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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CPC is forecasting above normal precip for the Mid Atlantic and NE in the 6-10 day time frame... I have doubts as to whether that's Sandy related precip though.

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Quoting Thing342:
Sandy is not exclusively a female name. It can also be short for Sanford.
But if you remember Rafael was the name before..male,female,male,female,male,female
Member Since: October 3, 2008 Posts: 0 Comments: 5928
Lets the jokes with Sandy Cheeks Start.:)
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further south means hispanola landfall?
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Sandy is not exclusively a female name. It can also be short for Sanford.
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If the center makes it to 80-81W, The Caymans and Florida could be in play.
Member Since: April 29, 2007 Posts: 0 Comments: 8001
Member Since: July 15, 2006 Posts: 175 Comments: 54827
Recon appears to be done. A big success as usual.
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And to break in and interrupt- I just added 4 fall foliage pictures to my blog. I have been on vacation from work for a few days, and finally had time to play a little. Enjoy!
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Member Since: April 29, 2007 Posts: 0 Comments: 8001

Tropical Storm SANDY Forecast Discussion

Home Public Adv Fcst Adv Discussion Wind Probs Graphics Archive

000
WTNT43 KNHC 222101
TCDAT3

TROPICAL STORM SANDY DISCUSSION NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
500 PM EDT MON OCT 22 2012

THE AIR FORCE HURRICANE HUNTERS FOUND A BAND OF SURFACE WINDS NEAR
35 KT OVER THE SOUTHEASTERN QUADRANT OF THE CYCLONE...SO THE SYSTEM
IS BEING NAMED AT THIS TIME. THE ENVIRONMENT SHOULD BE
CHARACTERIZED BY WEAK SHEAR...AND THE STORM WILL BE OVER WARM
WATERS...FOR THE NEXT COUPLE OF DAYS SO ADDITIONAL STRENGTHENING IS
LIKELY. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS
FORECAST AND CLOSE TO THE MODEL CONSENSUS. THIS COULD BE
CONSERVATIVE...HOWEVER...AS THE RAPID INTENSIFICATION INDEX SHOWS A
SIGNIFICANT POSSIBILITY OF RAPID STRENGTHENING DURING THE NEXT DAY
OR SO.
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Quoting CybrTeddy:
No change to the forecast intensity, no real change to the track. I'd have gone with 50mph IMO.

Based on what?
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Quoting CybrTeddy:
No change to the forecast intensity, no real change to the track. I'd have gone with 50mph IMO.
LOL
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Quoting Seflhurricane:
you are killing us with the same posts keeper
they are not same they run from 00 hr to 84 hr at random choices
Member Since: July 15, 2006 Posts: 175 Comments: 54827
S FL is now in it!!
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Quoting Seflhurricane:
it appears the center is reforming around based on recon info


On what info do you base your statement?
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No change to the forecast intensity, no real change to the track. I'd have gone with 50mph IMO.
Member Since: July 8, 2005 Posts: 259 Comments: 24468
No big shift west just a slight one on day 4-5. Basely a straight NNE path.
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Sub 1000mb cyclone and dropping according to recon.
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...DEPRESSION STRENGTHENS INTO TROPICAL STORM SANDY...
5:00 PM EDT Mon Oct 22
Location: 12.5°N 78.5°W
Moving: Stationary
Min pressure: 999 mb
Max sustained: 40 mph
Public
Advisory
#2
Member Since: March 16, 2012 Posts: 127 Comments: 7958
BULLETIN
TROPICAL STORM SANDY ADVISORY NUMBER 2
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
500 PM EDT MON OCT 22 2012

...DEPRESSION STRENGTHENS INTO TROPICAL STORM SANDY...


SUMMARY OF 500 PM EDT...2100 UTC...INFORMATION
----------------------------------------------
LOCATION...12.5N 78.5W
ABOUT 395 MI...640 KM SSW OF KINGSTON JAMAICA
MAXIMUM SUSTAINED WINDS...40 MPH...65 KM/H
PRESENT MOVEMENT...STATIONARY
MINIMUM CENTRAL PRESSURE...999 MB...29.50 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

THE GOVERNMENT OF HAITI HAS ISSUED A TROPICAL STORM WATCH FOR HAITI.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* JAMAICA
* HAITI

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS. A
HURRICANE WATCH AND/OR A TROPICAL STORM WARNING COULD BE REQUIRED
FOR JAMAICA TONIGHT.
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Sandy confirmed!! 40mph
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...DEPRESSION STRENGTHENS INTO TROPICAL STORM SANDY...
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...DEPRESSION STRENGTHENS INTO TROPICAL STORM SANDY...
Member Since: July 15, 2006 Posts: 175 Comments: 54827
I think 45mph seems like a good bet for the new advisory, which should be out any second.
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Quoting Seflhurricane:
95% chance we will have TS Sandy
I say 99%
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999.1 MB!! wow
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Quoting KEEPEROFTHEGATE:
18Z NAM FINAL(NON TROPICAL MODEL) hr 084 TILL 84




NEXT UP 18Z GFS RUN IN ABOUT 40 MINUTES

you are killing us with the same posts keeper
Member Since: July 14, 2009 Posts: 0 Comments: 3029
*Jeopardy Music playing*
Refresh...... Refresh.... Refresh....
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18Z NAM FINAL(NON TROPICAL MODEL) hr 084 TILL 84




NEXT UP 18Z GFS RUN IN ABOUT 40 MINUTES

Member Since: July 15, 2006 Posts: 175 Comments: 54827
it appears the center is reforming around based on recon info
Member Since: July 14, 2009 Posts: 0 Comments: 3029
Member Since: April 29, 2009 Posts: 75 Comments: 14553
95% chance we will have TS Sandy
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380. Skyepony (Mod)
Looks like recon turned around. Just trying to confirm the closed surface low.
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18Z NAM(NON TROPICAL MODEL) hr 075 TILL 84


Member Since: July 15, 2006 Posts: 175 Comments: 54827
looking at computer models i do not see a reason to shift the forecast cone maybe a slight west shift but models are in pretty good agreement. as for us here in SE FLA the winds are beginning to crank up and will continue to increase to wind advisory criteria.
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Quoting trHUrrIXC5MMX:


Still waiting to confirm Sandy.
it will be done shortly
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375. Skyepony (Mod)
Recon~ just a hint of NNW wind 999.0 mb (~ 29.50 inHg)
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Quoting Seflhurricane:
hurricane watches will likely go up for jamaica and portions of central and eastern cuba expect a tropical storm warning for jamaica and if Td 18 moves further west a watch may be needed for the caymans
don't tell wkcayman...
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341 trHUrrIXC5MMX: Would TWC use a winter storm name for [AL18] besides its tropical name?

From it's own list? Nah, they'd go for SnowicaneSquirrel along with the rest of the media.
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18Z NAM(NON TROPICAL MODEL) hr 069 TILL 84


Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting weatherh98:


My real answer:

They will name it major super winter storm sandy.


Still waiting to confirm Sandy.
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hurricane watches will likely go up for jamaica and portions of central and eastern cuba expect a tropical storm warning for jamaica and if Td 18 moves further west a watch may be needed for the caymans
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Quoting trHUrrIXC5MMX:


I love your confidence


My real answer:

They will name it major super winter storm sandy.
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Quoting weatherh98:


Does the rooster crow in the morning?


I love your confidence
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18Z NAM(NON TROPICAL MODEL) hr 060 TILL 84


Member Since: July 15, 2006 Posts: 175 Comments: 54827
Quoting PalmBeachWeather:
trHU....It's only Monday....Please don't ask such a difficult question
someone already answered it...
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Quoting CybrTeddy:
IMO, 50mph Tropical Storm Sandy with a pressure of 1001mb seems the best guess for me.


Are serious all the way up to 50mph. I think hurricane watches will be good up for Jamaica if not Central/Eastern Cuba.
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18Z NAM(NON TROPICAL MODEL) hr 048 TILL 84


Member Since: July 15, 2006 Posts: 175 Comments: 54827

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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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