2018 Indicators: SST's / MSLP / Sal / Steering / Shear / Instability (Graphic updates at first post)

[NotSparta]

Interesting thread on Twitter by Eric Webb.

@webberweather
Atlantic MDR may be cold now, but if the EPS monthly verifies w/ a quasi-stationary relaxed trade regime, the Atlantic MDR would warm up a lot going into Aug/Sep, putting some seasonal forecasts in trouble. This also has ENSO implications: a warmer Atlantic resists oncoming Ninos

 https://twitter.com/webberweather/status/1015592309109370882




 https://twitter.com/webberweather/status/1015592511996215297




@webberweather
We're clearly starting to move away from the pattern that made the Atlantic cold in the first place, just goes to show how difficult seasonal forecasting is. Even if the MDR warms a lot it doesn't automatically favor a very active season however given the subtropics are also warm

 https://twitter.com/webberweather/status/1015593879821692928

Now keep in mind this is only showing the Equatorial Atlantic, I'm not entirely sure what the trades look like specifically in the 10-20N belt over the tropical Atlantic but this reduction in trades near the Equator has also coincided w/ the Atlantic warming over the past few weeks or so, it seems like we're going to keep this up going forward. It's a much different pattern than the one that led to the -AMO SST configuration over the Atlantic MDR.

I found a 10-20N plot on Michael Ventrice's site, based on the GFS. Looks like an underlying slightly slower than normal trade state, but it looks pretty contaminated by passing tropical waves.

[NotSparta]

I expect a bit of cooling in the MDR soon though, with intraseasonal forcing that would favor enhanced trades.

[Eric Webb]

I'll leave these here for everyone on the forum to ponder.
 https://twitter.com/webberweather/status/1016115482674380800





 https://twitter.com/webberweather/status/1016116679225401344





 https://twitter.com/webberweather/status/1016128341198307328

[cycloneye]

@webberweather
Atlantic TC activity up to this pt in the season isn’t a good indicator of seasonal activity but active Julys are often a sign of a +AMO. For ex: since 1870, 12 of 13 seasons w/ @ least 2 hurricanes in July occurred in a +AMO era. Something to ponder as Chris becomes a hurricane

[tolakram]

I wonder if we will see some Nino years go from the expected inactive to normal while other years get more active than normal? By normal I mean numbers ... I suspect most storms would be forming outside of the MDR in areas that are not usually favorable for tropical development.

[StruThiO]

Interesting thread on Twitter.

 https://twitter.com/webberweather/status/1016435499131658240




Edit:

 https://twitter.com/philklotzbach/status/1016431615621427201

[NDG]

I wouldn't be surprised if 2018 turns out to be closer to an average season versus a below average season by the way things are looking so far, especially if Nino 1+2 stays in the "cool" side and the MDR gets closer to average SSTs as we get closer to the peak of the season, IMO.
The only area that may indeed stay very hostile most of the time during the rest of the season is the central and parts of eastern Caribbean.
IMHO.

[NotSparta]

There are indications for the trades to slow down soon. That's happened this year, but was almost always related to some kind of favorable subseasonal forcing that was temporary. Currently, both the phase 5/6 MJO and the suppressive CCKW should be enhancing the trades. But the trades being slowed in spite of subseasonal forcing is at odds w/ what has happened the rest of 2018. This suggests it's not quite temporary.

 https://twitter.com/NotSparta_wx/status/1016549057949585408

[Eric Webb]

This is just to reaffirm what Notsparta has posted above and what I've been discussing wrt how a wetter Africa has been playing into the hands of the Atlantic MDR warming we've seen lately.

To quote my earlier tweet
"If you compare satellite era yrs where the Atlantic MDR SSTAs warmed the most vs those that cooled the most between the spring & summer, you see a signal for a wet Africa in years that warm a lot during the summer."



Now look at this year, notice how wet Africa is this year and how closely it matches the composite.



Should make more sense to those here why this is happening.

[Siker]

This is just to reaffirm what Notsparta has posted above and what I've been discussing wrt how a wetter Africa has been playing into the hands of the Atlantic MDR warming we've seen lately.

To quote my earlier tweet
"If you compare satellite era yrs where the Atlantic MDR SSTAs warmed the most vs those that cooled the most between the spring & summer, you see a signal for a wet Africa in years that warm a lot during the summer." <image deleted>

Now look at this year, notice how wet Africa is this year and how closely it matches the composite. <image deleted>

Should make more sense to those here why this is happening. <image deleted>

Just curious, are you using the same MDR bounds in your top warmest and coldest years as in Levi’s graph? Interested in the anomalous sinking over the Caribbean and whether it should experience similar warming as the East Atlantic when that anomaly would suggest enhanced trades to its west.

[Eric Webb]

Just curious, are you using the same MDR bounds in your top warmest and coldest years as in Levi’s graph? Interested in the anomalous sinking over the Caribbean and whether it should experience similar warming as the East Atlantic when that anomaly would suggest enhanced trades to its west.

Yes the bounds are the same, the enhanced trades over the EP at least in that regard don't hurt the Caribbean (they help it if anything), and the sinking air in the Caribbean increases incident shortwave radiation to the sea surface, warming it. Some of the years also had corresponding upward motion over the EP, but the Atlantic MDR SSTs still warmed a lot.

[chaser1]

SST's aside one would think there should be a direct correlation between an anomalous wet Africa and a significant decrease in SAL outbreaks, right? If that were true though, I'm not sure that I'm seeing it thus far.

[NotSparta]

SST's aside one would think there should be a direct correlation between an anomalous wet Africa and a significant decrease in SAL outbreaks, right? If that were true though, I'm not sure that I'm seeing it thus far.

From what I'm seeing, the wet Africa so far actually enhances these SAL outbreaks. What happens is the stronger easterlies on the north part of AEWs goes thru the Sahara, where it helps kick up more dust than usual, and thus causes more intense SAL.

[chaser1]

SST's aside one would think there should be a direct correlation between an anomalous wet Africa and a significant decrease in SAL outbreaks, right? If that were true though, I'm not sure that I'm seeing it thus far.

From what I'm seeing, the wet Africa so far actually enhances these SAL outbreaks. What happens is the stronger easterlies on the north part of AEWs goes thru the Sahara, where it helps kick up more dust than usual, and thus causes more intense SAL.

I think that's a sensible argument for enhanced "cause and effect"; Given that line of thinking though, I would think that the density spread of these SAL outbreaks would be a bit further north and perhaps less impacting to the MDR lower latitudes. On a separate but related note, if we do in fact begin to see a significantly reduced E. Atlantic 850mb Easterly trade flow then it stands to reason that -
1) stronger easterlies on the north part of the AEW going through the Sahara should soon abate, but at minimum become less broad and perhaps contained to somewhat higher latitudes
2) MDR SST's will continue to significantly warm
3) a healthy W. African monsoon trough will likely bear a noticeable increase of vigorous waves that will move into the E. Atlantic.

One thing i'm not sure if touched on however, is whether a relaxed W. African/E. Atlantic low level Easterly trade flow will necessarily correlate to a lessened Easterly flow aloft as well? If not, an anomalously stout 200mb - 300 mb flow might still inhibit MDR development until reaching longitudes a bit further west (such as Beryl).

If the above assumptions come to fruition then most of us along with most professional seasonal forecasts included, may well have been lulled into a false sense of minimally anticipated MDR activity. It may very well be that Beryl was less of "an aberration" and perhaps more of a indication of upcoming MDR production to come. As for ENSO, it's a "NO-SO" lol. Sure, maybe as the season wanes in October but for the prime development period of August and September I just don't think it'll be a factor impacting tropical development.

[NotSparta]

SST's aside one would think there should be a direct correlation between an anomalous wet Africa and a significant decrease in SAL outbreaks, right? If that were true though, I'm not sure that I'm seeing it thus far.

From what I'm seeing, the wet Africa so far actually enhances these SAL outbreaks. What happens is the stronger easterlies on the north part of AEWs goes thru the Sahara, where it helps kick up more dust than usual, and thus causes more intense SAL.

I think that's a sensible argument for enhanced "cause and effect"; Given that line of thinking though, I would think that the density spread of these SAL outbreaks would be a bit further north and perhaps less impacting to the MDR lower latitudes. On a separate but related note, if we do in fact begin to see a significantly reduced E. Atlantic 850mb Easterly trade flow then it stands to reason that -
1) stronger easterlies on the north part of the AEW going through the Sahara should soon abate, but at minimum become less broad and perhaps contained to somewhat higher latitudes
2) MDR SST's will continue to significantly warm
3) a healthy W. African monsoon trough will likely bear a noticeable increase of vigorous waves that will move into the E. Atlantic.

One thing i'm not sure if touched on however, is whether a relaxed W. African/E. Atlantic low level Easterly trade flow will necessarily correlate to a lessened Easterly flow aloft as well? If not, an anomalously stout 200mb - 300 mb flow might still inhibit MDR development until reaching longitudes a bit further west (such as Beryl).

If the above assumptions come to fruition then most of us along with most professional seasonal forecasts included, may well have been lulled into a false sense of minimally anticipated MDR activity. It may very well be that Beryl was less of "an aberration" and perhaps more of a indication of upcoming MDR production to come. As for ENSO, it's a "NO-SO" lol. Sure, maybe as the season wanes in October but for the prime development period of August and September I just don't think it'll be a factor impacting tropical development.

As for upper lvl flow, it has (somewhat surprisingly) been slightly anomalously easterly thru the MDR, and have strengthened recently (though there are some decent westerlies in the Caribbean which would weaken systems headed there).



Figure 1. Anomalous 200mb wind in MDR and surrounding regions, June 1-July 8, 2018



Figure 2. Anomalous 200mb wind in MDR and surrounding regions, June 15-July 8, 2018. Note the increased easterly anomalies in most areas, signifying a strengthening of these anomalies as of late

[chaser1]

From what I'm seeing, the wet Africa so far actually enhances these SAL outbreaks. What happens is the stronger easterlies on the north part of AEWs goes thru the Sahara, where it helps kick up more dust than usual, and thus causes more intense SAL.

I think that's a sensible argument for enhanced "cause and effect"; Given that line of thinking though, I would think that the density spread of these SAL outbreaks would be a bit further north and perhaps less impacting to the MDR lower latitudes. On a separate but related note, if we do in fact begin to see a significantly reduced E. Atlantic 850mb Easterly trade flow then it stands to reason that -
1) stronger easterlies on the north part of the AEW going through the Sahara should soon abate, but at minimum become less broad and perhaps contained to somewhat higher latitudes
2) MDR SST's will continue to significantly warm
3) a healthy W. African monsoon trough will likely bear a noticeable increase of vigorous waves that will move into the E. Atlantic.

One thing i'm not sure if touched on however, is whether a relaxed W. African/E. Atlantic low level Easterly trade flow will necessarily correlate to a lessened Easterly flow aloft as well? If not, an anomalously stout 200mb - 300 mb flow might still inhibit MDR development until reaching longitudes a bit further west (such as Beryl).

If the above assumptions come to fruition then most of us along with most professional seasonal forecasts included, may well have been lulled into a false sense of minimally anticipated MDR activity. It may very well be that Beryl was less of "an aberration" and perhaps more of a indication of upcoming MDR production to come. As for ENSO, it's a "NO-SO" lol. Sure, maybe as the season wanes in October but for the prime development period of August and September I just don't think it'll be a factor impacting tropical development.

As for upper lvl flow, it has (somewhat surprisingly) been slightly anomalously easterly thru the MDR, and have strengthened recently (though there are some decent westerlies in the Caribbean which would weaken systems headed there).

No, July climo typically favors higher pressures/strong Easterly trades. What i'm questioning refers in part to a statement that Webb make ".....Atlantic MDR may be cold now, but if the EPS monthly verifies w/ a quasi-stationary relaxed trade regime". Therefore pondering whether EPS verification of near term relaxed trades, will not only verify..... but whether this will also be reflected at the upper levels as well.

[NotSparta]

I think that's a sensible argument for enhanced "cause and effect"; Given that line of thinking though, I would think that the density spread of these SAL outbreaks would be a bit further north and perhaps less impacting to the MDR lower latitudes. On a separate but related note, if we do in fact begin to see a significantly reduced E. Atlantic 850mb Easterly trade flow then it stands to reason that -
1) stronger easterlies on the north part of the AEW going through the Sahara should soon abate, but at minimum become less broad and perhaps contained to somewhat higher latitudes
2) MDR SST's will continue to significantly warm
3) a healthy W. African monsoon trough will likely bear a noticeable increase of vigorous waves that will move into the E. Atlantic.

One thing i'm not sure if touched on however, is whether a relaxed W. African/E. Atlantic low level Easterly trade flow will necessarily correlate to a lessened Easterly flow aloft as well? If not, an anomalously stout 200mb - 300 mb flow might still inhibit MDR development until reaching longitudes a bit further west (such as Beryl).

If the above assumptions come to fruition then most of us along with most professional seasonal forecasts included, may well have been lulled into a false sense of minimally anticipated MDR activity. It may very well be that Beryl was less of "an aberration" and perhaps more of a indication of upcoming MDR production to come. As for ENSO, it's a "NO-SO" lol. Sure, maybe as the season wanes in October but for the prime development period of August and September I just don't think it'll be a factor impacting tropical development.

As for upper lvl flow, it has (somewhat surprisingly) been slightly anomalously easterly thru the MDR, and have strengthened recently (though there are some decent westerlies in the Caribbean which would weaken systems headed there).

No, July climo typically favors higher pressures/strong Easterly trades. What i'm questioning refers in part to a statement that Webb make ".....Atlantic MDR may be cold now, but if the EPS monthly verifies w/ a quasi-stationary relaxed trade regime". Therefore pondering whether EPS verification of near term relaxed trades, will not only verify..... but whether this will also be reflected at the upper levels as well.

I'm confused. Do you mean more westerly winds in the upper lvls?

[Kingarabian]

 https://twitter.com/MJVentrice/status/1016456053876195333

[SFLcane]

 https://twitter.com/MJVentrice/status/1016456053876195333

So far its been anything but below average.

[Kingarabian]

Agreed. This Euro forecast is for ASO basically.