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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Quoting 954FtLCane:

Your going to Davie, I take you're going by horse then so yes.... leave very early.
I hate riding my horse down I-95. It's so hard to text with people honking their horn
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18Z NAM(NON TROPICAL MODEL) hr 024 TILL 84


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Little shift west with the models. NHC is the eastern outlier.

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TD19 is closer to becoming Sandy than TD18 is.
AL, 19, 2012102218, , BEST, 0, 218N, 517W, 30, 1006, DB
Member Since: July 8, 2005 Posts: 259 Comments: 23565
Recon got 39mph winds- that's a TS.
Member Since: February 11, 2012 Posts: 82 Comments: 7612
Quoting PalmBeachWeather:
Gro.......... I was going to visit my aunt that lives in Davie the day before Thanksgiving.... I was going to head down there about 3:00 PM... Do you think the weather will be ok, or should I leave around noon to be on the safe side.???

Your going to Davie, I take you're going by horse then so yes.... leave very early.
Member Since: September 30, 2008 Posts: 0 Comments: 108
18Z NAM(NON TROPICAL MODEL) hr 021 TILL 84


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Quoting Grothar:
As someone mentioned earlier, most of the models keep the convection to the west, which is unusual.

Gro.......... I was going to visit my aunt that lives in Davie the day before Thanksgiving.... I was going to head down there about 3:00 PM... Do you think the weather will be ok, or should I leave around noon to be on the safe side.???
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Updated 18z Best Track with recon position.

AL, 18, 2012102218, , BEST, 0, 129N, 788W, 25, 1002, TD
Member Since: April 29, 2009 Posts: 75 Comments: 14000
Quoting SunriseSteeda:


That is odd... isn't the increasing wind shear supposed to be coming from the SW?


Yes, but it doesn't seem to be on this one. Almost all the models are showing a stronger west side than east side in the later frames.
Member Since: July 17, 2009 Posts: 69 Comments: 25333
19L CYCLONE DEPRESSION
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Quoting ncstorm:
Just hypothetically asking a question but has there ever been an evacuation for a nor'easter before?

Theres a first for everything
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T.C.F.A
18L/TD/NN/XX
MARK
13.79N/77.89W
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Quoting Grothar:
As someone mentioned earlier, most of the models keep the convection to the west, which is unusual.



You listen to Levi's video? He explains in detail why.
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Quoting SunriseSteeda:


Remember a few years ago when there was not much of Ft Lauderdale Beach at all?


I forget which storm (Frances?) where I ventured out to Sunrise Blvd and A1A only to find everything north of there completely part of the ocean. An eerie feeling it was, at midnight, the Atlantic Ocean lapping at my car door. I didn't stay long.


Yup that was Frances. here's a pic I took the morning after.
Member Since: September 30, 2008 Posts: 0 Comments: 108
Much warmer SST's in the NE than usual.

Member Since: July 17, 2009 Posts: 69 Comments: 25333
297. 7544
one mb drop down to 1002 ?
Member Since: May 6, 2007 Posts: 0 Comments: 6690
18Z NAM(NON-TROPICAL MODEL) hr 015 TILL 84


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The ECWMF forecast for the next 5 days with 18L is very reasonable, based on the current trends. A dive to the SW, then hooks NE with the trough, with a strengthening storm making landfall in Cuba. After that, it's questionable. Shows an area of low pressure developing on the western side of the circulation that draws it fairly close to Florida, before sending it up to New England as a horrific nor'easter, though that is overdone.
Member Since: July 8, 2005 Posts: 259 Comments: 23565
Quoting Grothar:
As someone mentioned earlier, most of the models keep the convection to the west, which is unusual.


And doesn't make a lot of sense, since a huge trough is coming down by Saturday. It seems like, if the storm really stays west, the west side should get torn up by dry air and wind shear, not to mention getting a pretty good push to the east. What happens with TD18 is totally dependent how fast TD18 moves north and the strength and timing of the trough. A whole bunch of things have to happen to turn this into an east coast storm, with the left being the strong side. Anything could happen, of course, but this is why I don't draw to a pair of tens in blackjack. :)
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Quoting Grothar:
As someone mentioned earlier, most of the models keep the convection to the west, which is unusual.



That is odd... isn't the increasing wind shear supposed to be coming from the SW?
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Recon needs to take a sample of the eastern side of the center of circulation, looks interesting.
Member Since: July 8, 2005 Posts: 259 Comments: 23565
18Z NAM(NON-TROPICAL MODEL) hr 012 TILL 84


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290. 7544
fl should keep one eye out remember this is not 10 days out close to home only 4 days out stay tuned
Member Since: May 6, 2007 Posts: 0 Comments: 6690
18Z NAM(NON-TROPICAL MODEL) hr 009 TILL 84


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Quoting 954FtLCane:

Yup not good for the beaches. Some erosion is sure to come out of this. I wonder how close Fort Laudy beach will come to A1A this time.


Remember a few years ago when there was not much of Ft Lauderdale Beach at all?


I forget which storm (Frances?) where I ventured out to Sunrise Blvd and A1A only to find everything north of there completely part of the ocean. An eerie feeling it was, at midnight, the Atlantic Ocean lapping at my car door. I didn't stay long.

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A perfectly phased Nor'Sandy ai?

If this indeed pans out, someone in the east is gonna get

...A cool/cold Halloween!

...A white Halloween!

...A mild/wet Halloween!

...Or all of the above!!!
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Just hypothetically asking a question but has there ever been an evacuation for a nor'easter before?
Member Since: August 19, 2006 Posts: 13 Comments: 14434
Quoting trHUrrIXC5MMX:


Im freaked out already. I live in the woods in CT... that VERY...VERY...VERY.. is not working for me here


I'm not trying to freak people out, as the ECMWF/CMC often have way to low and unrealistic pressures, one of the ECMWF's only downsides actually, but it will be interesting to see how this one plays out. For now, watch and wait.
Member Since: July 8, 2005 Posts: 259 Comments: 23565
Quoting MAweatherboy1:
Um... yeah....

Ladies and gentlemen, your winner of the 2012 "Model Doomcane of Doom" award goes to...
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Quoting trHUrrIXC5MMX:
who says TD18 or Sandy/Tony this is The EAST COAST KATRINA

What? No one except you is saying this. This thing hasn't even developed into a tropical storm yet, and the models still don't have a good handle on either path or intensity. It's way too early to even be thinking such a thing.
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Member Since: April 29, 2009 Posts: 75 Comments: 14000
Quoting HurricaneKing:


Neither am I, though I have seen them disagree with the HPC if they thought other models like in this case the GFS looked more realisitic. So it's giving the EURO more credit that the HPC and some of the NWS's are leaning towards its solution.

My thoughts on this storm are that we need to watch the trough. It all depends on the tilt the trough takes as to which direction the storm will go. A positive tilt the storm doesnt get captured and goes harmlessly out to sea.(Well harmless for the east coast. The poor Caribbean islands are going to take a beating either way.) Negative tilt tends to include capture and a Euro like solution. I will say that even if it gets captured I think the EURO and CMC are overkill pressure wise. We have to remember what they were showing with Irene when she was in a similar location.

I agree
Member Since: August 19, 2006 Posts: 13 Comments: 14434
As someone mentioned earlier, most of the models keep the convection to the west, which is unusual.

Member Since: July 17, 2009 Posts: 69 Comments: 25333
Quoting CybrTeddy:


A very, very, very, very, VERY strong Nor'easter. I've never seen a sub 930mb nor'easter ever predicted before by the CMC, or the ECMWF.


Im freaked out already. I live in the woods in CT... that VERY...VERY...VERY.. is not working for me here
Member Since: April 23, 2011 Posts: 104 Comments: 14870
Quoting Wunderwood:


Well stated. The rule of thumb for those of us in South FL is that we should keep an eye on any storm to our south or southeast. This does not mean that we are wishcasting, we are being prudent. No track is set in stone this early. Crazy things can happen, like Wilma intensifying before hitting us when it was supposed to be sheared and weakened.


...and because of Wilma, sometimes the Southwest! Especially this part of the season.
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18Z NAM(NON-TROPICAL MODEL) hr 006 TILL 84


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Quoting Chucktown:


I heard that Press. LOL !! We shouldn't have any problems here, other than some marine issues. The trough will dig pretty hard over the SE US as it goes negative and becomes NW - SE oriented. Now, folks from the OBX to New England are going to have to watch very closely, as this could be a strong nor'easter by this time next week.


A very, very, very, very, VERY strong Nor'easter. I've never seen a sub 930mb nor'easter ever predicted before by the CMC, or the ECMWF. If in the event the models were correct, it would be a nor'easter unlike the which we have ever seen.
Member Since: July 8, 2005 Posts: 259 Comments: 23565
18Z NAM(NON-TROPICAL MODEL) hr 003 TILL 84


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Quoting ncstorm:


with the HPC shifting its track closer to NC, Im not surprise that the NWS in Newport is siding with them


Neither am I, though I have seen them disagree with the HPC if they thought other models like in this case the GFS looked more realisitic. So it's giving the EURO more credit that the HPC and some of the NWS's are leaning towards its solution.

My thoughts on this storm are that we need to watch the trough. It all depends on the tilt the trough takes as to which direction the storm will go. A positive tilt the storm doesnt get captured and goes harmlessly out to sea.(Well harmless for the east coast. The poor Caribbean islands are going to take a beating either way.) Negative tilt tends to include capture and a Euro like solution. I will say that even if it gets captured I think the EURO and CMC are overkill pressure wise. We have to remember what they were showing with Irene when she was in a similar location.
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Quoting 7544:
it be interesting to see the model runs once they get the hh data


Low level HH data does not help the models all that much. The high level Gulfstream IV flights do.


How are tropical cyclones represented in operational model initial conditions?
And why does it matter?
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Quoting GTcooliebai:
Surf is going to increase up and down the East Coast.

Yup not good for the beaches. Some erosion is sure to come out of this. I wonder how close Fort Laudy beach will come to A1A this time.
Member Since: September 30, 2008 Posts: 0 Comments: 108
Quoting presslord:
I see my friend Chucktown has gone on record as saying this thing is definitely gonna obliterate Charleston...


I heard that Press. LOL !! We shouldn't have any problems here, other than some marine issues. The trough will dig pretty hard over the SE US as it goes negative and becomes NW - SE oriented. Now, folks from the OBX to New England are going to have to watch very closely, as this could be a strong nor'easter by this time next week.
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Recon has yet to take a sample of the core, they've been dancing around outside it. They're heading into it now. This system appears to have a very tight and small windfield. What's more so, the environmental pressures are rather low. 18L is nicely organizing. Classic monsoonal October system.
Member Since: July 8, 2005 Posts: 259 Comments: 23565
If this thing is further southwest, then does what mean the track will be shifted further west? I am here in West Palm Beach, Florida wondering if I need to keep an eye on this storm.
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Tropical Depression 19.
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Quoting GTcooliebai:
Tropical Depression 19 and Tropical Storm Sandy to come at 5PM.


So they found TS force winds?
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Quoting GTcooliebai:
Tropical Depression 19 and Tropical Storm Sandy to come at 5PM.


the blog will be going fast..the 6pm local news on the east coast will have a lot to talk about..
Member Since: August 19, 2006 Posts: 13 Comments: 14434
Member Since: April 29, 2009 Posts: 75 Comments: 14000
Tropical Depression 19 and Tropical Storm Sandy to come at 5PM.
Member Since: August 31, 2009 Posts: 0 Comments: 5628

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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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