Tropical Wave off the African Coast (Is Invest 92L)

[LarryWx]

18z GEFS...

https://i.postimg.cc/pLQ3Bpn6/A7-DA9-F88-02-E8-4656-9-FEB-DCDAFE3474-F9.png

The OTS camp on this 18Z GEFS is further OTS overall. So, the spread is larger than the prior 2 runs since they didn’t have as many well OTS.

[LarryWx]

18z EPS...Huge latitude spread

https://i.imgur.com/wtkt3Bm.png

The overall features over NA and the W ATL are somewhat further east than the 12Z had. That kind of thing along with a further east TC are what we need to root for to minimize the chance of this coming all the way to the Bahamas and Conus. But we have a long way to go and no nobody knows and the ones furthest west in this group are the most dangerous ones.

[ColdMiser123]

Very complicated pattern verbatim, I suspect we will see EPS members all the way to the southeast US coast and members recurve east of Bermuda given the complicated progression with the mid-level trough moving westward, and how exactly it erodes the ridge to the north.

Yes, perhaps you can explain this anomalous movement that is being shown by ECWMF, UKMET and CMC? They all show the wave developing and then basically stopping in the central atlantic, something you might see in late October, as opposed to early Sept. Is this due to an unusually deep trough?

A mid to upper level trough is forecast to move westward, which should erode the ridge to the north somewhat. Eventually though on the 12z Euro, the trough gets kicked eastward. On that particular run of the Euro, you have conflicting steering flow in the mid-levels, with the western portion of the ridge favoring a net southwest movement, while the eastern part of the ridge favors a more northeastward movement. These two flows cancel each other out to an extent, which gives you the slow movement that some operational guidance is showing.

The final track for this may end up being determined by which part of the ridge ends up being slightly stronger. No way of knowing this far out.

[storminabox]

This wave will probably turn OTS if it strengthens early on, due to its interaction with the strong TUTT nearby, which weakens the southern flank of the ridge.

This looks to be another case of: the longer it stays weak, the more trouble it could cause. I would prefer a quickly intensifying storm that stays strong for a while and recurved relatively early. I’m not like the recent model trend of persistent ridging off the east coast...

[LarryWx]

For the SE US. the 0Z GEFS of 9/3 is more benign for the SE CONUS and Bahamas with only 1 member landfalling in the SE and 2 others skirting NC compared to 5, 7, and 5 landfalls on the prior three runs. OTOH, the NE US is more threatened on this run.

[AJC3]

Tropical Weather Discussion
NWS National Hurricane Center Miami FL
205 AM EDT Thu Sep 03 2020

...TROPICAL WAVES...

A tropical wave is along 21W, from 18N southward, moving
westward 10 to 15 knots. The wave is expected to merge with a
disturbance, that is centered a few hundred miles to the
southeast of the Cabo Verde Islands, toward the end of the week.
Gradual development of this system is possible. It is possible
that a tropical depression may form during the weekend or early
next week, while it moves westward in the eastern and central
tropical Atlantic Ocean. Please, read the North Atlantic
Tropical Weather Outlook for the latest updates. Precipitation:
any nearby precipitation is in the monsoon trough.

[us89]

I’m surprised this hasn’t been designated Invest 92L yet, since NHC has consistently given this wave higher development odds than the nearby 91L. Latest TWO puts this at 20/70, with 91L only at 20/40.

[cycloneye]

A tropical wave located off the coast of west Africa is merging with
another disturbance located a couple of hundred miles south of the
Cabo Verde Islands, resulting in an extensive area of disorganized
showers and thunderstorms. Development of this system is likely to
be slow during the next couple of days while it moves west-
northwestward at about 15 mph, and a tropical depression is more
likely to form early next week over the central tropical Atlantic
where environmental conditions are forecast to be more favorable
for development.
* Formation chance through 48 hours...low...20 percent.
* Formation chance through 5 days...high...70 percent.

[plasticup]

18z GEFS...

https://i.postimg.cc/pLQ3Bpn6/A7-DA9-F88-02-E8-4656-9-FEB-DCDAFE3474-F9.png

The OTS camp on this 18Z GEFS is further OTS overall. So, the spread is larger than the prior 2 runs since they didn’t have as many well OTS.

I don't see any OTS solutions there. I see a lot of Bermuda solutions.

[gatorcane]

06Z GFS track animation, turning north and recurving east of the Lesser Antilles:

[hurricaneCW]

06Z GFS track animation, turning north and recurving east of the Lesser Antilles:

https://i.postimg.cc/g2BFSXdW/gfs-mslp-pcpn-atl-fh6-240.gif

Actually ends up between Bermuda & east coast at end of run.

I'd be willing to bet this doesn't harmlessly recurve and wouldn't be surprised to see models keep adjusting west with it.

[Aric Dunn]

dont expect 91L to survive.

the two waves off africa have already begun to merge and is mich larger than 91L

and 91L has really begun to stretch out and is beginning to get absorbed.

we will probably only get 1 system out of this whole mess.

[ConvergenceZone]

The general consensus is always out to sea when storms this Far East, not to mention the time of year But there is always a very slight chance otherwise

[LarryWx]

18z GEFS...

https://i.postimg.cc/pLQ3Bpn6/A7-DA9-F88-02-E8-4656-9-FEB-DCDAFE3474-F9.png

The OTS camp on this 18Z GEFS is further OTS overall. So, the spread is larger than the prior 2 runs since they didn’t have as many well OTS.

I don't see any OTS solutions there. I see a lot of Bermuda solutions.

Bermuda is well out in the middle “of the sea” so to speak. So, anything near there is OTS from my perspective. OTS doesn’t at all mean Bermuda can’t be affected.

Late morning update through 6Z model consensus: well OTS possibility is higher than it was 24 hours ago although it is still VERY early. But that might mean higher risk to Bermuda.

I’m still a bit nervous for the CONUS about how mid Sept will play out due to a combo of near record warm W Pacific waters, La Niña, and the +AMO. If not the SE, the NE US may have a threat.

Even if no MDR wave gets close, don’t discount the chance for something homegrown that can turn out to be dangerous in this environment. When there are strong highs to the north, that is the JB named “ridge over troubled water” pattern because the strong high leads to low level convergence to their south, which tends to lead to rising air because the low level air piles up and it has to go somewhere. This rising air then causes low pressure to form at the surface.

[Spacecoast]

ECMF Wind tracks Trend:
09/02 12z

09/03 00z

Track Density Trend:
09/02 12z - 3 potential cyclones

09/13 00z -6 potential cyclones

[cycloneye]

Real Earth visible loop. I can see two circulations.

https://realearth.ssec.wisc.edu/?produc ... HyT53X_Kk#

[SFLcane]

12z GFS much weaker as other models continues to recurve this wave near 60w.

[LarryWx]

GFS as other models continues to recurve thus wave near 60w.

There’s no reason imo based on model consensus trends to not increasingly favor this particular wave to recurve well OTS regardless of how much ridging there is in the W Atlantic at times during the first half of Sep. If so, the CONUS may end up having to watch for something else, including homegrown.

['CaneFreak]

Thank you for posting. Seeing some interesting trends here. The 12Z runs are consistently north and the 00Z runs are consistently south. Hmmm. This latest run shows that one disturbance pretty far to the southwest. The GFS op the past several runs has also been trending more to the southwest with time. Keep posting these. This will be interesting to follow in the days ahead.

ECMF Wind tracks Trend:
09/02 12z
https://i.ibb.co/J2vnkJr/basin-wind-ecmf-gen-atl-2020090212.png
09/03 00z
https://i.ibb.co/yQqZBg7/basin-wind-ecmf-gen-atl-2020090300.png
Track Density Trend:
09/02 12z - 3 potential cyclones
https://i.ibb.co/stLGPPt/ecmf-gen-atl-2020090212.png
09/13 00z -6 potential cyclones
https://i.ibb.co/3rhdY7b/ecmf-gen-atl-2020090300.png

[gatorcane]

Saved 12Z GFS loop with a recurve out into the Central Atlantic and even with it weak. The storm to the east also heads towards the North Atlantic graveyard: