Occasionally with the combination sû there is a tendency to palatalise fully and pronounce the.    From Wordnik.com.  [Citizendium, the Citizens' Compendium - Recent changes [en]] Reference

Occasionally with the combination sû there is a tendency to palatalise fully and pronounce the s as sh, as for example in sûre certain, which BrE speakers can make sound like the name Shåw, and which never sounds like sewêr waste.    From Wordnik.com.  [Citizendium, the Citizens' Compendium - Recent changes [en]] Reference