TD 2 nearly dead; African disturbance 90L gathering strength

By: Dr. Jeff Masters , 2:38 PM GMT on August 13, 2009

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Tropical Depression Two is near death, but is still worth watching. The dry, Saharan air to the north and west of the depression, combined with moderately high levels of wind shear of 15 - 20 knots, have almost completely destroyed all of TD 2's heavy thunderstorms. Satellite loops of the storm show a well-formed circulation, but almost no heavy thunderstorm activity.

Wind shear over TD 2 is expected to remain in the modereate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C three days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to to TD 2's north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that TD 2 will not be able to intensify quickly, and some of the models indicate the TD 2 may get destroyed in the next day or two. However, several models still predict TD 2 will become a tropical storm. The HWRF model predicts TD 2 will become a hurricane five days from now, but this seems unlikely given the dry air and relatively high wind shear affecting the storm.


Figure 1. Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

African tropical wave 90L
A strong tropical wave with a large circulation and plenty of heavy thunderstorm activity is a few hundred miles south of the Cape Verdes Islands, off the coast of Africa. NHC dubbed this disturbance 90L this morning. This morning's QuikSCAT pass shows that 90L has a very large circulation, and top winds of about 30 mph. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are in two major bands, to the north and to the south of the center. There is no heavy thunderstorm activity near the center yet, and this would have to happen before 90L can be named Tropical Depression Three. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two has been. Wind shear is about 20 knots over 90L, and is forecast to remain in the moderate range, 10 - 20 knots, over the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days, which are high enough above the 26°C threshold for tropical cyclone formation to allow some slow development to occur. The GFS and ECMWF models continue to predict the development of this wave, though they are now less aggressive about intensifying it than they were in earlier runs. The consensus among the reliable HWRF, GFDL, GFS, and ECMWF models is to bring 90L to point near or just north of the northernmost Lesser Antilles Islands 6 - 8 days from now. The storm could be at hurricane strength by then, as forecast by the SHIPS intensity model.

I'll have an update Friday morning.

Jeff Masters

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2487. jdjnola
Quoting TampaSpin:
TD2 is actually tapping in to some moisture supplied by 90L it appears......hum this could get interesting in 2 days...


I've noticed some of the models indicating a slight Fujiwhara effect between the two lows... thought it was interesting, but didn't think much of it beyond that.
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2486. hahaguy
Quoting weatherblog:


I am not here to save lives. That's not my job. Sure, it would be nice if I did, but I doubt my opinion will save someone's life.


I'm not a doctor but I play one on tv.
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2485. Drakoen
SHIPS 00z take 90L up to 93knots!
Member Since: October 28, 2006 Posts: 57 Comments: 29714
what seems to be the thought on these waves for the 11pm update?
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Quoting weatherblog:


I am not here to save lives. That's not my job. Sure, it would be nice if I did, but I doubt my opinion will save someone's life.
hope it does.
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Quoting stormwatcherCI:
Do you think if it it gets in the Caribbean there is any chance for it to develop ?

I think it has a chance of develop before it reaches the caribbean and looking at the 850 mb vorticity in the last 6hours till now if you look at it close you can see that the vorticity has increased




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The NHC gives the blob near the Carib a low change of developing into anything. I do think we can see an increase in POPS this weekend in FL though. Who knows, this time of year and a system in that location, anything is possible.
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Quoting weatherblog:


I am not here to save lives. That's not my job. Sure, it would be nice if I did, but I doubt my opinion will save someone's life.


I'm just here 'cause I can't stand to watch Greta van Susteren...
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2478. jpsb
Speculation on where 90L is going as a Cat5 hurricane is, perhaps, a bit premature. So far this year we've seen EVERYTHING die before even making it to TS status. Maybe 90L will fare better maybe not. I live on Galveston Bay so am payng attention to the topics. My experience is tracking models are unreliable after three days and intensity models are unreliable period. As an experienced hurricane dodger I only worry at landfall -48 hours. 48 hours out tracking models start getting reliable, then I watch to see witch side of the storm I am going to be on. Dirty side, very bad, good side not so bad.
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I remember everyone giddy about TS Ana ... wonder where it went? Follow this Link. It basically exploded and left a moist environment for 90L to feed upon, I suppose. As someone here said, it was "the sacrificial lamb", or the "sacrifice fly to advance the runners".

One moment huge convective cold cloud tops, then boom, gone are the clouds.

That's what I love about this... so unpredictable! As in full of surprises.
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Quoting kingzfan104:


hey man, thanks for all your help throughout your time here. what do you think 90l will do, track and intensity wise?


For right now, this all remains pure speculation, but my thinking lies pretty much with the 18Z GFDL track but not as intense since it will take some time to organize into a tropical cyclone with the immense size.
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Quoting mobilegirl81:
Impressive convection, if it gets by the keys..... thats hot water, something could possibly morph.

It shall fade with every frame...pfffft coming soon to a wave near you.
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TD2 is actually tapping in to some moisture supplied by 90L it appears......hum this could get interesting in 2 days...
Member Since: September 2, 2007 Posts: 177 Comments: 20430
2473. jdjnola
Quoting mobilegirl81:
Do not take your eyes off that wave in the carribean.


Good advice. Not doomcasting, but anything is possible...

Hurricane Katrina formed as Tropical Depression Twelve over the southeastern Bahamas on August 23, 2005 as the result of an interaction of a tropical wave and the remains of Tropical Depression Ten.
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Quoting TampaSpin:


Yes i do....it just needs some moisture to tap into...and it won't need much...as long as the low level stays together the way it is....yes.
Thanks for answering. I respect and value your knowledge.
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Quoting BILOXISAINT2:
Chill out dude, we are all here for the same reason. TOO SAVE LIVES!


I am not here to save lives. That's not my job. Sure, it would be nice if I did, but I doubt my opinion will save someone's life.
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Quoting BrandiQ:
I haven't seen any images of 90L in a while. Is it due to the fact that it is dark right now over there?


The main satellite most images come from is blacked out right now due to a station keeping maneuver, they are moving the satellite into its normal position. It drifts over time and they have to correct the drift.
Member Since: September 23, 2005 Posts: 13 Comments: 10473
Impressive convection, if it gets by the keys..... thats hot water, something could possibly morph.
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2467. Patrap
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Quoting stormwatcherCI:
Do you think if it it gets in the Caribbean there is any chance for it to develop ?


Yes i do....it just needs some moisture to tap into...and it won't need much...as long as the low level stays together the way it is....yes.
Member Since: September 2, 2007 Posts: 177 Comments: 20430
Quoting mobilegirl81:
NOAA is calling it a strong tropical wave that could become a depression in the gulf.


Down the road, that might be possible, but not right now.
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Hi Weather4Me - good to see you around. We are attempting to round up the sane few left tonight to see if we have any information about 90L or the other yellow and orange blobs.

What do you thing?


Good to see you too. I see my avitar did not make it on your map last season. Do you still have the map active? I think that was you that did that last season. As far as 90 I'm looking at the NHC web site and they have been pretty informational so far.
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2463. Patrap
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Thanks KoritheMan.
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Quoting HaboobsRsweet:
My beef is when people shut down other folks that are suggesting where they think a storm may go and the only reason someone is shutting them down is the same excuse we hear all the time, it is too far out to say that. This is not an offical forecast so who cares if they say they think the storm is GOM bound or east coast bound. More power to them for trying. Not everyone has to explain in detail why they feel how they feel, it would help the rest out but it is not needed.


Yeah, everyone has opinions. This is all just speculation until we have a better idea of where it will go.
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2437. Skyepony 10:26 PM EDT on August 13, 2009
Quoting Tazmanian:
has any one noted how big 90L is ???


Yes Taz, I brought this up 2 nights ago. We may see another well defined tight swirl Felicia type suck dry a too big & blobby to get turning Enrique type. TD2 still has a nice swirl, keeping just enough convection to get by but now slowing the forward speed as 90L gets closer because it's forward speed is faster. By tonight's quikscat 90L has a ways to go to a closed low. Looked like 02L was tapping into 90L, the pic up top that Masters hung shows it well. Hard to tell now since the sun went down. I haven't ruled it out as a good possibiblity. Something with defined lower spin & structure ramps up way faster than a huge, cumbersome, wet blob. Remember too that many models don't do well when 2 storms are close together, combined with how weak they are & it's best to not use models as gospel..


Taz you have not read my updates....been saying that for 2 days. TD2 is much better organized than 90L.
Member Since: September 2, 2007 Posts: 177 Comments: 20430
hey all.

i remember someone on here mentioned not too long ago that they were looking to start a hurricane/tropical weather related site. I forgot who that was and I had meant to send them a message and let them know I have a few good domains that I have been waiting to do something with but haven't gotten around to yet. If you're still out there shoot me a WU-Mail when you get a chance. Thanks!


Local weather here has been playing up 90L and the wave over Puerto Rico tonight. Hopefully the wave won't develop and we'll get some nice rains here this weekend.
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NOAA is calling it a strong tropical wave that could become a depression in the gulf.
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Quoting DestinJeff:
Time again to re-visit some of the most posted words/expressions on the blog. Here now, the Top 10 (presented in no particular order)

10. The latest model run is worthless (used especially by those in areas where forecast tracks don't point)

9. The word "poleward" (many people know this as simply North)

8. IMO / JMO / My two cents / etc

7. Long time lurker, first time poster

6. AOI (this one seemed to start this season)

5. teh

4. Can I get the link to the models (rarely posted by someone that just wants it, always someone who's computer crashed/is at work and doesn't have it/etc etc)

3. NEW BLOG

2. Polls of any sort (and for a few days, poetry)

1. Any reference to Ignore List

8.
Very clever and insightful! How funny and true!!!
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Quoting mobilegirl81:
Whats up with the burst of covection over hispaniola?


Tropical wave interacting with an upper level low. Divergent flow aloft is helping to generate deep convection. No threat for tropical cyclogenesis, but some flooding rains are possible across Haiti and the Dominican Republic.
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Hi Weather4Me - good to see you around. We are attempting to round up the sane few left tonight to see if we have any information about 90L or the other yellow and orange blobs.

What do you thing?
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Quoting TampaSpin:
Looks like TD2 or the Low which ever one want to refer to it is heading into the Caribbean.....
Do you think if it it gets in the Caribbean there is any chance for it to develop ?
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Whats up with the burst of covection over hispaniola?
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Quoting kingzfan104:
uhhhhh, it has been forecasted to go west for a while.


Haha, yup. It'll continue west for awhile.
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Quoting cchsweatherman:
For right now, here's the best advice in regards to the current situation. Continue to keep an eye on the situation over the coming days. Just in the case that this system becomes a threat, make sure everyone in the Caribbean, U.S. East and Gulf Coasts, Bahamas, and Bermuda have your hurricane preparedness plans in place since nobody knows what exactly will happen. All that I know is that it pays (in some case quite literally) to be safe than unprepared. Just remember that this system remains about 1500 miles from making any land threat which means that we still have much time to watch the progress and evolution. Also, just because the computer models seem to be in very good agreement right now, doesn't mean that that will be the outcome. In the tropics, the No. 1 Rule of Thumb is nothing is guaranteed. Mother Nature plays by her own rules and things will likely change throughout the coming days. All you can do right now is remain informed and prepared.


hey man, thanks for all your help throughout your time here. what do you think 90l will do, track and intensity wise?
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Quoting presslord:


disturbing in here sometimes


Kind ok like Alice going down the rabbit hole
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Quoting BILOXISAINT2:
Chill out dude, we are all here for the same reason. TOO SAVE LIVES!
All I know is that I'm getting out the garlic, crosses and silver bullet for whatever thinks of coming our way...it is way too soon for us to see anything after what we went through 4 years ago
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Quoting DM21Altestic:
POLL: What kind of storm will 90L resemble most, as far as track and intensity?


A) Hurricane Bertha (2008)
B) Hurricane Georges (1998)
C) Hurricane Isabel (2003)
D) Hurricane Ivan (2004)
E) Hurricane Andrew (1992)
F) Hurricane Floyd (1999)
G) Hurricane Helene (2006)
H) Hurricane Allen (1978)
Z) 90L won't become a hurricane at all.

...Bold your choice...

Isabel-or- The 1903 Atlantic City Vagabond Hurricane or the Great Atlantic Hurricane of '44....maybe the remnants of Karen.
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Quoting Joshfsu123:


Yeah, cause models out two weeks tell you this? Yeah, next week the models will give us a better idea... until then, it is just your opinion.


Yup, we all have opinions. If some people are not smart enough to know I don't work at the NHC, that's not my problem.
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Quoting Skyepony:


Yes Taz, I brought this up 2 nights ago. We may see another well defined tight swirl Felicia type suck dry a too big & blobby to get turning Enrique type. TD2 still has a nice swirl, keeping just enough convection to get by but now slowing the forward speed as 90L gets closer because it's forward speed is faster. By tonight's quikscat 90L has a ways to go to a closed low. Looked like 02L was tapping into 90L, the pic up top that Masters hung shows it well. Hard to tell now since the sun went down. I haven't ruled it out as a good possibiblity. Something with defined lower spin & structure ramps up way faster than a huge, cumbersome, wet blob. Remember too that many models don't do well when 2 storms are close together, combined with how weak they are & it's best to not use models as gospel..



ok
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Quoting HaboobsRsweet:
My beef is when people shut down other folks that are suggesting where they think a storm may go and the only reason someone is shutting them down is the same excuse we hear all the time, it is too far out to say that. This is not an offical forecast so who cares if they say they think the storm is GOM bound or east coast bound. More power to them for trying. Not everyone has to explain in detail why they feel how they feel, it would help the rest out but it is not needed.


I would just prefer that people make statements that have some backup. Saying opinion is not nearly as interesting when there arent any details or reasoning to discuss. Maybe someone does see something that others havent seen yet. I would like to know why they have a certain opinion
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Been lurking all season thus far and have not posted yet. I see some familiar faces but many new comers since last season. Welcome all. I see things are starting to pop a bit as the MJO has appeared to move in to our neck of the woods. Still too soon to tell where any of these features will end up and what they will become, if anything. I do feel that 90 may get named within the next 48 hours though and looking at current steering agree with the models taking a W to WNW track initially. Everything depends on the BH and future steering currents. In a nut shell. Too early to sit around the computer round the clock just yet. It is sooo addicting though. Take care.
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Do not take your eyes off that wave in the carribean.
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I have no PHD in metereology but I enjoy researching and following weather around the globe. I am a spectator here and I will never claim to be able to predict anything. So please cut me some slack. I love the info I get here. There is some good discussions here too.
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Quoting weatherblog:


That's fine, but at least say who you are referring to.
Chill out dude, we are all here for the same reason. TOO SAVE LIVES!
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Quoting Tazmanian:
if 90L dos not become TD 3 or a name storm


this hurricane season will be dead


Taz that is not a very intelligent statement coming from you!
Member Since: September 2, 2007 Posts: 177 Comments: 20430
For right now, here's the best advice in regards to the current situation. Continue to keep an eye on the situation over the coming days. Just in the case that this system becomes a threat, make sure everyone in the Caribbean, U.S. East and Gulf Coasts, Bahamas, and Bermuda have your hurricane preparedness plans in place since nobody knows what exactly will happen. All that I know is that it pays (in some case quite literally) to be safe than unprepared. Just remember that this system remains about 1500 miles from making any land threat which means that we still have much time to watch the progress and evolution. Also, just because the computer models seem to be in very good agreement right now, doesn't mean that that will be the outcome. In the tropics, the No. 1 Rule of Thumb is nothing is guaranteed. Mother Nature plays by her own rules and things will likely change throughout the coming days. All you can do right now is remain informed and prepared.
Member Since: Posts: Comments:
2437. Skyepony (Mod)
Quoting Tazmanian:
has any one noted how big 90L is ???


Yes Taz, I brought this up 2 nights ago. We may see another well defined tight swirl Felicia type suck dry a too big & blobby to get turning Enrique type. TD2 still has a nice swirl, keeping just enough convection to get by but now slowing the forward speed as 90L gets closer because it's forward speed is faster. By tonight's quikscat 90L has a ways to go to a closed low. Looked like 02L was tapping into 90L, the pic up top that Masters hung shows it well. Hard to tell now since the sun went down. I haven't ruled it out as a good possibiblity. Something with defined lower spin & structure ramps up way faster than a huge, cumbersome, wet blob. Remember too that many models don't do well when 2 storms are close together, combined with how weak they are & it's best to not use models as gospel..
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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.