LONG FRONT CLOSE-MID UNROUNDED VOWEL [eː]
In open syllables, Tiberian Hebrew ṣere is normally pronounced as a long e-vowel.
EXTRA LONG FRONT CLOSE-MID UNROUNDED VOWEL [eːe]
In a closed syllable, ṣere is pronounced as an extra long vowel [eːe].
(in stressed closed syllable)
SOURCES AND FURTHER READING
Khan, Geoffrey. 2020. The Tiberian Pronunciation Tradition of Biblical Hebrew. Cambridge: Cambridge and Open Book Publishers. §I.2.