Tropical Depression 18 forms south of Jamaica

By: Dr. Jeff Masters , 3:34 PM GMT on October 22, 2012

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Tropical Depression Eighteen is here, and appears poised to become Tropical Storm Sandy by early Tuesday morning. TD 18 is over very warm waters of 29.5°C, is in a moist environment, and has light wind shear of 5 - 10 knots. These conditions are very favorable for intensification, and TD 18's heavy thunderstorms are steadily organizing into curved spiral bands, as seen on visible satellite loops. An Air Force hurricane hunter aircraft will investigate TD 18 this afternoon.


Figure 1. Morning satellite image of Tropical Depression Eighteen.

Forecast for TD 18
Wind shear is forecast to be in the low to moderate range, 5 - 20 knots, through Tuesday night. This should allow for some steady development of TD 18. On Tuesday, a trough of low pressure to the north is expected to pull TD 18 to the north-northeast, which should put the storm in the vicinity of Jamaica on Wednesday and Eastern Cuba on Thursday. The 11 am EDT NHC Wind Probability Forecast gives a 32% chance that TD 18 will be a hurricane by 8 am EDT Wednesday, when the center should be close to Jamaica. Wind shear will rise to a high 25 - 30 knots by Thursday, which should make it difficult for TD 18 to intensify. By Friday, TD 18 should be in the Central or Eastern Bahamas, and wind shear may increase further, making TD 18 more of a hybrid subtropical storm. It is unclear at this point whether or not the trough pulling TD 18 to the north will be strong enough to pull the storm all the way out to sea to the northeast; a very complicated steering environment will develop late this week, and it is possible that a narrow ridge of high pressure could build in over TD 18 and force the storm to the west-northwest, with a potential threat to the Northwestern Bahamas and U.S. East Coast by Saturday, as predicted by the ECMWF model. TD 18 will be capable of bringing heavy rains of 5 - 10 inches, with isolated amounts of up to 15 inches in mountainous areas, to Jamaica and Haiti, Monday night through Thursday. Heavy rains will begin on Tuesday in Eastern Cuba, and spread northwards into the Central and Eastern Bahamas by Wednesday. Heavy rains of 3 - 6 inches can be expected in the Cayman Islands and Dominican Republic, Tuesday through Thursday.

Invest 90L in the middle Atlantic
A small low pressure system (Invest 90L) about 700 miles east-northeast of the northernmost Lesser Antilles Islands is headed northward at about 10 mph. The disturbance has a modest area of heavy thunderstorms, as seen on visible satellite images, and is struggling with cool, dry air from the upper-level low pressure system that it is trying to form underneath. This upper-level low has provided 90L the spin it needs to become a tropical cyclone, though. Wind shear is a moderate 10 - 20 knots, and is forecast to remain in the moderate range until Wednesday morning. This may allow 90L to develop into a tropical cyclone before it encounters high wind shear of 20 - 30 knots on Wednesday. It's unlikely that 90L will affect any land areas. In their 8 am EDT tropical weather outlook, NHC gave 90L a 50% chance of developing into a tropical cyclone by Wednesday morning.

Jeff Masters

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Time: 17:11:30Z
Coordinates: 19.25N 84.1333W
Acft. Static Air Press: 409.8 mb (~ 12.10 inHg)
Acft. Geopotential Hgt: 7,389 meters (~ 24,242 feet)
Extrap. Sfc. Press: -
D-value: 374 meters (~ 1,227 feet)
Flt. Lvl. Wind (30s): From 324° at 17 knots (From the NW at ~ 19.5 mph)
Air Temp: -16.0°C (~ 3.2°F)
Dew Pt: -49.9°C (~ -57.8°F)
Peak (10s) Flt. Lvl. Wind: 17 knots (~ 19.5 mph)
SFMR Peak (10s) Sfc. Wind: 18 knots (~ 20.7 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data

Recon due west of Grand Cayman now.
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The storm is traveling west right now and getting better every frame. I'd be surprised if they don't find a TS when the plane gets there. If it doesn't stall or change direction soon Nicaragua mayn't be out of play. Look at the RGB in motion at the NHC.
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CMC cuts off the space between 99L and the north atlantic low, and also elongates 99L much later than does the GFS:

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111. 7544
hmm pretty darn close to so fl this run again

Link

new speghtti might shift west again imo
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It looks like a spinup/splitoff in 90Ls wake will give rise to the big North Atlantic low that gives 99L its biggest weakness to pass through, so the evolution of 90L is crucial to this storm too.
If it pulls a Michael and gets away too fast, things might end up very different.
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Quoting 954FtLCane:
anyone think this could go thru a RI phase? what are the possibilities?

If you mean before it gets past Cuba, I think the odds are very low. It may get to a cat 1 by the time it's ove the eastern Bahamas, but I think that's also unlikely. I still think it goes out to sea and become a threat to Bermuda. Once it's past 30N, then it has a chance to become a larger hurricane. If it indeed follows the high pressure ridge off the east coast and stays over the Gulf Stream, then it has the best chance of developing into a cat2/cat3 storm. No matter what, there aren't many ingredients in place that would promote RI in any case.
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Quoting GTcooliebai:
For some reason when the models show a tighter storm they move the system further west and it is elongated out to sea, why is that?


I believe it's sheer from the front. I could be wrong though
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Quoting ncstorm:
umm...12Z

CMC


Large shift west...

Quoting ncstorm:
12z Nogaps


Large shift west...

Ugh... I just aided My family in putting up $125 dollars worth of Halloween Lights.
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Quoting TXCWC:
12Z CMC = 0Z Euro solution...NE hit

Link
I've noticed the CMC has been the most consistent model for this storm. GFS and Euro have flip-flopped from run to run.
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Member Since: July 15, 2006 Posts: 178 Comments: 56140
Quoting GTcooliebai:
For some reason when the models show a tighter storm they move the system further west and when it is elongated out to sea, why is that?


Taller storm will feel the trough more than a weaker storm thus getting more of a tug NW.
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Looking to be a low strike threat ATM for the US. It will serve to destroy the FL beaches however, again.
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Quoting ncstorm:
12z Nogaps


ummmmm.... much further west.
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For some reason when the models show a tighter storm they move the system further west and when it is elongated out to sea, why is that?
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NON TROPICAL MODEL NAM AT 60 HRS

Member Since: July 15, 2006 Posts: 178 Comments: 56140
12Z CMC = 0Z Euro solution...NE hit

Link
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12z Nogaps
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How likely would RI be? Even if it doesn't happen, I think the NHC is underestimating the future intensity of TD18.
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TRMM pass shows how organized TD 18 is.

Member Since: April 29, 2009 Posts: 75 Comments: 14904
umm...12Z

CMC
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Quoting stormpetrol:
This is looks like a Michelle 2001 or Paloma 2008 track to me, just my take.


Hush with that "P" name please :-)
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I've really got an uneasy RI feeling on this one.... JMHO.
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90L could, and probably will, be upgraded to TD19 later today. The question will be in that case, which one becomes Sandy, and which one becomes Tony.


TD18 is ramping up, the satellite presentation has improved remarkably since 8 hours ago.
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89. 7544
cmc comin in soon lets see if it shifts gain
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Quoting stormpetrol:
This is looks like a Michelle 2001 or Paloma 2008 track to me, just my take.


Oh that crazy Paloma, she was a surprise that year, becoming the second strongest Atlantic hurricane ever in November and all that. Her sudden strengthening and equally sudden weakening makes me think of another P storm... Paul of this year in the Eastern Pacific.

I'm trying to get attention on 90L as well, as I'm pretty certain we could see a TS out of it, it's been impressing me today.
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Quoting 954FtLCane:
anyone think this could go thru a RI phase? what are the possibilities?


It's certainly swimming in gasoline .
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This is looks like a Michelle 2001 or Paloma 2008 track to me, just my take.
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anyone think this could go thru a RI phase? what are the possibilities?
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Poor Jamaica.
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81. 7544
Quoting wxchaser97:
Thanks Dr. Masters!
TD18 really wrapped up and is looking good. I could see it becoming a hurricane sometime in its life. I will make my forecast when I get home from school.


maybe a ts strom when the plane gets done imo looks like one now
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Thanks Dr. Masters!
TD18 really wrapped up and is looking good. I could see it becoming a hurricane sometime in its life. I will make my forecast when I get home from school.
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Although there are many vortexs.. the LLC is pretty close to 13.4N and 78.8W moving just south of due west around 5mph
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T.C.F.A
18L/TD/NN/XX
MARK
13.89N/77.59W
Member Since: July 15, 2006 Posts: 178 Comments: 56140
I wonder if there is any feedback in here between 99L and 90L where the GFS tries to merge their low pressure/precip areas together.


Either way 99L is elongated way east into a weakness south of what I believe is a result of 90L, and eventually moves in that direction.
It would be interesting to see if the system wont phase, if it could get stretched enough to split.
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892

NOUS42 KNHC 221519

REPRPD

WEATHER RECONNAISSANCE FLIGHTS

CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.

1115 AM EDT MON 22 OCTOBER 2012

SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)

VALID 23/1100Z TO 24/1100Z OCTOBER 2012

TCPOD NUMBER.....12-156



I. ATLANTIC REQUIREMENTS

1. TROPICAL DEPRESSION EIGHTEEN

FLIGHT ONE -- TEAL 71 FLIGHT TWO -- TEAL 72

A. 24/0000Z,0600Z A. 24/1200Z,1800Z

B. AFXXX 0318A CYCLONE B. AFXXX 0418A CYCLONE

C. 23/1945Z C. 24/0745Z

D. 15.7N 77.6W D. 17.4N 77.0W

E. 23/2330Z TO 24/0600Z E. 24/1130Z TO 24/1800Z

F. SFC TO 10,000 FT F. SFC TO 10,000 FT



2. OUTLOOK FOR SUCCEEDING DAY.....CONTINUE 6-HRLY FIXES

WHILE SYSTEM REMAINS A THREAT.



II. PACIFIC REQUIREMENTS

1. NEGATIVE RECONNAISSANCE REQUIREMENTS.

2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.



$$

JWP




Member Since: July 15, 2006 Posts: 178 Comments: 56140
270

NOUS42 KNHC 211528

REPRPD

WEATHER RECONNAISSANCE FLIGHTS

CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.

1115 AM EDT SUN 21 OCTOBER 2012

SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)

VALID 22/1100Z TO 23/1100Z OCTOBER 2012

TCPOD NUMBER.....12-155



I. ATLANTIC REQUIREMENTS

1. SUSPECT AREA (WESTERN CARIBBEAN)

FLIGHT ONE -- TEAL 71 FLIGHT TWO -- TEAL 72

A. 22/1800Z A. 23/1200Z

B. AFXXX 01EEA INVEST B. AFXXX 0218A CYCLONE

C. 22/1330Z C. 23/0730Z

D. 13.8N 78.5W D. 14.2N 78.6W

E. 22/1730Z TO 22/2030Z E. 23/1130Z TO 23/1400Z

F. SFC TO 10,000 FT F. SFC TO 10,000 FT



2. OUTLOOK FOR SUCCEEDING DAY.....CONTINUE 12-HRLY FIXES

IF SYSTEM DEVELOPS.

3. REMARKS: THE LOW-LEVEL INVEST MISSION FOR 21/2100Z WAS

CANCELED BY NHC AT 21/1230Z. THE 22/1200Z INVEST IN TCPOD

12-154 HAS BEEN RE-TASKED FOR 22/1800Z AS SPECIFIED ABOVE.



II. PACIFIC REQUIREMENTS

1. NEGATIVE RECONNAISSANCE REQUIREMENTS.

2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.



$$

SEF
Member Since: July 15, 2006 Posts: 178 Comments: 56140
62. stormpetrol 4:23 PM GMT on October 22, 2012 +0
Time: 16:12:30Z
Coordinates: 23.65N 87.05W
Acft. Static Air Press: 409.8 mb (~ 12.10 inHg)
Acft. Geopotential Hgt: 7,396 meters (~ 24,265 feet)
Extrap. Sfc. Press: -
D-value: 385 meters (~ 1,263 feet)
Flt. Lvl. Wind (30s): From 344° at 9 knots (From the NNW at ~ 10.3 mph)
Air Temp: -17.0°C (~ 1.4°F)
Dew Pt: -48.4°C (~ -55.1°F)
Peak (10s) Flt. Lvl. Wind: 10 knots (~ 11.5 mph)
SFMR Peak (10s) Sfc. Wind: 14 knots (~ 16.1 mph)
SFMR Rain Rate: 1 mm/hr (~ 0.04 in/hr)
(*) Denotes suspect data

Recon well on the way
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73. 7544
hmmm

THIS HAZARDOUS WEATHER OUTLOOK IS FOR SOUTH FLORIDA.

.DAY ONE...TODAY AND TONIGHT

RIP CURRENTS: NORTHEAST WINDS OF 15 TO 20 MPH WITH HIGHER GUSTS ALONG
THE ATLANTIC COAST WILL RESULT IN A MODERATE RISK OF RIP CURRENTS
AT THE BEACHES.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY

THE NATIONAL HURRICANE CENTER HAS ANNOUNCED THE FORMATION OF A
TROPICAL DEPRESSION LOCATED OVER THE CENTRAL CARIBBEAN. CURRENT
FORECASTS TRACK STILL TRACK THE DEPRESSION NORTHEAST OVER THE
BAHAMAS. AT THIS TIME, THE EXACT TRACK AND INTENSITY IS UNCERTAIN
BUT THIS COULD LEAD TO POTENTIAL LOCAL WEATHER IMPACTS LATE THIS
WEEK, ESPECIALLY ACROSS THE LOCAL ATLANTIC WATERS AND ALONG THE
ATLANTIC COAST. SOME POSSIBLE IMPACTS, NOTING THE HIGH DEGREE OF
UNCERTAINTY, MAY BE STRONG WINDS, HIGH SEAS, MAJOR BEACH EROSION
ALONG THE ATLANTIC COAST, AND POSSIBLE LOCALLY HEAVY RAINFALL OVER
THE EAST COAST METROPOLITAN AREAS. STAY TUNED TO THE LATEST
FORECAST UPDATES OVER THE COMING DAYS.
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Quoting CybrTeddy:
Spiral banding becoming very pronounced on TD-18. This might very well be a stronger system than we might think. It's small, over very deep TCHP with a favorable environment, with a lot of moisture for it to feed off.


well the HH is just about to enter the SE GOM/yucatan channel so we should soon find out
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GFS sticking to no worries:
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Boomers have moved on East, rain has let up some, but sure filled the ditches in a hurry. Looking at WU's lightning feature out of Lincoln, appears Peoria area had the most strikes about an hour ago.
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NOUS42 KNHC 221519
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1115 AM EDT MON 22 OCTOBER 2012
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 23/1100Z TO 24/1100Z OCTOBER 2012
TCPOD NUMBER.....12-156

I. ATLANTIC REQUIREMENTS
1. TROPICAL DEPRESSION EIGHTEEN
FLIGHT ONE -- TEAL 71
A.,24/0000Z,0600Z
B.,AFXXX 0318A CYCLONE
C.,23/1945Z D.,15.7N 77.6W
E., 23/2330Z TO 24/0600Z
F.,SFC TO 10,000 FT

FLIGHT TWO -- TEAL 72
A. 24/1200Z,1800Z
B. AFXXX 0418A CYCLONE
C. 24/0745Z
D. 17.4N 77.0W
E. 24/1130Z TO 24/1800Z
F. SFC TO 10,000 FT



2. OUTLOOK FOR SUCCEEDING DAY.....CONTINUE 6-HRLY FIXES
WHILE SYSTEM REMAINS A THREAT.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.

$$
JWP

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Spiral banding becoming very pronounced on TD-18. This might very well be a stronger system than we might think. It's small, over very deep TCHP with a favorable environment, with a lot of moisture for it to feed off.
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Quoting 7544:
was the plane cancel for today or is it ago tia
its a go
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Tropical Cyclone Formation Alert (TCFA)
18L CYCLONE DEPRESSION
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UKMET doesn't like Jamaica apparently.
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It does create a buzz though when they show a 956mb storm heading toward the mid-Atlantic this time of year!
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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