ATL: DORIAN - Post-Tropical - Discussion

[gatorcane]

12Z CMC, just north of the Leewards at 132 hours:

[beoumont]

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

If the forecaster on duty at the NHC thought it was a tropical storm at the surface, he would call it a tropical storm. The only "fudging" I can imagine by the most conservative of NHC personnel would be to make sure a system of a particular intensity or surface organization persists for at least 3-6 hours. (There are boats and ships and lives out in the ocean that rely on accurate observations for safety concerns; hence, IMO, the weather service personnel charged with the duty and responsibility to provide those accurate observations has no room to play games).

[CrazyC83]

What is that second low between Bermuda and Atlantic Canada - tropical?

[Blown Away]

12z GEM (CMC - Global Environmental Multiscale Model) has developed low landfalling in Central Florida in 10 days...
http://www.tropicaltidbits.com/analysis ... opics.html
OR http://www.tropicaltidbits.com/analysis ... opics.html

[cycloneye]

18z Best Track

AL, 98, 2013072318, , BEST, 0, 123N, 237W, 25, 1008, LO

[cycloneye]

TROPICAL CYCLONE GUIDANCE MESSAGE
NWS NATIONAL HURRICANE CENTER MIAMI FL
1725 UTC TUE JUL 23 2013

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

DISTURBANCE INVEST (AL982013) 20130723 1800 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
130723 1800 130724 0600 130724 1800 130725 0600

LAT LON LAT LON LAT LON LAT LON
BAMS 12.3N 23.7W 13.4N 26.8W 15.0N 30.4W 16.4N 34.5W
BAMD 12.3N 23.7W 13.2N 26.7W 14.3N 29.7W 15.5N 32.7W
BAMM 12.3N 23.7W 13.5N 26.6W 15.0N 30.0W 16.4N 33.7W
LBAR 12.3N 23.7W 13.0N 26.5W 14.2N 29.8W 15.4N 33.0W

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
130725 1800 130726 1800 130727 1800 130728 1800

LAT LON LAT LON LAT LON LAT LON
BAMS 17.3N 39.0W 18.5N 48.2W 19.4N 56.7W 20.3N 63.7W
BAMD 16.5N 35.9W 18.1N 41.8W 18.8N 45.9W 18.1N 47.6W
BAMM 17.6N 37.6W 19.2N 45.1W 19.9N 51.8W 20.2N 57.5W
LBAR 16.4N 36.4W 17.2N 42.9W 18.2N 48.0W .0N .0W

...INITIAL CONDITIONS...
LATCUR = 12.3N LONCUR = 23.7W DIRCUR = 275DEG SPDCUR = 10KT
LATM12 = 12.2N LONM12 = 21.7W DIRM12 = 270DEG SPDM12 = 10KT
LATM24 = 12.2N LONM24 = 19.3W
WNDCUR = 25KT RMAXWD = 40NM WNDM12 = 25KT
CENPRS = 1008MB OUTPRS = 1013MB OUTRAD = 150NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

[gatorcane]

12z GEM (CMC - Global Environmental Multiscale Model) has developed low landfalling in Central Florida in 10 days...
http://www.tropicaltidbits.com/analysis ... opics.html

The NAVY model kills 98L near the Northern Leewards. GFS moves 98L into Hispanolia which kills it. I wonder if the GFS shifts a little north in the long-range if it will redevelop 98L like the CMC is doing as it looks like conditions could be better next week when it is further west assuming it survives this week?

[Hybridstorm_November2001]

What is that second low between Bermuda and Atlantic Canada - tropical?

A subtropical system that the CMC alone, thus far, spins up in the vicinity of Bermuda near the end of the period.

[ROCK]

I dont think anyone is playing games. We were just stating the obvious....

[cycloneye]

Up to 60%

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
200 PM EDT TUE JUL 23 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A SURFACE LOW PRESSURE SYSTEM LOCATED A COUPLE OF HUNDRED MILES
SOUTH OF THE CAPE VERDE ISLANDS IS MOVING WESTWARD AT ABOUT 10 MPH.
THIS SYSTEM HAS A WELL-DEFINED CIRCULATION...AND ONLY A SMALL
INCREASE IN THE AMOUNT AND ORGANIZATION OF THE THUNDERSTORM
ACTIVITY WOULD RESULT IN THE FORMATION OF A TROPICAL DEPRESSION.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE FAVORABLE FOR
DEVELOPMENT DURING THE NEXT DAY OR SO BEFORE UPPER-LEVEL WINDS AND
OCEAN TEMPERATURES BECOME LESS CONDUCIVE BY THURSDAY. THIS SYSTEM
HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.


$$
FORECASTER STEWART

[gatorcane]

and note they indicate it is moving westward now not west-northwestward...

[ninel conde]

they may not want to name another system thats destined to fall apart a few advisories after getting named. Atlantic still dominated by dry air. easterly shear is also pushing the convection away from the center.

[cycloneye]

and note they indicate it is moving westward now not west-northwestward...

And also note that now they say Thursday instead of Wednesday when things turn less favorable.

[gatorcane]

Luis yeah I noticed that also, gives it more of a chance to become a named system.

Mariner's rule graphic updated:

[SouthDadeFish]

What I don't get is how "ONLY A SMALL INCREASE IN THE AMOUNT AND ORGANIZATION OF THE THUNDERSTORM ACTIVITY WOULD RESULT IN THE FORMATION OF A TROPICAL DEPRESSION" but yet it is only 60%.... Last year the NHC consistently underestimated the probability of genesis and anything that they gave a 70% chance or greater became a tropical cyclone. Last year when then gave a 60% chance, the disturbance developed 75% of the time. Chances of development look good to me, but whether or not it will survive over the next five days is highly questionable.

[Gustywind]

2 PM discussion.

...SPECIAL FEATURES...
A TROPICAL WAVE IS JUST SE OF THE CAPE VERDE ISLANDS EXTENDING
FROM 15N22W TO 09N22W MOVING AT 10 KT.
A 1009 MB LOW IS EMBEDDED ON THE WAVE AXIS NEAR 12N22W. THIS SYSTEM IS IN A HIGH MOIST
ENVIRONMENT AS NOTED BY THE SSMI TOTAL PRECIPITABLE WATER IMAGERY. SCATTERED MODERATE CONVECTION IS FROM 11N-14N BETWEEN 22W-26W.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BECOME MORE FAVORABLE FOR TROPICAL CYCLONE DEVELOPMENT. CURRENTLY...THERE IS A HIGH CHANCE FOR THIS SYSTEM TO BECOME A TROPICAL CYCLONE
DURING THE NEXT 48 HOURS.

[SouthDadeFish]

A recent microwave pass reveals some deep convection with a somewhat sheared look:

[Aric Dunn]

we have all seen worse looking TS .. by definition its technically already a TC .. they will probably wait till morning to see if more convection can fire

[SouthDadeFish]

The NHC may be waiting for T Numbers to come in at 1.5 or higher... Let's see what the 18Z analysis shows.

[gatorcane]

Looking at the latest SHIPS model guidance, it looks like it is seeing a little bit less shear over the coming days than what it was showing yesterday. I posted this in the models thread.