                    I-ju-MA-a       1
                                    I-JU-maa        2
                    jamaa                               relative ( family)
                                    ja-MA-a         1
                                    JA-maa          2
                    kadhaa                              some; several
                                    ka-DHA-a        1
                                    KA-dhaa         2
                    kileo                               liquor
                                    ki-LE-o         1
                                    KI-leo          2
                    kituo                               station
                                    ki-TU-o         1
                                    KI-tuo          2
                    kofia                               hat
                                    ko-FI-a         1
                                    KO-fia          2
                    maendeleo                           progress
                                    ma-e-nde-LE-o   1
                                    ma-e-NDE-leo    2
                    pomboo                              dolphin
                                    po-MBO-o        1
                                    PO-mboo         2
                    redio                               radio
                                    re-DI-o         1
                                    RE-dio          2
                    shujaa                              hero
                                    shu-JA-a        1
                                    SHU-jaa         2
                    ubao                                board
                                    u-BA-o          1
                                    U-bao           2
                    ufunguo                             key
                                    u-fu-NGU-o      1
                                    u-FU-nguo       2
# "short" verbs                                     
                    -jua                                to know
                                    JU-a            1
                                    JUA             2
                    -kaa                                to sit/stay (loc.), live (loc.)
                                    KA-a            1
                                    KAA             2
                    -lea                                to raise (child)/rear
                                    LE-a            1
                                    LEA             2
                    -lia                                to cry
                                    LI-a            1
                                    LIA             2
                    -nyoa                               to cut hair
                                    NYO-a           1
                                    NYOA            2
                    -oa                                 to marry ( for men)
                                    O-a             1
                                    OA              2
                    -tia                                to put
                                    TI-a            1
                                    TIA             2
                    -tii                                to obey
                                    TI-i            1
                                    TII             2
                    -ua                                 to kill
                                    U-a             1
                                    UA              2
                    -vaa                                to wear
                                    VA-a            1
                                    VAA             2
                    -ao                                 their(s)
                                    A-o             1
                                    AO              2
                    -faa                                suitable (be –); beneficial (be –)
                                    FA-a            1
                                    FAA             2
                    -jaa                                full (become/be)
                                    JA-a            1
                                    JAA             2
                    -kuu                                main
                                    KU-u            1
                                    KUU             2
                    -zee                                old
                                    ZE-e            1
                                    ZEE             2
# "short" non-verbs                                 
                    chai                                tea
                                    CHA-i           1
                                    CHAI            2
                    ua                                  flower
                                    U-a             1
                                    UA              2
                    ua                                  fence
                                    U-a             1
                                    UA              2
                    bao                                 board game; goal (in game)
                                    BA-o            1
                                    BAO             2
                    yai                                 egg
                                    YA-i            1
                                    YAI             2
                    juu                                 over; up; on top
                                    JU-u            1
                                    JUU             2
                    jua                                 sun
                                    JU-a            1
                                    JUA             2
                    bei                                 price
                                    BE-i            1
                                    BEI             2
                    choo                                bathroom
                                    CHO-o           1
                                    CHOO            2
                    chuo                                college
                                    CHU-o           1
                                    CHUO            2
                    kiu                                 thirst
                                    KI-u            1
                                    KIU             2
                    leo                                 today
                                    LE-o            1
                                    LEO             2
                    mguu                                leg
                                    MGU-u           1
                                    MGUU            2
                    mia                                 hundred
                                    MI-a            1
                                    MIA             2
                    mzee                                elder
                                    MZE-e           1
                                    MZEE            2
                    nguo                                clothes
                                    NGU-o           1
                                    NGUO            2
                    njaa                                hunger
                                    NJA-a           1
                                    NJAA            2
                    njia                                way; pathway
                                    NJI-a           1
                                    NJIA            2
                    pia                                 also; too (also)
                                    PI-a            1
                                    PIA             2
                    pua                                 nose
                                    PU-a            1
                                    PUA             2
                    saa                                 watch (time); clock; hour
                                    SA-a            1
                                    SAA             2
                    taa                                 lamp
                                    TA-a            1
                                    TAA             2
                    wao                                 them
                                    WA-o            1
                                    WAO             2

Answer 1

From an orthographic POV, stress is on the second to last vowel of the word ([púa] "nose", and if there is only a single orthographic vowel but there is an NC sequence before the vowel, the stress is on the nasal (which is syllabic" [ḿbwa] "dog", [ḿtu] "person"). So if I parsed your examples, pattern 1 is right, and you never get pattern 2. Glides would have no effect, so [bomówa] would be the same as [bomóa]. There are lexical exceptions like barábara "exactly" vs. barabára "highway" although I can't say I've ever heard anyone say barábara, and lázima "necessary" ((most?) often lazíma. There are problematic words like γáfla "suddenly" which can be pronounced as [{g,γ}á{f,Ø}la] i.e. with a stop or fricative and with or without an epenthetic vowel: I doubt that you ever get [gafúla]. You get somewhat different results depending on how Kisanifu you (your speaker) is.

You may also want to know that the double vowel spelling of ndoo, njoo etc. is an orthographic means of indicating that stress is not on the nasal, otherwise these would be *[ńdo, ńjo]. Stress can be on a prefix, e.g. ní-pe "give me", kú-pa "to give", kí-su "knife". The language conspires to prevent inflectable monosyllables, so there can't be a paradigmatic alternation with stress on the root in one form and stress on a prefix in another form.

Answer 2

In words that are stressed regularly, the stress will be on the second last orthographic vowel or on a syllabic nasal if it is the second last syllable. (Unless the morpheme is only two syllables, as in nchi, nge, mbwa, where a simple prenasalisation has been forced to be syllabic, it is always m, as in kuaḿka, kucheḿsha.)

E and i before another vowel are not distinguished from ey and iy. An epenthetic /j/ may be pronounced by some speakers and there is no meaning difference, so that is why you don't see words ending with "eya" etc. except for where the grammar conditions it. For example, ndiyo and ndio are pronounced identically. The spelling difference reflects the grammatical difference between the suffix -yo (C3, C6, C9) and the suffix -o (C2, C4, C11, C14).

O and u before another vowel are not distinguished from ow and uw. An epenthetic /w/ may be optionally pronounced between them. This is why verbs that end with -oa and -ua don't form their passives like other verbs. Kubomoa would be indistinguishable from its passive *kubomowa. For this reason, the applicative suffix is used as a buffer and the passive of kubomoa is kubomolewa. Verbs ending with -oa and -ua become -olewa and -uliwa in the passive. The dialect of Unguja, which has been chosen as standard Swahili, also has this change for verbs ending with -aa, so kuzaa becomes kuzaliwa in passive, even though it is perfectly easy for -aa to be acoustically distinguished from -awa.

In native Swahili words, sequences of two vowels at the end of a result from the loss of the consonant between the second last and last vowel, /l/ which accounts for a lot of things. The initial /l/ that appears in the applicative in verbs that end in -VV in their base form is the resurfacing of the /l/ from the base word. E.g. originally "kuzaa" was "kuzala". The applicative form was "kuzalila", adding -il-. In both cases, the /l/ between the last two vowels was deleted, giving their modern forms kuzaa (to bear, to give birth) and kuzalia (to bear for, to give birth for).

It also accounts for the /z/ appearing in a lot of causative words. "To become full" was originally kujala. The causative "to make full" was kujalya and this y /j/ after another consonant usually changed it. In the case of /lj/ it became /z/.

You can still hear this /l/ in dialects, particularly in the west. In Congolese Swahili, you will hear njala for "hunger" instead of njaa and kuzala for "give birth". If you look further afield, other Bantu languages such as Zulu also preserved it. The Zulu word impala is a direct cognate of the Swahili word paa "duiker". Another pair is indlela in Zulu, which is a cognate of njia "way" in Swahili.

Swahili:
kupika "to cook"
kupikia "to cook for"

Zulu:
ukupheka "to cook"
ukuphekela "to cook for"

So the doubling of vowels at the ends of words is not just a way to show stress. It results from the loss of a consonant. Each vowel is a separate syllable although the boundary between them may be imperceptible.

We can see this in words like taa "light". There are no Swahili nouns that are only one syllable. Monosyllabic stems, such as -ta, -cho, -pya always require an additional syllable to take the stress, so this results in prefixes being used when they usually aren't. For example, class 9/10 generally has no prefix before voiceless consonants such as /t/, /p/ and /t͡ʃ/, but in nta "wax", nchi "country" and mpya "C9-new", a syllabic nasal is needed. In class 5, the removable prefix ji- is not added to many words, but it is with monosyllabic-stemmed words such as jicho "eye", jiwe "rock" and jipya "C5-new". Taa exists without a prefix because it is already two syllables, satisfying the length constraints of nouns. (Cognates include tawa in Kikuyu, etaala in Luganda and itara in Rwanda-Rundi.)