2017 indicators: SST's / MSLP / SAL / Steering / Instability

[Hammy]

Vertical instability is slipping below normal yet again. The longer range models are also starting to trend towards less favorable conditions (particularly more shear) during August and September, and I've had a gut feeling since about April that this season is going to massively under-perform everyone's expectations.

Weren't you just the other day calling for the opposite?

I don't recall calling for an active season at any point, only noting that the waves appeared stronger than I'd seen recently--that says nothing for what the atmospheric conditions will be down the road. I also mentioned (after checking my posts, as I honestly didn't remember) on June 2 that the instability appeared to be leveling off (which it has in fact done.)

[TheAustinMan]

...
http://i.imgur.com/s0ipeci.png

Is that massive sudden drop in mid-June of 2013 about when the thermohaline circulation weakened, which is what the quiet season has since been attributed to?

The weakening of the AMO/THC proxies as identified by Gray and Klotzbach over at CSU took place between late March and late June, so it was a multi-month collapse. CSU's index fell from 3.91 in March to -5.60 in May. The May-June value was the lowest in any year since at least 1950. The THC was at its weakest in May, and recovered by July, though CSU's post-season verification report hints that the effects of the THC's collapse lagged and thus were felt during peak season.

[Hammy]

...
http://i.imgur.com/s0ipeci.png

Is that massive sudden drop in mid-June of 2013 about when the thermohaline circulation weakened, which is what the quiet season has since been attributed to?

The weakening of the AMO/THC proxies as identified by Gray and Klotzbach over at CSU took place between late March and late June, so it was a multi-month collapse. CSU's index fell from 3.91 in March to -5.60 in May. The May-June value was the lowest in any year since at least 1950. The THC was at its weakest in May, and recovered by July, though CSU's post-season verification report hints that the effects of the THC's collapse lagged and thus were felt during peak season.

Is there any way to check this in real time as a potential factor this year?

[tolakram]

I don't recall calling for an active season at any point, only noting that the waves appeared stronger than I'd seen recently--that says nothing for what the atmospheric conditions will be down the road. I also mentioned (after checking my posts, as I honestly didn't remember) on June 2 that the instability appeared to be leveling off (which it has in fact done.)

Hi Hammy,

use this link for the instability chart as the one I usually watch is not updating correctly.

http://www.ssd.noaa.gov/PS/TROP/TCFP/atlantic.html

[tolakram]

VI Forecasts appear to predict VI falling over the next 48 hours but this may be pulsing up and down, I've never tracked it.






Tropical tidbits has this groovy Marine Instability chart from the GFS that includes predicted soundings if you click on a location.

http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=atl&pkg=thdv

[tolakram]

Another one to watch from the GFS is the relative humidity. Dry air has been a real storm killer the last few years.

http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=atl&pkg=midRH

[gatorcane]

Another one to watch from the GFS is the relative humidity. Dry air has been a real storm killer the last few years.

http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=atl&pkg=midRH

Yes it has but so far it is nothing like 2013 where there was plenty of mid-level dry air around South Florida preventing shower and thunderstorm development you would normally see in June sometimes the wettest month of the year. These dry airmasses pushed into South Florida from the Atlantic that summer so could be an indicator of a more moist Atlantic this year.

[OuterBanker]

Of interest this morning was JB's daily update in which he mentions that in 2013 the pressures were higher in the Azores which caused the dry air coming off Africa and the upwelling that occurred which put the kabash on the season. This season it's reversed, there's lower pressures in the Azores and the waters have warmed up. Could have a major effect on this year’s season. We shall see.
Catch the link before tomorrows posting.
https://www.weatherbell.com/premium/

(public videos) which are free to the public.

[TheAustinMan]

Is there any way to check this in real time as a potential factor this year?

I don't know of any real time way to check the current strength of the thermohaline circulation, though I imagine daily data for the variables used in Klotzbach and Gray's formulation of their THC proxy.

Reading through their 2013 verification report, there's a section that discusses their THC proxy. If I'm reading it right, their formula is the standard deviation of the surface meridional wind anomaly plus the standard deviation of the SST anomaly minus the standard deviation of the sea-level pressure anomaly (all concerning the Eastern Atlantic).

Using the NCEP Reanalysis Dataset over at ESRL I decided to use their formula to see what their THC proxy would say for this year. According to my calculations the THC proxy increased significantly between March and May 2017, and is presently quite positive. However, my calculations might be wrong because my values for 2013 don't match their published 2013 THC values (though that may be due to different datasets used; however, the general trends are somewhat there).

Regardless of the raw values, the qualitative parameters for a strong THC according to Klotzbach/Gray's formulation are all there. May 2017's Eastern Atlantic meridional wind anomalies were anomolously southerly (and, in fact, the most southerly for any May since the NCEP dataset began in 1948). Sea surface temperature anomalies were also anomolously warm, and the second warmest of any May since 1948 (behind 1995). May 2017's Eastern Atlantic sea level pressure anomalies were also anomolously low, and were the lowest May pressures for the region since records began in 1948.

[Hammy]

Is there any way to check this in real time as a potential factor this year?

I don't know of any real time way to check the current strength of the thermohaline circulation, though I imagine daily data for the variables used in Klotzbach and Gray's formulation of their THC proxy.

Reading through their 2013 verification report, there's a section that discusses their THC proxy. If I'm reading it right, their formula is the standard deviation of the surface meridional wind anomaly plus the standard deviation of the SST anomaly minus the standard deviation of the sea-level pressure anomaly (all concerning the Eastern Atlantic).

Using the NCEP Reanalysis Dataset over at ESRL I decided to use their formula to see what their THC proxy would say for this year. According to my calculations the THC proxy increased significantly between March and May 2017, and is presently quite positive. However, my calculations might be wrong because my values for 2013 don't match their published 2013 THC values (though that may be due to different datasets used; however, the general trends are somewhat there).

Regardless of the raw values, the qualitative parameters for a strong THC according to Klotzbach/Gray's formulation are all there. May 2017's Eastern Atlantic meridional wind anomalies were anomolously southerly (and, in fact, the most southerly for any May since the NCEP dataset began in 1948). Sea surface temperature anomalies were also anomolously warm, and the second warmest of any May since 1948 (behind 1995). May 2017's Eastern Atlantic sea level pressure anomalies were also anomolously low, and were the lowest May pressures for the region since records began in 1948.

Does all of this point to 2017 not being a repeat of 2013? It's been a lingering suspicion of mine given how the late winter/early spring pattern was shaping up, having more of a winter-type pattern with the storms (tracking much further south than normal, to the point of having snow flurries in GA in mid-March), rather than the large north-south oriented fronts more typical of spring.

[tolakram]

Does all of this point to 2017 not being a repeat of 2013? It's been a lingering suspicion of mine given how the late winter/early spring pattern was shaping up, having more of a winter-type pattern with the storms (tracking much further south than normal, to the point of having snow flurries in GA in mid-March), rather than the large north-south oriented fronts more typical of spring.

New England has been unusually cold but the pattern has flipped to unusually warm. I do think it's a fair question, I wish we had better indicators but I'm a little lost on what to look for as well.

[chaser1]

Does all of this point to 2017 not being a repeat of 2013? It's been a lingering suspicion of mine given how the late winter/early spring pattern was shaping up, having more of a winter-type pattern with the storms (tracking much further south than normal, to the point of having snow flurries in GA in mid-March), rather than the large north-south oriented fronts more typical of spring.

New England has been unusually cold but the pattern has flipped to unusually warm. I do think it's a fair question, I wish we had better indicators but I'm a little lost on what to look for as well.

The falling pressures and possible development over the W. Caribbean and Central America foretasted by most models seem in-line with Climatology. On the other hand, I'm curious if it could be determined whether the seemingly anomalous high amplitude tropical waves that we're seeing emerge off the African coastline, are Kelvin wave enhanced? If so, might this be indicative of a weakening Pacific MJO condition with the MJO migrating to a position that would enhance Atlantic tropical development?

[Hammy]

Average of the MDR instability is slipping further away from normal, as expected.

[chaser1]

I'd be willing to bet that we'll soon see a reversal with regards to Atlantic MDR instability. I think that this increase in Atlantic MDR instability will be persistent through most of August and September

[tolakram]

Average of the MDR instability is slipping further away from normal, as expected.

http://i.imgur.com/FXyjYVp.png

I would not make this statement, in my opinion anyway, until I see the next rise. Instability normally pulses up and down so it's the average we are looking for. I would like to see it rise above the long term average line as well. There's also the question of weather this is a leading or trailing indicator.

This was 2006 ... not a big year.

[Bocadude85]

Average of the MDR instability is slipping further away from normal, as expected.

We could potentially see two tropical cyclones in the next 7 days. Obviously something in the Atlantic is favorable this year. We have some pretty active tropical waves traversing the MDR currently, I would bet that you will see a rise in vertical instability in the coming weeks.

[tatertawt24]

Average of the MDR instability is slipping further away from normal, as expected.

We could potentially see two tropical cyclones in the next 7 days. Obviously something in the Atlantic is favorable this year. We have some pretty active tropical waves traversing the MDR currently, I would bet that you will see a rise in vertical instability in the coming weeks.

lol I wouldn't go that far yet. 2013 had two June storms too.

[weathaguyry]

Average of the MDR instability is slipping further away from normal, as expected.

We could potentially see two tropical cyclones in the next 7 days. Obviously something in the Atlantic is favorable this year. We have some pretty active tropical waves traversing the MDR currently, I would bet that you will see a rise in vertical instability in the coming weeks.

lol I wouldn't go that far yet. 2013 had two June storms too.

At this time in 2013, there was noticeably drier air off the coast of Africa, and the waves were much less robust. There was also a lot of cold water off the coast of Spain, running down the coast of Africa which is essentially the opposite this year.

[RL3AO]

The instability chart is nice and all that, but what does it mean? How meaningful is it to have the tropical Atlantic slightly below climatology using this parameter? From my understanding, it's taking the surface theta-e parcel and subtracting it from the vertical mean theta-es (saturation equivalent potential temperature), and then averaging that over the entire region. It's not entirely clear to me how well this will account for things like mid-level dry air. Obviously, it will some since that layer would have a lower theta-es if it's drier. I'd be much more interested in tracking mid-level moisture vs climatology and wind shear vs climatology. They're more direct and express more meaningful data. It doesn't take much to create thunderstorms in the tropics if you have some sort of disturbance (tropical wave, Kelvin wave, favorable MJO, and so on). I'd just recommend people not put too much emphasis on an instability chart that is averaging out a lot of things over a very large area. It doesn't exactly tell you how the conditions are at a specific location where a storm wave is, for example.

[Bocadude85]

Average of the MDR instability is slipping further away from normal, as expected.

We could potentially see two tropical cyclones in the next 7 days. Obviously something in the Atlantic is favorable this year. We have some pretty active tropical waves traversing the MDR currently, I would bet that you will see a rise in vertical instability in the coming weeks.

lol I wouldn't go that far yet. 2013 had two June storms too.

The difference is we are talking about a possible storm in the MDR in June. It very well may not develop (chances are that it won't) but the waves are very healthy for so early in the year.