Atlantic Tropical Action 2012 - Part II

[Superstorm93]

And now we have 2 Mandarins and 1 Cherry-- and a TS. Will one of these systems please become interesting?

I wouldn't hold your breath.

Just hope for this to come true. A solid month of MJO activity in our basin during the peak season...

Something is bound to happen

[HurricaneJosh]

[EasternUSWX]

Another wave coming off Africa. Stack em up

[yoda]

lolz

https://twitter.com/BigJoeBastardi/status/237806153143300096/photo/1

[Derecho!]

Wave behind TD10 ends up pretty interesting on the new ECMWF...

Looking at METSAT some pretty decent turning over Africa with this one at the moment.

[Riptide]

18z GFS joins the 12z Euro in developing the wave in Western Africa; the conus may not be in the all clear after Isaac and his remnants move out into the Atlantic; assuming Isaac doesn't get stuck over the midwest.

[Superstorm93]

Not even off of the continent yet.

Methinks a storm is likely to come out of this one.

1. SHOWERS AND THUNDERSTORMS NEAR THE WEST COAST OF AFRICA ARE

ASSOCIATED WITH A TROPICAL WAVE. DEVELOPMENT IS EXPECTED TO BE

SLOW TO OCCUR...AND THIS SYSTEM HAS A LOW CHANCE...10 PERCENT...OF

BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES

WESTWARD AT ABOUT 15 MPH.

[wxmx]

With the naming of Joyce, we are currently tied with 2005 wrt named storms to date (Jose 2005 was named 22/08/2005)...Katrina was named the 24th

[eurojosh]

GFS gives Bermuda a run for its money with the wave now coming off Africa.

Of course, that is in the 350hr+ frames....

http://raleighwx.americanwx.com/models/gfs/12zgfstropical850mbVortSLPGFSLoop.html

[PSUBlizzicane2007]

With the naming of Joyce, we are currently tied with 2005 wrt named storms to date (Jose 2005 was named 22/08/2005)...Katrina was named the 24th

Interesting... And Kirk shouldn't be too far away, with models implying that Leslie may follow up Kirk.

[phil882]

Interesting... And Kirk shouldn't be too far away, with models implying that Leslie may follow up Kirk.

I am not as optimistic as the numerical guidance about the forthcoming waves emerging off Africa. The MJO is continuing to progress eastward and is now only favorable for the Central and East Atlantic. In another 5-10 days, the entire Atlantic basin will be under the suppressed phase of the MJO which will tend to produce a lower than normal amount of tropical activity for the same time frame. In addition, a suppressed kelvin wave is also superimposed on this already negative signal, so we could enter a quieter period of tropical cyclone activity after the end of the August.

[PSUBlizzicane2007]

I am not as optimistic as the numerical guidance about the forthcoming waves emerging off Africa. The MJO is continuing to progress eastward and is now only favorable for the Central and East Atlantic. In another 5-10 days, the entire Atlantic basin will be under the suppressed phase of the MJO which will tend to produce a lower than normal amount of tropical activity for the same time frame. In addition, a suppressed kelvin wave is also superimposed on this already negative signal, so we could enter a quieter period of tropical cyclone activity after the end of the August.

Ehh... I'm going to disagree simply because the reliable models are pretty excited at producing a Kirk within the next week. While the MJO is important, it's not the end-all, be-all... especially right now at the very peak of hurricane season.

[phil882]

Ehh... I'm going to disagree simply because the reliable models are pretty excited at producing a Kirk within the next week. While the MJO is important, it's not the end-all, be-all... especially right now at the very peak of hurricane season.

I should mention the short term environment in the East Atlantic is favorable, so if the African wave can develop pretty early on, its got a shot to be a significant system. My comment is mainly for the GFS pseudo systems following Kirk.

[Superstorm93]

BEGIN

NHC_ATCF

invest_al972012.invest

FSTDA

R

U

040

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0000

201208240625

NONE

NOTIFY=ATRP

END

INVEST, AL, L, , , , , 97, 2012, DB, O, 2012082406, 9999999999, , , , , , METWATCH, , AL972012

AL, 97, 2012082406, , BEST, 0, 135N, 210W, 25, 0, DB, 0, , 0, 0, 0, 0, '

[Mike.Ventrice]

Ehh... I'm going to disagree simply because the reliable models are pretty excited at producing a Kirk within the next week. While the MJO is important, it's not the end-all, be-all... especially right now at the very peak of hurricane season.

Even though we are entering the peak of the season climatologically, it doesn't necessarily mean we will see this year's peak in tropical cyclone activity during the climatological peak. Unfortunately I'm writing this from my iPhone and am not able to link up a picture but we are observing the transition into an unfavorable intraseasonal state for Atlantic tropical cyclone activity. This unfavorable state is timed well with the passage of the suppressed phase of a strong kelvin wave. It'd be helpful if someone could link up my forcast page or one of my space-time VP200 plots to illustrate this.

[QVectorman]

Even though we are entering the peak of the season climatologically, it doesn't necessarily mean we will see this year's peak in tropical cyclone activity during the climatological peak. Unfortunately I'm writing this from my iPhone and am not able to link up a picture but we are observing the transition into an unfavorable intraseasonal state for Atlantic tropical cyclone activity. This unfavorable state is timed well with the passage of the suppressed phase of a strong kelvin wave. It'd be helpful if someone could link up my forcast page or one of my space-time VP200 plots to illustrate this.

[Derecho!]

A lot of model enthusiasm for the next wave coming off Africa (behind 97L) - hits the Carolinas in GFS fantasy territory.

[phil882]

With the favorable MJO state currently, the GFS is really going bonkers with cyclogenesis over the next 120 hours. We have 5 low-level vort maxes on the map in 72 hours (one in the Gulf of Mexico, One in the Caribbean, Three in the Atlantic). Obviously the probability of all of these systems developing is low, but I think a short term burst of 2-3 tropical cyclones is not out of the question before the 25th of August.

Verification: TCs Isaac and Joyce formed in this period, so it was relatively active, despite the fact that Joyce was a short lived TC.

Given the current tropical equatorial wave state, I want to throw caution to the wind about having a similarly activity period over the next 10-15 days. Both the GFS and ECMWF are showing robust activity continuing, with two possible TCs during this period. I remain a bit skeptical and my hunch is that that models will tone down the intensity of these threats in the shorter range. This is a low confidence forecast however given how agressive the modeling has been for 4+ model cycles.

[Mike.Ventrice]

A lot of model enthusiasm for the next wave coming off Africa (behind 97L) - hits the Carolinas in GFS fantasy territory.

GFS appears to be acting like it did one-to-two years ago. Recently, it has been doing a fairly good job propagating eastward convective disturbances. However, it seems the model is not correctly capturing these eastward propagating disturbances (i.e., the MJO/Kelvin waves), indicated by the time-longitude plot of 200 hPa Velocity Potential with appended GFS forecast. I have annotated this plot to illustrate my point. I have also attached the link to verify this with time. There is a westward propagating disturbance associated with a negative VP200 anomaly currently at 60E, however the model forecast suggests that its superposition with the eastward propagating positive VP200 anomaly will not affect it, and keeps it prominent. Not something you'd like to see if you want to observe a few more strong African easterly waves come off Africa and develop into tropical cyclones.

[Riptide]

Euro and GFS are now both on board with the wave about to emerge from Africa. Looks like a potential long tracker too. There is hardly any SAL left, so it could develop faster than Isaac did.

This is pretty much going to happen during the peak of the season; despite other indications. There is too much negativity; 2012 also continues to travel at a 2005-like speed (albeit slightly behind in named systems and even further behind in intensity).

[phil882]

GFS appears to be acting like it did one-to-two years ago. Recently, it has been doing a fairly good job propagating eastward convective disturbances. However, it seems the model is not correctly capturing these eastward propagating disturbances (i.e., the MJO/Kelvin waves), indicated by the time-longitude plot of 200 hPa Velocity Potential with appended GFS forecast. I have annotated this plot to illustrate my point. I have also attached the link to verify this with time. There is a westward propagating disturbance associated with a negative VP200 anomaly currently at 60E, however the model forecast suggests that its superposition with the eastward propagating positive VP200 anomaly will not affect it, and keeps it prominent. Not something you'd like to see if you want to observe a few more strong African easterly waves come off Africa and develop into tropical cyclones.

Great illustration Mike. This strongly suggests that the model is not correct in projecting a similar string of activity like we just saw the last 5-10 days. I agree with you that we should see much more limited activity than we had had over the past 2 weeks thanks to the unfavorable MJO state.

[CoastalWx]

Interesting points Mike and Phil. As someone who's bread and butter is with winter storms, I've learned a good deal in tropical forecasting from you guys..Adam..and other mets who have good tropical insight. Keep up the nice work.

[MarkSC]

Looks like Isaac and the trough that pick it up create enough weakness for a relatively early recurve anyway if that wave develops. I disagree, though, in placing so much emphasis on MJO. At the height of the season, almost any strong wave exiting Africa can and often does develop even when the MJO is unfavorable. Sure, a favorable MJO increases the odds and unfavorable decreases it, but there are a lot of other factors as well that the models incorporate. Those are all pretty favorable now at the historical peak of the season. Given that it is the peak and our two best models have been on board for several runs in a row, my money is on development late this week.

[Mike.Ventrice]

Looks like Isaac and the trough that pick it up create enough weakness for a relatively early recurve anyway if that wave develops. I disagree, though, in placing so much emphasis on MJO. At the height of the season, almost any strong wave exiting Africa can and often does develop even when the MJO is unfavorable. Sure, a favorable MJO increases the odds and unfavorable decreases it, but there are a lot of other factors as well that the models incorporate. Those are all pretty favorable now at the historical peak of the season. Given that it is the peak and our two best models have been on board for several runs in a row, my money is on development late this week.

You have to keep in mind on average, 85% of all African easterly waves do not develop. Even very strong African easterly waves propagating off the coast of West Africa occasionally do not develop. There's a paper by Hopsch et al. (2011) that looks at this very problem. So knowing the intraseasonal state of convection in the tropics is useful to identify periods where conditions become more or less favorable for genesis. You have to keep in mind that meteorology comes down to probabilities. Further, intraseasonal weather phenomena such as Kelvin waves and the MJO affect the frequency of easterly waves propagating over the Atlantic.

That being said, I do not rule out the potential for the genesis of a tropical cyclone during the peak of the season due to chaotic noise. It is just much less likely to occur during unfavorable intraseasonal states.

[geoffs]

is it more likely there will be home grown TC's during the coming weeks? can TC's form and become major hurricanes in the gulf or do they have to come from africa?

[Visiteur]

is it more likely there will be home grown TC's during the coming weeks? can TC's form and become major hurricanes in the gulf or do they have to come from africa?

The MJO's active and suppressed phases have a large enough wavelength that they tend to impact a large portion of the basin at any given time. So if African waves are experiencing MJO phases that aren't conducive to their development (descending/suppressed phase, shown in Mike's website using warm colors), chances are high the same influence is being exerted over the Caribbean, Gulf and locations closer to the U.S. So home grown TCs aren't really more likely, we'll just see a generally less active trend across the basin for the next couple weeks.

That being said, TCs can still form if seed disturbances are presented with a favorable local environment (ex. front stalling out over the warm waters of the Gulf). However, major TCs are more likely to come from Africa, simply because they have plenty of time to traverse the warm, heat energy-laden waters of the tropical Atlantic. In sum, they don't need to come from Africa to be TCs, nor major TCs, but it helps.

[Ed Lizard]

12Z GFS - mid-level remnants of Isaac may determine whether/where system that comes from behind 97L to develop affects US?

Wave passing 20ºW, I assume.

[Mike.Ventrice]

The MJO's active and suppressed phases have a large enough wavelength that they tend to impact a large portion of the basin at any given time. So if African waves are experiencing MJO phases that aren't conducive to their development (descending/suppressed phase, shown in Mike's website using warm colors), chances are high the same influence is being exerted over the Caribbean, Gulf and locations closer to the U.S. So home grown TCs aren't really more likely, we'll just see a generally less active trend across the basin for the next couple weeks.

That being said, TCs can still form if seed disturbances are presented with a favorable local environment (ex. front stalling out over the warm waters of the Gulf). However, major TCs are more likely to come from Africa, simply because they have plenty of time to traverse the warm, heat energy-laden waters of the tropical Atlantic. In sum, they don't need to come from Africa to be TCs, nor major TCs, but it helps.

Well said.. Note how the GFS has backed off of the development of invest 97L and the AEW coming off Africa. The time-longitude plot of VP200 shows that the eastward propagating postive VP200 anomaly (associated with the convectively-suppressed phase of the Kelvin wave) has overpowered the westeward propagating negative VP200 anomaly signature. This is *different* to what was forecasted a couple days ago, and was illustrated in one of my previous posts. The forecast still tries to bring back a westward propagating VP200 anomaly disturbance... suggesting it is still struggling with correctly propagating the eastward propagating Kelvin wave.

[Ed Lizard]

^^ 12Z GFS has AEW that came off Africa in the Bahamas in 8 days...

[geoffs]

what dates can we expect the activity to pick up again after the lull?