I could see it working for a variety of reasons.
1. Air conditioned. Although, it's more likely to be placed inside a mall anyway.
2. Free Wifi...usually lightning fast.
3. Frappuccinos are a huge hit in hot climates. Hell, they're even a huge hit in Norway in the summers....and it only gets up to 75f on a hot day!
4. Consistency, consistency, consistency.
5. Location, location, location.
6. Good consistent product.
7. Extremely well-informed marketing & research teams.
Having said this, they have failed before, They had issues in Russia and some other countries, but that was mostly for political reasons--bribery, graft, etc.
My friend Jeremy L (comes down to Cabarete every year for Kite surfing) should know something about it. Jeremy's in charge of the entire North American Sales team (14,000 stores and a team of ten people--with sub-sets of teams underneath them). I would think he would know something. I'll ask him.