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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Question:
If Invest 90L were to become TD#19 and then a tropical storm before TD#18 reaches tropical storm status, would it be named Sandy or Tony?
If the answer to that question is Sandy, and I think it is, does anyone know when the last time storm names were out of sequence with the TD numbers (taking into consideration, of course, that there are no 'Q' storms).
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Quoting superpete:


Kman
Hows things with you? Any thoughts on TD 18 getting as far west as 80 Degrees, or are we out of the woods ?


We are on the edge of the woods :-).

It may drift West close to 80 but unless the trough is weaker and shallower than forecast I do not see this coming our way at this time.
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Quoting GTcooliebai:
Boy that is a bold prediction considering how well the GFS has done all year.


I know right..LOL..trust me, his "fans" turn on him all the time
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Quoting ncstorm:
from Henry Margusity Fan Page on Facebook

GFS model is wrong with it's solution. A storm will end on the coast, but which storm is the question.
Boy that is a bold prediction considering how well the GFS has done all year.
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Quoting ncstorm:
the CMC is also back to bombing back over the NC/VA and DC



939 MB.."Elizabeth, Im coming to join you with a CMC doom model"
I see the CMC is going all "Storm of the Century" on you guys.
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Quoting presslord:


I'm certain I read in Beowulf that you drank mead...


Never had the need for mead.


GFS



Member Since: July 17, 2009 Posts: 64 Comments: 23749
Quoting kmanislander:
TD 18 is looking more and more like a TS. Would not be surprised if HH finds winds supporting an immediate upgrade. Pressure may be near 1001 mbs if the actual obs correlate to the appearance of the system.


Kman
Hows things with you? Any thoughts on TD 18 getting as far west as 80 Degrees, or are we out of the woods ?
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from Henry Margusity Fan Page on Facebook

GFS model is wrong with it's solution. A storm will end on the coast, but which storm is the question.
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I see my friend Chucktown has gone on record as saying this thing is definitely gonna obliterate Charleston...
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Quoting sar2401:

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.


Yup I meant before it reaches Cuba, in the next 48-72 hours. The satellite presentation was the reason I asked.
Someone mentioned earlier, and I tended to agree, why not raise hurricane watches for Jamaica and Eastern Cuba since their is a 32% chance that in 48 hours this may be a hurricane.
The NHC forecast has this as a 70 mph TS going into Jamaica...



INIT 22/1500Z 13.5N 78.0W 25 KT 30 MPH
12H 23/0000Z 13.7N 78.3W 35 KT 40 MPH
24H 23/1200Z 14.3N 78.1W 45 KT 50 MPH
36H 24/0000Z 15.7N 77.6W 55 KT 65 MPH
48H 24/1200Z 17.4N 77.0W 60 KT 70 MPH
72H 25/1200Z 20.5N 76.0W 55 KT 65 MPH...INLAND OVER CUBA
96H 26/1200Z 24.5N 74.5W 55 KT 65 MPH...OVER WATER
120H 27/1200Z 27.0N 73.0W 50 KT 60 MPH...SUBTROPICAL
Member Since: September 30, 2008 Posts: 0 Comments: 108
the CMC is also back to bombing back over the NC/VA and DC



939 MB.."Elizabeth, Im coming to join you with a CMC doom model"
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Member Since: July 17, 2009 Posts: 64 Comments: 23749
Appears to be consolidating nicely this afternoon. Wouldn't be surprised to see this upgraded to Sandy at 5PM.

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TD 18 is looking more and more like a TS. Would not be surprised if HH finds winds supporting an immediate upgrade. Pressure may be near 1001 mbs if the actual obs correlate to the appearance of the system.
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90L up to 70%.

SHOWERS AND THUNDERSTORMS ASSOCIATED WITH A SMALL AREA OF LOW
PRESSURE OVER THE CENTRAL ATLANTIC ABOUT 700 MILES EAST-NORTHEAST
OF THE LEEWARD ISLANDS CONTINUE TO SHOW SIGNS OF ORGANIZATION...AND
THE LOW-LEVEL CIRCULATION IS BECOMING BETTER DEFINED.
ENVIRONMENTAL CONDITIONS ARE EXPECTED TO BE CONDUCIVE FOR
DEVELOPMENT BEFORE UPPER-LEVEL WINDS BECOME LESS FAVORABLE ON
TUESDAY. THIS SYSTEM HAS A HIGH CHANCE...70 PERCENT...OF BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES NORTHWARD
AT ABOUT 10 MPH.
Member Since: April 29, 2009 Posts: 75 Comments: 13336
Thank you
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148. 7544
looks like 99l beats 90l and will be sandy sometime today looking good at this hour stationary
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Quoting presslord:


I'm certain I read in Beowulf that you drank mead...
Damn dragons
Member Since: October 3, 2008 Posts: 0 Comments: 5754
Quoting BrickellBreeze:


Large shift west...



Large shift west...

Ugh... I just aided My family in putting up $125 dollars worth of Halloween Lights.

CMC initialized very badly. WAY too far SW.
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Quoting GeorgiaStormz:


models are trying to put all mositure on the west side for some reason.

Which doesn't make any sense, since the shear will be coming out of the W or SW, and continental air will be filtering in from the W and NW as is passes by land. Not to mention inflow will be from that direction.

It doesn't make sense.
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Quoting 954FtLCane:




I tend to agree


Looking at that image it looks like the mixed band/comma head that a subtropical cyclone tends to pick up.

When I was doing research at the nws this summer I found in some of the records a discussion about how to forecast a storm going through extratropical transition.

The Canadian Hurricane Center and the NWS's out of the northeast had agreed during the time before we had better modeling and radar that the western side would have higher rainfall amounts and the eastern side of the cyclone would have higher winds during the transition process.
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BULLETIN
TROPICAL DEPRESSION EIGHTEEN INTERMEDIATE ADVISORY NUMBER 1A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL182012
200 PM EDT MON OCT 22 2012

...AIR FORCE HURRICANE HUNTER PLANE EN ROUTE TO INVESTIGATE THE
DEPRESSION...


SUMMARY OF 200 PM EDT...1800 UTC...INFORMATION
----------------------------------------------
LOCATION...13.5N 78.5W
ABOUT 325 MI...525 KM SSW OF KINGSTON JAMAICA
MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H
PRESENT MOVEMENT...STATIONARY
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES


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

NONE

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

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

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 LATER TODAY.

INTERESTS IN EASTERN CUBA...HISPANIOLA...AND THE BAHAMAS SHOULD
MONITOR THE PROGRESS OF THIS SYSTEM.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 200 PM EDT...1800 UTC...THE CENTER OF TROPICAL DEPRESSION
EIGHTEEN WAS LOCATED NEAR LATITUDE 13.5 NORTH...LONGITUDE 78.5 WEST.
THE DEPRESSION HAS MOVED LITTLE DURING THE PAST FEW HOURS AND SHOULD
DRIFT GENERALLY WESTWARD THROUGH TONIGHT. A NORTH-NORTHEASTWARD
MOTION WITH AN INCREASE IN FORWARD SPEED IS EXPECTED TUESDAY
THROUGH EARLY WEDNESDAY. ON THE FORECAST TRACK...THE CENTER OF THE
CYCLONE SHOULD APPROACH JAMAICA TUESDAY NIGHT OR EARLY WEDNESDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 30 MPH...45 KM/H...WITH HIGHER
GUSTS. STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...AND THE
DEPRESSION IS EXPECTED TO BECOME A TROPICAL STORM LATER TODAY OR
TONIGHT. THE CYCLONE COULD BE NEAR HURRICANE STRENGTH AS IT IS
APPROACHING JAMAICA ON WEDNESDAY. AN AIR FORCE HURRICANE HUNTER
AIRCRAFT IS EN ROUTE TO INVESTIGATE THE DEPRESSION.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB...29.62 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE IN JAMAICA BY TUESDAY
NIGHT.

RAINFALL...TROPICAL DEPRESSION EIGHTEEN IS EXPECTED TO PRODUCE TOTAL
RAINFALL AMOUNTS OF 5 TO 10 INCHES ACROSS JAMAICA...HAITI...THE
DOMINICAN REPUBLIC...AND EASTERN CUBA...WITH ISOLATED MAXIMUM
AMOUNTS OF 16 INCHES POSSIBLE...ESPECIALLY IN AREA OF MOUNTAINOUS
TERRAIN AREAS. THESE RAINFALL AMOUNTS MAY PRODUCE LIFE-THREATENING
FLASH FLOODS AND MUD SLIDES.


NEXT ADVISORY
-------------
NEXT COMPLETE ADVISORY...500 PM EDT.

$$
FORECASTER BERG/AVILA


Member Since: April 29, 2009 Posts: 75 Comments: 13336
Quoting Grothar:


Old Gro does not imbibe. I never drank.


I'm certain I read in Beowulf that you drank mead...
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Quoting GeorgiaStormz:
Clear central rotation and CDO forming, might be a TS already.
Crazy what a difference in just 12 hours....YIKES.
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Quoting Chucktown:
Just remember, this is late October, not August. This system will most likely not be your classical looking tropical entity. It is probably going to be sheared on the west side, mainly due to strong SW winds ahead of the digging trough. Secondly, there is going to be a tremendous moisture gradient on the west side of the storm. You can already notice this as future Sandy is having some difficulty wrapping anything on the west side. This will be an ongoing struggle through its life.


Late October,but still not November - conditions are still quite favorable,especially if TD18 crosses 80W(more time to organise)
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Quoting GeorgiaStormz:


models are trying to put all mositure on the west side for some reason.




I tend to agree
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Quoting cwf1069:
Good afternoon. Can somebody give me the link for the hurricane hunter at google earth, please. Thank you


http://www.tropicalatlantic.com/recon/ge/Atlantic .kmz
Welcome.
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Quoting Chucktown:
Just remember, this is late October, not August. This system will most likely not be your classical looking tropical entity. It is probably going to be sheared on the west side, mainly due to strong SW winds ahead of the digging trough. Secondly, there is going to be a tremendous moisture gradient on the west side of the storm. You can already notice this as future Sandy is having some difficulty wrapping anything on the west side. This will be an ongoing struggle through its life.


models are trying to put all mositure on the west side for some reason.
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Quoting Chucktown:
Just remember, this is late October, not August. This system will most likely not be your classical looking tropical entity. It is probably going to be sheared on the west side, mainly due to strong SW winds ahead of the digging trough. Secondly, there is going to be a tremendous moisture gradient on the west side of the storm. You can already notice this as future Sandy is having some difficulty wrapping anything on the west side. This will be an ongoing struggle through its life.


Actually, the models are showing it being more eastern lopsided.
Member Since: July 8, 2005 Posts: 259 Comments: 23015
Time: 17:21:00Z
Coordinates: 18.6833N 83.45W
Acft. Static Air Press: 410.1 mb (~ 12.11 inHg)
Acft. Geopotential Hgt: 7,384 meters (~ 24,226 feet)
Extrap. Sfc. Press: -
D-value: 374 meters (~ 1,227 feet)
Flt. Lvl. Wind (30s): From 258° at 23 knots (From the WSW at ~ 26.4 mph)
Air Temp: -16.3°C (~ 2.7°F)
Dew Pt: -31.6°C (~ -24.9°F)
Peak (10s) Flt. Lvl. Wind: 24 knots (~ 27.6 mph)
SFMR Peak (10s) Sfc. Wind: 19 knots (~ 21.8 mph)
SFMR Rain Rate: 0 mm/hr (~ 0 in/hr)
(*) Denotes suspect data
Member Since: April 29, 2007 Posts: 0 Comments: 7506
Will be interested to see what TS Wind Fields the HH sortie discovers - TD 18 is "visibly" a relatively large system.
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Quoting GeorgiaStormz:
CMC cuts off the space between 99L and the north atlantic low, and also elongates 99L much later than does the GFS:


The model runs are still crazed right now, since they seem to be intializing on different supposed COC's. There appear to multiple vortexes spinning around in the area of TD18. I hope the HH plane is able to fix a better COC. The models than should start running based on the same data. As it is, the ensemble model of taking it over the eastern Bahamas and then out to sea still look the most plausible. We shall see, but I doubt we'e going to get a good handle on this one until it finally starts moving and gets away from South America.
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I just have a hunch that this isn't going to get anywhere near the east coast. I think it will pass over Bermuda though as it transitions into an extratropical system.
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130. 7544
Quoting stormpetrol:
TD 18 appears to be moving due west now.


yeap lets see if it reaches 80 west then all bets are off imo
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Quoting Grothar:


Old Gro does not imbibe. I never drank.
In the words of the famous Dr. McCoy...........Dammit Jim
Member Since: October 3, 2008 Posts: 0 Comments: 5754
Just remember, this is late October, not August. This system will most likely not be your classical looking tropical entity. It is probably going to be sheared on the west side, mainly due to strong SW winds ahead of the digging trough. Secondly, there is going to be a tremendous moisture gradient on the west side of the storm. You can already notice this as future Sandy is having some difficulty wrapping anything on the west side. This will be an ongoing struggle through its life.
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127. flsky
Remember when one of the models predicted a storm like TD 18 about 2 weeks ago! Rather incredible forecasting.
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However, unlike Irene which was a similar distance away from FL, the pressure gradient should be much greater with this storm which could give the east coast a good lashing with wind and rain.
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TD 18 appears to be moving due west now.
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Ok so the high is centered pretty much right over Atlanta, GA and is expected to shift east which would also turn the storm to the Northeast, think clockwise flow around the high. Now look up over the Dakotas, Minnesota, and Iowa and noticed the change in the white lines from North to Northwest feeding that ULL over Saskatchewan. If everything is progressing west to east that could be part of the reason why the storm turns back to the Northwest and merges with that ULL. Now feel free to chime in and point out any errors I have in my analysis.

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Quoting PalmBeachWeather:
Thank you Gro..... The south Florida folks were freekin' out with the more westerly tracks.Much too early. Have you tried the vodka flavored vodka Gro?


Old Gro does not imbibe. I never drank.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
Good afternoon. Can somebody give me the link for the hurricane hunter at google earth, please. Thank you
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If a high builds in north of the storm it makes a better environment shear wise, and also moves the storm the storm further west. If the trough picks up the storm it shears the system as if pushes it off to the NE. This is what the Doc means when he says the steering environment is up in the air. The models are having the same problem. Stay tuned is all we can do.
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I don't see any shift west yet.


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Quoting Grothar:
Thank you Gro..... The south Florida folks were freekin' out with the more westerly tracks.Much too early. Have you tried the vodka flavored vodka Gro?
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Where is a TCTrak for TD18?
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Clear central rotation and CDO forming, might be a TS already.
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Member Since: July 17, 2009 Posts: 64 Comments: 23749
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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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.