AL092020 – Still “Potential” (Wed 29 July AM)

Rules! We’ve got some rules around here”  And so it is with what is and isn’t a Tropical Cyclone (the technical name for depressions, tropical storms, and hurricanes).  The system NHC is tracking as AL09, “Potential Tropical Cyclone Nine,” doesn’t meet the formal criteria to be a tropical storm, even though it is producing tropical storm force winds in places.  As of this morning though there are thunderstorms (convection) flaring up near the center, indicating better organization.  It will likely be declared Tropical Storm Isaias later today.  Here is what it looks like at sunrise … left is infrared, right is visual (still a bit dark).  Click to embiggen:

So what does that mean in practical terms?  It means the wind field is broader than a typical tropical storm – but not as strong in the core.  It is slower to organize even with somewhat favorable conditions. It also makes forecasting much harder because we don’t have a good center fix and motion.  Depending on where the center finally coalesces,  On the current track across the Greater Antillies (Puerto Rico/Hispaniola/Cuba), the high mountains should inhibit much strengthening.  The official forecast keeps AL09 as at best a middling tropical storm.  But that can still cause a lot of misery, especially in Puerto Rico, as they have are still struggling to recover from Maria or the recent earthquakes.  Beyond that, it is likely the storm will curve north into Florida.  But it wouldn’t surprise me if it doesn’t survive the trip over Hispaniola and Cuba intact, or enters the Gulf of Mexico and strengthens.  Or something else (yeah, that’s a lot of help).  That’s how it goes with disorganized storms …

On this track it would cause upwards of $100 Million in damage across the Caribbean, and maybe $700 million in impacts in Florida.  A big question is if it triggers evacuations and shelters – that has major implications for the COVID19 pandemic we will look at later today …

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