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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Quoting hydrus:
lol


its catchy haha
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Quoting mikatnight:


I heard that Florida is the "lightning capital of the world" (that true?), but when I was in Boulder, CO there was a mountain west of there that supposedly would practically guarantee getting struck if you were up there during the afternoon hours.


From NASA. LINK




From The Observer News.
Florida leads the nation in deaths caused by lightning. The reasons for that are straightforward %u2013 Florida has both a high population and typically a large amount of lightning. In Hillsborough County, 32 people were killed by lightning between 1959 and 2003 %u2013 a number matched only by Miami-Dade County.

Only South and Central America, tropical Africa and Asia tend to have more lightning than Florida. Rwanda in Africa is generally considered to be the lightning capital of the world. But that is a fine distinction as Florida %u2013 and more specifically Hillsborough County %u2013 is thought to be the lightning capital of the U.S.
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Quoting PalmBeachWeather:
I'm sorry this is not weather related, but I have been racking my brain here in Palm Beach county by an earlier quote...Here goes.... "Is (firstly) a correct term or word"? I have used it myself, but I really do not know if it is correct.


Firstly
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Quoting tornadodude:
for shear's a jolly good fellow,

for shear's a jolly good fellow,

for shear's a jolly good felloooow,

that el nino intensified!
lol
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Quoting mikatnight:


I heard that Florida is the "lightning capital of the world" (that true?), but when I was in Boulder, CO there was a mountain west of there that supposedly would practically guarantee getting struck if you were up there during the afternoon hours.

True.
Pondering the dynamics about that mountain...would have to be an upslope flow...
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Quoting Weather456:


That is becuz water vapor imagery mainly show the vapor in the mid-upper levels, while products like SAL, and TPW show the water vapor content through a column of the entire atmosphere.

I thought so, but could not immediately find the SAL description.

So without a sounding, any way to figure which levels are the driest ahead of 99?
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Quoting atmoaggie:

Actually, there have been studies that show that large urban areas contribute to lightning frequencies downwind. There was one in/around Houston that comes to mind...
It is caused by the excessively heated man-made surfaces assisting in lift, er, lapse rates, if memory serves.
So if you live downwind of an urban area during a stormy season, your lightning frequency could be partly a product of human contribution to your weather.


I heard that Florida is the "lightning capital of the world" (that true?), but when I was in Boulder, CO there was a mountain west of there that supposedly would practically guarantee getting struck if you were up there during the afternoon hours.
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Weather456.I do not post very often, but I listen intently with what you have to say
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AOI

AOI

AOI

AOI
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99L will be going out to sea as several deep-layered long-wave troughs influence the system.
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Quoting atmoaggie:
This makes it look like 99L is on the edge of a pretty good amount of dust:


But it appears to be a far less substantial swath of dry air in the WV:


That is becuz water vapor imagery mainly show the vapor in the mid-upper levels, while products like SAL, and TPW show the water vapor content through a column of the entire atmosphere.
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I see this thing getting to no more than a 55mph ts. the dry air will slow its development and then shear should end its short life.
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A pronounce surge of dry air digging into the GOM and Caribbean Sea, probably locking off potential development.

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Ike, I love your posts.But please don't make me listen to Cashmir anymore
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I still don't know where everyone stands on this GW issue, but if anyone's interested (and I'm almost, but not quite completely 100% sure that no one is), I would have to say that I can find nothing on the subject by Dr. Masters that I disagree with.
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What is the future of the newest African wave other than its curve out to sea, is it supposed to develop?
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POSS T.C.F.A.


INV/99/L
MARK
16N/32W
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I'm sorry this is not weather related, but I have been racking my brain here in Palm Beach county by an earlier quote...Here goes.... "Is (firstly) a correct term or word"? I have used it myself, but I really do not know if it is correct.
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Quoting mikatnight:
Poor Ike. I feel for ya boss, I really do. And I promise not to mention the G word any more (don’t know what got into me – I’m not what anyone would call religious). But I do find the discussions on GW fascinating. Years before anyone ever mentioned the subject, I remember wondering if all the heat that humans create contributed to the weather in some fashion (I think I was lighting a cigarette at the time). Then at some point in time around the late 90’s I started hearing conspiracy theories about how the liberals are trying to take over the world and they’re using GW as the lever (I still don’t get that). The whole thing became political before anyone had time to ponder the question without political bias.
And now, back to your regularly scheduled program…

Actually, there have been studies that show that large urban areas contribute to lightning frequencies downwind. There was one in/around Houston that comes to mind...
It is caused by the excessively heated man-made surfaces assisting in lift, er, lapse rates, if memory serves.
So if you live downwind of an urban area during a stormy season, your lightning frequency could be partly a product of human contribution to your weather.
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Quoting mikatnight:
Very Good TD!


thanks :)

its quite chilly today

Lafayette, Purdue University Airport
Lat: 40.43 Lon: -86.93 Elev: 623
Last Update on Sep 25, 1:54 pm EDT

Light Rain

61 °F
(16 °C)
Humidity: 81 %
Wind Speed: E 10 G 20 MPH
Barometer: 30.12" (1019.8 mb)
Dewpoint: 55 °F (13 °C)
Visibility: 5.00 mi.
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Very Good TD!
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Now you're just messing with me, right?
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99L has become better organized and it appears a tropical depression is forming.
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The system is small in size, likely due to the presence of dry air to the west, preventing much expansion.
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for shear's a jolly good fellow,

for shear's a jolly good fellow,

for shear's a jolly good felloooow,

that el nino intensified!
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Global warming seems to affect areas in the Arctic most severely!! As that Permafrost melts, it messes with homes/ businesses sitting on piers that start to shift, plus released pent up methane gas from frozen bogs!!
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In this image, you can see the orientation of the new thunder heads - radially orientated - indicating the system is banding or has banded.



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Had to laugh - Radar settings "hide clutter" hides hard rain.
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Quoting mikatnight:


Please Bordonaro? It is of global significance, and it helps when there is a reasonable and thoughtful discussion. We’ve been getting some good info I think.

Sorry, a lil too quick to jump the gun!!
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99L..curve banding continues to grow, also notice what appears to be future 90L.

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Atmoaggie - you still around?
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Quoting Bordonaro:
NO!! Please NO MORE GW arguments!!!


Please Bordonaro? It is of global significance, and it helps when there is a reasonable and thoughtful discussion. We’ve been getting some good info I think.
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NO!! Please NO MORE GW arguments!!!
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a depression is forming in the Eastern Atlantic. We may have Grace in a couple of days
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Good day fellow bloggers!! Thanks Dr. Masters for the update!! Thankfully, today, everyone's playing/chatting nicely!!!

Be blessed all! I'll be around, occassionally tossing in my $.02!! Bob Bordonaro
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Quoting iluvjess:
If we are going to get so far OFF topic lets talk about some football!!

Great game last night!

Yes that was a good game, gives the Canes a chance to move up a couple of spots if they beat VaTech.....
PS, Please no more Global Warming folks....arrrrgggghhhhhh
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Good afternoon

How is everyone

Tropical Update
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Just saw this video of Interstate traffic through flood waters. Me? No way.
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Quoting iluvjess:
If we are going to get so far OFF topic lets talk about some football!!

Great game last night!


Seemed like a poorly played game (at least by both QBs)... 5 straight 3 and outs in the 4th quarter by South Carolina and they still won!
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Quoting Seflhurricane:
looks like we may have a tropical depression later today if trends continue


Already looks like one to me. We have any satellite estimates of strength handy?
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Quoting atmoaggie:

I guess the conflict could be a product of measuring the signal of different vertical layers.
Edit: Quote does not = modify, atmoaggie.


Aggie, you sound like you know your stuff.
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Poor Ike. I feel for ya boss, I really do. And I promise not to mention the G word any more (don’t know what got into me – I’m not what anyone would call religious). But I do find the discussions on GW fascinating. Years before anyone ever mentioned the subject, I remember wondering if all the heat that humans create contributed to the weather in some fashion (I think I was lighting a cigarette at the time). Then at some point in time around the late 90’s I started hearing conspiracy theories about how the liberals are trying to take over the world and they’re using GW as the lever (I still don’t get that). The whole thing became political before anyone had time to ponder the question without political bias.
And now, back to your regularly scheduled program…
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Quoting atmoaggie:
This makes it look like 99L is on the edge of a pretty good amount of dust:


But it appears to be a far less substantial swath of dry air in the WV:

I guess the conflict could be a product of measuring the signal of different vertical layers.
Edit: Quote does not = modify, atmoaggie.
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This makes it look like 99L is on the edge of a pretty good amount of dust:


But it appears to be a far less substantial swath of dry air in the WV:
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1. SHOWER ACTIVITY ASSOCIATED WITH A TROPICAL WAVE LOCATED ABOUT
400 MILES WEST OF THE CAPE VERDE ISLANDS HAS CONTINUED TO BECOME
BETTER ORGANIZED. A TROPICAL DEPRESSION COULD FORM IN THIS AREA
DURING THE NEXT 24 HOURS BEFORE UPPER-LEVEL WINDS BECOME LESS
CONDUCIVE. THERE IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF
THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

NHC
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Quoting StormChaser81:


uh oh
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Quoting yonzabam:


True what you say about carbon particulates. They absorb sunlight and then act as microscopic airborne storage heaters, reradiating infrared. However, the fact that they prevent sunlight reaching the ground is (I think) believed to be their major influence and this is a cooling one.

No, they stop clouds from forming and do not block much...net heating of surface when aloft and also once on the surface. All bad (if a few degrees warmer is bad).
Excellent paper detailing all of the behaviors of aerosols (many types) and clouds in the Arctic here: http://www.atmos-chem-phys-discuss.net/5/9039/2005/acpd-5-9039-2005-print.pdf

And additional work on the sources of soot in the Arctic: http://pubs.giss.nasa.gov/abstracts/2005/Koch_Hansen.html
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Quoting Santamaria:
What is important to see in these graphs is that there was a natural cooling cycle as we go into another glacial period over the last 2000 years (we've been in an interglacial period), but that this has been superceded by warming in the last 200 years or so,

That warming is man-made and is very rapid in millenium terms.

These graphs confirm the original "hockey stick" scenario,

So, let's help the Chinese and Indians with stack scrubbers and be done with it.
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Quoting yonzabam:


Firstly, I'm not sure if soot is classed as aerosol, I believe it's classed as 'particulate', and although carbon on snow will absorb heat and promote melting, carbon in the air will probably have a cooling effect by blocking sunlight. This is called 'global dimming' and is believed by some scientists to have been offsetting the warming trend and may explain why global increases in temperature did not begin until the late 70s despite increased atmospheric CO2, when clean air laws were introduced in North America and Europe.

An important aerosol produced by coal burning is sulfur dioxide. This causes cooling by reflecting sunlight back into space and also by acting as a condesation nucleus for water vapour, thus speeding up cloud formation and contributing to global dimming. Soot particles also do this.

It's all very complicated stuff and scientists have a very poor understanding of many of the physical processes. aircraft get a bad rep for their contribution to atmospheric CO2, but when aircraft were grounded in the US after 9/11, there was an increase in temperature in the US due to the lack of contrails reflecting back sunlight. So you could argue that aircraft are actually beneficial.

Anything particulate that is carried long distances by the air is an aerosol.

And you are thinking of Sulfate aerosols, which are the ones related to the global dimming, solar reflection phenomenon.
Black carbon aerosols are known to negatively effect cloud coverage when in the atmosphere and then (obviously) aid in the absorption of sunlight once on the formerly white surface.

Not sure about the data behind this plot, so take a large grain of salt with it. But, think industrial output combined with environmental regulation around the world over these years. Makes sense to me.

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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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