Last year I grimaced every time I heard someone talk about how devastating Hurricane Matthew would be for Florida. It didn't look great but it wasn't anywhere near a worst case scenario. Hurricane Irma, however, truly scares me.
Irma's track is becoming a bit more clear. The storm will take a hard right turn into Florida. Yesterday there was a cluster of computer models that brought Irma east of Florida - which would have greatly reduced the impact in Miami. That eastern cluster is now gone. You can see on the European and GFS ensembles below which both agree on tracks very close to - or over - the Florida peninsula. Each line indicates a different model and the colors represent how clustered the models are (the brighter the colors the more models bring Irma over that location).
This represents a pretty close to worst case scenario for South Florida. A powerful category 4 hurricane emerging from the Florida Straits and putting Miami-Dade and Broward Counties on the most dangerous right hand side of the storm is currently forecast. The left side, not quite as strong, would still produce widespread and serious coastal flooding on the Gulf Coast.
What Could Change?
While it looks like Irma will be devastating there are things that could make it better. A track east or west of Florida could spare the state a direct landfall. While this seems unlikely the "cone of uncertainty" still remains very large at this juncture.
The storm's intensity is also a bit uncertain. While the most likely scenario (as currently forecast) is a category 4 hurricane there is certainly an opportunity for the storm to weaken a bit more OR strengthen more than forecast. Hurricane intensity is notoriously challenging to forecast.
It's not a certainty this will be catastrophic but it sure doesn't look good now.
Will it Be Worse Than Andrew?
Maybe. Maybe Not. Until we know exactly the path and intensity of Irma it's too early to draw comparisons. One thing that is clear is that Irma will be much larger in size than compact Andrew was. This could make storm surge worse and spread damaging winds across a larger area.
Should I Be Worried About Friends and Family?
If they live in a mandatory evacuation zone they need to leave. Storm surge and flooding is what kills people during a hurricane. Outside of storm surge zones hurricanes are quite survivable - event category 5 storms.
That said, anyone in South Florida should prepare for days and days without power and be able to shelter in place for an extended period of time veen if not in an evacuation zone.