Atlantic Tropical Action 2011 - Part IV

[WishingForWarmWeather]

They do have five slots, but most of the time there isn't a need to run GFDL/HWRF simulations on five different storms (obviously). Unused slots from hurricane model simulations are designated to be filled with the HiresWindow runs (NMM/ARW); I believe (in other words, if there are enough hurricane runs, the HiresW runs don't get completed for that given cycle).

So what happens when there are 5 hurricanes at one time, and another is developing close enough that it needs to have floaters and things designated to it? They just have to wait? Has that ever happened before?

[Martin]

I love tracking these systems, but this one has me slightly on edge, this could be a system that is talked about for ages if the GFS run happens to come true, and bacause of the consistancy of the runs, it may happen

If I had a dollar for every time I heard that....

[WishingForWarmWeather]

My dear little children-- I'd like for you all to settle down, stop throwing food, and play nice!

No more fighting. Thank you.

Sorry, but it's really frustrating. I come here to read and to learn, and ask questions when necessary; comment when I want to. I find it very obnoxious, irritating and unfair that some people find themselves above others and think it's okay to be completely rude at times that are completely unwarranted. I'm sure many others feel the same as I do, and to be truthful I wouldn't doubt that it does discourage many from posting.

Idk, many people seem to adore you, maybe you should set them straight every once in awhile.

[WishingForWarmWeather]

The Central Atlantic wave is considerably ahead of 93L in terms of its vorticity and convective structure at the same location, leading me to believe that it will develop somewhat more quickly. Another potential contributing factor is the interaction between this wave and an upcoming Kelvin wave passage across the Atlantic basin. On August 15, a Kelvin wave (green outlines) was diagnosed near 180W in the Pacific, while another was around 80-90W and possibly assisted in the current attempt at TC genesis by 93L:

This KW currently over the Pacific is also diagnosed by Roundy's updated methodology. Given typical Kelvin wave propagation speeds, this should cross the easterly wave's longitude somewhere around August 20-22, resulting in enhanced TC genesis probabilities around and for a couple days after this time frame. This occurs just as the wave is entering warmer SSTs west of 50W, and the influence of the environmental dry air should gradually wane as well. To sum up, I think this has a pretty high chance of developing sometime between August 20-23. I think the GFS right now somewhat too quick with genesis in its latest runs, but I don't think it'll perform as horribly as it did with 92L and 93L given the boost by this KW.

Given the delayed genesis and the strength of the ridging to its north over the next 4-5 days, I think this has a high chance of impacting the Lesser Antilles. The ridge does weaken somewhat after next Monday, which will allow for this to gain some latitude. I do not think this has any chance of crashing into South America, as the ridging is not strong enough and the initial starting point is too far north for that to happen.

Thank you for your observations, you certainly seemed to have thought this out. Can you explain to me what a Kelvin Wave is, please?

[WishingForWarmWeather]

There was a post asking for an explanation on KW waves and TC genesis which is no longer here. But to answer the question as simply as I can:

Atmospheric Kelvin waves are eastward moving waves of alternating suppressed and enhanced convection in the tropics. They are comprised of zonal wind anomalies, with converging wind anomalies near and to the east of the convection. The phase of the KW that has westerly low-level wind anomaly also has upper-level easterly anomalies, and vice versa.

KWs can influence TC genesis by affecting the large-scale environment through several mechanisms: 1) shear anomalies, 2) low-level vorticity due to zonal wind anomalies, 3) moisture anomalies, 4) large-scale subsidence or ascent. In the Atlantic, recent research has suggested that TC genesis is about twice likely to occur during to a few days after a Kelvin wave passage. By no means are Kelvin waves the only influence on TC genesis, but they can be important at times.

Here's a relevant poster on the topic (large file): http://grip.nsstc.na..._Thorncroft.pdf

Thank you, I had just asked this. Appreciate the explanation. I've never heard of a KW, is this a relatively new discovery, or have I just never heard of one? Are they rare? Do they happen every year, every month?

[Scott747]

If I had a dollar for every time I heard that....

You could say that for his entire post.

Every year there are multiple model runs that show the 'big one' and the proclamations begin.....

[cdawgga1]

Thank you for your observations, you certainly seemed to have thought this out. Can you explain to me what a Kelvin Wave is, please?

I asked the same thing earlier and he posted a good explanation and link for you. It is a few posts back.

[Dunkman]

So what happens when there are 5 hurricanes at one time, and another is developing close enough that it needs to have floaters and things designated to it? They just have to wait? Has that ever happened before?

I remember it happening at least once...I want to say they tasked a pacific floater to it but I may be imagining things.

[cdawgga1]

The University of Georgia has a great slideshow depicting the history of Georgia hurricanes and their paths. Even though my state hasn't had any real landfalls in a long time except David in 79, there were more paths than I expected. Check out the link.My link

[WishingForWarmWeather]

I asked the same thing earlier and he posted a good explanation and link for you. It is a few posts back.

Yes, I saw that already and thanked him. Thanks though.

[LithiaWx]

Good bye Keys

That 00Z model snapshot shows a 989 Low. How is that good bye keys? It could be stronger or weaker, but no model is showing a devastating storm at this point.....

[Stebo]

That 00Z model snapshot shows a 989 Low. How is that good bye keys? It could be stronger or weaker, but no model is showing a devastating storm at this point.....

Global models grossly underdo the strength of a tropical system typically.

[cdawgga1]

That 00Z model snapshot shows a 989 Low. How is that good bye keys? It could be stronger or weaker, but no model is showing a devastating storm at this point.....

IF it makes into the GOM the very warm SST there could be the catalyst for a rapid strengthening. Upper Gulf temps are in the upper 80s to near 90 degrees.

[LithiaWx]

Global models grossly underdo the strength of a tropical system typically.

So is intensity basically worthless on a global model? Once it forms into a TC with recon data, do global models initialize with the correct pressures? Are pressures always off even until landfall or is it a problem in the formative stages only?

[Scott747]

IF it makes into the GOM the very warm SST there could be the catalyst for a rapid strengthening. Upper Gulf temps are in the upper 80s to near 90 degrees.

And the same could be said almost every year.

Other sites post this spooky map that scares people on how strong a hurricane is gonna get.

http://wxmaps.org/pix/hurpot.html#ATL

It's more than just sst's.

[cdawgga1]

And the same could be said almost every year.

Other sites post this spooky map that scares people on how strong a hurricane is gonna get.

http://wxmaps.org/pix/hurpot.html#ATL

It's more than just sst's.

I realize it's more than SST's but I didn't want to start a thesis. Just a little blurb to keep conversation going.

[Sleetfreak]

I wonder when is the last hurricane to go through the Florida Straits east-west? Labor Day 1935?

The last major hurricane to take this sort of path was Donna in September 1960. It's track and the 1935 Labor Day hurricane track were almost identical; tonight's GFS depicts a very similar path through the Keys and beyond.

[it*has*an*i]

Just wondering if the GFS is any more accurate at forecasting a Hurricane hitting Florida/deep south 8 days out than it is forecasting a snowstorm in Florida/deep south less than 5 days out? A lot of people including Pro mets both on TV and online seem to give the GFS some credibility for an undeveloped tropical system such as this and even advise to at least keep an eye on it whereas they either don't mention or laugh when the same model shows a snowstorm in the same areas. IMO a hurricane in FL happens with about the same frequency as snowfall in Florida so it would appear that GFS does better at forecasting tropical cyclogenesis than it does winter storm formation?.

[GaWx]

The 0Z Euro appears to be slightly more robust with pouch 17L near the L.A.'s vs. the prior Euro run but still not nearly as strong as the GFS fwiw.

[OHweather]

Just some quick thoughts on the system over the eastern Tropical Atlantic:

A fairly large tropical wave is currently approaching 40W over the Tropical Atlantic. The tropical wave is currently characterized by a large, broad mid level rotation and is clearly separated from the ITCZ. However, the wave is also surrounded by a fairly significant amount of mid level dry air/SAL off of Africa, and for now is exhibiting rather poor outflow. Given the dry air and poor outflow, the wave is currently struggling to maintain consistent deep convection near the center.

The wave is associated with a fairly large and given this stage in its life and a potent area of vorticity that is fairly well stacked from 850mb up through 500mb (850mb shown above). This is likely responsible for the rather good mid level rotation noted on satellite loops, and may owe to surface low development down the road should better convection maintain itself.

The steering pattern influencing our tropical wave is highly straight-forward in the near term, with a large area of low level high pressure stretching from the southern US east through the Bermuda area and towards the Azores. This will force the pouch to move generally west until it begins to develop/intensify.

The 12z ECM holds the tropical wave at near steady state or slightly weakens it through hour 48, then shows a well defined area of low level vorticity approaching the northern Lesser Antilles hours 72-96. The model then guts the system over the Greater Antilles by hour 144, but shows potential for further development by the end of the run over the western Caribbean or near the Yucatan Channel.

The 0z GFS (along with most recent runs) show development as the system approaches the Lesser Antilles. The model shows a somewhat potent cyclone that gets caught up in the Greater Antilles, before moving north if Hispaniola and bringing what would likely be a hurricane towards Florida that then recurves up the east coast.

The 12z CMC shows development over the Eastern Caribbean, and then brings a moderate tropical cyclone towards Hispaniola.

The 12z UKMET shows an increasing area of vorticity and potentially a closed low approaching the Lesser Antilles at hour 72.

The key things to take away from the global models involving possible TC-genesis are:

1) Immediate development not likely, but good consensus at development within a few degrees of 60W.

2) An early recurve is not being shown consistently by any model.

3) Possibly tug north in 4-5 days as a trough moves off the east coast.

First, we will look at if this is a reasonable guess at genesis. To do this we will look at three variables.

1) Dry air/SAL. It is no secret that this tropical wave is surrounded by a fairly significant amount of dry air that is likely limiting convection right now. Models show an increasing area of higher mid level relative humidities around the tropical wave as it begins approaching the Lesser Antilles in about 3.5 days, with few bone dry mid level relative humidities around the wave. Will use the 12z ECM valid at 96 hours as an example:

2) Possibility of an upper high developing over the tropical wave/possible retrograding TUTT creating a better opportunity for good outflow and deep convection, along with low shear.

As was mentioned above, the tropical wave is not under a particularly good upper level environment for good outflow and further development at the moment. The system is under moderately strong upper level easterlies (which are not creating strong shear due to some good low level easterlies as well), which are not providing a significant outflow channel in any direction. However, the TUTT NE of the Lesser Antilles will gradually fill and move NE in the coming days, as the upper level anti-cyclone builds west and the tropical wave slips under it. This scenario is agreed upon fairly well by most global models, and we will use the 0z GFS as an example:

This will provide for a low shear, good outflow environment for the wave as it approaches the Lesser Antilles should the global models' upper level depiction pan out.

3) Possible Kelvin Wave. My understanding of tropical forcing is admittedly amateur; however with a weak MJO some negative 200mb motion anomalies are slowly progressing eastward from the eastern Pacific (where two tropical waves have recently developed into one tropical storm and one hurricane) into the western Atlantic/Caribbean.

This suggests some type of Kelvin wave is propagating eastward towards the western Atlantic given the rather weak MJO. This increases the chances for tropical-cyclone genesis in the western Atlantic as it increases upper level lift and thus the potential for convection and generally weakens wind shear as the wave passes.

The GFS, CMC, and EWP model upper level motion forecasts all suggest neutral to slightly negative upper level motions moving into the western Atlantic/Caribbean as this system approaches, suggesting increased chances for TC formation.

As for an early track guess, this wave should continue generally west until it begins deepening given strong low level ridging over much of the Atlantic.

However, with some deepening likely by 60W and a shortwave beginning to lower heights along the east coast by day 4, a bend more to the right will likely occur:

The ECM ENS mean kept a general weakness in ridging over the eastern US through 10 days:

This makes for a tough early forecast. It seems strait forward enough that this wave, in some way, shape, or form will likely impact the Lesser Antilles in 3-4 days. From there, a weak system may continue to follow the weaker steering currents towards the western Caribbean/central American, ALA 93L. The ECM ensemble means seemed to indicate this, with a large area of lower pressures generally moving through the Caribbean towards central America/Mexico/the southern Gulf by day ten (above). A stronger system may bend more to the northwest and possibly interact with the big islands, and given the large weakness in ridging shown over the eastern US, possibly become a Gulf coast/SE US coast threat.

[GaWx]

Fwiw, the 0Z THU Canadian hits near West Palm Beach as a H on 8/26 and then goes back offshore GA/lower SC by 100+ miles moving NNE.

[WishingForWarmWeather]

OHWeather, great write up as always-- good to see you on these forums! Question-- for you, or anyone who knows-- do you happen to know if the hurricane models can "see" the KW's and accurately use them within their equations?

[WishingForWarmWeather]

Fwiw, the 0Z THU Canadian hits near West Palm Beach as a H on 8/26 and then goes back offshore GA/lower SC by 100+ miles moving NNE.

So, even more models are jumping on the FL bandwagon? I really cannot remember a time that I have seen this much consistency so far out... Do you know which other models besides the GFS and the Canadian that are forecasting FL hits?

[GaWx]

Fwiw, the 0Z Euro has a good bit stronger sfc low vs. the 12Z Euro of ~1002 mb moving NW near the SE Bahamas. Much different sceanario vs. its earlier runs. Its lack of consistency vs. the GFS is evident.

[Cheeznado]

Don't look now, the Euro is beginning to come on board, has a bit stronger low than previous runs NW of Hispaniola at 156 hours....

[U_Thant]

The surface low in the 00Z ECM is right on top, and I mean RIGHT on top of the GFS at H144. Interesting that the lower res grids have a slightly different position and intensity than do the high res grids, however the centers are no more than 20-30 miles apart in the higher res grids, and probably 5-10 miles apart at lower res.

[CUmet]

OHWeather, great write up as always-- good to see you on these forums! Question-- for you, or anyone who knows-- do you happen to know if the hurricane models can "see" the KW's and accurately use them within their equations?

I don't know about the hurricane models, since they haven't been evaluated on how well they represent KWs. The global models (GFS, ECMWF, etc.) don't tend to do well with propagating KW's eastward. It's been speculated that this may have significant impacts on how well the models can forecast TC genesis in the medium range, but how much of an impact has not been quantified as far as I'm aware of.

[Cheeznado]

Ruh Roh Scooby, the Euro is deepening the low quite a bit by 174, down to 995....

[GaWx]

So, even more models are jumping on the FL bandwagon? I really cannot remember a time that I have seen this much consistency so far out... Do you know which other models besides the GFS and the Canadian that are forecasting FL hits?

Only three go out far enough in time to even have a chance to hit FL: GFS, CDN, and Euro. Euro hadn't hit FL prior to the currently updating run, but the current one may hit. At 192 hours, is in NW Bahamas moving slowly NNW with blocking high pressure to its north likely preventing it from recurving east of the SE US.

Edit: look out N FL/GA/S SC.

[WishingForWarmWeather]

I don't know about the hurricane models, since they haven't been evaluated on how well they represent KWs. The global models (GFS, ECMWF, etc.) don't tend to do well with propagating KW's eastward. It's been speculated that this may have significant impacts on how well the models can forecast TC genesis in the medium range, but how much of an impact has not been quantified as far as I'm aware of.

Well, it seems to me that is something very significant to keep in mind with this TC... if the models can't forecast it correctly we could be looking at something significantly stronger at that point in time, seeing as the KW's may help to enhance the genesis or propagation of a TC. Further, a stronger cane means a different track (in the hurricane models eyes) than one which is weaker. I just think that this throws a wrench in the whole thing. It's especially weird that all of the models seem to be jumping on the same bandwagon and really sticking to their guns. What are your personal thoughts? Do you think the KW will play a significant role in regard to possibly having the TC be completely different than what all these models are saying, or is that maybe a reason they are all in the same boat? What are your personal thoughts in general on this possible TC?