ATL: ISAAC - Post-Tropical - Discussion

[Gustywind]

For the first time and given the latest TWD, 94L is officialy mentionned as a special feature....

2AM TWD

000
AXNT20 KNHC 180602
TWDAT

TROPICAL WEATHER DISCUSSION
NWS NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT AUG 18 2012

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS OF
SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM THE
EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON SATELLITE
IMAGERY...WEATHER OBSERVATIONS...RADAR...AND METEOROLOGICAL
ANALYSIS.

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0545 UTC.

...SPECIAL FEATURES...

A TROPICAL WAVE IS LOCATED IN THE ERN ATLC EXTENDING FROM 18N22W
TO A 1009 MB LOW NEAR 11N25W...EMBEDDED WITHIN THE MONSOON GYRE
DESCRIBED BELOW. SCATTERED SHOWERS AND THUNDERSTORMS ARE FROM
10N-15N BETWEEN 23W-28W...WITHIN THE BROAD CONVECTIVE REGION
ASSOCIATED TO THE MONSOON TROUGH. SLOW DEVELOPMENT OF THIS WAVE
IS POSSIBLE DURING THE NEXT FEW DAYS AS IT MOVES TOWARD THE WEST
AT 13 TO 17 KT. THIS SYSTEM HAS A MEDIUM CHANCE OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

[Gustywind]

Stu Ostro, Senior Meteorologist, The Weather Channel

Aug 18, 2012 12:54 am ET

http://www.weather.com/newscenter/hurri ... index.html

ATLANTIC

- The healthy disturbance we tracked across Africa for days in the "monsoon trough" of low pressure is now over the water and has a high probability of becoming a tropical cyclone as it traverses the Atlantic, though so far it's being slow to develop. Models had been mostly depicting a track in which it at most brushes the Leewards as it turns northwest, then stays out at sea with the only land areas potentially in play being Bermuda or the eastern Canadian Maritimes. However, an alternative scenario has been for it to more directly affect the northeast Caribbean islands and/or come closer to the United States, and some recent model runs have trended in that direction. Upshot: those islands are potentially in play, and the jury is still out on the system's ultimate destination.

[Gustywind]

This morning's discussion of 94L by Rob of Crown Weather.

The following post is NOT an official forecast and should not be used as such. It is just the opinion of the poster and may or may not be backed by sound meteorological data. It is NOT endorsed by any professional institution including storm2k.org. For Official Information please refer to the NHC and NWS products.

http://www.crownweather.com/?page_id=4557

Invest 94L:
Invest 94L, a tropical wave which is located about 250 miles or so to the southwest of the Cape Verde Islands, is of significant concern to me and I will say that right up front. Latest analysis early this morning shows that shower and thunderstorm activity is gradually becoming more consolidated and is slowly increasing. Additionally, the 850 millibar vorticity chart shows that the amount of spin associated with 94L is also slowly increasing.

Invest 94L is currently tracking to the west at a forward speed of 15 to 20 mph and I expect this westward track to continue right into a majority of next week. As for strengthening, I think we will see gradual intensification and this system seems destined to become Tropical Storm Isaac by either Sunday night or during the day Monday. Beyond that, environmental conditions are favorable for strengthening throughout much of next week and I do feel confident enough to say that I think this will become a hurricane by about the middle part of next week.

The latest GFS model guidance has shifted further west with the overall track of 94L and forecasts it to significantly impact Barbados and much of the Lesser Antilles with hurricane conditions from Thursday afternoon through Thursday night and into Friday morning. After that, the GFS model forecasts future Isaac to impact Puerto Rico with hurricane conditions by next Saturday. From there, the longer range GFS model seems to suggest a track north and then northeast about halfway between the US East Coast and Bermuda during the week of August 27th.

The latest European model guidance has a much weaker system that never really closes off into a storm. This leads to a Caribbean cruiser by late next week into next weekend. Right now, given the presentation of how 94L looks and that the overall pattern in the Atlantic Basin is favorable for an intensifying tropical cyclone, I think the European model guidance forecast seems unlikely and I’m leaning much more towards the stronger GFS model forecast.

So, here are my thoughts on Invest 94L: I do think that this system poses an eventual threat to the Lesser Antilles. Given the fact that the ridge of high pressure to the north of 94L is fairly strong, I see no evidence of a turn to the northwest before it reaches the Lesser Antilles. Additionally, the fact that the intensity guidance is insistent on significant strengthening to not only hurricane strength, but major hurricane strength leads me to believe that all interests in the Lesser Antilles, as well as Barbados should closely monitor the progress of this system for you may have a hurricane knocking on your door by Thursday.

Needless to say, I will be monitoring Invest 94L closely and will keep you all updated.

[cycloneye]

Up to 40%

SHOWER AND THUNDERSTORM ACTIVITY CONTINUES IN ASSOCIATION WITH A
TROPICAL WAVE LOCATED A COUPLE HUNDRED MILES SOUTHWEST OF THE CAPE
VERDE ISLANDS. CONDITIONS APPEAR CONDUCIVE FOR GRADUAL DEVELOPMENT
DURING THE NEXT FEW DAYS...AND THIS SYSTEM HAS A MEDIUM CHANCE...40
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS
AS IT MOVES WESTWARD AT 15 TO 20 MPH.

[tolakram]

Latest saved loop

[tolakram]

Latest Sahara Air Layer Analysis (saved)

[Gustywind]

Concerning 94L here is an interresting snippet from our Pro Mets of Meteo-France Guadeloupe (latest weather forecast 4AM) see below. Looks like they're pretty confident on thing : a cyclonic feature should cross somewhere, maybe enough close the Leewards.
I'm a bit surprised, honestly, that's pretty rare to read so early a thing like that from Meteo France while 94L is (for the moment) far away from the Carib islands . Those who live in the Eastern Carib should stay vigilant during the next couple of days.

Trend for Wednesday August 22 and Thursday 23 August:
"Wednesday and Thursday, the proximity of a cyclonic phenomenon could result in a perturbed weather, with probably heavy rains, and a strengthening of the wind and swell, which may also take unusual directions. The path and the strengh of this phenomenon are still very uncertain, also keep you well informed about the weather forecast next week"!

[Gustywind]

8 AM TWD

A TROPICAL WAVE IS LOCATED IN THE ERN ATLC EXTENDING FROM 18N23W
TO A 1008 MB LOW NEAR 12N27W...EMBEDDED WITHIN THE MONSOON GYRE
DESCRIBED BELOW. SCATTERED SHOWERS AND THUNDERSTORMS ARE FROM
11N-15N BETWEEN 26W-31W...WITHIN THE BROAD CONVECTIVE REGION
ASSOCIATED TO THE MONSOON TROUGH. CONDITIONS APPEAR CONDUCIVE
FOR GRADUAL DEVELOPMENT DURING THE NEXT FEW DAYS...AND THIS
SYSTEM HAS A MEDIUM CHANCE OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS...AS IT MOVES WESTWARD AT 15 TO 20 MPH.

[GCANE]

Strong rain-rate cell firing in the middle of a strong and very wide anti-cyclone.

http://www.nrlmry.navy.mil/htdocs_dyn_p ... W.70pc.jpg

http://tropic.ssec.wisc.edu/real-time/s ... 000&loop=0


Looks like core is heating up.

http://rammb.cira.colostate.edu/product ... 9_TANO.GIF

[jinftl]

NOAA is getting bullish on development...if we get the 9th storm of the season before August 23, the 2012 season will move ahead of the 1933 season as the 2nd earliest season, behind 2005, to reach the 9th named storm so early!!!

[rainstorm]

Joe Bastardi ‏@BigJoeBastardi

day 11 analogs frame the Carol-Edna period in 1954 Weatherbell Atmospheric Avenger video looks at this

jb is comparing this to the carol-edna period back in 1954. can anyone see his video?

[cycloneye]

This is a good jump more north as it organizes and reforms.

18/1200 UTC 13.2N 30.0W T1.0/1.0 94L -- Atlantic

[Gustywind]

Idem given the latest SSD numbers . Good jump to the north but to the west too, already the 30W

18/1200 UTC 13.2N 30.0W T1.0/1.0 94L
18/0600 UTC 12.2N 26.7W T1.0/1.0 94L

http://www.ssd.noaa.gov/PS/TROP/tdpositions.html

[cycloneye]

I imagine that ATCF is in a delay about releasing the 12z Best Track as they are fixing it to the new position more north.

INVEST, AL, L, , , , , 94, 2012, DB, O, 2012081700, 9999999999, , , , , , METWATCH, , AL942012
AL, 94, 2012081606, , BEST, 0, 106N, 120W, 15, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081612, , BEST, 0, 107N, 136W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081618, , BEST, 0, 109N, 155W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081700, , BEST, 0, 111N, 173W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1014, 90, 60, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081706, , BEST, 0, 113N, 196W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081712, , BEST, 0, 115N, 219W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081718, , BEST, 0, 117N, 236W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081800, , BEST, 0, 119N, 251W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081806, , BEST, 0, 121N, 268W, 25, 1008, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

[Aric Dunn]

quickly beginning to organize now. convection minimal but should start coming back in the next couple hours. low level structure is improving. beginning to detach from the little bit of itcz boundary thats left.

[Aric Dunn]

I imagine that ATCF is in a delay about releasing the 12z Best Track as they are fixing it to the new position more north.

INVEST, AL, L, , , , , 94, 2012, DB, O, 2012081700, 9999999999, , , , , , METWATCH, , AL942012
AL, 94, 2012081606, , BEST, 0, 106N, 120W, 15, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081612, , BEST, 0, 107N, 136W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081618, , BEST, 0, 109N, 155W, 20, 1010, DB, 0, , 0, 0, 0, 0,
AL, 94, 2012081700, , BEST, 0, 111N, 173W, 20, 1010, DB, 0, , 0, 0, 0, 0, 1014, 90, 60, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081706, , BEST, 0, 113N, 196W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081712, , BEST, 0, 115N, 219W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081718, , BEST, 0, 117N, 236W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081800, , BEST, 0, 119N, 251W, 20, 1009, DB, 0, , 0, 0, 0, 0, 1012, 150, 50, 0, 0, L, 0, , 0, 0, INVEST, S,
AL, 94, 2012081806, , BEST, 0, 121N, 268W, 25, 1008, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

THe gfs actually indicated this would occur. then it gets pushed west as it organizing. the jump north is typical and is due to rotational dynamics among other things.

[cycloneye]

12z Best Track

There is a difference between ATCF and Dvorak SSD in terms of the position as SSD has 13.2N-30.0W and Best Track is at 12.3N-27.7W.

AL, 94, 2012081812, , BEST, 0, 123N, 277W, 25, 1008, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

[Aric Dunn]

Although they will wait. this looks a lot better the td7 ever did. the boundary is breaking down very fast. once convection increase later given there appears to be a developing or a llc now ... it would be quite likely a TD at that time. but of course must persist for the nhc to upgrade out in the middle of the atlantic.

[SFLcane]

One thing that's looking rather probable is a threat to the islands from future isaac. After its really anyones guess. Dont see any reason why this storm wont intensify rather quickly as it treks towards the islands in time.

[abajan]

12z Best Track

There is a difference between ATCF and Dvorak SSD in terms of the position as SSD has 13.2N-30.0W and Best Track is at 12.3N-27.7W.

AL, 94, 2012081812, , BEST, 0, 123N, 277W, 25, 1008, DB

ftp://ftp.nhc.noaa.gov/atcf/tcweb/inves ... 012.invest

13.2 and 12.3 contain the same digits. Could there have been an error on someone's part?