Are We Going to Get Any Hurricanes This Year?

"Are we going to get any hurricanes this year?"

This is probably the #1 question that people ask when they find out I'm a hurricane researcher, especially now that we live in South Florida.  I wish I could provide an exact answer, but unfortunately our science is not at a point where I can answer that question with even moderate confidence.

There are several groups that do seasonal predictions of hurricane activity.  NOAA Released Theirs Yesterday.  These forecasts account for various things like ocean temperatures in the Atlantic (warmer water tends to favor hurricanes) and ocean temperatures in the Pacific (when the Equatorial Pacific is warm, called "El Nino", the thunderstorms there produce upper level winds that tend to destroy Atlantic hurricanes).  This year, there is a weak El Nino, but the Atlantic is also pretty warm, and Western Africa (the area where most Atlantic Hurricanes are born) is also fairly wet, which would favor Atlantic storms.  So there are a lot of competing factors, and it's too early to say if this will be a "quiet" or "busy" season.

The thing is, these seasonal forecasts, while quite interesting scientifically, simply predict how many storms will form in the entire Atlantic Basin over the whole season.  They don't tell you where the storms will go, or when they will be there.  There are researchers that try to assess the landfall risks in their seasonal outlooks (my friends at Weather Tiger are one), but that science is not to the point where we can say with any accuracy whether Miami, or Lakeland, or Tallahassee, or Houston, will be hit by a Category 3 hurricane this season.

And it doesn't necessarily matter (for landfall risks) whether a season was "busy" or not.  2010 was one of the busiest recent seasons, but almost all big storms avoided the U.S.:



On the other hand, 1992 was one of the most overall inactive seasons in recent history, with only 6 tropical storms and 4 hurricanes:



There was one that hit the U.S., however, known as Hurricane Andrew.  One of the worst natural disasters in U.S. history.



So you can see that bad hurricane hits can happen in "active" or "quiet" years.  The cliche saying is "it only takes one", and that is quite true.

It's a little depressing to know that we probably won't be able to tell you whether a hurricane could hit your house more than 3-5 days out, but the good news is that you can take this time before the busy part of the season to get ready in case one does come!

Here Are Some Hurricane Preparedness Tips

It's Also Important to Know if You Are in an Evacuation Zone

Hopefully, there won't be any bad hurricane landfalls, whether the Atlantic as a whole has 20 storms or 5, but just be ready either way!

A Fascinating Structure in Hurricane Michael

Mesovortices in Hurricane Michael

By now, most people have heard that Hurricane Michael was recently upgraded from Category 4 to 5 at landfall.  I tuned in to a webinar recently where NHC Hurricane Specialists Stacy Stewart and Jack Beven explained the troves of data (radar, satellite, and aircraft) used in this decision.  The webinar should be posted online here soon:

https://www.regions.noaa.gov/secar/index.php/highlights/announcing-the-2019-resilience-webinar-series/

One of the interesting things about this case that Stacy Stewart mentioned was the fact that the decision on what wind data to use was complicated by the presence of mesovortices in the eyewall.  Now, if you're not a hurricane person, you may not have heard of these.  Basically, they're small-scale cyclones (mesocyclones) in the hurricane eyewall.  A little bigger than a tornado, but much smaller than the scale of the storm itself.  They make the eyewall take on shapes like a triangle, or pentagon, or other shapes rather than the typical smooth, circular eyewall we see.  Here are a couple of radar images from during our last flight into Michael, illustrating these unusual shapes.

Mesovortices Were Also Observed in Hurricane Andrew at Landfall

The mesovortices can cause small-scale local increases in wind speed.  This makes it hard to tell if the wind being measured by the plane/radar is representative of the hurricane circulation as a whole, or just the small-scale mesovortex (which typically don't last very long).  Now, as Forecaster Stewart mentioned, the difference doesn't matter to the people being hit by it (although they determined the winds were Cat 5 with or without these mesovortices, and there weren't as many in Michael by the time it made landfall).  But what's interesting to me is I was able to replicate this structure in a simulation of Hurricane Michael using a test model (called HAFS, the Hurricane Analysis and Forecast System) that is a high-resolution nested version of the FV3GFS model.

Here is a forecast for Michael at landfall (started using data from October 7, right after Michael formed) for 3 days later.  The track is just a little bit off (not bad for a 3-day forecast), and the storm is strong but not quite as strong as the real one (Category 4 in the model, Category 5 in reality).  

Now, go back an hour earlier:

Notice the mesovortex (enhanced vorticity) in the SW eyewall?  There were winds over 165 mph with that!  But then, an hour later, the feature was mostly gone, and the maximum winds were about 140 mph (again, the model forecast was not bad but overall a little weak).  I just thought it was interesting that you could see a feature like this in both the real storm and in the model!  

This was a pretty nerdy post - I'll probably write a couple more general ones about hurricane forecasting as Hurricane Season approaches :)

Andy