Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. 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 was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


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

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Quoting KoritheMan:


Circulation is still broad.


Even though it may be broad due to the sheer size, the circulation most importantly is CLOSED. I will admit the satellite presentation is quite unusual, more typical of a Pacific system, but with all the data available and given the fact convection has been building and persisting over the circulation center, it has all the factors in my mind to become a tropical depression. Of course, thats the NHC's call so I could be wrong.
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Quoting IKE:


Yes it was. I'm up on Lake Holley. Branches...everywhere from Opal.
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Quoting louisianaboy444:
When will they issue the first advisory on TD2 or resume advisories


11pm.
Member Since: June 9, 2007 Posts: 4 Comments: 15864
Quoting KerryInNOLA:
90L pressure 1007mb. Has fallen ONLY 1mb in 24hr!


That is to be expected with large systems with broad circulations like 90L. These things take time to consolidate.
Member Since: March 7, 2007 Posts: 572 Comments: 20344
No
Quoting canesrule1:
might just be a wobble, nothing to get worried.


no one is getting worried, just an obs that was confirmed.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
When will they issue the first advisory on TD2 or resume advisories
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Quoting extreme236:


Uh not really no.


Agreed, 90L is building convection over the COC, it's starting to look more impressive frame by frame, we could see a spike in T# by the next run. But I do think at 5 or 11 AM tomorrow Ana and TD3 will be about.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting Chucktown:


As a TV meteorologist now for over 10 years, its not as easy as you think. Doing the weather on TV is sometimes just like being an actor. We need to keep the attention of the audience so they don't flip the channel and so I keep my job.


Ever have one of these moments??

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I owed you that one Tampa, but the rest of them are all you buddy! lol
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Quoting Weather456:


I compared two ascat passes and ur correct.
might just be a wobble, nothing to get worried.
Quoting cchsweatherman:
To be honest, I don't see any reason besides waiting for further persistence to not classify Invest 90L as a tropical depression at 11PM.


Circulation is still broad.
Member Since: March 7, 2007 Posts: 572 Comments: 20344
Quoting futuremet:
LOL storm master G


Storm Master G is the man!
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Quoting DM21Altestic:

90L looks horrible.


90L may be attempting to wrap convection into its center, based on the latest satellite loops. Will have to persist, though.
Member Since: March 7, 2007 Posts: 572 Comments: 20344
Quoting canesrule1:
yup.
"yup"? your the one that said it was renumbered. What are you agreeing with him for...LOL He is debating what you said.
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Quoting TampaSpin:
We just might see at 11pm Tropical Storm ANA and TD3....that appears to me to be the case.


Agree. Cold cloud ramping around CoC of 90L.
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Quoting IKE:
Look at the outflow on TD2 now....



I like TD2's compact structure. It does not need excessive ambient energy to intensify. The conditions are expected to become very favorable as it nears the Bahamian waters, and there is no reason for it to really organize quickly in those waters.
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Quoting IKE:
Look at the outflow on TD2 now....



Southwesterly shear associated with the upper low to its north is ventilating the northern side. I had thought that this might be possible this afternoon when I looked at everything.
Member Since: March 7, 2007 Posts: 572 Comments: 20344
Quoting rareaire:
Tampa my prediction on td-2 looking better and better!!!!


Bro i'm so glad you told me what it was going to do and where it was going.......LMAO
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Evening SW
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting DM21Altestic:

90L looks horrible.


Uh not really no.
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Quoting sammywammybamy:
FELLOW BLOGGERS ...


NOW IS NOT THE TIME TO PANIC...

JUST KEEP A KEEN EYE TOWARD THE TROPICS..

YES A CONUS LANDFALL PERCENTAGE HAS INCREASED BECAUSE OF STEERING...AND THE ALARMING MODELS OF A TD2 LANDFALL ON SFLA

BUT I URGE YOU TO REMAIN CALM..

1 EXAMPLE : IS WHEN IKE WAS PROJECTED TO GO TO SOUTH FLA ASA CAT 5 ...

WATER WAS SOLD OUT.. AND I WAS GOING CRAZY...

I HAVE LEARNED FROM MY MISTAKE ... AND I URGE YOU TO REMAIN CALM AND KEEP SUPPLIES HANDY ANYWHERE THE STORMS CAN HIT


Member Since: June 9, 2007 Posts: 4 Comments: 15864
Quoting DM21Altestic:

90L has also taken a south jog.


I compared two ascat passes and ur correct.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2756. hahaguy
Quoting StormW:


As long as Cantore doesn't show up!


I got my shotgun ready in case he comes by my house LOL.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting TampaSpin:
We just might see at 11pm Tropical Storm ANA and TD3....that appears to me to be the case.
agreed!
To be honest, I don't see any reason besides waiting for further persistence to not classify Invest 90L as a tropical depression at 11PM.
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Quoting futuremet:
LOL storm master G



OMG, I just threw up in my mouth a little bit.

But I did LOL when it said "Hail"..."yeah!"
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Quoting TampaSpin:


Still could.
oh ok, lol
00z NAM's starting to come out.....GFS shouldnt be too far behind
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Can someone give me data about the recent forward speed of exTD2?

Thanks.
CRS
Member Since: July 12, 2007 Posts: 0 Comments: 6004
We just might see at 11pm Tropical Storm ANA and TD3....that appears to me to be the case.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
Quoting Weather456:
Nothing is working this year

I found out where 95L was.....




I guess 96L was the little spot on the left.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting MississippiWx:
I'm sure most people on here could do a better job at presenting the weather than the people on TWC. All that TWC is in it for now is show-boating and trying to impress their audience.

Example: Storm Master G!! Seriously, WTF???

Whatever happened to just giving the weather and how it is and leaving it at that?

Nonetheless, I never listen to TWC when it comes to tropical weather. I get much better info on this blog and just doing research myself.


As a TV meteorologist now for over 10 years, its not as easy as you think. Doing the weather on TV is sometimes just like being an actor. We need to keep the attention of the audience so they don't flip the channel and so I keep my job.
Member Since: August 27, 2006 Posts: 0 Comments: 1735
2743. IKE
Look at the outflow on TD2 now....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting BenBIogger:
tight circulation, should be a TD at 11.
If Td 2 reaches our that could really suck. 90L was thought to be the threat but it seems TD 2 wants to follow suits.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Hi guys.
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Quoting canesrule1:
but how come all the models forecast a SFLA hit?


Still could.
Member Since: September 2, 2007 Posts: 178 Comments: 20439
TD's for sure. But more alarming NO recurvature in there track. In fact both systems appear to have, and be on sinking south of a due west motion. NOT good. Bet 'Models' will continue trending / shifting farther west. .....GOM residents stay tuned!
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Hey StormW
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Quoting Stormchaser2007:
TD2 and 90L



This image reminds me of the movie "Twins." LOL.
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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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