Atlantic Tropical Action 2013

[Ed Lizard]

What Mike said.

 

Don't 5 post me bro, but local Texas thread and KHOU-TV 11 (KHOU stands for Houston) forum, storms in the Gulf associated with a 500 mb and above upper low- developed by Crazy Uncle Canadian and hits Lake Charles in 5 days as a high end TS or low end hurricane.  The CMC has been on the upper low that was East of Bermuda 10 days ago to develop off and on about 10 days now and hit Louisiana, or occasionally SE Texas, so at least the model is consistent with itself.

 

I wouldn't post this in August or if we had even a lemon.

 

Nobody can ever accuse me again of being an anti-weenie.

[Srain]

^^

 

Surface analysis suggests a trough axis SE of Vermillion Bay and over the Bahamas. While the Gulf is unsettled and PW's have increased to 2+ inches to that of what is a more typical summertime pattern that we have not seen over the past few years, development is unlikely other than increased rain and storm chances along Gulf Coastal Mexico, Texas and Louisiana. Once we get into August and the MJO becomes more favorable, the Western Caribbean and Gulf will be an area to watch for development, IMO. The monsoonal trough is certainly showing its hand and any TC development would tend to be closure to the Pacific Coast of Mexico in the EPAC in the near term. Give it another month for the NATL Basin and my hunch is the Western part of the Basin will be the area to monitor for TC genesis. The 'Carla Cradle' is where my money is...

 

[TropicalAnalystwx13]

The UKMET has changed from a forecast of cool-Neutral conditions for the ASO period last month to a forecast of a moderate La Nina for the ASO period this month. Above-average precipitation and sea surface temperatures across the MDR/Caribbean, plenty of ridging over southeastern Canada.

 

SST:

 

[TropicalAnalystwx13]

Invest 97L:

 

[icebreaker5221]

Invest 97L:

 

 

 

Model analyses e.g. RAP showing this invest along a north-south oriented axis of elevated 850 mb vorticity.  All day this has primarily been an axis of speed-shear - strong southerlies to the east with near calm winds to the west - with low okubo-weiss parameters.  We don't know for sure what's going on beneath the convection but most recent ASCAT passes don't indicate much. 

 

Whether further organization occurs or not, it will most likely move quickly inland into MX with the strong background easterly steering. 

[TropicalAnalystwx13]

From the NHC --

We've gotten at least one phone call from someone wondering why guidance models were run on "Invest AL97" today, even though we're not mentioning anything in our Tropical Weather Outlook. This invest was started purely for testing purposes in connection with the planned transition to the new NWS supercomputer next week. Once the testing has been completed, the invest AL97 will be deactivated. 

We know that people tend to follow these invest systems more closely now than in the past, but this should serve as a reminder that invests can be opened for a variety of reasons, not all of them meteorological.

[icebreaker5221]

From the NHC --

We've gotten at least one phone call from someone wondering why guidance models were run on "Invest AL97" today, even though we're not mentioning anything in our Tropical Weather Outlook. This invest was started purely for testing purposes in connection with the planned transition to the new NWS supercomputer next week. Once the testing has been completed, the invest AL97 will be deactivated. 

We know that people tend to follow these invest systems more closely now than in the past, but this should serve as a reminder that invests can be opened for a variety of reasons, not all of them meteorological.

 

Hmm, makes sense.  As I mentioned in my previous post, it's more of a horizontal shear-zone with embedded convection than anything else.  I figured they were just fishing for 0% or 10% areas in a slow pattern. 

[hurricaneman]

The pattern is slow because the MJO is in a dead phase and stable air has taken over the atlantic but the MJO probably will be in favorable phase 2 the last week of July or first week of August so the first week of August things should start to develop in earnest

[jordanwx]

There is no such thing as a retrograding MJO.

What prevents the MJO from moving west? Do we even fully understand what causes it to move east?

 

Mike Ventrice, if you see this, any response explaining the forcing mechanisms which move the MJO east would be appreciated.

[Ed Lizard]

What prevents the MJO from moving west? Do we even fully understand what causes it to move east?

 

Mike Ventrice, if you see this, any response explaining the forcing mechanisms which move the MJO east would be appreciated.

 

I know the MJO propagates Eastward (for one thing, Wiki says so ) but I'd love a simplified for a science savvy but not met trained person why the MJO does propagate the way it does.

[jordanwx]

I know the MJO propagates Eastward (for one thing, Wiki says so ) but I'd love a simplified for a science savvy but not met trained person why the MJO does propagate the way it does.

Yea, I know that. I just want to know why it does so and what's preventing it from moving the other way. I know it's phase velocity can change, so what's preventing that from going negative?

[icebreaker5221]

What prevents the MJO from moving west? Do we even fully understand what causes it to move east?

 

Mike Ventrice, if you see this, any response explaining the forcing mechanisms which move the MJO east would be appreciated.

 

 

I know the MJO propagates Eastward (for one thing, Wiki says so ) but I'd love a simplified for a science savvy but not met trained person why the MJO does propagate the way it does.

 

 

There is not precise mathematical formulation for the MJO the way there is for Rossby waves and Kelvin waves.  Since you can't derive a phase velocity or group velocity from a system of equations, there is no precise answer to this question.  The 5 m/s eastward propagation of the MJO is just an empirical calculation.  But, by definition, it cannot be stationary or move westward.  I'd be interested to hear Mike's answer tho since it's more his research area. 

[phil882]

There is not precise mathematical formulation for the MJO the way there is for Rossby waves and Kelvin waves.  Since you can't derive a phase velocity or group velocity from a system of equations, there is no precise answer to this question.  The 5 m/s eastward propagation of the MJO is just an empirical calculation.  But, by definition, it cannot be stationary or move westward.  I'd be interested to hear Mike's answer tho since it's more his research area. 

 

Yep... Some of the big names in MJO research (Paul Roundy, Chidong Zang, George Kaladis) have gone on record to say we still really don't know what the MJO is since it can't simply be derived from the shallow water equations like Kelvin and mixed Rossby Gravity Waves can.

 

However, some research is starting to suggest that the MJO could merely be a combination of a bunch of different wavelength Kelvin waves, which might help to explain the eastward propagation with time. When Kelvin waves become convectively coupled, they slow down substantially relative to the mathematical "dry" kelvin waves which zip along around 50 m/s. Its not that much of a stretch to call the MJO a supermassive Kelvin wave that propagates at very slow speeds (5 m/s). Moreover, the MJO has a tilted vertical structure similar to Kelvin waves.

[Mike.Ventrice]

What prevents the MJO from moving west? Do we even fully understand what causes it to move east?

 

Mike Ventrice, if you see this, any response explaining the forcing mechanisms which move the MJO east would be appreciated.

 

 

There is not precise mathematical formulation for the MJO the way there is for Rossby waves and Kelvin waves.  Since you can't derive a phase velocity or group velocity from a system of equations, there is no precise answer to this question.  The 5 m/s eastward propagation of the MJO is just an empirical calculation.  But, by definition, it cannot be stationary or move westward.  I'd be interested to hear Mike's answer tho since it's more his research area. 

 

 

Yep... Some of the big names in MJO research (Paul Roundy, Chidong Zang, George Kaladis) have gone on record to say we still really don't know what the MJO is since it can't simply be derived from the shallow water equations like Kelvin and mixed Rossby Gravity Waves can.

 

However, some research is starting to suggest that the MJO could merely be a combination of a bunch of different wavelength Kelvin waves, which might help to explain the eastward propagation with time. When Kelvin waves become convectively coupled, they slow down substantially relative to the mathematical "dry" kelvin waves which zip along around 50 m/s. Its not that much of a stretch to call the MJO a supermassive Kelvin wave that propagates at very slow speeds (5 m/s). Moreover, the MJO has a tilted vertical structure similar to Kelvin waves.

 

Hi guys.. these questions that you ask are all very good ones. So unfortunately the only way that I could illustrate the reason behind why the MJO only moves to the east will be very scientific, and thus may be a bit hard to follow. There's a particular method that allows us to monitor tropical waves, called wavenumber and frequency filtering. This is what I do to get all of my real-time plots running to monitor the MJO or Kelvin waves. Now this is DIFFERENT to the standard real-time multivariate MJO index, for there is no wavenumber-frequency filter but instead an EOF application. 

 

lets get back to why the MJO has been declared an eastward propagating only phenomena. If you look at the power of Outgoing long wave radiation using a wavenumber-frequency diagram (Kiladis et al. 1999), you will see many different power peaks for both antisymmetric waves, and symmetric waves. There symmetric waves are known to be equatorial Rossby waves, Kelvin waves, and the MJO. Now there's a whole lot that goes into making this figure, where you have to remove an estimated red-background specturm.. I won't get into it. But there's a vertical dashed black line in the middle of the figure. Anything to the right of that line only propagates to the EAST, anything to left of the line propagates to the west. The y-axis represents your period, or time, where faster moving waves are at the top of the figure, and slower moving ones are at the bottom. So the increased power at the bottom left is the equatorial Rossby wave band. The increased power on the middle-right is the Kelvin band, which is outlined by blue lines. The strongest signal is at the bottom-right, close to the center- this is the MJO band. It is at wavenumbers 0-4, periods 30-96 days. If you look immediately to the left, you do not see any significant power for these wavenumbers at the same period (with exception of some bleeding I guess you could call it of the MJO signal to the left of the black-dashed line which is a fake result created by removing an estimated, very smoothed redbackground spectrum. You do see the ERW signal at higher wavenumbers and periods, however which is a real signal.

 

     

 

Now as Phil stated above, we are not really sure what the MJO truely is. We have some ideas, some theories. What we do know is that MJO is baroclinic in circulation and often couples to large-scale variations of convection in the tropics. There are many tropical extratropical interactions that takes place and often composes the anatomy of the MJO. Paul Roundy's most recent research, that matches my observations, is that the MJO is often composed of a signal, very strong, convectively coupled atmospheric Kelvin wave (which propagates to the East like the MJO). 

 

Now the reason why people seperate CCKWs with the MJO is because there is a gap of power between the MJO and Kelvin band at around 20 days, wavenumber 1. Paul's research has shown this gap does not exist over the warm pools, where convection is more prominent over the equator. The gap is mainly derived from the Western Hemisphere, where typically the MJO speeds up to more of a CCKW phase speed.

 

Now there's alot here and more to be talked about but I have some stuff I need to take care of at work- I hope this helps! 

[Ed Lizard]

'Dry' non-coupled Kelvin waves move at 50 m/s? 

 

That just seems awfully fast.

 

ETA:  How does the Euro resolve the not well understood factors such that it forecasts the MJO better, and, why wouldn't statistical analysis (I believe CPC has some) for the MJO not work fairly well, even if it does slow down and speed up?

 

[Ed Lizard]

Posted by the statistical specialist on the KHOU-TV 11 weather forum (KHOU has stood for Houston for 60 years), inland warm core tropical cyclones.

 

I do not have the knowledge base to either agree with or refute the concepts.

 

 

http://www.nasa.gov/content/goddard/brown-ocean-can-fuel-inland-tropical-cyclones/#.Ueal7kDbiDe

 

Based on TS Erin.

[am19psu]

Hi guys.. these questions that you ask are all very good ones. So unfortunately the only way that I could illustrate the reason behind why the MJO only moves to the east will be very scientific, and thus may be a bit hard to follow. There's a particular method that allows us to monitor tropical waves, called wavenumber and frequency filtering. This is what I do to get all of my real-time plots running to monitor the MJO or Kelvin waves. Now this is DIFFERENT to the standard real-time multivariate MJO index, for there is no wavenumber-frequency filter but instead an EOF application. 

 

lets get back to why the MJO has been declared an eastward propagating only phenomena. If you look at the power of Outgoing long wave radiation using a wavenumber-frequency diagram (Kiladis et al. 1999), you will see many different power peaks for both antisymmetric waves, and symmetric waves. There symmetric waves are known to be equatorial Rossby waves, Kelvin waves, and the MJO. Now there's a whole lot that goes into making this figure, where you have to remove an estimated red-background specturm.. I won't get into it. But there's a vertical dashed black line in the middle of the figure. Anything to the right of that line only propagates to the EAST, anything to left of the line propagates to the west. The y-axis represents your period, or time, where faster moving waves are at the top of the figure, and slower moving ones are at the bottom. So the increased power at the bottom left is the equatorial Rossby wave band. The increased power on the middle-right is the Kelvin band, which is outlined by blue lines. The strongest signal is at the bottom-right, close to the center- this is the MJO band. It is at wavenumbers 0-4, periods 30-96 days. If you look immediately to the left, you do not see any significant power for these wavenumbers at the same period (with exception of some bleeding I guess you could call it of the MJO signal to the left of the black-dashed line which is a fake result created by removing an estimated, very smoothed redbackground spectrum. You do see the ERW signal at higher wavenumbers and periods, however which is a real signal.

 

     

 

Now as Phil stated above, we are not really sure what the MJO truely is. We have some ideas, some theories. What we do know is that MJO is baroclinic in circulation and often couples to large-scale variations of convection in the tropics. There are many tropical extratropical interactions that takes place and often composes the anatomy of the MJO. Paul Roundy's most recent research, that matches my observations, is that the MJO is often composed of a signal, very strong, convectively coupled atmospheric Kelvin wave (which propagates to the East like the MJO). 

 

Now the reason why people seperate CCKWs with the MJO is because there is a gap of power between the MJO and Kelvin band at around 20 days, wavenumber 1. Paul's research has shown this gap does not exist over the warm pools, where convection is more prominent over the equator. The gap is mainly derived from the Western Hemisphere, where typically the MJO speeds up to more of a CCKW phase speed.

 

Now there's alot here and more to be talked about but I have some stuff I need to take care of at work- I hope this helps!

Good post, Mike. It's a lot easier to refute the contrapositive in one sentence than to actually explain why it's the case.

[am19psu]

'Dry' non-coupled Kelvin waves move at 50 m/s? 

 

That just seems awfully fast.

Think about how fast they move across the entire Atlantic basin. On the order of 2-3 days.

ETA:  How does the Euro resolve the not well understood factors such that it forecasts the MJO better, and, why wouldn't statistical analysis (I believe CPC has some) for the MJO not work fairly well, even if it does slow down and speed up?

Just because something isn't well described by the shallow water equations doesn't mean it isn't subject to the primitive equations of motion. There is no "Kelvin wave parameterization" in the models, just like there is no "MJO parameterization," but they still follow the basic physics of equatorially-trapped, moist waves.

[am19psu]

P.S. The reason why the Euro does so well with forecasting the MJO is because it has a dynamic ocean and the best convective physics.

[dtk]

P.S. The reason why the Euro does so well with forecasting the MJO is because it has a dynamic ocean and the best convective physics.

 

 

The dynamic ocean (i.e. full dynamic coupling to an ocean GCM, NEMO) is part of the monthly/seasonal forecasts, and not the high resolution deterministic.   The deterministic run is only coupled to an interactive wave model (called WAM).  I'm sure this is documented on their website.

 

I'm not sure about the EPS....I'd have to do some digging.

 

Coupling to a dynamic ocean certainly helps, which is why the CFSv2 (dynamically coupled to MOM4) has much more skill in predicting the MJO than say our GEFS (which is uncoupled).

[am19psu]

The dynamic ocean (i.e. full dynamic coupling to an ocean GCM, NEMO) is part of the monthly/seasonal forecasts, and not the high resolution deterministic.   The deterministic run is only coupled to an interactive wave model (called WAM).  I'm sure this is documented on their website.

 

I'm not sure about the EPS....I'd have to do some digging.

 

Coupling to a dynamic ocean certainly helps, which is why the CFSv2 (dynamically coupled to MOM4) has much more skill in predicting the MJO than say our GEFS (which is uncoupled).

Yeah, sorry, I should have clarified that I was talking about the Euro weeklies/seasonal model. They've shown skill out to 20 days, IIRC.

The Euro ensemble is better than the GEFS, but still sucks after about 7-8 days.

[HurricaneFrances04]

Posted by the statistical specialist on the KHOU-TV 11 weather forum (KHOU has stood for Houston for 60 years), inland warm core tropical cyclones.

 

I do not have the knowledge base to either agree with or refute the concepts.

 

 

http://www.nasa.gov/content/goddard/brown-ocean-can-fuel-inland-tropical-cyclones/#.Ueal7kDbiDe

 

Based on TS Erin.

 

Tropical storm Fay could be another example.

 

[Ed Lizard]

Tropical storm Fay could be another example.

 

I will say, I suspect Florida has higher soil mean moisture content, more percentage of area with a liquid water surface (no Everglades in Oklahoma) and much flatter terrain than Texas or Oklahoma.

[dtk]

Yeah, sorry, I should have clarified that I was talking about the Euro weeklies/seasonal model. They've shown skill out to 20 days, IIRC.

The Euro ensemble is better than the GEFS, but still sucks after about 7-8 days.

I only mentioned for clarification....no apology necessary.  We are moving toward dynamically coupled models (ocean/land/atmosphere) for short/medium-range prediction (deterministic and ensemble), though we aren't quite there yet.

 

I plead the 5th on the GEFS.

[jordanwx]

Thanks for the responses, guys. So since we don't completely understand the MJO, nor the physical equations the MJO follows, we can't really say why it travels east and not west. However, by definition, the MJO travels east. Interesting stuff.

[am19psu]

Thanks for the responses, guys. So since we don't completely understand the MJO, nor the physical equations the MJO follows, we can't really say why it travels east and not west. However, by definition, the MJO travels east. Interesting stuff.

To be clear, the MJO manifests out of the basic primitive equations, which is why it exists in model simulations. It exhibits Kelvin wave-like behavior, but isn't predicted by the shallow water equations. But the shallow water equations are just simplifications of the primitive equations. There is likely some influence of global circulations like the Hadley Cell involved in its genesis and restoring forces as well, we just haven't discovered it yet.

[hurricaneman]

We may have a tropical development for the first week of August, this possible storm per the GFS doesn't start to really develop until then and now the Euro is starting to develop something in the 240 hr timeframe also so we might have the first true Cape Verde system of the year if the models are right and the fact that the MJO will probably be in phase 2 would also be a plus for development now the only thing that could hamper development is if the trade winds don't slow down and the instability stays low, and the shear stays higher than normal

[am19psu]

Find the period and comma keys.

[Marion_NC_WX]

Posted by the statistical specialist on the KHOU-TV 11 weather forum (KHOU has stood for Houston for 60 years), inland warm core tropical cyclones.

 

I do not have the knowledge base to either agree with or refute the concepts.

 

 

http://www.nasa.gov/content/goddard/brown-ocean-can-fuel-inland-tropical-cyclones/#.Ueal7kDbiDe

 

Based on TS Erin.

 

 

I remember Danny (1997) as it was exiting the Southeast began to strengthen over The Great Dismal Swamp in far Eastern North Carolina...

[Visiteur]

At the risk of straying off-topic here, I remember a presentation from (yet another) Albany guy who did a lot of research with intensity increases in TCs after landfall:

 

http://www.atmos.albany.edu/student/mpotter/research.html

 

Research tied intensity increases with TC Danny to interactions with an upper-level midlatitude jet - diabatic heating impacts, negative PV advection, and frontogenesis in the divergent equatorward entrance region of the jet. Too bad his written thesis isn't online.