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 Patrap:
Fortunately Gut feelings have no Basis In Fact or forecasting,if that were true,JFV would have Obliterated S Fla,10 Times over since June I 2007


Ok Patrap, now THAT was funny!
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Quoting Drakoen:


Look at the trough
hey drak wat are the chances of Ex TD 2 to regenerate later today ??? your opinion
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Quoting reedzone:


no lol, but the pattern is setting up for an east Coast event. Everybody is screaming GOM when the pattern just doesn't favor it. A trough will lift this up eventually and either move it out to sea WEST of Bermuda, or take it up the Eastern Seaboard. Not just South Florida either, us people here in Central/Northeast Florida have to watch it to. Bastardi even mentioned that he knows he always predicts Northeast storms but he showed evidence proving that the pattern is quite similar from a week before Floyd hit in 1999. He also showed some NAO charts and tracks from the 1950s thru 80s. He's not just wishcasting this, more METS are also saying this could be more of an East Coast event.


I'm glad we have a week to watch this ting.
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trough is stronger on 12z gfs at 174
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"Hebert",..in a Box
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Quoting drg0dOwnCountry:
Study Finds Big Storms on a 1,000-Year Rise

The North Atlantic Ocean has spawned more hurricanes and tropical storms over the last decade than it has since a similarly stormy period 1,000 years ago, according to a new study.

The research, published yesterday in the journal Nature, tries to trace the pattern of storms along North America's Atlantic and Gulf coasts back to A.D. 500, well before humans were recording weather observations.

Taken together, he said, they suggest that warmer temperatures produce more storm activity -- meaning that coming climate change could increase the frequency of hurricane activity.

"The paleoclimate evidence seems to reinforce the notion that, all other things being equal, when you have warm sea surface temperatures in the tropical Atlantic, you see more activity," he said.

Kerry Emanuel, a climatologist at the Massachusetts Institute of Technology who has published studies linking climate change to stronger hurricanes, called the new research "an impressive piece of work, melding two completely independent approaches to estimating past hurricane activity."

Emanuel said the Nature study "shows that hurricane activity is indeed quite sensitive to climate, and although we are still not completely sure about global warming effects, the paper raises again the flag that potentially they could be large."

NyTimes


Does this mean they potentially had SUV's in A.D. 500?
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Quoting RayRayfromLa:



Please do not jump the gun... about a NOLA hit at this point! This system is not even classified yet and is way too far off to worry about a hit. Forcasting a hit this far out is not possible.
We


That is exactly what I meant!!
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Quoting tornadofan:


90L won't make it to TD status at this rate - not today anyway. Maybe tomorrow.


Its organization is sufficient enough to setup the possibility of a TD later this afternoon or evening. Just needs a slight uptick in the dvorak numbers and I imagine the center will become a bit less elongated as it organizes. Shear should drop further later today.
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quick mid afternoon poll

A) Ex TD2 regerates at 5PM
B) Ex TD 2 regenerates tonight
C) Ex TD2 Regenerates near the islands
D) Ex TD 2 never regenerates
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Quoting WxLogic:
12GFS still consistent that in a week... next Friday AM it will be N of Hispanola:



Look at the trough
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Quoting CaneWarning:


Bastardi is that you???


no lol, but the pattern is setting up for an east Coast event. Everybody is screaming GOM when the pattern just doesn't favor it. A trough will lift this up eventually and either move it out to sea WEST of Bermuda, or take it up the Eastern Seaboard. Not just South Florida either, us people here in Central/Northeast Florida have to watch it to. Bastardi even mentioned that he knows he always predicts Northeast storms but he showed evidence proving that the pattern is quite similar from a week before Floyd hit in 1999. He also showed some NAO charts and tracks from the 1950s thru 80s. He's not just wishcasting this, more METS are also saying this could be more of an East Coast event.
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Fortunately Gut feelings have no Basis In Fact or forecasting,if that were true,JFV would have Obliterated S Fla,10 Times over since June I 2007
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Quoting CaneWarning:


But what about the Hebert Box?


Hehe... I don't pay too much attention to the Herbert box.
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Quoting WxLogic:
12GFS still consistent that in a week... next Friday AM it will be N of Hispanola:



But what about the Hebert Box?
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can someone tell me what CMC means, thanks a lot!
12GFS still consistent that in a week... next Friday AM it will be N of Hispanola:

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Quoting tornadofan:


90L won't make it to TD status at this rate - not today anyway. Maybe tomorrow.
yes but that was 5 hours ago it is much tighter now.
Quoting saintsfan06:
Pat - if the GFS shows a NOLA hit it can't possibly hit us. I wonder what the odds are for a model correctly forcasting a hit this far out???



Please do not jump the gun... about a NOLA hit at this point! This system is not even classified yet and is way too far off to worry about a hit. Forcasting a hit this far out is not possible.
We
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GFS 162 hours

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Study Finds Big Storms on a 1,000-Year Rise
The North Atlantic Ocean has spawned more hurricanes and tropical storms over the last decade than it has since a similarly stormy period 1,000 years ago, according to a new study.

The research, published yesterday in the journal Nature, tries to trace the pattern of storms along North America's Atlantic and Gulf coasts back to A.D. 500, well before humans were recording weather observations.

Taken together, he said, they suggest that warmer temperatures produce more storm activity -- meaning that coming climate change could increase the frequency of hurricane activity.

"The paleoclimate evidence seems to reinforce the notion that, all other things being equal, when you have warm sea surface temperatures in the tropical Atlantic, you see more activity," he said.

Kerry Emanuel, a climatologist at the Massachusetts Institute of Technology who has published studies linking climate change to stronger hurricanes, called the new research "an impressive piece of work, melding two completely independent approaches to estimating past hurricane activity."

Emanuel said the Nature study "shows that hurricane activity is indeed quite sensitive to climate, and although we are still not completely sure about global warming effects, the paper raises again the flag that potentially they could be large."

NyTimes
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Quoting reedzone:


Also there's a good possibility it doesn't enter the GOM but heads up the East Coast, maybe even up to Long Island, NY.. That's my gut feeling.


Bastardi is that you???
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Quoting canesrule1:
and now 4 hours ago, the COC is broad:


90L won't make it to TD status at this rate - not today anyway. Maybe tomorrow.
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Quoting CaneWarning:


If that happens, it will finish what Katrina started.



Its only insight thru the Long term,and completely discount these Nutz who willy nilly about "finishing",only a fool would wish calamity on another.

Folks been washing us away for Centuries,way before they were here as a family,.

And as one who Lost Loved ones in the storm,they Know not what they say, As many found out with Ike,you can easily become "They",..overnight
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Quoting FLHurricaneChaser:
People you need to stop worrying about the Gulf. The islands and Florida are first up.


Also there's a good possibility it doesn't enter the GOM but heads up the East Coast, maybe even up to Long Island, NY.. That's my gut feeling.
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Quoting canesrule1:
8 hours ago, tight circulation:

The western side looks a little suspect.
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Quoting Drakoen:
The circulation on 90L is not tight. It is zonally elongated
look at post 402, and what i wrote, lol.
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237
fxus64 klix 141326
afdlix


Area forecast discussion
National Weather Service New Orleans la
826 am CDT Friday Aug 14 2009


Update...


..sounding discussion...


No problem with the flight this morning. The atmosphere remains
relatively dry with a precipitable water value of 1.76 inches. The air
near the surface remains moist with significantly drier er air
above 600 mb. Storm motion is out of the southeast at about 4
knots. Winds near the surface and lower levels are out of the
east... while in the upper levels winds are out of the west-
northwest.




&&


Previous discussion... /issued 617 am CDT Friday Aug 14 2009/


Update...


.06z aviation discussion...


Isolated convective activity will persist through the day...with
the most likely areas for convection along or near lingering
outflow and seabreeze/lakebreeze boundaries. However...given the
low chance of occurrence of these thunderstorms forming near any
of the terminals...have opted to leave it out of the tafs. If any
convection does develop near the terminals...the forecast can be
quickly updated. Outside of the isolated thunderstorms...VFR
conditions will be rule through 12z at all terminals.


Previous discussion... /issued 439 am CDT Friday Aug 14 2009/


Short term...
no major changes to the ongoing package. Interesting features on
the map this morning though. Two types of dynamic features
occurring...the first is associated with the stalled frontal
boundary seen by dew pt diff. Ts developed earlier along this
boundary due to deep horizontal easterly flow forcing the deeper
moisture up the frontal slope. Could call this isentropic lifting.
Good thing we are strongly capped at 15k feet. Once ts hit this
level...momentum is the only thing driving the ts core allowing
tops to maximize around 40k feet or all of this activity would have
potentially gone severe. The next area of interest is
thermodynamic forcing. This is seen over the Gulf waters as
buoyancy and deep moisture are driving sh/ts development. Sounding
at 00z showed moisture up to roughly 600mb. This is deep enough to
get a 20 to 30% pop. Do believe we are experiencing a range of
different sounding profiles from northwest to southeast.


Analyzing the global models this morning...the GFS is still too
strong with the upper trough over the east Continental U.S. By about 10kt.
The European model (ecmwf) is a little better but still stronger by 5kt according
to actual East Coast sounding profiles.


The long wave upper trough will begin to cut off an upper low
today through Saturday. This feature will head west with the
strong tropical wave close on its heels. The tropical wave that
will eventually affect US is causing issues over the north central
Carribean...Hispaniola and the Bahamas this morning. As it interacts
with the stalled boundary in the Gulf...global solutions want to
develop an area of strong convection on the east side of two upper
lows. The first is the TUTT low moving west over Cuba. This one
will sink beneath the secondary cut off low over the northern
Gulf. As these two become meridionally oriented...a very large and long
area of convective activity should break out from the western
Carribean through the northern Gulf. The strongest convective
bursts looks to move into the NE Gulf while the wave continues its
progress westward bringing a deep layer of moisture to our area.
This should also cause a pretty good convective burst off our
shoreline as well by Sunday and Monday. We will continue monitoring
fetch and wind strength along the mentioned fetch over the next
few days to determine if tides will be an issue along the Gulf
Coast by Monday morning.


Long term...
once the wave passes to the west...a quick but short lasting surge
of dry air should make its way around the Bermuda ridge and give
US a dry Wednesday. By the end of the week...most attention will be
on the tropics once again as the next well structured tropical
system moves across the Atlantic. Drawing any conclusions at this
time from US or any other met outlet would simply be conjecture.
So at this time...will only say that the system at about 28w 13n has the
best chances for becoming a tropical storm and/or hurricane.
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The circulation on 90L is not tight. It is zonally elongated
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People you need to stop worrying about the Gulf. The islands and Florida are first up.
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Quoting canesrule1:
8 hours ago, tight circulation:
and now 4 hours ago, the COC is broad:
Quoting saintsfan06:
Pat - if the GFS shows a NOLA hit it can't possibly hit us. I wonder what the odds are for a model correctly forcasting a hit this far out???


If that happens, it will finish what Katrina started.
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Quoting Txrainstorm:

I don't like that one...next!


No Siree...we dont Like that one. But we have to be vigilante as to trend. Models are insight as to what May occur and arent Gospel.But weve seen that track in 3 runs in 30 Hours.


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Quoting ackee:
what the chance we see TD#2 again by 5pm

If it continues to organize, then it might have a chance.
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8 hours ago, tight circulation:
Quoting Patrap:


its in the mid levels
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ex-TD2 is firing some convection over it's center
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Pat - if the GFS shows a NOLA hit it can't possibly hit us. I wonder what the odds are for a model correctly forcasting a hit this far out???
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02 not so puny anymore
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LMAO LOL LOL
Quoting PcolaDan:


Cue Jaws music.

Quoting PcolaDan:


Cue Jaws music.

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Quoting Patrap:
06 GFS Run

I don't like that one...next!
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Quoting Drakoen:


I'm thinking it will track just north of the islands
same here.
Quoting Patrap:
06 GFS Run


NOLA! lol just a model folks
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Watch out SFLA:
Quoting Grothar:
Thank you Drak.

As I may have mentioned before, I have a very good friend who is a meterologist. She informed me this morning that former TD 2 has a very good chance of strengthening again, although a much smaller system. Their test models would have TD2 coming very close to the islands and staying at a much lower latitude and maintaining a westerly movement before a turn to the WNW. Anyone have any opinions in reference to this scenario? I do not mean to be condescending to myself, but you all seem to have a much better understanding of these dynamics than do I.


I'm thinking it will track just north of the islands
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Quoting Patrap:
06 GFS Run
I don't think 90L will interfere with Haiti or Cuba, imo.
thank you thecanewhisperer
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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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