ATL: FOUR - Remnants - Discussion

[weathaguyry]

a TS can intensity under 10-20 kts of shear

Not always, see Adrian, Beatriz, and Calvin. Struggled with 10-15kts of shear under very high OHC/SST's.

think those had mid level shear, which is far more destructive as it disrupts the column far lower in the troposphere

To add, Beatriz and Calvin formed very close to land, so there was little time to intensify, and more land interaction

[cycloneye]

, Kingarabian ,what do the EC ensembles have?

[Kingarabian]

a TS can intensity under 10-20 kts of shear

Not always, see Adrian, Beatriz, and Calvin. Struggled with 10-15kts of shear under very high OHC/SST's.

think those had mid level shear, which is far more destructive as it disrupts the column far lower in the troposphere

How's the midlevels looking for 94L?

[Kingarabian]

, Kingarabian ,what do the EC ensembles have?

I'll take a look right now and then post it after.

And 12z Euro Parallel just came out.

[tolakram]

Last one from me in this run. Wondering why a TC wouldn't intensify in an environment like this.

I posted an SST map but it got moved. I was wondering if the lower SST's in this area is something the GFS is picking up on? 27+ should be warm enough but they are marginal.

[Bocadude85]

tolakram meaning unfavorable for threats coming from the east in terms of trofiness. Some say its luck past few years but its hard to lean either way honestly as i think its possible overall gerneral steering pattern has changed. Not complaining either way.

To add i think over favorable environment in the MDR " could " mean a rather active capeverde season.

The 12Z Euro 240 hr vort is over S. Fla, 12Z Canadian is into E. Fla coast, 12Z JMA is in the Central Bahamas and the 18z GFS has shifted southwest by a good 500 miles at its 240 hour point. Most of the Global models have shifted southwest today. Albeit weaker in some cases.

[Kingarabian]

, Kingarabian ,what do the EC ensembles have?

So for the 51 EPS members:

Generally through 5-7 days as it gets closer to the Lesser Antilles
24 have a weak low between 1011mb-1013mb about to go just north or across the lesser ants.
23 have no development
4 have TC development east of the Lesser Antilles

Through 10 days it's virtually gone. I see like maybe 5-6 members trying to recurve a weak low, and around 4 members have a weak vort over Florida.

[Kingarabian]

12z Euro Parallel is not done rolling but so far it's the same story. More north than the operational Euro, but weaker as it opens up the low into a wave over Puerto Rico. So a lot of rain for you, Cycloneye.

Actually the 12z Euro Parallel is considerably weaker after 144 hours compared to the OP. The vort signature is almost non existent.

[abajan]

The 8 PM TWO shows a somewhat surprising curve in the "cone".

[cycloneye]

8 PM TWO: 40%-70%

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Mon Jul 3 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

Showers and thunderstorms associated with a nearly stationary area
of low pressure located about 700 miles southwest of the Cabo Verde
Islands have become a little better organized since yesterday.
Additional development is likely, and a tropical depression could
form during the next several days before environmental conditions
become a little less conducive for development at the end of the
week. The disturbance is expected to begin moving slowly
northwestward on Tuesday, followed by a faster west-northwestward
motion across the tropical Atlantic Ocean through the remainder of
the week.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...high...70 percent.

$$
Forecaster Berg

[tarheelprogrammer]

18z GEFS much weaker with development.

12z:


18z:


Trending toward Euro and its ensembles.

[cycloneye]

The 8 PM TWO shows a somewhat surprising curve in the "cone".

Yes but also it weakens as it approaches the islands.

[AJC3]

looks to be overdoing the weakening. It's acting as if it is running into 40 kt of shear

Shear is shear even if it's 10-20kts.

While "Shear is shear", not all shear is created equally. In addition to how the shear vector varies in magnitude, consideration has to be given to:

1) Both components of the 3D spatial variance - i.e. height/pressure level (z), in addition to LALO (x/y). i.e. shear below outflow level (say 500-300MB rather than 200MB), often referred to as "undercutting shear" seems to be worse than shear AT outflow level,
2) Whether the shear is divergent, neutral, or convergent. Shear is generally more detrimental the less divergent it is.
3) The ambient environment . Shear plus lower MRH mid level air is worse than shear with higher MRH mid level air. I believe this is an area Alyono's research/expertise.

So, we need to look at all the aspects of the shear involved, and how much weight should be given to each one.

[ScottNAtlanta]

Is it not pretty unusual for something this early in the season to move so slowly? That tends to happen much later in the season and certainly not in the beginning of July. Also might indicate the SAL wont be as strong this year

[floridasun78]

this case with early july system coming off Africa their not going strong system not time season for Africa system not surprise see nhc making system near islands

[floridasun78]

their reason we don't go first few runs models you see their showing weakling system as get close islands when first few run show stronger system that i wait later runs as get past 50w see how runs doing with system

[msbee]

The 8 PM TWO shows a somewhat surprising curve in the "cone".

Yes but also it weakens as it approaches the islands.

Luis, it should weaken? I did not see mention of that. Can you clarify please?

[gfsperpendicular]

The 8 PM TWO shows a somewhat surprising curve in the "cone".

Yes but also it weakens as it approaches the islands.

Also worth noting that the development area has lengthened again .. meaning either it will speed up ... or development will be slower.

[GCANE]

I hate to say it, but I am not buying 18Z GFS weakening it in the Bahamas.

355K PV realitively weak ahead of its track and a TUTT to the east for ventilating a poleward outflow channel.

There will be enough unstable air to keep convection firing.

If this tracks a bit more south, afternoon thunderstorms firing over Cuba / Hispaniola could keep mid-levels moist and feeding into it.

[cycloneye]

00z Best Track:

AL, 94, 2017070400, , BEST, 0, 88N, 332W, 25, 1011, LO