New tropical depression could form off the coast of Africa

By: Dr. Jeff Masters , 1:12 PM GMT on September 25, 2009

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A tropical wave (99L) is located near 15N, 30W, about 300 miles west of the Cape Verdes Islands. This wave has seen an increase in heavy thunderstorm activity this morning, and low-level spiral bands have formed. The system can already be classified as a tropical depression using the satellite-based Dvorak technique. This morning's QuickSCAT pass showed a loose but closed circulation, with top winds of 30 mph in the heaviest thunderstorms. Wind shear is moderate, about 10 - 20 knots. There is a modest amount of dry air to 99L's west that does not appear to be interfering with the storm's organization.


Figure 1. Morning visible satellite image of Invest 99L (left side of image) and a new tropical wave moving off the coast of Africa.

As 99L moves west-northwest over the next two days, sea surface temperatures will cool by 1°C and winds shear will remain in the moderate range. Some dry air may also affect the storm. These conditions give 99L a good chance of forming into a tropical depression, and NHC has given the system a moderate (30 - 50%) chance of developing into a tropical depression by Sunday. By Monday, wind shear will increase to the high range, 20 - 30 knots, and 99L will probably weaken or be torn apart. None of the computer models forecast development of 99L or any other system in the Atlantic over the next seven days.

A new tropical wave with plenty of heavy thunderstorm activity and some spin is moving off the coast of Africa today. This wave is under a moderate amount of wind shear, 10 - 20 knots, and has some potential for development this week as it moves west or west-northwest past the Cape Verdes Islands.

The latest wind shear forecasts from our major computer models show high values of wind shear affecting most of the tropical Atlantic for the next ten days. This is typical for an El Niño year, and it will be difficult for any storms to get to hurricane strength over the next ten days because of the high shear. The latest 16-day GFS forecast predicts wind shear will decline some by the 2nd week of October, though.


Figure 2. Wind shear forecast for Thursday, October 2 at 00 UTC made by last night's 00Z run of the GFS model. Wind shear is expected to be high over most of the tropical Atlantic for the next ten days, including the Caribbean. Wind shear values below 8 m/s (about 15 knots, red colors), are typically needed to support tropical storm formation.

Jeff Masters

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Hi StormW!
You know I meant to call the last time you were on the BB show and ask both of you guys about that darned Hebert box, and then forgot to listen in. You going back on the show anytime soon?
Member Since: October 18, 2005 Posts: 4 Comments: 3052
From the FNMOC site:

2009 Storms
All Active Year


Atlantic
08L.EIGHT

East Pacific
17E.NORA

Central Pacific

West Pacific
99W.INVEST
98W.INVEST
17W.SEVENTEEN
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For the moment and from my amatuer weather eyes. Doesn't appear that TD8 will significantly strenghten or have a chance at affecting CONUS.

Member Since: March 10, 2006 Posts: 0 Comments: 10572
Quoting OSUWXGUY:
The AMSU satellite, and its associated intensity estimate had 99L as a 47 knot tropical storm way back at 1541UTC or 11:41 am EDT.

This new method of satellite intensity estimation uses microwave data, and is apparently significantly more accurate that the DVORAK technique currently used by the NHC.

Read More Here:

Bottom of the pages shows the Dvorak vs AMSU comparison - less error for AMSU.

AMSU Description

The 1541UTC overpass hit the center almost dead on, giving more confidence in the intensity estimate.



so this could actually be Grace at 5pm?
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The AMSU satellite, and its associated intensity estimate had 99L as a 47 knot tropical storm way back at 1541UTC or 11:41 am EDT.

This new method of satellite intensity estimation uses microwave data, and is apparently significantly more accurate that the DVORAK technique currently used by the NHC.

Read More Here:

Bottom of the pages shows the Dvorak vs AMSU comparison - less error for AMSU.

AMSU Description

The 1541UTC overpass hit the center almost dead on, giving more confidence in the intensity estimate.

Member Since: Posts: Comments:
Quoting jeffs713:
Just to guess at some posts to come over the next few hours:

"What are the chances of Grace forming?"
"Could someone post the shear maps?"
"What are the landfall chances of Grace?"
"There is no way Grace will survive!"
"Stop calling it Grace, its not named yet"
"When DMAX hits, Grace/TD8 will explode."
"Why isn't the NHC naming it yet? That looks like a 50mph TS to me."
"SAL will do TD8 in, for sure. RIP."
"How strong can Grace get?"
"Grace will be our next Cat 5, for sure."

And to save the best for last...

WS:
"What are the chances of TD8/Grace having a South Florida landfall?"
Florida, down fall, NONE<< you don't have to be an expert to know that.
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I mean, isn't that the most important thing for a scientist, to be known for discovering the truth?
Member Since: October 18, 2005 Posts: 4 Comments: 3052
Unamed Category 5 50mph TS GraceX out-2-sea azores sheared-fish spinner.
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Wow! I step out for the day and we have TD-8!
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Atmoaggie (#231) –
Oh man, I asked and boy did you ever deliver! Thanks so much. A point I’d like to discuss is bias among scientists…If some are too fervent in trying to prove something one way or the other (first of all, isn’t that against the “scientific method”), won’t the general scientific community be forced to follow their own rules and find the truth (convenient or otherwise) or risk embarrassment and ridicule by history?
Member Since: October 18, 2005 Posts: 4 Comments: 3052
Quoting Dakster:


I take it TD8 won't end GRACEfully then?

*BOOM BOOM DING*
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invest_RENUMBER_al992009_al082009.ren

there is your confirmation, this is the 1st sign of an upgrade, NHC will wait til 5pm
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BAMM and BAMD are interesting, aren't they?
Member Since: April 5, 2007 Posts: 83 Comments: 12345
254. JRRP
Quoting BurnedAfterPosting:


that is interesting, well a low in the Caribbean in the beginning of October makes sense

If 99L becomes Grace, the wave behind 99L could be Henri; then we could have Ida

9 named storms isnt all that bad considering so many here said we wouldnt get any


Personally with post season analysis upgrading 1 or 2 systems; I think we end up with more than 10 storms officially for the season.

That would maybe shut some people up lol

lol...
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Quoting JRRP:

i think is because is not near land
When Fred developed he wasn't near land either so it can't be that.
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Quoting Dakster:


They are waiting for absolute confirmation from Wunderground bloggers.
It would seem so because I checked the NRL site also and not on there as a depression either.
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Quoting JRRP:
low near nicaragua/honduras


that is interesting, well a low in the Caribbean in the beginning of October makes sense

If 99L becomes Grace, the wave behind 99L could be Henri; then we could have Ida

9 named storms isnt all that bad considering so many here said we wouldnt get any


Personally with post season analysis upgrading 1 or 2 systems; I think we end up with more than 10 storms officially for the season.

That would maybe shut some people up lol
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Quoting markymark1973:
Td 8 will not last too long out there. Shear is going to blast this baby apart when it gets further west. Can you say another ex Fred hehe


I take it TD8 won't end GRACEfully then?
Member Since: March 10, 2006 Posts: 0 Comments: 10572
247. JRRP
Quoting stormwatcherCI:
If it is a depression why doesn't the NHC site show it as one ?

i think is because is not near land
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Quoting Dakster:


They are waiting for absolute confirmation from Wunderground bloggers.


LMAO
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Quoting stormwatcherCI:
If it is a depression why doesn't the NHC site show it as one ?

Because the advisory is at 5pm.

They ran the models for tropical depression 8.
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Quoting stormwatcherCI:
If it is a depression why doesn't the NHC site show it as one ?


They are waiting for absolute confirmation from Wunderground bloggers.
Member Since: March 10, 2006 Posts: 0 Comments: 10572
242. JRRP
low near nicaragua/honduras
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Td 8 will not last too long out there. Shear is going to blast this baby apart when it gets further west. Can you say another ex Fred hehe
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Quoting Stormchaser2007:



Read the past 50 or so posts.

It is a tropical depression.
If it is a depression why doesn't the NHC site show it as one ?
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Quoting jeffs713:
Just to guess at some posts to come over the next few hours:

"What are the chances of Grace forming?"
"Could someone post the shear maps?"
"What are the landfall chances of Grace?"
"There is no way Grace will survive!"
"Stop calling it Grace, its not named yet"
"When DMAX hits, Grace/TD8 will explode."
"Why isn't the NHC naming it yet? That looks like a 50mph TS to me."
"SAL will do TD8 in, for sure. RIP."
"How strong can Grace get?"
"Grace will be our next Cat 5, for sure."

And to save the best for last...

WS:
"What are the chances of TD8/Grace having a South Florida landfall?"


yep - I guess we can just close the blog now that all questions have been asked... lol.

Nice post and so true...
Member Since: March 10, 2006 Posts: 0 Comments: 10572
Quoting Stormchaser2007:



Read the past 50 or so posts.

It is a tropical depression.

If I would have seen the post I would have been 100% sure of it.
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Quoting Floodman:


The disturbances are lining up and the "tacomen" in this blog will be in short supply...LOL

This place is very amusing


It is isn't it.
Member Since: August 22, 2008 Posts: 12 Comments: 6010
Quoting PcolaDan:


So far so good, yea. Like to try and keep some levity. Gets intense at times in here.
Something else I learned about lightning. If it hits near a building, it can change the electrical potential of that building. If this building is connect to another building through phone or computer cable, the two buildings will try and neutralize through the cable. Guess what happens to all the components. POOF.
Let me clarify though. Both buildings had earth grounds when built. Rods went down about 50 ft (iirc) but both did not ground the same potential. They were not originally connect 25 years ago. We had to get grounding rods down over 100 feet to get properly grounded. Plus underground cable connecting them together on the electrical ground, plus lightning protectors. Finally worked. This was in Crestview Florida.


Yeah, ground rods are about the worst way to get EG. Everything tied to rebar now. I used to service some of the Home Depots around here, and the one in Boynton Beach (I-95 & Woolbright) seemed to get hit by lightning every year. Always going for the light poles (the roof had lgtng protection), then into the Main Electric room, blowing all the covers off the contactors, and melting the coils.
Member Since: October 18, 2005 Posts: 4 Comments: 3052
Quoting Ameister12:
Good Afternoon and Happy weekend!

Just look at 99L! This storm is more then likely already a tropical depression or tropical storm.
Link






Read the past 50 or so posts.

It is a tropical depression.
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Good afternoon and happy weekend!

Just look at 99L! This storm is more then likely already a tropical depression or tropical storm.
Link



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Quoting Floodman:


The disturbances are lining up and the "tacomen" in this blog will be in short supply...LOL

This place is very amusing


lol he should stick to making burritos lmao
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The area behind 08L is significantly larger.

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Quoting mikatnight:
Aggie -
and I ask you this with the utmost respect - what exactly to you believe as far as GW is concerned (I apologize for not knowing, as I%u2019m sure you%u2019ve answered that question somewhere before that I missed).

My opinions on the subject (from a previous post):
(http://www.wunderground.com/blog/RickyRood/comment.html?entrynum=106 comment 27)
Quoting streamtracker:
#16 - Before I would seriously reply, you'd have to be much more specific then to just say "many of the premises of CO2-AGW". Exactly, what premises give you a problem?


1. That man has contributed carbon in a closed steady-state natural chemistry system beyond that system's ability to increase sinks. More available carbon in natural processes where the available carbon is usually the limiting factor. We have not proven that man is actually responsible for the measured carbon increase. Correlation of mankind's energy use to CO2 at Muana Loa is not causation. Say what you will about different carbon isotopes; I have seen the work in support and opposition to it and both make very good points.

2. That the globe is actually warming beyond that expected with respect to a baseline constructed during less than one multidecadal cycle and does not include any variability associated with the sum of multiple natural cycles and the teleconnections affecting measurements showing a warming signal. This statement applies to measurements by satellite only. Warming with respect to a baseline that is likely not representative of natural variability and the possible varying amplitudes is, in itself, not trustworthy. The globe probably is on a slight warming trend, but how much? Using a 30-year average baseline for an anomaly is not a lot different than saying global warming is over based on 2008, as the PDO switched phases. 30 years is not climate.

3. The spatially discontinuous surface obs have too much of a primarily land, population center, UHI with muddy corrections, lack of precision, etc. influence to be applied to warming at the tenth of a degree level to be trustworthy.

4. That we know the other anthropogenic effects well enough to avoid misreading their signal as AGW evidence.

5. That we know the teleconnections of certain anthropogenic effects (such as aerosols/Arctic ice), natural cycles (PDO), and natural cycles in concert ( PDO with AMO) to recognize what is anthropogenic warming and what is natural. For example, it has been hypothesized that the PDO phase can increase SSTs in the Atlantic through influencing available water vapor for cloud formation (more troughs in US...more ridges in N Atlantic). Not proven, but what if?

6. That we, mankind, assuming all above is true, have subjected the planet to something it has not seen before and/or would be bad thing anyway.

7. That we have enough knowledge about the natural systems of either chemistry and/or radiation balance to effectively model the system.

8. That we have successfully accounted for positive and negative feedback of existing on the planet. Soot and aerosols have been claimed as a negative feedback for a long time, now, but the positive feedback of decreasing albedo at the poles, in my opinion, need more work.

9. Assuming all else comes to pass just as the IPCC says, I am still not certain that we have a full grasp on positive and negative feedbacks as potential future CO2 and warming changes occur.

There is LOT to be done. I do hope that one day we will have real answers, rather than circumstantial evidence. I could probably go on for quite a while, but this is plenty.

I put nothing here about who gets the grant funding nowadays. I really only work in the realm of ideas, "why not?", "are we certain?", and "Why are we so certain? Do we have a singular causation as proof?".

Addendum: And this is coming from someone that was involved with atmo chem work, had a climate change internship, that once was employed in an atmo chem by IR satellite analysis position with NASA LaRC. In all of it, there was a lot of uncertainty. So much, in fact, that the standard deviation of models and measurements were routinely as large or larger than the magnitude of the numbers we were trying to make conclusions from. I see worse than that in most of the subjects I posted above.

Add ons as of today:
10. that the relative contributions of aerosol pollution is not well understood
11. I have suspicions that few, if any, of the things we fear (TCs, floods, severe wx, etc.) are connected to AGW as well as we have been told. For example, it has been shown that out of all TCs before and after the launch of satellites, that the percent of all TCs that made landfall somewhere, anywhere, went down by more than 10 percent. Did the TCs change because we launched a satellite? No. We missed a lot of them that didn't impact land before 1966(?).
12. I do think we should work on our carbon footprint. The whole enchilada. Particulate emissions. Urban sprawl. VOC's (which lead to troposheric ozone). There is a lot of positive we could do now. Right now. But the AGW crew is burning all of the environmental/political favor on CO2, a non-toxic gas that other life forms depend on that may or may not negatively impact us in the future.
13. Even if (given that someone is going to ask if we shouldn't do something just in case)...even if CO2 really is going to raise our temps a couple of degrees, raise our seas, the time to "fix" it is probably gone. Mitigation strategies is where I would focus. That and alternative fuel/fuel efficiency research, as that is going to have to happen eventually, anyway. Legislation to use a certain fuel, etc. doesn't make that fuel cost effective and reliable. Only research into accessing, transporting, and applying other sources of energy can do that. So let's do it.
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Quoting BurnedAfterPosting:


Nah season is over LOL


The disturbances are lining up and the "tacomen" in this blog will be in short supply...LOL

This place is very amusing
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Quoting mikatnight:
They never cease to crack me up Dan. Good for the blog. Keeps people smiling (and apparently ban-proof).


So far so good, yea. Like to try and keep some levity. Gets intense at times in here.
Something else I learned about lightning. If it hits near a building, it can change the electrical potential of that building. If this building is connect to another building through phone or computer cable, the two buildings will try and neutralize through the cable. Guess what happens to all the components. POOF.
Let me clarify though. Both buildings had earth grounds when built. Rods went down about 50 ft (iirc) but both did not ground the same potential. They were not originally connect 25 years ago. We had to get grounding rods down over 100 feet to get properly grounded. Plus underground cable connecting them together on the electrical ground, plus lightning protectors. Finally worked. This was in Crestview Florida.
Member Since: August 22, 2008 Posts: 12 Comments: 6010
Quoting PalmBeachWeather:
additional post......

With that being said
IMHO
I'm not an expert , but..

in line for south Florida


The steering currents would take it out to sea.
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Quoting Stormchaser2007:
Looks like we'll have to monitor the vigorous wave behind 08L as well. Very nice anticyclone and no SAL could give it a chance at becoming something.


Nah season is over LOL
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Looks like we'll have to monitor the vigorous wave behind 08L as well. Very nice anticyclone and no SAL could give it a chance at becoming something.
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additional post......

With that being said
IMHO
I'm not an expert , but..

in line for south Florida
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#220

LOLOLOL!!
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Quoting Stormchaser2007:
A good call by the National Hurricane Center.



yup I agree
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A good call by the National Hurricane Center.

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"In Graceland Graceland,
I'm going to Graceland,
For reasons I cannot explain
There's some part of me wants to see
Graceland,
And I may be obliged to defend
Every love every ending
Or maybe there's no obligations now,
Maybe I've a reason to believe
We all will be received
In Graceland"
Member Since: October 18, 2005 Posts: 4 Comments: 3052
Just to guess at some posts to come over the next few hours:

"What are the chances of Grace forming?"
"Could someone post the shear maps?"
"What are the landfall chances of Grace?"
"There is no way Grace will survive!"
"Stop calling it Grace, its not named yet"
"When DMAX hits, Grace/TD8 will explode."
"Why isn't the NHC naming it yet? That looks like a 50mph TS to me."
"SAL will do TD8 in, for sure. RIP."
"How strong can Grace get?"
"Grace will be our next Cat 5, for sure."

And to save the best for last...

WS:
"What are the chances of TD8/Grace having a South Florida landfall?"
Member Since: Posts: Comments:

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.