Atlantic Tropical Action 2011

[am19psu]

West good, East bad.

Yeah, that goes back to the tropopause height that Phil (and others) have mentioned. Westerly QBO leads to a higher tropopause (and therefore more MPI) from thermal wind arguments

Back when sub-Saharan rainfall was also a predictor.

The latest research shows that sub-Saharan rainfall is a significant predictor when the Atlantic is cooler than normal/shear is higher than normal, but is not significant in warm/low shear regimes.

[turtlehurricane]

It's a sign of the QBO phase shift. The westerly anomalies are steadily weakening and the easterlies have started to descend over the last month. At this rate the overall characteristic of the stratosphere will be dictated by easterly vertical shear by the autumn.

Interesting... might be the end of this active TC period if that's the case.

[phil882]

All of the research I've seen shows basically no significant effect from wind stress at the tropopause, either by easterly winds decreasing shear or westerly winds increasing shear.

Yeah, that goes back to the tropopause height that Phil (and others) have mentioned. Westerly QBO leads to a higher tropopause (and therefore more MPI) from thermal wind arguments

Yea I always wondered about that... I would feel that overshooting tops don't contribute much to latent heat flux considering the ambient environment of the stratosphere contains very little moisture despite saturation thanks to the low temperatures. It makes much more sense that west QBO's are favorable because there is a larger tropospheric column, allowing for a warmer temperatures at higher heights in the atmosphere, which will allow for more moisture, and hence increased latent heat due to deeper convection.

In any event... looks like the QBO might not be in our favor this year.

Interesting... might be the end of this active TC period if that's the case.

Consiering the QBO flips directions every 1.5-2 years... I doubt it has much impact on the decadal cycle of tropical cyclone activity.

[am19psu]

Yea I always wondered about that... I would feel that overshooting tops don't contribute much to latent heat flux considering the ambient environment of the stratosphere contains very little moisture despite saturation thanks to the low temperatures. It makes much more sense that west QBO's are favorable because there is a larger tropospheric column, allowing for a warmer temperatures at higher heights in the atmosphere, which will allow for more moisture, and hence increased latent heat due to deeper convection.

In any event... looks like the QBO might not be in our favor this year.

Not sure if it was a typo or not, but you mean colder temps aloft. Hurricane thermodynamics can be approximated to a Carnot engine, so colder exhaust temps (i.e. the tropopause) means more energy available to do work.

[wxmx]

About the QBO... It's current progression is something in between 1995 and 2005, so I'm not that worried.

[OKpowdah]

Hmm that sounds like it would have a general negative impact on TC's due to the lower tropopause, meaning deep convection won't attain as high of an altitude than under a westerly QBO configuration. In addition, an east based QBO will provide additional easterly shear above the troposphere, so what overshooting tops do occur will likely not be as vertically stacked.

1) Yes, the lowered tropopause would suppress deep convection and tropical cyclone development.

2) QBO-induced shear at the tropopause is very small at 10-15 degrees and so that aspect is negligible when it comes to long range TC forecasting.

The QBO has a greater relation to shear near the tropopause at the equator -- which is one factor relating it to ENSO

[k***]

the QBO....yawn

[OKpowdah]

About the QBO... It's current progression is something in between 1995 and 2005, so I'm not that worried.

I think the QBO is significantly under-analyzed sometimes. The QBO is too often treated like a one dimensional index, which it is NOT (e.g. a QBO near 0 is NOT "weak"). I would rather see the index analyzed as a phase and amplitude, like the MJO.

This year, the QBO is completely different from 2005, so that comparison is completely irrelevant. 1995 is definitely closer, but is actually about 60 degrees out of phase with the current QBO progression

[OKpowdah]

the QBO....yawn

[k***]

Every time I hear about it there is a totally different interpretation of its significance...this discussion and the one a little while further back about its influence being modulated by PDO phase lead me to just ignore it as something I think about in some deterministic sense for the hurricane season, since it's pretty obvious that we dont have a great understanding of how it all works.

[Cyclonicjunkie]

Wake me up in July when the first Atlantic cyclone gets a name

[OKpowdah]

Every time I hear about it there is a totally different interpretation of its significance...this discussion and the one a little while further back about its influence being modulated by PDO phase lead me to just ignore it as something I think about in some deterministic sense for the hurricane season, since it's pretty obvious that we dont have a great understanding of how it all works.

It's sad, but that's a pretty common reaction among the meteorological community. I dismissed the QBO for a while; until ~3 years ago, then HM's discussions got me more interested in the stratosphere.

The thing is that the QBO has the most periodic oscillation of any atmospheric index discovered/defined so far. So understanding its ramifications can go a long ways to improving long range forecasting

[k***]

It's sad, but that's a pretty common reaction among the meteorological community. I dismissed the QBO for a while; until ~3 years ago, then HM's discussions got me more interested in the stratosphere.

The thing is that the QBO has the most periodic oscillation of any atmospheric index discovered/defined so far. So understanding its ramifications can go a long ways to improving long range forecasting

just because it has the HM stamp of approval doesn't make it not diffuse gobbledygook

[OKpowdah]

just because it has the HM stamp of approval doesn't make it diffuse gobbledygook

true; he usually embraces the diffuse gobbledygook!

[Supercane]

This year, the QBO is completely different from 2005, so that comparison is completely irrelevant. 1995 is definitely closer, but is actually about 60 degrees out of phase with the current QBO progression

How would transitioning to an easterly QBO be any less favorable than a stronger, ascending easterly QBO like we saw in 2005?

[phil882]

Not sure if it was a typo or not, but you mean colder temps aloft. Hurricane thermodynamics can be approximated to a Carnot engine, so colder exhaust temps (i.e. the tropopause) means more energy available to do work.

Ahh yes, I guess its the increased contrast between the warm sea surface temperatures and the colder atmosphere in the upper levels increases the total APE for the barotropic systems.

This might be a dumb question... but when the tropopause is higher up in altitude, does it bottom out at a colder temperature? For some reason I had always thought there was some general threshold temperature value that the upper troposphere reaches before becoming isothermal at the tropopause, and the added altitude in summer was just the fact that the surface was warmer, and taking a dry adiabat to the same temperature value at the tropopause takes additional height.

[am19psu]

This might be a dumb question... but when the tropopause is higher up in altitude, does it bottom out at a colder temperature? For some reason I had always thought there was some general threshold temperature value that the upper troposphere reaches before becoming isothermal at the tropopause, and the added altitude in summer was just the fact that the surface was warmer, and taking a dry adiabat to the same temperature value at the tropopause takes additional height.

Yes, the tropopause is colder when it is higher. Warmer SSTs provide more energy for convective mixing in the troposphere, so that parcel you're lifting moist adiabatically (in the deep tropics) has a bit more energy to ascend higher than it otherwise would and has a bit more energy to overshoot and mix the tropopause higher. Here are the 0z soundings from Guadeloupe and Guam to illustrate the difference (since the WPAC is always warmer than the Atlantic).

[wxmx]

I think the QBO is significantly under-analyzed sometimes. The QBO is too often treated like a one dimensional index, which it is NOT (e.g. a QBO near 0 is NOT "weak"). I would rather see the index analyzed as a phase and amplitude, like the MJO.

This year, the QBO is completely different from 2005, so that comparison is completely irrelevant. 1995 is definitely closer, but is actually about 60 degrees out of phase with the current QBO progression

My comment was tongue in cheek, mostly, though, technically we are indeed in a progression in between 1995 and 2005 (not comparing to any of those, just where we are right now).

My research shows that the QBO has it's main effects in the tropical Atlantic (the closer to the equator, the higher the correlation), with the correlation dwindling down near Central America. So if we have healthy but non developing waves south of Cape Verde, but blooming out near the Caribbean, so be it.

[am19psu]

2010 NHC forecast verification report.

http://www.nhc.noaa.gov/verification/pdfs/Verification_2010.pdf

Here are my general takeaways from the report:

• As we all suspected, the upgrade to the GFS in July was a significant improvement to its skill. You can see the difference between the EPAC and NATL verification stats for the GFSI. The EPAC season was heavily influenced by the pre-upgrade GFS while the Atlantic statistics are mainly post-upgrade.
  
• Using a GFS/ECM blend was the best forecasting tool available in general last year.
  
• NOGAPS is a terrible model and has been dropped from TVCN in the Atlantic. There are now two variable consensus models, TVCA and TVCE. TVCA is run in the Atlantic and has at least two of the following: GFSI, EGRI, GHMI, HWFI, GFNI, EMXI. TVCE is run in the EPAC and includes all of the aforementioned models plus NGPI.
  
• HWRF remains a garbage model for both track and intensity. It is one of the biggest busts in numerical modeling history.
  
• Forecasters and the global models continue to exhibit a north and east bias in their track forecasts, generally due to recurving storms too quickly.
  
• The GFS Ensemble is useless as a track predictor. Hopefully, once the GEFS upgrades to the new version of the Op GFS, it will begin to show skill
  
• Unless rapid intensification is suspected, forecasters should rarely stray from ICON.
  
• We still know next to nothing about intensity forecasting. The current state of intensity forecasting is similar to track forecasting in the 80s, when statistical-dynamical models were the best predictors. Discoveries in both physics (intensification processes) and modeling (better parameterization of eyewall processes?) will be needed to increase intensity forecasting skill.
  
• There is nothing on the horizon in 2011 that suggests any meaningful increase in intensity forecasting skill due to higher resolution models or models with better physics.
  
• NHC genesis probabilities are highly skillful at the extremes of the spectrum, but the intermediate band (40-70%), while still exhibiting some skill, is less so.
  

[wxmx]

Here are my general takeaways from the report:

• As we all suspected, the upgrade to the GFS in July was a significant improvement to its skill. You can see the difference between the EPAC and NATL verification stats for the GFSI. The EPAC season was heavily influenced by the pre-upgrade GFS while the Atlantic statistics are mainly post-upgrade.
• Using a GFS/ECM blend was the best forecasting tool available in general last year.
• NOGAPS is a terrible model and has been dropped from TVCN in the Atlantic. There are now two variable consensus models, TVCA and TVCE. TVCA is run in the Atlantic and has at least two of the following: GFSI, EGRI, GHMI, HWFI, GFNI, EMXI. TVCE is run in the EPAC and includes all of the aforementioned models plus NGPI.
• HWRF remains a garbage model for both track and intensity. It is one of the biggest busts in numerical modeling history.
• Forecasters and the global models continue to exhibit a north and east bias in their track forecasts, generally due to recurving storms too quickly.
• The GFS Ensemble is useless as a track predictor. Hopefully, once the GEFS upgrades to the new version of the Op GFS, it will begin to show skill
• We still know next to nothing about intensity forecasting. The current state of intensity forecasting is similar to track forecasting in the 80s, when statistical-dynamical models were the best predictors. Discoveries in both physics (intensification processes) and modeling (better parameterization of eyewall processes?) will be needed to increase intensity forecasting skill.
• Unless rapid intensification is suspected, forecasters should rarely stray from ICON.
• There is nothing on the horizon in 2011 that suggests any meaningful increase in intensity forecasting skill due to higher resolution models or models with better physics.
• NHC genesis probabilities are highly skillful at the extremes of the spectrum, but the intermediate band (40-70%), while still exhibiting some skill, is less so.

citation needed

Posted something similar at DBM.

[OKpowdah]

How would transitioning to an easterly QBO be any less favorable than a stronger, ascending easterly QBO like we saw in 2005?

You have to look at the whole vertical profile. Also, there's no such thing as an "ascending" easterly QBO. Wind anomalies descend through the stratosphere.

See my other posts too. Again, the QBO should NOT be treated as a one dimensional index as it so often is. The "transition" to an easterly QBO that you note yields easterly vertical shear through the stratosphere, at the equator. Which through the thermal wind relationship, results in an anomalously warm stratosphere ~10-15 degrees off the equator. A warmer stratosphere is linked with lower tropopause heights, which limits convective potential and TC development.

In 2005, we were squarely within a strong easterly phase of the QBO. This did present net easterly shear in the stratosphere for at least the first half of the season. By October, we saw a switch to net westerly shear. Note that most of the activity that year was relatively "high latitude", away from strongest influence of the QBO induced anomalies.

[phil882]

Yes, the tropopause is colder when it is higher. Warmer SSTs provide more energy for convective mixing in the troposphere, so that parcel you're lifting moist adiabatically (in the deep tropics) has a bit more energy to ascend higher than it otherwise would and has a bit more energy to overshoot and mix the tropopause higher. Here are the 0z soundings from Guadeloupe and Guam to illustrate the difference (since the WPAC is always warmer than the Atlantic).

Excellent... learn something new everyday! Less than 2 months till the start of hurricane seasons and I am itching to get started!

[Ed Lizard]

[rainstorm]

The whole country is doomed. Especially Virginia!

[/rainstorm]

[am19psu]

Using April GoM SSTAs for any seasonal forecast is foolish.

[Scott747]

I love those maps.

Modern day etch a sketch rocks!

[HurricaneJosh]

I love those maps.

Modern day etch a sketch rocks!

Oh, hey!

You punishin' me with silence?

[Scott747]

Oh, hey!

You punishin' me with silence?

Carla was a low end four at landfall.

Metz backs me up.

[am19psu]

Carla was a low end four at landfall.

Metz backs me up.

Uh oh. Are the hurtyhurtz bigger in Texas too?

[Srain]

Uh oh. Are the hurtyhurtz bigger in Texas too?

Don't mess with Carla...

[am19psu]

Don't mess with Carla...

I've a feeling you're not going to like Josh's upcoming new thread.