2021 Indicators: SST's / SAL / MSLP / Shear / Steering / Instability / Sat Images

[Category5Kaiju]

One of the major issues with using 2013 as an analog is the complete lack of an Atlantic Nino. In fact, the Atlantic equatorial mode remained anomalously cool throughout the Summer months (JJA) and into SON for 2013:
https://s6.gifyu.com/images/Webp.net-gifmaker-228030d05b8907f59.gif

This promotes a sinking cell in the Atlantic (particularly the SATL) and negates rising motion over Africa, weakening the WAM:
https://i.imgur.com/gJd6TFO.png

In contrast, we've had a vigorous Atlantic Nino beginning in April that has persisted through MJJ:
https://i.imgur.com/kYSsLpz.png

If seasonal model SSTA forecasts are accurate for SON, we're likely to have what is classified as a persistent Atlantic Nino mode. The warmer waters in the Atlantic equatorial zone promotes rising motion over Africa, and enhances the WAM. We can see this using the analog years that exhibited a persistent Atlantic Nino:
https://i.imgur.com/apYt53C.png

This is right on. I mean, among other things as well, but 2013 and 2021 share very little (if anything) in common when you look at the broader picture in terms of Atlantic and Northern Hemisphere activity by this time of the year (as well as what's predicted). 2013 definitely had no Atlantic Nino while this year is literally the complete opposite.

[psyclone]

The missing ingredient we need is....time. 3 weeks until the bell tolls. It's pretty amazing how often the first half of August is dead. It's frequently like the 2nd half of july. 2 or 3 more weeks before we should feel entitled to anything

[SFLcane]

One of the major issues with using 2013 as an analog is the complete lack of an Atlantic Nino. In fact, the Atlantic equatorial mode remained anomalously cool throughout the Summer months (JJA) and into SON for 2013:
https://s6.gifyu.com/images/Webp.net-gifmaker-228030d05b8907f59.gif

This promotes a sinking cell in the Atlantic (particularly the SATL) and negates rising motion over Africa, weakening the WAM:
https://i.imgur.com/gJd6TFO.png

In contrast, we've had a vigorous Atlantic Nino beginning in April that has persisted through MJJ:
https://i.imgur.com/kYSsLpz.png

If seasonal model SSTA forecasts are accurate for SON, we're likely to have what is classified as a persistent Atlantic Nino mode. The warmer waters in the Atlantic equatorial zone promotes rising motion over Africa, and enhances the WAM. We can see this using the analog years that exhibited a persistent Atlantic Nino:
https://i.imgur.com/apYt53C.png

Yeah that's a big difference from 2013 should not be as stable. Just need to see when the wavebreaking will calm down

[cycloneye]

I am posting the link to the August poll here because is the most visited thread right now so those members who have not voted yet do so fast as the poll closes for voting on Saturday at 2:48 PM EDT.

viewtopic.php?f=31&t=122013&p=2918259#p2918259

[tolakram]

The wave train is starting to show up over Africa now. Just one of the ingredients, but lack of waves should not be an issue this year.

[Category5Kaiju]

The wave train is starting to show up over Africa now. Just one of the ingredients, but lack of waves should not be an issue this year.

https://i.imgur.com/YlIWGn8.png

That looks pretty healthy!

[SFLcane]

The wave train is starting to show up over Africa now. Just one of the ingredients, but lack of waves should not be an issue this year.

https://i.imgur.com/YlIWGn8.png

Train is in the station. Waiting for the tracks to clear

[cycloneye]

 https://twitter.com/AndyHazelton/status/1421191945389543424

[AnnularCane]

A lot of seasons, and maybe including this one to a somewhat lesser extent, kind of make me think of the May 31, 1985, tornado outbreak, where nothing happened and nothing happened and nothing happened and then BOOM! Everything happened.

(Don't mind me, just a casual observation. )

[cycloneye]

FYI off Topic. Two Tropical Cyclones have formed in the EPAC, TD NINE-E and TS Hilda. For more details go to the active storms forum.

viewforum.php?f=59

[psyclone]

A lot of seasons, and maybe including this one to a somewhat lesser extent, kind of make me think of the May 31, 1985, tornado outbreak, where nothing happened and nothing happened and nothing happened and then BOOM! Everything happened.

(Don't mind me, just a casual observation. )

This northeast ohio native can relate. We're still in shallow section but the drop off is quickly approaching. That sat pic of the African wave train is very telling. Those eastern waves will be moving across the atlantic deep into August so it's possible one or more of those will be named systems down the road.

[aspen]

FYI off Topic. Two Tropical Cyclones have formed in the EPAC, TD NINE-E and TS Hilda. For more details go to the active storms forum.

viewforum.php?f=59

Both have the possibility of becoming hurricanes, but they’ll all be quite far west. How much will that impact shear over the Caribbean/tropical Atlantic? If both under-perform, will shear be lower?

[Kingarabian]

FYI off Topic. Two Tropical Cyclones have formed in the EPAC, TD NINE-E and TS Hilda. For more details go to the active storms forum.

viewforum.php?f=59

Both have the possibility of becoming hurricanes, but they’ll all be quite far west. How much will that impact shear over the Caribbean/tropical Atlantic? If both under-perform, will shear be lower?

TC activity in the EPAC usually affects the Atlantic via large scale rising/sinking motion. When there's TC activity on either side, the other side is usually under sinking motion.

[Yellow Evan]

FYI off Topic. Two Tropical Cyclones have formed in the EPAC, TD NINE-E and TS Hilda. For more details go to the active storms forum.

viewforum.php?f=59

Both have the possibility of becoming hurricanes, but they’ll all be quite far west. How much will that impact shear over the Caribbean/tropical Atlantic? If both under-perform, will shear be lower?

Over the Caribbean? Yes but it's expected to be hostile there anyway. Less so the tropical/subtropical Atlantic.

[AlphaToOmega]

Activity will resume in early August. Mark my words
The MJO pattern for 2021 has been very similar to that of 2017 so far. 2017 had an active June and a lull of activity in July, just like 2021. Activity resumed in early August in 2017.

[USTropics]

FYI off Topic. Two Tropical Cyclones have formed in the EPAC, TD NINE-E and TS Hilda. For more details go to the active storms forum.

viewforum.php?f=59

Both have the possibility of becoming hurricanes, but they’ll all be quite far west. How much will that impact shear over the Caribbean/tropical Atlantic? If both under-perform, will shear be lower?

TC activity in the EPAC usually affects the Atlantic via large scale rising/sinking motion. When there's TC activity on either side, the other side is usually under sinking motion.

As Kingrabian stated, it's not really the tropical cyclones that are imparting shear over the Caribbean. While cyclones that form close to Central America and Mexico in the EPAC can impart localized shear in the Caribbean, these systems are being boosted due to intraseasonal oscillations (in this case, MJO) and largescale atmospheric weather systems that propagate eastward (CCKWs). From a meteorological standpoint, when we have rising motion, high temperatures in the lower troposphere cause the air density (and weight) to decrease in local air columns, which promotes lower surface pressure. As the rising air reaches the tropopause, it begins to spread out at the top of the ascending branch. This creates a return loop, and we end up with upper-level divergence that further reduces the weight of local air columns. An oversimplification here, but what goes up must come down, and when we have rising motion we must have offsetting sinking motion.

Using VP anomalies from the past 7 days, we can see much of the Pacific is under a large scale rising cell (green arrows). When air begins to sink, it does two major things: (1) creates stability in the air column and (2) must move somewhere when it reaches the surface. In this case, as the sinking air reaches the Caribbean surface and accelerates, it creates wind shear vectors from west to east.

[aspen]

Both have the possibility of becoming hurricanes, but they’ll all be quite far west. How much will that impact shear over the Caribbean/tropical Atlantic? If both under-perform, will shear be lower?

TC activity in the EPAC usually affects the Atlantic via large scale rising/sinking motion. When there's TC activity on either side, the other side is usually under sinking motion.

As Kingrabian stated, it's not really the tropical cyclones that are imparting shear over the Caribbean. While cyclones that form close to Central America and Mexico in the EPAC can impart localized shear in the Caribbean, these systems are being boosted due to intraseasonal oscillations (in this case, MJO) and largescale atmospheric weather systems that propagate eastward (CCKWs). From a meteorological standpoint, when we have rising motion, high temperatures in the lower troposphere cause the air density (and weight) to decrease in local air columns, which promotes lower surface pressure. As the rising air reaches the tropopause, it begins to spread out at the top of the ascending branch. This creates a return loop, and we end up with upper-level divergence that further reduces the weight of local air columns. An oversimplification here, but what goes up must come down, and when we have rising motion we must have offsetting sinking motion.

Using VP anomalies from the past 7 days, we can see much of the Pacific is under a large scale rising cell (green arrows). When air begins to sink, it does two major things: (1) creates stability in the air column and (2) must move somewhere when it reaches the surface. In this case, as the sinking air reaches the Caribbean surface and accelerates, it creates wind shear vectors from west to east.

https://i.imgur.com/lb5Rm0p.png

https://i.imgur.com/bKDbE1f.png

Thank you for your great analysis as usual. So any phase of EPac activity will cause sinking motion and shear over the Atlantic. I’m guessing that’ll be the case even if all of the storms struggle, because there’s still rising motion.

Seems like until the WAM kicks into overdrive starting around August 7-14th and outcompetes the EPac cell, the best spot for any AEW-based system will probably be between 40W and 60W, below 15N. This will be before the wall of shear that awaits in the Caribbean, and SSTs are warm enough to support something. Just needs to avoid the other problems of dry air and typical shear, but these should lessen over the next 2+ weeks.

[USTropics]

TC activity in the EPAC usually affects the Atlantic via large scale rising/sinking motion. When there's TC activity on either side, the other side is usually under sinking motion.

As Kingrabian stated, it's not really the tropical cyclones that are imparting shear over the Caribbean. While cyclones that form close to Central America and Mexico in the EPAC can impart localized shear in the Caribbean, these systems are being boosted due to intraseasonal oscillations (in this case, MJO) and largescale atmospheric weather systems that propagate eastward (CCKWs). From a meteorological standpoint, when we have rising motion, high temperatures in the lower troposphere cause the air density (and weight) to decrease in local air columns, which promotes lower surface pressure. As the rising air reaches the tropopause, it begins to spread out at the top of the ascending branch. This creates a return loop, and we end up with upper-level divergence that further reduces the weight of local air columns. An oversimplification here, but what goes up must come down, and when we have rising motion we must have offsetting sinking motion.

Using VP anomalies from the past 7 days, we can see much of the Pacific is under a large scale rising cell (green arrows). When air begins to sink, it does two major things: (1) creates stability in the air column and (2) must move somewhere when it reaches the surface. In this case, as the sinking air reaches the Caribbean surface and accelerates, it creates wind shear vectors from west to east.

https://i.imgur.com/lb5Rm0p.png

https://i.imgur.com/bKDbE1f.png

Thank you for your great analysis as usual. So any phase of EPac activity will cause sinking motion and shear over the Atlantic. I’m guessing that’ll be the case even if all of the storms struggle, because there’s still rising motion.

Seems like until the WAM kicks into overdrive starting around August 7-14th and outcompetes the EPac cell, the best spot for any AEW-based system will probably be between 40W and 60W, below 15N. This will be before the wall of shear that awaits in the Caribbean, and SSTs are warm enough to support something. Just needs to avoid the other problems of dry air and typical shear, but these should lessen over the next 2+ weeks.

In terms of VP anomalies, the 2nd-3rd week of August is as active of a look as you can get for the Atlantic:


Shear forecasts are of low skill, but the trend from the past 3-4 days of CFS runs has really backed off on shear across much of the Atlantic for this time period:

[Hammy]

CFS (after seemingly having a limit on how far out it would go) is back up and running, the model shows the Atlantic remaining largely quiet for the first half of August and then picking up after that. Looks like a burst of MDR activity in the last week of August into early September, a short lull, and then more continuous activity with the MDR remaining in play through mid-October.

Most MDR storms seem to recurve, including 4-5 long trackers, but a few make it to the Bahamas. Gulf/Caribbean maps are not loading beyond about 400h but there were a few storms that crossed over Florida and appeared to strengthen after so that could be a hot spot.

[Category5Kaiju]

CFS (after seemingly having a limit on how far out it would go) is back up and running, the model shows the Atlantic remaining largely quiet for the first half of August and then picking up after that. Looks like a burst of MDR activity in the last week of August into early September, a short lull, and then more continuous activity with the MDR remaining in play through mid-October.

Most MDR storms seem to recurve, including 4-5 long trackers, but a few make it to the Bahamas. Gulf/Caribbean maps are not loading beyond about 400h but there were a few storms that crossed over Florida and appeared to strengthen after so that could be a hot spot.

I thought there was a ridge predicted to be over Eastern Canada, making recurves less likely (if I recall Eric Webb was the one who showed that first)? Also how exactly is the CFS able to forecast storm tracks that far out (I did not know CFS even had that ability until now to be honest)