Major Hurricane Irma

[weathernerd]

Reviewing the last 20 IR slides, the circumference of Irma is getting larger now. She may have lost some bite but she is definitely increasing in overall mass. 

[jbcmh81]

Overall circulation has been expanding quite a bit on satellite this morning. 

[CTWeatherFreak]

6 minutes ago, Raine1212 said:

The weather channel just said Irma is 700 miles wide, Is that true?

That's the diameter of the total circulation, not the core.

[winterymix]

Wave heights for SE Florida:

 

[Mountain_Patch]

This will likely be my last post for the day as this forum is decidedly against me communicating. So I figure I'll leave today with this gem. Amazing. Just absolutely amazing.

[Raine1212]

2 minutes ago, CTWeatherFreak said:

That's the diameter of the total circulation, not the core.

 

2 minutes ago, CTWeatherFreak said:

That's the diameter of the total circulation, not the core.

I understand that, is this the largest ever recorded that size in the Atlantic?

[JC-CT]

I understand that, is this the largest ever recorded that size in the Atlantic?

Nah, not even top 5.

Sandy is the biggest.

[winterymix]

4 minutes ago, Raine1212 said:

 

I understand that, is this the largest ever recorded that size in the Atlantic?

Everything you could want is here:   http://www.nhc.noaa.gov/dcmi.shtml

[Bostonseminole]

1 minute ago, JC-CT said:

Nah, not even top 5.

Sandy is the biggest.

Sandy 1000m

Igor

Olga

Liill

Karl

Katrina 415m

 

That's story is from 2012 so not sure if a stormed moved into the top 6 since

http://www.huffingtonpost.com/2012/10/30/hurricane-sandy-largest-hurricane_n_2045163.html

 

[jaxjagman]

 

Pretty storm,taking more of the wobble towards the west the last couple frames

[JC-CT]

What would be interesting to see is how Irma's diameter of hurricane force winds compares to storms of the past.

[NavarreDon]

For those newer forum members in SFL asking questions here is what NWS-Miami is saying this morning.

AFDMFL

Area Forecast Discussion
National Weather Service Miami FL
404 AM EDT Thu Sep 7 2017

.DISCUSSION...

...THREAT OF HURRICANE IRMA INCREASES ACROSS SOUTH FLORIDA...

Rest of the week: Afternoon thunderstorm activity is expected
through the end of the week as ridge remains in control of the
weather pattern. Best chance of showers and thunderstorms will
mainly be in the interior and west. Friday will be the last day to
finalize all your hurricane preparations. If you are in an
evacuation zone or live in a mobile home, you should be moving to a
safe location no later than Friday evening. If you are not in an
area under evacuation orders, you should shelter in place during the
storm.

Friday night, Major Hurricane Irma will be approaching South
Florida. At this time, NHC is forecasting Irma to move near or
possibly be over South Florida. At this point, the environment ahead
of the hurricane looks supportive for it to remain a strong major
hurricane. The weather should start to deteriorate over South
Florida pre-dawn Saturday as Irma approaches the area. Closest
approach and worst conditions could occur anytime from Saturday
afternoon through Sunday night. Stay tuned for any updates today as
watches will likely be issued for S FL. The potential impacts that
look more likely to occur with Irma will be destructive hurricane
force winds, significant storm surge over the coastal areas of South
Florida and flooding rains.

In summary: All of South Florida visitors and residents should not
focus on the "skinny black line" of the exact track of Irma because
impacts mentioned above are likely to extend far from the storm`s
center.

Here are the latest key messages as they relate to South Florida:

1. The threat for direct impacts is becoming more likely for all of
South Florida. The time window of greatest concern is pre-dawn
Saturday through early Monday morning.

2. Potential threats: destructive winds, significant storm surge
along South Florida coastal areas and flooding rains.

3. Don`t focus on the hour to hour changes in the computer models,
they will tend to shift around at this time range. Irma is will
likely be a rather large hurricane by the time it approaches FL,
with destructive impacts extending out far from the center.

[jaxjagman]

[eaglesin2011]

8 minutes ago, Bostonseminole said:

Sandy 1000m

Igor

Olga

Liill

Karl

Katrina 415m

 

That's story is from 2012 so not sure if a stormed moved into the top 6 since

http://www.huffingtonpost.com/2012/10/30/hurricane-sandy-largest-hurricane_n_2045163.html

 

I believe the weather channel just showed this and mentioned that it was already bigger then Katrina in overall size.. 

 

[MillvilleWx]

I wanted to expand on something this morning to explain why NHC and some models show a decrease in max winds with Irma as she heads into the Bahamas and eventually up into CONUS waters. The reason NHC and some models have the storm weakening as far as max wind speeds is due to the expected expansion of the wind field within the cyclone. As the storm gains latitude, we're going to see the size of Irma increase and the hurricane/tropical storm force wind field expand out incrementally. When the system does that, it mimics the figure skater analogy with the conservation of angular momentum. As the wind field moves out, the central area of strongest winds will also expand and the system will see a incremental drop in max wind potential. This does not mean the storm will necessarily continue to drop speeds through the entire life span of increasing in size. The system will undergo fluctuations in intensity with regards to pressure and deep convection wrapping around the eyewall will allow for system to drop pressures once again, even as it undergoes the change in the wind field. It's basically a ratios game with how much the wind speed drops in conjunction with drops in the central pressure. @LakeEffectKing when he did his first call map yesterday had the pressures decreasing down to sub 900 south of the Southern FL Peninsula but "only" had speeds around 155mph. That's because of the expected expansion of the wind field once it reaches toward the Western side of the Bahamas and has been showed by multiple areas of guidance (At least I think, because I don't speak for him, but that's my wag). Models show a sharp decrease in pressures within that same zone due to the very high TCHP (Tropical Cyclone Heat Potential) located within the area of the Eastern Straits along with a very low shear environment due to cyclone remaining far enough south of the mid latitude trough to limit the deep layer shear present toward the FL/GA border. If Irma can make it 23N 78W, she will sit in the best environment there is north of the Western Caribbean for the best chance to intensify rapidly as long as she isn't undergoing an ERC. This is what the models have been doing over and over and will likely continue to be expressed in each run up until landfall. That part of Irma is a whole nother story...

[Mountain_Patch]

2 minutes ago, MillvilleWx said:

I wanted to expand on something this morning to explain why NHC and some models show a decrease in max winds with Irma as she heads into the Bahamas and eventually up into CONUS waters. The reason NHC and some models have the storm weakening as far as max wind speeds is due to the expected expansion of the wind field within the cyclone. As the storm gains latitude, we're going to see the size of Irma increase and the hurricane/tropical storm force wind field expand out incrementally. When the system does that, it mimics the figure skater analogy with the conservation of angular momentum. As the wind field moves out, the central area of strongest winds will also expand and the system will see a incremental drop in max wind potential. This does not mean the storm will necessarily continue to drop speeds through the entire life span of increasing in size. The system will undergo fluctuations in intensity with regards to pressure and deep convection wrapping around the eyewall will allow for system to drop pressures once again, even as it undergoes the change in the wind field. It's basically a ratios game with how much the wind speed drops in conjunction with drops in the central pressure. @LakeEffectKing when he did his first call map yesterday had the pressures decreasing down to sub 900 south of the Southern FL Peninsula but "only" had speeds around 155mph. That's because of the expected expansion of the wind field once it reaches toward the Western side of the Bahamas and has been showed by multiple areas of guidance (At least I think, because I don't speak for him, but that's my wag). Models show a sharp decrease in pressures within that same zone due to the very high TCHP (Tropical Cyclone Heat Potential) located within the area of the Eastern Straits along with a very low shear environment due to cyclone remaining far enough south of the mid latitude trough to limit the deep layer shear present toward the FL/GA border. If Irma can make it 23N 78W, she will sit in the best environment there is north of the Western Caribbean for the best chance to intensify rapidly as long as she isn't undergoing an ERC. This is what the models have been doing over and over and will likely continue to be expressed in each run up until landfall. That part of Irma is a whole nother story...

I appreciate you writing that up. I couldn't figure out where they were seeing it weakening from due to the environment they were in. You just saved me hours of reading studies. 

[Crazy4Wx]

6 minutes ago, jaxjagman said:

Worst case scenario on the Euro with that look. 

[Mountain_Patch]

Just now, Crazy4Wx said:

Worst case scenario on the Euro with that look. 

That's likely going to happen. This forum needs to stop obsessing about how it can avoid the worst case and figuring out what happens in the worst case. That way if people come here for information they won't be surprised why they extend evacuations to another zone. 

[jpeters3]

12 minutes ago, MillvilleWx said:

I wanted to expand on something this morning to explain why NHC and some models show a decrease in max winds with Irma as she heads into the Bahamas and eventually up into CONUS waters. The reason NHC and some models have the storm weakening as far as max wind speeds is due to the expected expansion of the wind field within the cyclone. As the storm gains latitude, we're going to see the size of Irma increase and the hurricane/tropical storm force wind field expand out incrementally. When the system does that, it mimics the figure skater analogy with the conservation of angular momentum. As the wind field moves out, the central area of strongest winds will also expand and the system will see a incremental drop in max wind potential. This does not mean the storm will necessarily continue to drop speeds through the entire life span of increasing in size. The system will undergo fluctuations in intensity with regards to pressure and deep convection wrapping around the eyewall will allow for system to drop pressures once again, even as it undergoes the change in the wind field. It's basically a ratios game with how much the wind speed drops in conjunction with drops in the central pressure. @LakeEffectKing when he did his first call map yesterday had the pressures decreasing down to sub 900 south of the Southern FL Peninsula but "only" had speeds around 155mph. That's because of the expected expansion of the wind field once it reaches toward the Western side of the Bahamas and has been showed by multiple areas of guidance (At least I think, because I don't speak for him, but that's my wag). Models show a sharp decrease in pressures within that same zone due to the very high TCHP (Tropical Cyclone Heat Potential) located within the area of the Eastern Straits along with a very low shear environment due to cyclone remaining far enough south of the mid latitude trough to limit the deep layer shear present toward the FL/GA border. If Irma can make it 23N 78W, she will sit in the best environment there is north of the Western Caribbean for the best chance to intensify rapidly as long as she isn't undergoing an ERC. This is what the models have been doing over and over and will likely continue to be expressed in each run up until landfall. That part of Irma is a whole nother story...

 

It's worth noting that a northward turn of a TC does not dynamically require that its wind field expand.  Likewise, TCs do not conserve angular momentum due to the excessive release of latent heat, so a widening TC does not guarantee that its maximum winds decrease.

 

I suspect that the unexpectedly low winds in model guidance for given pressures is not a result of the TC size - rather inadequate model resolution and/or pressure/wind relationship.

[dan11295]

Some decrease in wind speed is a given, based on what Millville said above. Additionally, Irma has now spent almost 48 hours as a strong cat 5 in a location where they are generally rare (North of PR) as TCHP is not quite as high.

[Radtechwxman]

14 minutes ago, MillvilleWx said:

I wanted to expand on something this morning to explain why NHC and some models show a decrease in max winds with Irma as she heads into the Bahamas and eventually up into CONUS waters. The reason NHC and some models have the storm weakening as far as max wind speeds is due to the expected expansion of the wind field within the cyclone. As the storm gains latitude, we're going to see the size of Irma increase and the hurricane/tropical storm force wind field expand out incrementally. When the system does that, it mimics the figure skater analogy with the conservation of angular momentum. As the wind field moves out, the central area of strongest winds will also expand and the system will see a incremental drop in max wind potential. This does not mean the storm will necessarily continue to drop speeds through the entire life span of increasing in size. The system will undergo fluctuations in intensity with regards to pressure and deep convection wrapping around the eyewall will allow for system to drop pressures once again, even as it undergoes the change in the wind field. It's basically a ratios game with how much the wind speed drops in conjunction with drops in the central pressure. @LakeEffectKing when he did his first call map yesterday had the pressures decreasing down to sub 900 south of the Southern FL Peninsula but "only" had speeds around 155mph. That's because of the expected expansion of the wind field once it reaches toward the Western side of the Bahamas and has been showed by multiple areas of guidance (At least I think, because I don't speak for him, but that's my wag). Models show a sharp decrease in pressures within that same zone due to the very high TCHP (Tropical Cyclone Heat Potential) located within the area of the Eastern Straits along with a very low shear environment due to cyclone remaining far enough south of the mid latitude trough to limit the deep layer shear present toward the FL/GA border. If Irma can make it 23N 78W, she will sit in the best environment there is north of the Western Caribbean for the best chance to intensify rapidly as long as she isn't undergoing an ERC. This is what the models have been doing over and over and will likely continue to be expressed in each run up until landfall. That part of Irma is a whole nother story...

Incredible post man. Thanks for the detail on that. That's what I was wondering yesterday why the winds were dropping. Makes perfect sense

[Crazy4Wx]

10 minutes ago, Mountain_Patch said:

That's likely going to happen. This forum needs to stop obsessing about how it can avoid the worst case and figuring out what happens in the worst case. That way if people come here for information they won't be surprised why they extend evacuations to another zone. 

I think for the most part people are beginning to accept this solution is most likely. The models are locked in, give or take some minor shifts. Sure a 100 mile swing east would nice...but every run that doesn't show it reduces the likelihood.

Miami to Palm Beach are basically under a 15-20 ft surge with 150mph (on the low end) winds. 

 

[JasonOH]

The winds on the SE eyewall are much weaker than last night.  This is most likely due to the ERC/attempt at ERC/whatever that was with concentric eyewalls last night. That was the weakest part when I went to bed so it bears watching it ramp back up.  There shouldn't be more than a 10-15kt drop between that and NW quad due to the direction of motion (in a perfect case).

[TPAwx]

GEFS and wind speed product

TS first two shades, hurricane third and up.

[NJwx85]

20 minutes ago, MillvilleWx said:

I wanted to expand on something this morning to explain why NHC and some models show a decrease in max winds with Irma as she heads into the Bahamas and eventually up into CONUS waters. The reason NHC and some models have the storm weakening as far as max wind speeds is due to the expected expansion of the wind field within the cyclone. As the storm gains latitude, we're going to see the size of Irma increase and the hurricane/tropical storm force wind field expand out incrementally. When the system does that, it mimics the figure skater analogy with the conservation of angular momentum. As the wind field moves out, the central area of strongest winds will also expand and the system will see a incremental drop in max wind potential. This does not mean the storm will necessarily continue to drop speeds through the entire life span of increasing in size. The system will undergo fluctuations in intensity with regards to pressure and deep convection wrapping around the eyewall will allow for system to drop pressures once again, even as it undergoes the change in the wind field. It's basically a ratios game with how much the wind speed drops in conjunction with drops in the central pressure. @LakeEffectKing when he did his first call map yesterday had the pressures decreasing down to sub 900 south of the Southern FL Peninsula but "only" had speeds around 155mph. That's because of the expected expansion of the wind field once it reaches toward the Western side of the Bahamas and has been showed by multiple areas of guidance (At least I think, because I don't speak for him, but that's my wag). Models show a sharp decrease in pressures within that same zone due to the very high TCHP (Tropical Cyclone Heat Potential) located within the area of the Eastern Straits along with a very low shear environment due to cyclone remaining far enough south of the mid latitude trough to limit the deep layer shear present toward the FL/GA border. If Irma can make it 23N 78W, she will sit in the best environment there is north of the Western Caribbean for the best chance to intensify rapidly as long as she isn't undergoing an ERC. This is what the models have been doing over and over and will likely continue to be expressed in each run up until landfall. That part of Irma is a whole nother story...

Thank you very much for this detailed and well thought out explanation. It's hard for us amateurs to sometimes wrap our heads around the notion that a hurricane can be 20mb deeper than it currently is with lower maximum sustained winds. I am guessing that if the TC was able to sit over these optimum conditions for a long enough time, eventually the winds would catch back up with the pressure.

[jpeters3]

14 minutes ago, dan11295 said:

Some decrease in wind speed is a given, based on what Millville said above. Additionally, Irma has now spent almost 48 hours as a strong cat 5 in a location where they are generally rare (North of PR) as TCHP is not quite as high.

 

Again, I don't necessarily think a decrease in wind is guaranteed.  There have been many large storms (Katrina) a similar latitudes that achieved very strong sustained winds.  The main players are going to be internal processes (eyewall replacement cycles), and vertical shear (I suspect there is a bit of Wly or NWly shear right now due to outflow restriction on that side of the storm).

[MillvilleWx]

18 minutes ago, jpeters3 said:

 

It's worth noting that a northward turn of a TC does not dynamically require that its wind field expand.  Likewise, TCs do not conserve angular momentum due to the excessive release of latent heat, so a widening TC does not guarantee that its maximum winds decrease.

 

I suspect that the unexpectedly low winds in model guidance for given pressures is not a result of the TC size - rather inadequate model resolution and/or pressure/wind relationship.

I agree 100%. This was just a generalization of why the forecast is what it is. The system could very well increase winds and expand wind field at same time and it doesn't necessarily always increase in size over time. Once the cyclone reaches Mid Latitudes, there's a greater potential for the system to expand in size and this one should given the divergent flow aloft with the orientation of the jet streak over the Northeast. I didn't want to write a book earlier, even though I'm positive I got in at least one chapter. 

[NJwx85]

Recon still supports a CAT 5

[jpeters3]

7 minutes ago, MillvilleWx said:

I agree 100%. This was just a generalization of why the forecast is what it is. The system could very well increase winds and expand wind field at same time and it doesn't necessarily always increase in size over time. Once the cyclone reaches Mid Latitudes, there's a greater potential for the system to expand in size and this one should given the divergent flow aloft with the orientation of the jet streak over the Northeast. I didn't want to write a book earlier, even though I'm positive I got in at least one chapter. 

 

I'll agree that an expanding wind field is likely once the system begins to interact with the baroclinic zone and starts undergoing ET.  Seems to me based on model guidance though that the forecast for decreasing intensity in models is (1) because they generally don't show maintained intensity Cat 5 for whatever dynamical or numerical reasons (they've been showing weakening for a day and a half), and (2) because they are fairly well anti-correlated with vertical shear (which should gradually increase over the next few days).  Human forecasts (NHC) have shown decreasing intensity in accordance with model guidance, and the low statistical likelihood that TCs maintain 150 kt + intensity for an extended period of time.
 

[NJwx85]

It's worth noting that the 06z HMON shows Irma temporarily struggling a bit over the next day or so before ramping back up to Category 5 tomorrow night. Peaks back out with 175mph winds near the FL straights before coming very close to landfall near Palm Beach as a cat 5.