ATL: SANDY - Remnants - Discussion

[cycloneye]

Remains at 60%

SATELLITE IMAGES INDICATE THAT SHOWERS AND THUNDERSTORMS ASSOCIATED
WITH A TROPICAL WAVE OVER THE CENTRAL CARIBBEAN SEA HAVE CHANGED
LITTLE IN ORGANIZATION DURING THE PAST SEVERAL HOUR. HOWEVER...
SURFACE PRESSURES ARE LOW IN THE AREA...AND ENVIRONMENTAL
CONDITIONS ARE EXPECTED TO BECOME CONDUCIVE FOR A TROPICAL
DEPRESSION TO FORM DURING THE NEXT COUPLE OF DAYS. THIS SYSTEM HAS
A HIGH CHANCE...60 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS THE WAVE MOVES SLOWLY WESTWARD. HEAVY RAINS
FROM THIS DISTURBANCE OR POSSIBLE TROPICAL CYCLONE ARE LIKELY TO
SPREAD OVER JAMAICA...EASTERN CUBA...AND HISPANIOLA OVER THE NEXT
SEVERAL DAYS. THESE RAINS COULD PRODUCE LIFE-THREATENING FLASH
FLOODS AND MUD SLIDES...ESPECIALLY NEAR AREAS OF HIGH TERRAIN.

[tropicana]

Sat Oct 20-12 730pmET

While the main cities of Kingston and Montego Bay Jamaica have not yet reported any significant rainfall today Saturday at the airports, a complex of thunderstorms developed over SW portions of Jamaica and has been deluging this part of the island.... thus far, only 61mm of rain has fallen at Bluefields, Westmoreland on the SW coast of Jamaica!

-justin-

[cycloneye]

8 PM Special Feature Discussion:

TROPICAL WAVE IN THE CARIBBEAN SEA EXTENDS FROM 20N75W TO A 1007
MB LOW AT 15N73W TO 12N72W MOVING W AT 5-10 KT. LOW-LEVEL
CYCLONIC FLOW IS EVIDENT ON VISIBLE SATELLITE IMAGERY WITH TOTAL
PRECIPITABLE WATER IMAGERY ALSO INDICATING MAXIMUM VALUES OF
DEEP LAYER MOISTURE ACROSS THE CENTRAL CARIBBEAN BETWEEN
69W-77W. SCATTERED MODERATE CONVECTION IS N OF THE LOW CENTER
FROM 15N-18N BETWEEN 69W-74W TO INCLUDE PORTIONS OF HISPANIOLA.
AN UPPER LEVEL ANTICYCLONIC CENTERED IS OVER THIS TROPICAL WAVE.
ENVIRONMENTAL CONDITIONS ARE FORECAST TO BECOME MORE FAVORABLE
FOR DEVELOPMENT DURING THE NEXT DAY OR TWO AS THE DISTURBANCE
MOVES WESTWARD. THIS SYSTEM HAS A HIGH CHANCE OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS. HEAVY RAINS ARE
POSSIBLE WITH THIS SYSTEM OVER JAMAICA...EASTERN CUBA...AND
HISPANIOLA OVER THE NEXT SEVERAL DAYS. FLASH FLOODING AND MUD
SLIDES COULD OCCUR ESPECIALLY NEAR HIGH TERRAIN.

[MiamiensisWx]

With all due respect I don't think Frank said anything prematurely.
He said that it looks better for Florida.
How is that a little premature?
I agree with Frank, no one is predicting this to be a Florida issue

Although I respect the views of others and professionals who discount such a threat, and although the system may well miss the United States altogether, I must disagree with the view that dismissing the possibility of a threat is not premature at this stage. Much of the uncertainty regarding 99L is related to 1) its movement within the next two days, 2) the depth and movement of an upper-level low within days 2-5, and 3) the strength of a ridge north of 99L during days 2-5. Although the most reliable models...the GFS / ECMWF and several of their ensembles...take 99L over eastern Cuba and the Bahamas within five days (25 October at the latest), other models with a known history of gauging late-season development--the BAMD and the climatological model CLP5--show a slower, drifting component to 99L within days 2-5. These models tend to recognize climatology better: as most models show 99L making its closest approach to FL by day 5, climatology for Caribbean systems on or before 25 October show a mean track NNW toward South FL, as opposed to that of systems making their closest approach after 25 October. Also, most late-season storms tend to move rather slowly for days in the Caribbean, at least before recurving.

The reasons for the differences in the models seem fairly clear:

1) The GFS and ECMWF models, at least operationally, posit a deeper and slower upper-level low dropping south into the W Caribbean by days 2-5. This pattern would tend to erode the mid-level ridge to the north of 99L. As these models also show 99L moving faster during and immediately preceding this time frame, they indicate that the upper low will cause 99L to turn NE across E Cuba and the Bahamas, posing a significant rain threat to Hispaniola and Jamaica but otherwise sparing South FL. However, they do suggest 99L may slow or stall east of the Bahamas after day 5, mainly due to rebuilding ridging to the north, before a trough sweeps in from the Great Lakes.

2) If the upper low is faster and shallower (weaker), and 99L moves more slowly, then the possibility arises that 99L, after briefly moving NE within days 2-4, may turn back to the N or NNW by day 5. If 99L is within 100-150 nautical miles of Nicaragua by the end of day 2, it would tend to drift NE in this pattern, but eventually come back under the influence of a rebuilding mid-level ridge to its north. Such a pattern actually occurred on 14-18 October 1950, when Hurricane King initially moved NE but gradually curved back to the NNW due to a rebuilding ridge, eventually making landfall on 18 October in South Florida. I have included a series of images showing this pattern, highlighting some similarities between the upcoming pattern and the one in 1950.

14 October 1950
15 October 1950
16 October 1950
17 October 1950
18 October 1950
Track of Hurricane King

Here is the projected GFS ensemble mean mid-levels by day 5:

GFS mid-levels by day 5

3) As you can see in the following spaghetti plot, there is some disagreement over where the upper low will be located by day 5--look at the different positions of the red circles south of FL (the white is the average of the different ensemble projections).

GFS (NCEP) model spread

4) Based upon soundings, the air mass is somewhat stable surrounding 99L, due to low instability. Therefore, the system may initially move farther west and take more time to organize over the next two days.

I am not suggesting that 99L will hit FL or the United States, and it is a threat in its own right to Cuba, Jamaica, and Haiti. But I do think the pattern bears watching in regard to a possible FL impact.

[cycloneye]

00z Best Track

AL, 99, 2012102100, , BEST, 0, 147N, 737W, 25, 1006, DB

http://ftp.nhc.noaa.gov/atcf/tcweb/inve ... 012.invest

[TropicalAnalystwx13]

99L continues to organize this evening with a favorable upper-air environment aloft...it should become a tropical depression tomorrow night or Monday morning at the latest. Wind shear is expected to remain low during the next 3-4 days as this system moves west-southwest and then abruptly north as it feels the effects of a trough moving into the East USA. This trough will induce moderate to strong wind shear on what should be "Sandy" by that time, causing it to stop intensifying and probably weaken. Rainfall will be a huge issue for most of the Greater Antilles, Bahamas, and potentially East Florida.

[ozonepete]

The majority of models in the latest NCAR analysis have it as a tropical storm by Monday morning.

[chaser1]

The majority of models in the latest NCAR analysis have it as a tropical storm by Monday morning

"Sandy" is gonna' need some convection first.......just sayin

[cycloneye]

Well,I an not talking about doom here but only to discuss possible scenarios as I did earlier with the 1950 Hurricane King,here is another possible good analog in terms of track, Hurricane #14 of 1932. This one was a cat 5 in the Western Caribbean,but I am not saying that 99L will be one,only about track is concerned. Anyone who may have more analog possible scenarios dont hesitate to post them.

[cycloneye]

Here is the 00z Surface Analysis made by TAFB.

[GCANE]

Anti-cyclone just about over the top of this.

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

Upper troposphere should be relatively cool this late in the season; which IMHO could develop some very strong & sustained convection.

[cycloneye]

I may be wrong on this but IMO,I think recon will not go this afternoon because of not a whole lot of convection,although the structure looks very good.

Welcome back GCANE. Your analysis of the enviroment always are good and are needed in these times of predevelopment of a system.

[GCANE]

I may be wrong on this but IMO,I think recon will not go this afternoon because of not a whole lot of convection,although the structure looks very good.

Welcome back GCANE. Your analysis of the enviroment always are good and are needed in these times of predevelopment of a system.

Morning Cycloneye and much thanks!

Looks like the entire Carib is embedded in high theta-e air and starting to see rotation on MIMIC-TPW.

http://tropic.ssec.wisc.edu/real-time/m ... /main.html

[GCANE]

Currently no warm core due to lack of deep convection.

http://rammb.cira.colostate.edu/product ... 1_TANO.GIF

However, good mid-level circulation and no UL PV anomalies anywhere around.

http://rammb.cira.colostate.edu/product ... 0_SWHR.GIF

http://tropic.ssec.wisc.edu/real-time/a ... g8vor1.GIF

[Caribwxgirl]

Currently no warm core due to lack of deep convection.

http://rammb.cira.colostate.edu/product ... 1_TANO.GIF

However, good mid-level circulation and no UL PV anomalies anywhere around.

http://rammb.cira.colostate.edu/product ... 0_SWHR.GIF

http://tropic.ssec.wisc.edu/real-time/a ... g8vor1.GIF

So how quickly do you think this will be me a TC? Our local weather says 24-48 hours but looking on it now it doesn't look that close to development.

[Extratropical94]

Up to 70%

SHOWERS AND THUNDERSTORMS HAVE BEEN INCREASING OVER THE PAST FEW
HOURS NEAR A TROPICAL WAVE AND BROAD AREA OF LOW PRESSURE OVER THE
CENTRAL CARIBBEAN SEA. ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE
FOR A TROPICAL DEPRESSION TO FORM DURING THE NEXT COUPLE OF DAYS...
AND THIS SYSTEM HAS A HIGH CHANCE...70 PERCENT...OF BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY
WESTWARD. HEAVY RAINS FROM THIS DISTURBANCE ARE LIKELY TO SPREAD
OVER JAMAICA...EASTERN CUBA...AND HISPANIOLA OVER THE NEXT SEVERAL
DAYS. THESE RAINS COULD PRODUCE LIFE-THREATENING FLASH FLOODS AND
MUD SLIDES...ESPECIALLY IN AREAS OF HIGH TERRAIN.

[GCANE]

Currently no warm core due to lack of deep convection.

http://rammb.cira.colostate.edu/product ... 1_TANO.GIF

However, good mid-level circulation and no UL PV anomalies anywhere around.

http://rammb.cira.colostate.edu/product ... 0_SWHR.GIF

http://tropic.ssec.wisc.edu/real-time/a ... g8vor1.GIF

So how quickly do you think this will be me a TC? Our local weather says 24-48 hours but looking on it now it doesn't look that close to development.

SSTs are just about 30C. UL temps have to be cold, but can't find a RT site to see for sure. The difference in temps is what drives strong convection development.

Seeing a flare fire up now at 14N 71.5W.

If it becomes a hot tower, mid-level air will heat up quickly and this could develop fast.

[Caribwxgirl]

Thanks for that info GCANE I'm a little antsy about this. Any heavy consistent rain will be a problem for us here.

[cycloneye]

12z Best Track

AL, 99, 2012102112, , BEST, 0, 147N, 755W, 25, 1006, DB

http://ftp.nhc.noaa.gov/atcf/tcweb/inve ... 012.invest

[Hurricane_Luis]