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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1734. JLPR
Interesting...
Ada Monsón here said that 02L should clear the dry air for 90L

02L should pass to the north of PR
and 90L is a bigger threat since it could pass according to her anywhere from 50 - 100 miles to our north or south or end up affecting us directly, she sounded a little worried =\
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Quoting RainyEyes:
Why does this blog become so hateful. This is not a highschool clique. It is a place to learn and take part in a profession, hobby, past time...why ever you are here. Either way, no one would be here if we weren't genuinely interested in the tropics. Cut some slack!
She says it so well! the lack of freedom of specch here is like being in a dictorship.
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1732. jipmg
Quoting Tazmanian:
is it this me and my eyes or am i seeing a pinehole eye???



Based on that image it looks like its going through an eye wall replacement cycle (considering its estimated to be a CAT 2), can you post some loops of Guillermo
1731. DDR
Good evening all
Wunderkid,it seems likely you'll get some rain tomorrow,as for me the itzc thinks Trinidad is a giant toilet Bowl,over a foot of rain in 2 weeks and we're only half way through August.
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02L looks a bit better, less amorphous than it was looking a few hours ago. Will be interesting to hear the NHC's take on it.
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is it this me and my eyes or am i seeing a pinehole eye???

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1727. jipmg
Quoting reedzone:
It appears that even though it's not classified, the open wave that was once known as "TD2" is now a Tropical Depression again, some deep convection firing up, Local6 MET Tom Sorrels said they might be issuing advisories on it again in a few hours if convection persists. Would not surprise me if they re-issue TD2 at 11 p.m. by the way it's going.


yes local met cbs4 David Brenard said something similar, he also gave a brief analyzes on the latest model runs saying most of them are taking what becomes of TD 2 towards SFLA.. and models are very consistent on the movement of 90L during the next 3-4 days generally moving it towards the northern carribean islands
1726. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 128240
Quoting reedzone:
It appears that even though it's not classified, the open wave that was once known as "TD2" is now a Tropical Depression again, some deep convection firing up, Local6 MET Tom Sorrels said they might be issuing advisories on it again in a few hours if convection persists. Would not surprise me if they re-issue TD2 at 11 p.m. by the way it's going.


Yea, ex/future-TD2 is looking much better. I'm even noticing banding appearing on the northern side, which suggests the atmosphere may be becoming more moist.
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Quoting wunderkidcayman:

what green updated data


Decoded recon data in the last 30 minutes:

Non-Tasked Mission Data (for at least one product)
Updated on our site 12 minutes ago


You should see something like that when you go to Tropical Atlantic

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Quoting Vortex95:


The effects is that S Fla gets some rain :P.


Which I have reflected in my forecast on the Florida Weather page of my website.

CCHS Weather Center Website
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1721. Drakoen
GFS 18z taking over all those mountains.
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Quoting Grothar:

Thank you. It just appeared to be a sound comment. English is not my first language so sometime I miss certain nuances. I certainly do not wish to offend anyone. All of the other bloggers whom I have asked questions were quite informative. I just find it to be an admirable quality that so many of you know so much about the weather. Could you answer my question in my first comment on the dynamics causing the elongation in both systems. I apologize if my English is not that good.


I cannot answer that.I am still learning as well.If you want to know who can just ask Weather456 or Keeper or even ask IKE or press who to listen to. Automag seems to be pretty informative of who to get info from as well.Never count Pat out but he won't give ya a definate just the info you want.There are really good and smart people here.Just ignore the bickering and stick with the big dogs that everyone listens to.
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It appears that even though it's not classified, the open wave that was once known as "TD2" is now a Tropical Depression again, some deep convection firing up, Local6 MET Tom Sorrels said they might be issuing advisories on it again in a few hours if convection persists. Would not surprise me if they re-issue TD2 at 11 p.m. by the way it's going.
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Quoting Patrap:



Hard to think Hugo was 20 years ago,,wowsa




Hugo's the one that gave me nightmares. Lucky for me it took a NNW jog the day that day before it hit. Unlucky for those who lost their lives or their property.

However, I will never again get into the mess I got myself into with Floyd. 12 hours sitting still in an overheating truck? No thanks, never again. I live 40 feet above sea level in a house built 100 years ago when storms were more common on the Georgia coast. I'll be ok, but I know many that won't when that day comes.
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1716. Patrap
Quoting cchsweatherman:


Because I don't see any development happening with that tropical disturbance since this is just another case where a tropical wave is interacting with an upper level disturbance.


See that wasnt too Hard.

And the effects are moot I gather?
Member Since: July 3, 2005 Posts: 423 Comments: 128240
1714. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 128240
Quoting Patrap:
Hey CCHSS,why no words on the first bugger..?



Because I don't see any development happening with that tropical disturbance since this is just another case where a tropical wave is interacting with an upper level disturbance.
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how long from one dropsonde to another
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1700. wunderkidcayman

When you select the "Updated on our site 4 minutes ago" in green it takes you to the non-tasked mission page. Select the top one, you go to the select observation page. Select go. The page that comes up will have Coordinates: 12.8N 49.4W (View map.

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this waiting for the next T #s too update wish sould be soon
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1708. Patrap
Quoting jipmg:


Are they going inside of it? Or just analyzing the atmosphere around it



G-IV Jet—Seeking the Storm's Path
Since the beginning of the 1997 hurricane season, the G-IV has flown missions around every Atlantic-based hurricane that has posed a potential threat to the United States. The jet's mission covers thousands of square miles surrounding the hurricane, gathering, with newly developed GPS dropwindsondes, vital high-altitude data needed for improved numerical forecast models. The G-IV has added a vital new dimension as it maps the steering currents that influence the movement of hurricanes.

Data from GPS dropwindsondes that measure pressure, temperature, humidity, and wind information are relayed to the aircraft for transmission by satellite to the National Hurricane Center in Miami and the National Centers for Environmental Prediction in Camp Springs, Md. There the data are available for many numerical forecast models, providing important information about regions—mostly over oceans—in which there are no other sources of weather data.

G-IV flight data are expected to help numerical guidance computer models improve hurricane landfall and track forecasts by up to 20 percent, and to further refine storm intensity forecasts.

After hurricane season, NOAA's interest in severe weather becomes focused on the winter storms affecting the western, central and northeastern United States. NOAA has used the G-IV to help monitor and study these storms to advance our understanding of them and improve winter storm forecasts. The G-IV has also been used to study clear air turbulence—a condition that threatens the safety of air traffic—over the Pacific Ocean, helping scientists increase their ability to understand and predict this potentially deadly phenomenon.
Member Since: July 3, 2005 Posts: 423 Comments: 128240
1707. jipmg
convection getting tighter around 90L's center
Look like the convection is attempting to wrap around the center.

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1705. Patrap
Hey CCHSS,why no words on the first bugger..?

Member Since: July 3, 2005 Posts: 423 Comments: 128240
Quoting Drakoen:


Wow, you can definitely tell where the center is, just needs convection and boda bing boda boom, a TD is born.
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1703. Grothar
Quoting adjusterx:


Hey there don't worry or quote WS. He is just following the lead.Follow the comments from the people actually putting up info, they usually have there own blogs and synops.

Thank you. It just appeared to be a sound comment. English is not my first language so sometime I miss certain nuances. I certainly do not wish to offend anyone. All of the other bloggers whom I have asked questions were quite informative. I just find it to be an admirable quality that so many of you know so much about the weather. Could you answer my question in my first comment on the dynamics causing the elongation in both systems. I apologize if my English is not that good.
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1702. jipmg
Quoting Vortex95:


going around it rather not inside.


Are they going inside of it? Or just analyzing the atmosphere around it
1701. Patrap
Quoting tiggeriffic:
hiya Patrap...how goes it...they learned a lot from hugo and no evacs in Charleston...then floyd came this way and everyone from florida to south carolina ended up evacing...that was a cluster and a half...just glad to be in a sturdy home...made it thru hugo...if anything that big comes round again i am history...lol



Hard to think Hugo was 20 years ago,,wowsa
Member Since: July 3, 2005 Posts: 423 Comments: 128240
Quoting nrtiwlnvragn:


All, you want to see wind direction/strength to guesstimate affect on steering. Your not going to see data in TD2, but around the storm. You can select the map to see where the dropsonde was launched.

what map
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CCHS Weather Center
Tracking The Tropics


Former Tropical Depression 2

Over the past few days, the National Hurricane Center had been tracking a strong tropical wave that came off Africa across the Atlantic which became Tropical Depression 2. Yesterday, the NHC dropped the tropical depression status as the disturbance had lost all thunderstorm and shower action as dry air got entrained into the system and upper level winds were too fast to allow for any showers or thunderstorms to develop.

Well, it seems Mother Nature's throwing yet another curveball as showers and thunderstorms have really fired and become organized. Its possible that this could be coming back to life and the NHC continues to monitor its progress. They are still running computer models on this system since they believe it could make a comeback and based upon the computer models, this system still needs to be watched since this could possibly become a threat down the road to people in the Northern Caribbean islands, the Bahamas, and quite possibly Florida down the road.

Invest 90L

This is the system thats really garnered much attention from the NHC, Weather Channel, and local NWS offices and news stations. Late Tuesday evening, a very impressive strong tropical wave rolled off Africa and out into the Atlantic. In the past couple days, this has become a massive system spanning nearly 600 miles with a well-defined spin.

But at this time, it really hasn't been getting going because the upper level winds are so fast they've blown the thunderstorms off the circulation center which has in turn mostly exposed the circulation to the elements. In order for tropical systems to be born and to survive, they need thunderstorms to protect their circulation. Think of it like your camping in the woods. When its a cold or rainy night, you need a "tent" to protect you from those elements. If you don't have that protection, you won't be able to survive the elements. Thats pretty much the same case with these systems.

In the coming days, the computer models show these upper level winds relaxing which will allow the thunderstorms to move back over the circulation and get this going. Now, reverting back to my opening remark on this system, the main reason why this has become the spotlight in the tropics is because the computer models the NHC and all us forecasters use to try and forecast these storms all suggest this could really become a major threat as most all the models show this impacting the Puerto Rico area as a major hurricane. Now, beyond that it remains uncertain.

The Bottomline

Even though the computer models are coming into good agreement showing these systems becoming possible threats, its too soon to become excited or concerned (depending upon your perspective with storms). Keep in mind what history has taught us: Mother Nature plays by her own rules and can change her mind whenever she wants. Computer models are not gods, but rather just guidance showing possible scenarios based upon the conditions at the time. When conditions change, so do the models. My best advice at this time is to just stay informed on the situation and just make sure you have your hurricane preparedness plans in place just in the case the computer models happen to come true. Its always better to be safe and not have a storm impact your area than to be caught unprepared.
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1698. SLU
Quoting Weather456:


I gave 90L a time frame between Friday and Sunday, and it seems resonable. It is slow no organize, no surprise there, since it is large.


Also, I mentioned it on the blog yesterday that the met officies and hurricane correspondents all across the Eastern Caribbean are monitoring this feature and only 2 storms I here everyone mentioning, Hugo and Georges. Marilyn 1995 comes to mind, thats what the ECMWF is showing.

Though this far out I havnt raise the concern much. As we enter next we should have a better idea. Though 90L is only 5-6 days away. To show how close that is, 99L developed about 5 days ago. Time can fly.



Yes this is a serious situation that's developing here. And like you said earlier, the similarities between 90L of today and 90L of August 2007 which became MH Dean are just so frighteningly similar.

Both took a couple days to ramp up
Both suffered from high easterly shear near the Cape Verdes
Both are traversing at the same latitude and the exact same dates

The one main difference I can see for now is that the SST is much higher this time around than when Dean formed.



When MH Dean developed.




Yesterday



Interest in the Eastern Caribbean should closely monitor the progress of this potentially dangerous system.

And even before that there is ex-TD #2 which looks like it will redevelop and perhaps affect the Lesser Antilles on Monday.
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ok...gotta bounce for a bit...maybe back later if work lets me...lol...
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Rainy I am a little on the hefty side myself who cares. Notice I didnt say anything about looks as beauty is always in the eye of the beholder,and comes in many forms even hurricanes when they dont hit land.
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Quoting wunderkidcayman:

what green updated data
That's what I was wondering too. I don't see it.
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1694. Drakoen
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Quoting nrtiwlnvragn:
The NOAA jet reported its first dropsonde data. You can view it at Tropical Atlantic by selecting Dropsonde Report (UZNT13) under Main NOAA Products (KWBC): on the right hand side of the page. Paste the data into the decoder..

They are updating automatically now, just select the green updated data.

what green updated data
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hiya Patrap...how goes it...they learned a lot from hugo and no evacs in Charleston...then floyd came this way and everyone from florida to south carolina ended up evacing...that was a cluster and a half...just glad to be in a sturdy home...made it thru hugo...if anything that big comes round again i am history...lol
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Quoting wunderkidcayman:

we should be looking at what level
1011mb
1000mb
925mb
850mb
700mb
500mb
400mb
300mb
250mb
200mb


All, you want to see wind direction/strength to guesstimate affect on steering. Your not going to see data in TD2, but around the storm. You can select the map to see where the dropsonde was launched.
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Quoting jasoniscoolman10:
water is getting hot here wow water temp in the 90F



you are Copyrighting it from TWC the Admin said you can not post any thing from TWC if you do it will be called Copyrighting with out the owner ok to post it i was doing the thing on my blog when i 1st came here but the Admin update my blog and re move it be come it was Copyright so now i no better so Please re move it
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is recon really in exTD 2 ???????
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1687. Patrap
Quoting Weather456:


I gave 90L a time frame between Friday and Sunday, and it seems resonable. It is slow no organize, no surprise there, since it is large.


Also, I mentioned it on the blog yesterday that the met officies and hurricane correspondents all across the Eastern Caribbean are monitoring this feature and only 2 storms I here everyone mentioning, Hugo and Georges. Marilyn 1995 comes to mind, thats what the ECMWF is showing.

Though this far out I havnt raise the concern much. As we enter next we should have a better idea. Though 90L is only 5-6 days away. To show how close that is, 99L developed about 5 days ago. Time can fly.




Last Nights 18Z run sure had me thinking about Georges in 98,..

...and on a side note,Georges in 98 was the First time in NOLA history that a Full evacuation was ordered,,the Storm veered Ne and made Landfall in Miss as well
Member Since: July 3, 2005 Posts: 423 Comments: 128240
hey all...just in for a sec...popping in to see what is up before we go to dinner...looks like the ensembles are pretty tight right now...too early to tell but the further south 90l stays, the better the chance that it has land impact...
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Quoting gordydunnot:
That's alright big fat guy its still a sexy name.


Lets see the Truffle Shuffle.
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Continues to show new cyclone

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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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