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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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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63. 7544
was the plane cancel for today or is it ago tia
Member Since: May 6, 2007 Posts: 0 Comments: 6874
62. SLU
Quoting JLPR2:


ASCAT caught half of 90: and it seems the highest winds are 30mph. But it is just one wind barb so maybe the NHC wont renumber just yet.


Considering the low bias of the ASCAT it could very well be generating 35mph winds.
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61. 7544
with this gfs run se fl could get some effects from this ?
Member Since: May 6, 2007 Posts: 0 Comments: 6874
12Z GFS hr 144 final


Member Since: July 15, 2006 Posts: 176 Comments: 55635
Any chance this happens again?
It was interesting being in DC on the edge of Snowtober, Originally I didnt think we would see anything.

Was calmer earlier in the week:


Then the snow:




And then we came back to the boring usual GA thunderstorms:
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Quoting nrtiwlnvragn:
Hope this would never happen in the USA:

L'Aquila quake: Italy scientists guilty of manslaughter

Excerpt:

Six Italian scientists and an ex-government official have been sentenced to six years in prison over the 2009 deadly earthquake in L'Aquila.

A regional court found them guilty of multiple manslaughter.

Prosecutors said the defendants gave a falsely reassuring statement before the quake, while the defence maintained there was no way to predict major quakes.


Good grief, nrt,

"And in other news, all Italian meteorologists have suddenly tendered resignation letters!"
;)
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12Z GFS hr 132 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
12Z GFS hr 123 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
Quoting tramp96:

Thanks buddy I guess this is the only place I can talk to you
now
tramp96............Check your email
Member Since: October 3, 2008 Posts: 0 Comments: 6000
It became very dark here in S C IL, now it's really booming outside! Haven't heard one like this in a while. Didn't think this one was supposed to develop this far south. Rain just got heavier too. Those to east should get ready!
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12Z GFS hr 117 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
See what happens once it crosses Cuba,then I would pay more attention to the models.
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At 117 hours, 12z is moving back in line with the 06z.
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50. 7544
looks like west shift this run
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102 hrs, 3 mb drop to 981.
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ASCAT caught half of 90: and it seems the highest winds are 30mph. But it is just one wind barb so maybe the NHC wont renumber just yet.
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12Z GFS hr 108 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
Expect hurricane watches to go up for parts of central and eastern cuba tomorrow
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12Z GFS hr 096 TILL 144


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the 12z looks to have shifted west
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96 hrs, 984 mb, sandy looks to be a bahama mama
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12Z GFS hr 084 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
Definate shift to the west at 102 hours (12z GFS vs. 06Z GFS).
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12Z GFS hr 072 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
the 12z run has a much tighter storm than the 06z

12z


06z
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12Z GFS hr 060 TILL 144


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84 hrs, most of the energy & winds seem to be west of the ctr, 988 mb
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12Z GFS hr 048 TILL 144


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12Z GFS hr 036 TILL 144


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34. 7544
Quoting Seflhurricane:
Td18 is very quickly organizing we may have a hurricane by tomorrow morning so intrests in jamaica , cuba and the bahamas now i am very concerned about the track i feel the models are not handling it very well looks to me that the cone will shift to the left closer to the NW bahamas and closer to se florida coast , for us here in se florida the question will be how close does it come to the coast


agree check it out
Link
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12Z GFS hr 024 TILL 144


Member Since: July 15, 2006 Posts: 176 Comments: 55635
I think there's actually a slight shift to the West on this run at 87 hours. It's not a lot but a slight shift to the West.
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12Z GFS hr 012 TILL 144


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72 hr, shear map
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Td18 is very quickly organizing we may have a hurricane by tomorrow morning so intrests in jamaica , cuba and the bahamas now i am very concerned about the track i feel the models are not handling it very well looks to me that the cone will shift to the left closer to the NW bahamas and closer to se florida coast , for us here in se florida the question will be how close does it come to the coast
Member Since: July 14, 2009 Posts: 0 Comments: 3029
Quoting SFLWeatherman:
81HR


So far the 12z looks almost identical to the 06z run. We'll have to see if that continues.
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27. 7544
Quoting rmbjoe1954:


It is an extreme outlier.


agree then look at the euro it takes it to the east if so fl then a push west enough to feel it the back ne so i do think the models will be shifting more west the next couple of runs imo
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invest_RENUMBER_al992012_al182012.ren or TropicalDepressionEighteen. The NHC hasn't posted its ATCF AL18 file yet so the below is still derived from NHC_ATCF data for Invest99L @ 22Oct.12pm ... All times in GMT.
Since the previous mapping, 99L's StormStatus between 21Oct.12am and 22Oct.12am has been reevaluated&altered from DisturBance to (closed)LOw
14.6n77.7w was reevaluated&altered to
14.5n77.5w-14.3n77.9w which in turn was reevaluated&altered to
14.4n77.2w-14.1n77.6w-13.7n77.9w as the now most recent positions

PUZ-PuertoCabezas :: PVA-Providencia :: ADZ-SanAndres :: BOC-Bocas del Toro :: ONX-Colon

The kinked line traces 99L's path as a closed low
The northernmost dot on the longest line is where 99L was declared to have become TD18

The longest line is a straightline projection through 99L's 2 most recent positions to its closest approach to an inhabited coastline; in this case, Panama
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25. afj3
Quoting PalmBeachWeather:
Whether it be human, machine, or model... south Florida is always in the bullseye.

So true!
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24. afj3

Quoting rmbjoe1954:


It is an extreme outlier.
Thanks!
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81HR
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.
Member Since: August 19, 2006 Posts: 13 Comments: 16215
72HR
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From me!
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Thanks Dr. Masters! :)
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I would hold off on to many predictions till the plane feeds the info into the computers. Looking to the NW of the storm, that is one giant circulation. I don't know enough to be an alarmist but, I would not sell this storm short if I was anyone. And if you look to the nw of the storm in the gulf where the circulation stops it seems most clouds are moving off to the NNW to NW in the gulf. I would agree that this storm may venture to the western side of Jamaica.Maybe all the trick without the treat we can handle this year.
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Hope this would never happen in the USA:

L'Aquila quake: Italy scientists guilty of manslaughter

Excerpt:

Six Italian scientists and an ex-government official have been sentenced to six years in prison over the 2009 deadly earthquake in L'Aquila.

A regional court found them guilty of multiple manslaughter.

Prosecutors said the defendants gave a falsely reassuring statement before the quake, while the defence maintained there was no way to predict major quakes.
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Hi tramp96, it becomes more spread out, less concentrated around it's center. It's wind field spreads out, but generally will not become "as strong" as a tropical system. There are other differences too.
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Quoting afj3:

Why is the NOGAPS so adamant about a SoFla landing??? It's sticking to its guns with only slight nods
Whether it be human, machine, or model... south Florida is always in the bullseye.
Member Since: October 3, 2008 Posts: 0 Comments: 6000

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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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