AL90, Invest area over the Florida Keys; where to find info

The Thing from The Gulf (2020 Remake) has moved over south Florida, and is expected to become a tropical depression in the Bahamas over the weekend.  So you know what that means … spaghetti maps!  Long time readers know that spaghetti must be cooked: if you don’t have years of training and experience (something that, no disrespect intended, even most working meteorologists don’t have, especially the local TV guys), interpreting tropical cyclone track forecast models is best left to the experts.  Don’t get caught up in the model guessing game, there is only one track that matters for your planning purposes: the official National Hurricane Center (NHC) forecast.  And, at this stage, there isn’t one, since official advisories have not started.  But NHC has a really great product that is started whenever something might have the potential to impact land: the key messages product. The “Key Messages” graphic should be your first step to see if you need to panic, and how frantic the panic should be. Don’t have a plan?  FEMA/DHS have a web site with lots of checklists and advice.  You paid for it, use it.  While this storm will probably not have any significant impacts, it should be a reminder that if you live on the coast, you need to have a plan.  Especially this year.  Look for a post in the next few days on how the COVID19 pandemic should change your hurricane evacuation plans.

Since AL90 is still an investigation area (INVEST), there is not official forecast track, only the five day outlook map.  That outlook is based on track models, global weather models, and forecaster experience.  The computer track forecasts look like this at the moment:

One thing to remember is that other than the colored lines, most of these tracks are actually variations on the same model designed to assess forecast uncertainty.  You can’t just pluck one line out and go “ZOMG!  That line hits my house!”  Let’s take one model, the US Global Forecast System (GFS):

The blue line (AVNO)  is the main model run.  The twenty thin gray lines are known as “ensemble members”.  These are model simulations that were started (“Initialized”) with slightly different, but reasonable, conditions.  For example, with a weak storm, we really don’t know exactly where the center is.  So the center is  started in different positions to see what happens.  The average of these ensemble members is the brown line (AEMN).  For this storm at this time, being so weak, this is a pretty tight grouping.

Normally we don’t do this with model forecasts, but since we don’t have an official track and want to see what this thing might do, we can run the GFS model track in our hurricane damage model to see what the winds and damage might be. Here is what that looks like …

So as we start another Atlantic Hurricane Season, please try to keep perspective.  We face many challenges between COVID19 and all of the fallout from that like the economy, and trying to think about One More Bad Thing is disheartening.  But, of all natural disasters, while hurricanes are destructive, you can see them coming.  We know, in comparatively accurate terms, who is at risk, and what they should to protect themselves.  Ignore the media hype and exaggeration, have a plan, be sensible, and you’ll be ok.

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