Atlantic Tropical Action 2012 - Part I

[Mike.Ventrice]

There's been a lot of statistical work on Sahel rainfall and seasonal Atlantic activity. There is no correlation when the AMO is positive and high correlation when the AMO is negative.

There's a strong correlation of Sahel rainfall and Gulf of Guinea sea-surface temperature anomalies. When there is anomalously cold tongue in the Gulf of Guinea, there's a stronger gradient of boundary layer entropy that drives the ITCZ northward. A weaker than normal cold tongue is associated with a more equatorward ITCZ, which results in less rainfall for the Sahel and more rainfall for sub-Saharan Africa.

Now to relate this to tropical cyclones- a colder than normal cold tongue in the Gulf of Guinea is associated with cooler than normal SSTs in the eastern tropical Atlantic- which then prevents genesis close to the coast of West Africa. Warmer than normal SSTs in the cold tongue is associated with warmer SSTs in the eastern tropical Atlantic and hence more genesis near the coast of West Africa and associated "Guinean Highlands type developments".

I never published the Gulf of Guinea Cold tongue intensity and Atlantic genesis locations. It's pretty striking though.

[Sunny and Warm]

There's been a lot of statistical work on Sahel rainfall and seasonal Atlantic activity. There is no correlation when the AMO is positive and high correlation when the AMO is negative.

I wonder if that is because the -AMO signal causes summer high pressure over S. Europe to settle further south over the mediterranean and cause more SAL intrusion? Don't know the answer, just trying out an idea.

[wxmx]

If I had my way, we'd pave over all of N Africa with asphalt. That or turn it into a manmade rainforest.

A rainforest would kill Tropical Waves

[wxmx]

Yep, saw that, and forgot to post it as the possible main culprit on non development in models.

[toad strangler]

If I had my way, we'd pave over all of N Africa with asphalt.

Gas would def be at least $10 a gallon here then

[wxmx]

Now, SAL affects development mostly in July and first half of August...a range which is still outside of the heart of the season.

Looking at how things have developed since the start of the season, warm ENSO has been stopped on it's heels, and in the short term it doesn't look that there will be a substantial push towards El Niño...I still think neutral warm for August, and warming could resume when fall is upon us. Shear has been below normal in the GoM and tropical Atlantic, and slightly above normal, especially in this month, in the Caribbean, but looks like it's going towards normal or a bit below in the next 2 weeks...while the GoM and TNA region stay below. TNA was positive for June, and it will probably be a bit higher for July...same for the Caribbean SSTs.

I think ASO will be near average in terms of activity, with slightly above either August and/or September and below in October.

[Sunny and Warm]

Now, SAL affects development mostly in July and first half of August...a range which is still outside of the heart of the season.

Couldn't one say that July and 1st half August are not the heart of the season due in part to SAL?

[wxmx]

Couldn't one say that July and 1st half August are not the heart of the season due in part to SAL?

Probably one of the reasons, coupled with stronger easterlies in the low levels.

[phil882]

Probably one of the reasons, coupled with stronger easterlies in the low levels.

Yea the easterly flow right now over the Atlantic is absolutely brutal. The GFS is analyzing 50 knot 700 hPa flow at 18-20N over this disturbance. The models have been drifting this system NW and as the weak circulation gets caught up in this low-level flow, it will quickly decouple from the convection.

[Ed Lizard]

As an eternal optimist, despite omens of 2009 or 1997 or 1986, I have searched diligently for a positive sign for August and have found one.

The CFS 850 mb wind anomaly for 8-14 August 2012 is almost zero in the MDR!

[HurricaneJosh]

Now, SAL affects development mostly in July and first half of August...a range which is still outside of the heart of the season.

Looking at how things have developed since the start of the season, warm ENSO has been stopped on it's heels, and in the short term it doesn't look that there will be a substantial push towards El Niño...I still think neutral warm for August, and warming could resume when fall is upon us. Shear has been below normal in the GoM and tropical Atlantic, and slightly above normal, especially in this month, in the Caribbean, but looks like it's going towards normal or a bit below in the next 2 weeks...while the GoM and TNA region stay below. TNA was positive for June, and it will probably be a bit higher for July...same for the Caribbean SSTs.

I think ASO will be near average in terms of activity, with slightly above either August and/or September and below in October.

[carley5]

i think the pattern favors several hurricanes threatening the east coast this season aug20-oct1

[am19psu]

i think the pattern favors several hurricanes threatening the east coast this season aug20-oct1

Why?

[wxmx]

Yea the easterly flow right now over the Atlantic is absolutely brutal. The GFS is analyzing 50 knot 700 hPa flow at 18-20N over this disturbance. The models have been drifting this system NW and as the weak circulation gets caught up in this low-level flow, it will quickly decouple from the convection.

Too bad, it looks decent, but things are forecasted to go downhill soon

[carley5]

Why?

Im liking the position of the atlantic ridge this season as opposed to the last several years. Also, atlantic sst's are getting quite a bit above normal, somewhat similar to 2005, though i dont expect a repeat of 2005 by any means. 13/8/3 seems about right.

[Ed Lizard]

Im liking the position of the atlantic ridge this season as opposed to the last several years. Also, atlantic sst's are getting quite a bit above normal, somewhat similar to 2005, though i dont expect a repeat of 2005 by any means. 13/8/3 seems about right.

Hmmm, I just checked last few days of JB's Tweets, and that doesn't seem to be the source of favoring the East Coast (my first suspect), and looking at the medium term forecast thread, while there are some 1950s analogs in there, it would seem the mean ridge position Don S seems to be implying would generally keep storms off the East Coast.

I should probably ask Don or HM if, in their educated opinions, if any US location is favored over another.

Warm water off the East Coast helps if anything is coming, but it is a yearly thing on the local forums when Gulf SSTs push 30º someone starts saying the Gulf is boiling and something is about to pop, and more years than not, nothing pops..

ETA- I am extrapolating off of somebody's August forecast, I suppose it could change for September....

[am19psu]

Hmmm, I just checked last few days of JB's Tweets, and that doesn't seem to be the source of favoring the East Coast (my first suspect), and looking at the medium term forecast thread, while there are some 1950s analogs in there, it would seem the mean ridge position Don S seems to be implying would generally keep storms off the East Coast.

I should probably ask Don or HM if, in their educated opinions, if any US location is favored over another.

Warm water off the East Coast helps if anything is coming, but it is a yearly thing on the local forums when Gulf SSTs push 30º someone starts saying the Gulf is boiling and something is about to pop, and more years than not, nothing pops...

I kinda like Bermuda or FL/E Gulf at this point.

[Ed Lizard]

I kinda like Bermuda or FL/E Gulf at this point.

I like that. If we have, say, a slow 10/5/2 season, but one of the 2 hits Florida is and is well videographed, I'd consider this season a winner.

Quantity over Quality.

[wxmx]

I kinda like Bermuda or FL/E Gulf at this point.

FL and E GoM are also my favored places, BDA not so much, N GoM looks more likely, especially if there's continued ridging for most of the CONUS east of the rockies and a stronger bermudan ridge (thanks to the mostly negative NAO) and a stronger El Niño pattern doesn't suddenly locks in. June's pattern might have favored a BDA track, but so far July, it looks like zonal ridging is the norm.

[am19psu]

FL and E GoM are also my favored places, BDA not so much, N GoM looks more likely, especially if there's continued ridging for most of the CONUS east of the rockies and a stronger bermudan ridge (thanks to the mostly negative NAO) and a stronger El Niño pattern doesn't suddenly locks in.

I only added BDA because I could see the -NAO creating a break well east of the EC. This pattern is not shaping up to be a classic EC pattern though, with the ridge over the Plains/Lakes.

[wxmx]

I only added BDA because I could see the -NAO creating a break well east of the EC. This pattern is not shaping up to be a classic EC pattern though, with the ridge over the Plains/Lakes.

Yep, I edited my post...June's pattern shows how could it happen...in July the NAO has seen a more zonal ridging around 30N, with little breaks, but as longwave lengthen in Sept and Oct, we could see the break well east of the coast. One minus is that I think activity will be no better than normal across the tropical Atlantic...with a gentle recurving pattern in the Wern part of the basin, opposed to the strong hooking fetching storms from the W Atl or Caribbean.

Just to add...the W GoM chances are probably limited to August...a narrower window than in colder ENSO years.

[am19psu]

Yep, I edited my post...June's pattern shows how could it happen...in July the NAO has seen a more zonal ridging around 30N, with little breaks, but as longwave lengthen in Sept and Oct, we could see the break well east of the coast. One minus is that I think activity will be no better than normal across the tropical Atlantic...with a gentle recurving pattern in the Wern part of the basin, opposed to the strong hooking fetching storms from the W Atl or Caribbean.

Just to add...the W GoM chances are probably limited to August...a narrower window than in colder ENSO years.

Yay, we agree. I'm sure we're both wrong.

[Derecho!]

Warm water off the East Coast helps if anything is coming, but it is a yearly thing on the local forums when Gulf SSTs push 30º someone starts saying the Gulf is boiling and something is about to pop, and more years than not, nothing pops..

I actually sat down and figured out how many TCs actually form WITHIN the GOM per year, on average, once - I think it was less than 0.5. In any event the number is far, far, far less than the casual observer would think.

I've been waiting for 15 years for board posters to finally not be astonished that SSTs in the GOM get hot and stay hot for a long time. Also they seem to be under the impression that warm SSTs spontaneously generate TCs.

[wxmx]

Yay, we agree. I'm sure we're both wrong.

Florida insurance rates are probably diving as we speak.

[am19psu]

Florida insurance rates are probably diving as we speak.

[wxmx]

I actually sat down and figured out how many TCs actually form WITHIN the GOM per year, on average, once - I think it was less than 0.5. In any event the number is far, far, far less than the casual observer would think.

I've been waiting for 15 years for board posters to finally not be astonished that SSTs in the GOM get hot and stay hot for a long time. Also they seem to be under the impression that warm SSTs spontaneously generate TCs.

Probably closer to 1. The figure below shows the tracks of TS+ originated around the GoM from the period 1900-2011...there are 112 tracks... 78 from the period 1950-2011.

[Ed Lizard]

Probably closer to 1. The figure below shows the tracks of TS+ originated around the GoM from the period 1900-2011...there are 112 tracks... 78 from the period 1950-2011.

But the basic point is that a lot of people think really warm water means TCs, and well, not so much. And I would add, thanks to he Weather Channel, people thing warm water and low shear is all that is required to pop TCs, and again, not so much.

I always get sad when the cold fronts start coming in October. Not sure if its the cold air, or the upwelling with offshore flow.

I wonder how many systems that develop in the Gulf (weren't already at least a depression when they entered) came from non-tropical systems. I can think of a few from the BoC that were tropical, but it seems most Gulf development is from non-tropical sources.

[icebreaker5221]

Yep, I edited my post...June's pattern shows how could it happen...in July the NAO has seen a more zonal ridging around 30N, with little breaks, but as longwave lengthen in Sept and Oct, we could see the break well east of the coast. One minus is that I think activity will be no better than normal across the tropical Atlantic...with a gentle recurving pattern in the Wern part of the basin, opposed to the strong hooking fetching storms from the W Atl or Caribbean.

Just to add...the W GoM chances are probably limited to August...a narrower window than in colder ENSO years.

Looks like NAO is going to fluctuate quite a bit over the next 10 days. Slightly neg now, then neutral, positive, probably back to neg. The pattern so far this July would have been pretty good for a slow recurve into the SE coast or maybe the Gulf, but with the variability of the NAO along with how much the pattern changed over the SE US from Jun to Jul probably gives even less confidence in a persistence forecast than usual. I agree tho that we haven't seen anything suggesting an east coast landfall so far.

But the basic point is that a lot of people think really warm water means TCs, and well, not so much. And I would add, thanks to he Weather Channel, people thing warm water and low shear is all that is required to pop TCs, and again, not so much.

I always get sad when the cold fronts start coming in October. Not sure if its the cold air, or the upwelling with offshore flow.

I wonder how many systems that develop in the Gulf (weren't already at least a depression when they entered) came from non-tropical systems. I can think of a few from the BoC that were tropical, but it seems most Gulf development is from non-tropical sources.

McTaggart-Cowan et. al 2008 (http://journals.ametsoc.org/doi/abs/10.1175/2007MWR2245.1) looks at TC genesis climatology by location. Broadly speaking, non-baroclinic and LL-baroclinic are "tropical" systems while the others are not. Looks like almost half of the genesis events in the SE Gulf are considered tropical, while about 85% of genesis in the NW Gulf is either tropical transition or transient trough interaction.

[wxmx]

Looks like NAO is going to fluctuate quite a bit over the next 10 days. Slightly neg now, then neutral, positive, probably back to neg. The pattern so far this July would have been pretty good for a slow recurve into the SE coast or maybe the Gulf, but with the variability of the NAO along with how much the pattern changed over the SE US from Jun to Jul probably gives even less confidence in a persistence forecast than usual. I agree tho that we haven't seen anything suggesting an east coast landfall so far.

As a matter of fact, the NAO variability has been a constant since it changed it's pattern back in May...1 day calculations have been something like 4-5 days mostly negative, 2-3 near neutral or slightly positive and then back to negative...this time the positives look a bit stronger (though, they have been overestimated a bit since the pattern began), but very short lived, with a rather strong consensus of a new dip to significant negatives.

[icebreaker5221]

As a matter of fact, the NAO variability has been a constant since it changed it's pattern back in May...1 day calculations have been something like 4-5 days mostly negative, 2-3 near neutral or slightly positive and then back to negative...this time the positives look a bit stronger (though, they have been overestimated a bit since the pattern began), but very short lived, with a rather strong consensus of a new dip to significant negatives.

Hasn't the NAO been negative since May 27? I see what you mean in that it's been variable tho, ranging from slightly negative to very negative, and also changing from west-based to east-based.