ATL: DORIAN - Post-Tropical - Discussion

[blp]

FWIW, The FIM still likes our system.

[cycloneye]

Latest ASCAT pass made at 6:38 AM EDT.

[Blown Away]

12z

[GCANE]

Latest core temp at 0.5C, narrow, no inversions.

http://rammb.cira.colostate.edu/product ... 4_TANO.GIF

Latest rain rate still strong, measured about 3 hrs ago which looked to have fired just east of the LLC.

http://www.nrlmry.navy.mil/htdocs_dyn_a ... W.73pc.jpg

http://rammb.cira.colostate.edu/product ... 230700.jpg

[gatorcane]

Not looking nearly as good as it did yesterday but still there is a very large moisture envelope when analyzing WV imagery of the system. We will see if it can rebuild some convection or not.

Also not sure why NHC states it is moving WNW either when it is moving W based on best track data.

[CalmBeforeStorm]

Not looking nearly as good as it did yesterday but still there is a very large moisture envelope when analyzing WV imagery of the system. We will see if it can rebuild some convection or not.

Also not sure why NHC states it is moving WNW either when it is moving W based on best track data.

http://www.ssd.noaa.gov/PS/TROP/floater ... short.html

I think the structure is better. It just needs convection.

[Gustywind]

From Dr. Jeff Masters on 98L.
http://www.wunderground.com/blog/JeffMa ... rynum=2470

African Tropical Wave 98L Moving Over Cooler Waters

A strong and well-organized tropical wave that moved off the coast of Africa on Monday (98L) is located a few hundred miles south of the Cape Verde Islands and is moving west-northwest at 15 - 20 mph. Satellite images show that 98L has a decent amount of spin, but only a modest amount of heavy thunderstorms that have not changed much in intensity or areal coverage this morning. The wave is under a moderate 10 - 20 knots of wind shear, which will tend to allow slow development. A large amount of dry air lies to the north and west of 98L, and this dry air will likely interfere with development later this week. The SHIPS model predicts that wind shear will stay in the moderate range through Saturday. Ocean temperatures are barely adequate for development, about 26.5°C today, and will be below average over the region of ocean 98L will be traversing on Wednesday and Thursday, 25 - 26°C. These temperatures are very marginal for development. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, does not favor increased chances of Atlantic tropical cyclone formation this week. The reliable computer models for tropical cyclone genesis do not predict that 98L will develop this week. In their 8 am EDT Tuesday Tropical Weather Outlook, NHC gave 98L a 40% chance of developing into a tropical cyclone by Thursday. 98L should maintain a west-northwest track through the week, and may spread heavy rains and gusty winds to the northern Lesser Antilles Islands beginning on Saturday night or on Sunday.

[cycloneye]

SSt's are marginal until 40W where they rise to above 80F westward from there.

[SouthDadeFish]

The earlier ASCAT pass shows the surface circulation becoming better defined, which was also suggested by the first visible satellite images today. Recently, a new convective burst has developed closer to the center. It looks like the system is experiencing a little bit of easterly shear judging the cloud pattern, but that is typical for tropical waves in this region. After seeing that ASCAT pass and the recent convective burst, I would put the odds of this system developing into a tropical cyclone a little higher, such as 60-70% within the next 48 hours. The main concern with development is the entrainment of dry air. Total Precipitable Water (TPW) imagery from CIMSS shows that some drier air is starting to push towards the system from the NE. There is also a large amount of dry air well to the NW of the system. The bursting convective pattern is very fragile to this dry air. If convection persists, I don't see too many reasons why this can't be classified as a tropical cyclone.

[SouthDadeFish]

Visible image from 14:15Z:

[Senobia]

12z

I'm not liking that lower track map at all.

I've been reading the discussion about this invest and the popular (here) opinion is - it's gonna poof, it's gonna get ripped apart, it's gonna die. So now I have some questions:

1. Is that still the popular consensus (dissipation, etc. in a few days)?
2. If not, is this going into the Gulf?
3. If it does, any guesses/estimates on intensity?

[Blown Away]

I'm not liking that lower track map at all.

I've been reading the discussion about this invest and the popular (here) opinion is - it's gonna poof, it's gonna get ripped apart, it's gonna die. So now I have some questions:

1. Is that still the popular consensus (dissipation, etc. in a few days)?
2. If not, is this going into the Gulf?
3. If it does, any guesses/estimates on intensity?

Models suggesting a minimal TS at best...I've seen no indication of a system more than minimal TS...

[ROCK]

agree...it looks like a TD from sat....clearly see the LLC as he is partly sheared...being so far out they probably wont call it for awhile, IMO....

[gatorcane]

The earlier ASCAT pass shows the surface circulation becoming better defined, which was also suggested by the first visible satellite images today. Recently, a new convective burst has developed closer to the center. It looks like the system is experiencing a little bit of easterly shear judging the cloud pattern, but that is typical for tropical waves in this region. After seeing that ASCAT pass and the recent convective burst, I would put the odds of this system developing into a tropical cyclone a little higher, such as 60-70% within the next 48 hours. The main concern with development is the entrainment of dry air. Total Precipitable Water (TPW) imagery from CIMSS shows that some drier air is starting to push towards the system from the NE. There is also a large amount of dry air well to the NW of the system. The bursting convective pattern is very fragile to this dry air. If convection persists, I don't see too many reasons why this can't be classified as a tropical cyclone.

I agree with you here. I had this system at a 50% chance of development yesterday evening and now may go with 60 or 70% also looking at the floater vis loop. It may not look as good from a convection perspective but the structure is excellent. Looks like it may even be a tropical storm but I am guessing it is so far out there and the models kill it off in a few of days anyway so the NHC won't pull the trigger as quickly.

http://www.ssd.noaa.gov/PS/TROP/floater ... short.html

[Gustywind]

Large Atlantic Tropical Disturbance Fights Dry Air

By Alex Sosnowski, Expert Senior Meteorologist
July 23, 2013; 8:45 AM

http://www.accuweather.com/en/weather-n ... r/15641010

An Atlantic tropical disturbance that moved off Africa Sunday is being monitored for development over the next couple of days and will reach some of the islands of the Caribbean this weekend.

The disturbance, a tropical wave of low pressure, was located near the Cape Verde Islands Tuesday and was producing spotty showers and thunderstorms in the region.

According to Hurricane Expert Dan Kottlowski, "This is the eighteenth and one of the largest tropical waves we have seen so far this season."

Slight circular motion to the cloud cover in the region has been observed Tuesday. Circular motion of clouds is an early sign of development for tropical systems.

The system appears to be experiencing some problems during the midday Tuesday," Kottlowski said.

Much of the tropical Atlantic was being influenced by dry air and dust this week. Dry air tends to work against tropical development.

As we have seen in the past, sometimes these systems, especially the larger ones, can overcome the surrounding dry air. However, the system would have a better chance of development through the middle of the week, rather than late in the week.
"As the feature continues to drift on a slightly north of west course, it is likely to encounter a zone of increasingly disruptive winds at mid-levels of the atmosphere this week," Kottlowski said.

At present course and speed, the system would be near the Leeward Islands this weekend and could brush some of the northern islands of the Caribbean next week as a tropical wave of low pressure or perhaps something stronger and more organized. Even if it does not develop fully, the system could bring a period of showers and thunderstorms to these islands.


We have already had three named tropical systems so far this season in the Atlantic. The next name on the list is Dorian.

Before a system becomes a tropical storm or hurricane, it must advance past a tropical disturbance (tropical wave) by developing a distinct circulation just above the sea surface.

Once this happens, it is upgraded to a tropical depression and assigned a number.

If sustained winds of 39 mph or higher are found, then the system is upgraded to a tropical storm and given a name.

Next, if sustained winds reach 74 mph or higher, then system upgraded to a hurricane.

Occasionally, a system can go right from a tropical disturbance to a tropical storm. This happens during rapid development and can occur when aircraft cannot investigate the system often enough or sufficient high-resolution satellite data are not available.

[cycloneye]

Here is a good loop. Posting link to not affect the TT bandwidch.

http://www.tropicaltidbits.com/satellit ... tl_vis.gif

[gatorcane]

Here is a good loop. Posting link to not affect the TT bandwidch.

http://www.tropicaltidbits.com/satellit ... tl_vis.gif

Nice loop Luis. How this is only an invest with a 40% of development is perplexing to me.

[GCANE]

Tropical Cyclone Formation Alert posted

http://www.nrlmry.navy.mil/atcf_web/ima ... 072306.gif

[Blown Away]

12z GFS...Uneventful...Weak low across the Atlantic that gets burried in Hispaniola...Once the low reaches 55W it dies down...GFS not seeing any development up to Aug 8th
http://www.tropicaltidbits.com/analysis ... opics.html

[gatorcane]

12Z NAVY model (NAVGEM) kills it off but then brings it back a little once it gets further west. Approaching the Northern Leewards at 138 hours: