Michael ... what caused him to behave the way he did?

This post deals with Hurricane Michael that made landfall on the Florida Panhandle Oct 10,2018. Prior to landfall Michael exploded in intensity. This caught many by surprise.  Many residents that stayed to ride out Michael most likely would have evacuated had they known how strong Michael would be at landfall. I will explain the processes that forced Michael to take the track he did...and try to offer some thoughts on why I think he intensified the way he did.  Due to its nature, the subject matter will be a little bit technical, but I will try to put it in a way that the general layperson can understand.    

In regards to Michael:

A few days ago I posted on my Facebook page, how my team and I handled Michael.

"I think the team and I did a good job with Michael.  He did get slightly stronger than I thought he would. But days ahead of landfall I said a Category 3/4 was going to strike the Florida Panhandle. He came in as a borderline Category 4/5.  As they did with Andrew, they very well could declare Michael was a Category 5 hurricane.   

  When Michael started forming, I thought he would make a land fall close to the Louisiana and Mississippi border. I soon corrected this and shifted my landfall idea farther east.   Tuesday I indicated landfall would be Wednesday  late morning into early afternoon, between Destin and Panama City, but he could go as far east as Mexico Beach.

It can be very difficult to accurately stay ahead of a storm like Michael.....but like we did with Florence, we did alright with Michael".

Most of today's meteorologist and meteorological students rely too much on computer model simulations. Don't get me wrong, I use models all the time too. But not to tell me what is going to happen.  Instead I use them to verify stuff I already know. I never rely on the models to do my homework for me, I do my own math, physics, and all the rest. There is a ton of mathematics involved in meteorology; the inability to do the math is the chief reason students quit school or look for another career path.      When doing weather forecasting of any type you have to get the overall picture of the pattern in your head.   You look at the data presented and dissect the atmosphere from the surface to 200 mb layer by layer.  Then you plug that into your brain to compare to what you already know about the existing pattern and how it evolved to get to this point. Then you compare the pattern you see developing and compare that to pass years.  Once you have all that in your head, you're ready to make some educated guesses and come up with a forecast.  

Anyway Back To Michael:

Michael made landfall Wednesday the 10th of October, 2018 around 1:35 p.m. as a top end Category 4 hurricane with max sustained winds of 155 mph, and a central pressure of 919 mb. This makes him the strongest hurricane to strike the Florida Panhandle over the last 150 years of records for that region.  This makes Michael an extremely rare event; But it was far from being unprecedented. There have been hurricanes in the past that behaved and  followed a track similar to Michael's.       

I'm seeing the inevitable and expected Hurricane Michael was caused by Climate Change and or Global Warming.  This stuff is popping up everywhere. A lot of emphasis is being placed on those very warm Sea Surface Temperatures (SST). But warm SST was only one part in a complex setup.    I will state for the record,  Hurricane Michael, wasn't caused by climate change.  The reasons for Michael were strictly environmental and climatology. 

The conditions in the Northeast Gulf Of Mexico (GOM) were textbook for rapid intensification.  We had very warm sea surface temperatures, lots of tropical moisture,  a very favorable upper air pattern caused by the MJO, and the time of year. As well as the northern ridge and approaching trough of cold air played a big role as well.  I will touch on why that cold air might have been very important to the rapid intensification Michael experienced.  Rapid intensification is when a hurricane increases it's sustained wind speed by at least 35 mph in a 24 hour period. 

  

Eye-Wall Replacement Cycles (ERC):

Michael went through three eye wall replacement cycles before landfall.   When Florence had her ERC's she increased the size of her wind field.  Michael went the opposite direction, following his ERC's he decided to deepen instead.

SST and moisture:

 

The Gulf Of Mexico was extremely warm in September; those waters were slowly cooling as we got into October, but they were still more than warm enough for a storm like Michael to form.  The water in parts of the northeast GOM were just over 3.5 degrees Fahrenheit above average.  Those waters weren't just warm on the surface. Subsurface water temperatures were well above average down to 300 /400 feet. That is a lot of heat potential for a hurricane to feed off of. There was also a lot of atmospheric moisture for Michael to tap into. Michael's large area of circulation was also able to pull in moist air from the Pacific. Midlevel relative humidity was 70% to near 80%   But because of his interaction with nearby land areas there was some dry air he had to deal with. 

Wind Shear:

At first the wind shear kept Michael's eye wall from completely inclosing his center.  On October 4th Michael wasn't even an Invest yet. Wind shear was very high at 20 to 40 knots.  This wind shear was blowing a lot of Michael's heavy thunderstorm activity to the east.  As the subtropical jet pulled north during the week wind shear lessened.  Wind shear was moderate at 20 knots on the 7th of October; Michael also had to deal with a Gyre over Central America.  A  Central America Gyre (CAG) is a large closed area of surface low pressure.  These Gyre's occur during the rainy season normally from May to November. SAG are typically fueled by phase 8 and 1 of the MJO.   When we have a tropical cyclone develop it is typically found on the GYRE's eastern side.  Tropical Storm Nicole formed south of Cuba in 2010 because of this process. Last October we saw Nate form from a CAG.  On early morning  October 9 moderate wind shear of 15-20 mph was still present. The eye was elliptical. But by mid morning the eye was much more circular. Temperatures in the eye were quickly rising at this time  and the eye wall was  beginning to close off.  The eye wasn't completely closed off by late afternoon.     Upper level dry air had been interfering with Michaels core development.  But as the eye wall closed off this dry air would be kept at bay.  The eye wall closed off during the evening of October 9th. This was caused by the upper level low to Michael's north weakening and pulling out of the way.   The upper air system pulling away also dissipated most of the wind shear clearing the way for Michael.  

 

Upper Air Features:

The MJO was the major key to how Michael behaved. I've been explaining how the MJO influences raising and sinking air as it moves through its eight phases.  The MJO. It is why we saw Rosa and Sergio in the eastern Pacific. MJO is also the reason we just had Florence and now Michael.  MJO phases 1 and 2  . The MJO went into Phase 2, this is a sign  that air would be rising in the western Caribbean and eastern Gulf.

A few hours before landfall, Michael was effected by a low level jet streak. This allowed him to finally develop excellent top level outflow. This allowed him to become completely vertically stacked.  Vertically stacked means the surface low and the upper level low are sitting on top of each other (not tilted with height).  Once a storm is vertically stacked it is like a chimney allowing a hurricane to exhaust  it's outflow quickly and efficiently  allowing the storm to  build vertically. The higher the cloud tops the colder and stronger they are.  Once this happened, Michaels eye wall  fully closed off insulating Michael's core from that layer of dry air.  

Time Of Year:

October is the time of year all eyes start to watch the southern and western Caribbean. In October climatology favors a northern turn for storms in the Caribbean where they track into the GOM. This is because that late in the year the northern hemisphere is switching from a summer pattern to a winter pattern.  Because of this we see strong cold fronts drop south out of the Plains.  This is why it is very difficult to have a land falling tropical system  in Texas during October. 

Here is a chart that shows where we expect to see hurricanes form in October.

 

Michael formed exactly where we would expect him to develop.  The SST were very warm for October. Michael was the perfect opportunist and took advantage of this fact and explosively developed.   Once Michael got into the Gulf he went from a category 1 to a top end category 4 hurricane in 24 hours. That is extremely rapid intensification. But again it isn't unprecedented. The 1935 labor day hurricane that struck the Florida Keys, went from a category 2 to a category 5 very quickly as well.   

 The high heat content. Time of year, and the overall pattern created the perfect environment for Michael.  An environment that allowed Michael to deepen in spite of moderate wind shear.  I will explain some ideas on why this most likely occurred.

Some thoughts on why Michael laughed at the shear: 

There is no doubt that the speed of Michaels intensification took many meteorologist and therefore the general public by surprise.  On its face value it was weird.  But we have to look deeper into the setup and pattern to discover why he strengthened in the face of moderate wind shear.  

Part of the reason Michael endured was the size of his eye wall and overall size. This helped protect his core to some degree.  But the real reasons are much more subtle.  To see how he reached major hurricane status without an intact eye wall, we have to look at the currents in the GOM and the 200 hpa wind speed and vector direction.

 

       1) the Gulf Loop Current And Loop Current Eddies:

When looking at a hurricane projected track, we look at the overall general SST's ahead of the storm.  The models factor in these general overall temperatures.  As I've already said, the subsurface temperatures were very warm deep down.  Wind and ocean currents and eddies are the major ways that heat can get to the surface.  Following Michael's passage, winds upwelled subsurface water, temperatures in Michaels' wake are cooler now than they were.   SST's are never uniform across any body of water.  There are areas were the water is much warmer or cooler than the overall average of the water.  The reason for this has to do with currents and eddies.

The GOM loop current , is a flow of warm water  from the Caribbean going into the GOM.  The current moves between the Yucatan and Cuba. From here it moves into the GOM and then loops back around and moves through the Florida Straits on its way to the Atlantic Ocean and the Gulf Stream. The extent of the loop varies; sometime it just makes it to the GOM before turning toward the Straits, other times it can extend almost all the way to Louisiana before looping back south and through the Straits.

 

We saw the effect of the loop current when Hurricane Katrina passed over the current in 2005 she quickly jumped to category 5. But once she moved away from the current she weakened back to a category 3 hurricane.   In 2008 we saw hurricane Ike move over a the loop current and a loop current eddy and rapidly intensify.  Gilbert in 1988 and Charley in 2004, another 2005 storm Rita also underwent rapid intensification passing over the loop current.  Michael formed in the same area that Hurricane Camille formed in 1969. The loop current is something that needs more research and study. But it makes late season tropical cyclones unpredictable in the Gulf.

The loop current is one of the major reasons Michael Intensified. The models didn't accurately account for temperature variance caused by the loop current. The temperature difference between the surface of the ocean and the upper atmosphere is one of the major reasons a storm intensifies.   But it doesn't explain how he shrugged off the wind shear the way he did.  For that we have to leave the surface of the GOM and look at the upper atmosphere jet stream. 

 

       2)  the200 hpa wind speed and vector direction:

 

   

When we look at the upper air pattern we can see the approaching trough over Texas.  This trough was responsible for the wind shear ahead of Michael.  Ahead of the trough we have very warm and moist air. But the trough is bringing much cooler air.   The jet that is running between the two air masses will respond to the temperature difference.  This setup enhanced the jet overhead. All of this changed the direction and strength of the shear ahead of Michael.  It is also enhancing upward motion ahead of Michael.   As Michael headed  into the ridge the atmospheric setup quickly becomes very favorable for rapid development.  The environment around Michael allowed him to develop his own anticyclone overhead....allowing him to take control of his environment all around him. That trickle of cold air could have helped Michael intensify as well.

 

The setup was different, but many of these same factors was the reason Sandy behaved and strengthened the way she did.  Storms that undergo rapid intensification are more dangerous than other storms , be it a hurricane or a nor'easter.  When Michael exploded in intensity it was during the overnight and there was no way to warn anyone about it.

In closing:

As have monster hurricanes in the past, Michael showed why you can't use a hurricanes current wind speed for deciding if you should evacuate. The same thing happened with Sandy, Florence, Andrew and many other past storms.

This covers the main reasons Hurricane Michael acted the way he did.  Intense hurricanes right on the coast are always worrisome. Days before landfall I warned about the dangers Michael posed, and that Michael would still be intensifying right up to landfall.   Michael took advantage of perfect conditions and a complacent public.  Michael showed why hurricane models are nowhere near sophisticated enough to make a complete forecast.  We have to look at the overall pattern; but we also have to look at the sub-pattern around the storm and how that sub-pattern could impact development down the road.

That about covers what I wanted to say..........I hope you found this educational and enjoyable to read. As always I will try to answer questions.

Images are from Tropical Tidbits, Weatherbell, and NOAA.