ATL: FIONA - Post-Tropical - Discussion

[gatorcane]

18Z Guidance:

[Hammy]

Based on the satellite presentation and microwave imagery, it seems the convection was racing westward yesterday and this morning due to the elongated nature of the system--the eastern convection was essentially slingshot around the northern side, but it seems like it's beginning the consolidation process now, even if it's still elongated at the moment.

[LarryWx]

12Z UKMET track:

Interestingly, this like the 12Z Euro shows a WSW path intitially before a sharp turn to the NW tomorrow. Let's see if that sharp of a turn actually happens tomorrow. If it does actually turn NW as a TC, a fish would be extremely likely per climo despite the progged temporary turn back to the W.

[Kazmit]

Models have a bad habit of bringing these things north way too quickly. I wouldn't be surprised if this is still south of 20N in 7 days.

Yeah, the NHC and all the models show an immediate trend north before a recurve, which takes in into the Central Atlantic, harmlessly. But it's already quite far south, and it could track into the Caribbean, or go north of the Leeward islands and Puerto Rico.

[Kazmit]

Woah, some intensity models show development into a Cat 1 or 2.

The models still show an immediate trend to the northwest. I still think it will go more south than predicted.

[LarryWx]

Up to 40%-50%

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT MON AUG 15 2016

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

1. Disorganized cloudiness and thunderstorms over the far eastern
Atlantic are associated with a tropical wave located a few hundred
miles south-southwest of the Cabo Verde Islands. Environmental
conditions are conducive for gradual development of this disturbance
during the next few days, but could become less favorable later this
week. The system is expected to move west-northwestward to
northwestward at 10 to 15 mph into the central tropical Atlantic
during the next several days.
* Formation chance through 48 hours...medium...40 percent
* Formation chance through 5 days...medium...50 percent

Forecaster Kimberlain

Note that this TWO expects it to move WNW to NW but it is not doing that yet and it has actually been moving WSW today.

From the best of my recollection, it's actually pretty common for these systems to move in a somewhat south of west direction while in the far eastern Atlantic. That motion has little, if any, bearing on the eventual track.

Interesting because I did a study a while back that showed that once a TC forms (which has yet to happen with 98L and it appears the WSW movement may have ended meaning it likely won't apply here), a SW or WSW move in the E Atlantic reduce the chance of an early recurve. I think that the idea is that the SW/WSW move means that the TC is to the east of the axis of the high to the north.

[Nimbus]

Following that reasoning if the ridging is migrating west then a slower forward motion means it stays further south?

I think part of the reason 98L has a low latitude rotational center is simply that it is finding better moisture near the ITCZ. If it closes off into a storm and swings poleward the steering might be different.

[LarryWx]

Following that reasoning if the ridging is migrating west then a slower forward motion means it stays further south?

That seems logical.

[USTropics]

Trio of tweets from Ryan Maue on 98L's future:

 https://twitter.com/RyanMaue/status/765252965984772096


 https://twitter.com/RyanMaue/status/765268516626989056

[cycloneye]

Up to 50%-70%

No mention of unfavorable conditions.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON AUG 15 2016

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

A large area of cloudiness and thunderstorms over the eastern
Atlantic several hundred miles southwest of the Cabo Verde
Islands is associated with a tropical wave. Environmental
conditions are expected to be conducive for development during
the next few days, and a tropical depression is likely to form
while the system moves west-northwestward to northwestward
toward the central tropical Atlantic.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

$$
Forecaster Brown

[Caneman12]

Up to 50%-70%

No mention of unfavorable conditions.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON AUG 15 2016

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

A large area of cloudiness and thunderstorms over the eastern
Atlantic several hundred miles southwest of the Cabo Verde
Islands is associated with a tropical wave. Environmental
conditions are expected to be conducive for development during
the next few days, and a tropical depression is likely to form
while the system moves west-northwestward to northwestward
toward the central tropical Atlantic.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

$$
Forecaster Brown

Yeah because it won't encounter unfavorable conditions

[cycloneye]

Up to 50%-70%

No mention of unfavorable conditions.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON AUG 15 2016

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

A large area of cloudiness and thunderstorms over the eastern
Atlantic several hundred miles southwest of the Cabo Verde
Islands is associated with a tropical wave. Environmental
conditions are expected to be conducive for development during
the next few days, and a tropical depression is likely to form
while the system moves west-northwestward to northwestward
toward the central tropical Atlantic.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

$$
Forecaster Brown

Yeah because it won't encounter unfavorable conditions

In case you missed the 2 PM TWO here is what they said about the environmental conditions.

Environmental
conditions are conducive for gradual development of this disturbance
during the next few days, but could become less favorable later this
week.

[tolakram]

Latest saved loop

[NDG]

Up to 50%-70%

No mention of unfavorable conditions.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT MON AUG 15 2016

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

A large area of cloudiness and thunderstorms over the eastern
Atlantic several hundred miles southwest of the Cabo Verde
Islands is associated with a tropical wave. Environmental
conditions are expected to be conducive for development during
the next few days, and a tropical depression is likely to form
while the system moves west-northwestward to northwestward
toward the central tropical Atlantic.
* Formation chance through 48 hours...medium...50 percent
* Formation chance through 5 days...high...70 percent

$$
Forecaster Brown

Yeah because it won't encounter unfavorable conditions

In case you missed the 2 PM TWO here is what they said about the environmental conditions.

Environmental
conditions are conducive for gradual development of this disturbance
during the next few days, but could become less favorable later this
week.

They went from "will encounter unfavorable conditions by the end of the week" at 8 AM to "could encounter unfavorable conditions" at 2 PM to no mention at all now of encountering unfavorable conditions.
I think at some point it will encounter less favorable conditions over the middle of the Atlantic especially if it indeed gains too much latitude, but by that time I think it will be already a named system, IMO.

[psyclone]

Those development probs have escalated quite rapidly. We've entered the time of the year where disturbances can form in less than ideal conditions, or the expectation of unfavorable conditions can change slightly or fail to materialize. in other words, vigilance is now warranted. While this system may not ultimately threaten anyone...we can be fairly confident that something else will be popping.

[Kazmit]

Code red. Here comes TD 6.

[cycloneye]

00z Best Track:

Location: 9.7°N 26.7°W
Maximum Winds: 25 kt Gusts: N/A
Minimum Central Pressure: 1008 mb
Environmental Pressure: 1012 mb
Radius of Circulation: 160 NM
Radius of Maximum Wind: 80 NM

[MGC]

Conditions don't look that unfavorable ahead of 98L. Little shear, fairly moist environment, not moving too fast. Only concern is some dry air to 98L north, but it is moving to the dry air not into it. 98L has been slowly getting better organized with time. I expect both the short and long term formation chances to increase with time.......MGC

[Frank2]

Like those models - it's the only time I like fish : )

[gatorcane]

Looking at the floater, seems a circulation is becoming more pronounced as it moves west or just south of west. I see it at 9N, 34W. That is not where the NHC put the X though:

http://rammb.cira.colostate.edu/ramsdis ... display=12