Miami lies on an outcropping of rock that is very close to sea level. On the inland side of that ridge is their aquifer. In a 6' scenario, most developed ground near Miami will literally be underwater, and the aquifer will be no longer be viable. Underwater isn't that melodramatic.

Considering that almost all projections have undershot global warming and sea level rise, and recent empirical observations have supported accelerating increases, we should be looking at worse that RCP8.5 scenarios which is already a full meter by 2080-2100.

Sea level rises by 2100 that are only 1"/.3m all rely on huge decreases in CO2 emission and global policy responses, which is unlikely based on existing evidence.

edit: https://pubs.er.usgs.gov/publication/70189089 (saline intrusion in Biscayne aquifer, access via referrer https://www.usatoday.com/story/news/2018/07/06/global-warmin... and free access)

edit: https://en.wikipedia.org/wiki/Representative_Concentration_P... (nomenclature for future climate scenarios)

edit: https://en.wikipedia.org/wiki/IPCC_Fifth_Assessment_Report (assessments and risks under future climate scenarios)

edit: https://www.nature.com/articles/s41561-018-0146-0 (evidence that projections are below current observed rates and overly conservative, even in some worst cases)