African tropical wave 99L slowly organizing

By: Dr. Jeff Masters , 1:26 PM GMT on July 31, 2012

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A tropical wave (Invest 99L) near 9°N 41°W, halfway between the Lesser Antilles Islands and the coast of Africa, has the potential to develop into a tropical depression later this week as it moves westward at 10 - 15 mph. Visible satellite loops show that the disturbance now has a moderate amount of poorly-organized heavy thunderstorms that continue to slowly increase in intensity and areal coverage. There is no surface circulation, but some counter-clockwise rotation of the large-scale cloud pattern is evident. Water vapor satellite loops show that 99L has a reasonably moist environment. The latest Saharan air layer analysis shows that the dry air from the Sahara lies to the north of 99L and is currently not affecting the storm. WInd shear over the disturbance is a light 5 - 10 knots, and ocean temperatures are 28°C, (82°F) which is well above the 26.5°C (80°F) threshold typically needed to allow formation of a tropical depression.


Figure 1. Morning satellite image of Invest 99L.

Forecast for 99L
Wind shear is expected to remain light through Friday, and ocean temperatures will remain near 28°C, according to the 8 am EDT run of the SHIPS model. However, a band of high wind shear of 20 - 40 knots associated with the subtropical jet stream lies just to the north of 99L, and it would not be a surprise to see 99L experience some higher shear conditions than are currently forecast. The farther north 99L gets, the higher the shear it will experience, and the SHIPS model is predicting shear in the moderate range, 10 - 20 knots, for Saturday - Sunday, as the storm works its way to 15°N. The disturbance is at 9°N, which is close enough to the Equator that the storm will have some difficultly getting spinning. Most of the models are showing some slow development of 99L. There are some major differences in the predicted forward speed of 99L, with the ECMWF and UKMET models predicting the storm will reach the Lesser Antilles on Friday, and the GFS predicting a later arrival, on Saturday. At 8 am Tuesday, NHC gave 99L a 20% chance of developing into a tropical depression by Thursday morning. I expect the storm will begin having trouble with tendrils of dry air reaching down from the north at times this week, but give 99L a 50% chance of eventually developing into Tropical Storm Ernesto sometime in the next ten days. Residents and visitors to the Lesser Antilles Islands should anticipate heavy rains and strong winds from 99L beginning to affect the islands as early as Friday morning. The long-range fate of 99L next week is uncertain. A track west to west-northwest through the Caribbean, or to the northwest towards the U.S. East Coast are both possible. The storm is less likely to survive if it heads northwest towards the U.S.

Extreme heat in the Central U.S.
The withering heat in America's heartland continued on Monday, with high temperatures of 112° recorded in Winfield, Kansas and Searcy, Arkansas. Little Rock, Arkansas hit 111°, their 3rd hottest temperature ever record, behind the all time record of 114° set just last year on August 3, and the 112° reading of 7/31/1986. Wichita and Coffeyville in Kansas both hit 111° Monday, and in Oklahoma, Enid, Tulsa Jones Airport, and Chandler all topped out at 111°. Carr Creek, Missouri hit 110°, the hottest temperature measured in the state so far this year. Highs temperatures Tuesday and Wednesday in this region could reach 110° again, as the most extreme heat this week will stay focused over Oklahoma and surrounding states.

Jeff Masters

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Quoting GTcooliebai:
I'm impressed at how close these two systems are because usually the larger system kills the smaller one when its this close together due to the outflow from the larger system that would induce shear on the smaller one.


The smaller one is about to get slung into China by Saola. Maybe a small Fujiwara Effect.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
Woow Here in the part were i live in Dominican R. right now is raining heavily , The blob is doing nice job here
Member Since: June 20, 2012 Posts: 0 Comments: 2169
1869. JLPR2
Quoting ProgressivePulse:


Could be up around 11N 44W too.


Yeah, in that general area, there were west winds across the 10N area so it's definitely above it. Almost seems like this is 99L's way of splitting from the ITCZ.
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting ProgressivePulse:


Kinda funny right, lol. Not your typical CAT5 crowd in here tonight.


I know. It's even more funny because I'm typically the conservative one. Lol.
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Quoting MississippiWx:
These WPac typhoons are just scary...Saola has improved overnight/this morning.

I'm impressed at how close these two systems are because usually the larger system kills the smaller one when its this close together due to the outflow from the larger system that would induce shear on the smaller one.
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Quoting KoritheMan:


Impressive inflow band to the south.


Indeed. If that stays in tact as it moves over Taiwan, someone is in trouble.
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Quoting JLPR2:


Around 10.5N, that's my bet where the LLC will finally establish itself.


Could be up around 11N 44W too.
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Quoting MississippiWx:
These WPac typhoons are just scary...Saola has improved overnight/this morning.



Impressive inflow band to the south.
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Quoting nigel20:
Have a good night everyone!


good night nigel

Member Since: June 20, 2012 Posts: 0 Comments: 2169
Quoting ProgressivePulse:


That could happen however, I was actually thinking follow the leader.


That would only happen if the wave became the stronger of the two. Somehow I don't think that's likely with all the westerly shear.
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Quoting stormchaser19:


And now looks like more to the north


Yep.
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These WPac typhoons are just scary...Saola has improved overnight/this morning.

Member Since: July 15, 2006 Posts: 17 Comments: 10284
1858. JLPR2
Quoting stormchaser19:


And now looks like more to the north


Around 10.5N, that's my bet where the LLC will finally establish itself, although it's also ASCAT's bet. xD
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting KoritheMan:


That's what I was thinking as well. With a low pressure field north of the Greater Antilles and east of the Bahamas, the ridge would remain strong to the north of 99L.


That could happen however, I was actually thinking follow the leader.
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Quoting KoritheMan:
Organizing again:



And now looks like more to the north
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Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+


B. Same
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it about 35 min till the TWO update
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Quoting MississippiWx:


Wow. Judging from the other responses, it looks like I'm the aggressive one tonight. I'm going with 60%.


Kinda funny right, lol. Not your typical CAT5 crowd in here tonight.
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1852. ryang
Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+


B
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1850. JLPR2
Yellow dot!



...
This is sad...
All anxious because of a dot? *sigh
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+


Wow. Judging from the other responses, it looks like I'm the aggressive one tonight. I'm going with 60%.
Member Since: July 15, 2006 Posts: 17 Comments: 10284
1848. JLPR2
Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+

B
Member Since: September 4, 2007 Posts: 7 Comments: 8747
Organizing again:

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Quoting nigel20:
Have a good night everyone!
Good night Nigel, convection looks to be slightly increasing in the NW quadrant.
Member Since: March 16, 2012 Posts: 127 Comments: 7972
1845. GetReal



The Cape Verde season is underway, and the wave train is leaving the station!!!
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Quoting Huracaneer:


Well that's a heck of a good answer to my earlier question about 0% circles. There is a reason! NHC does know what they are doing. Well signing out for the night, that's the most comments I have posted in a long time.


I actually answered your question some time ago.

1779. ProgressivePulse 4:10 AM GMT on August 01, 2012 +0

Quoting Huracaneer:


It would really have to thread the needle to take advantage of that, but possible (hence the near 0% chance). Of course the shear over Fl right now is pretty high, so it would probably be short lived if anything managed to form.




NHC sees a small window, hence the 0%. No way this develops 48hrs from the 8pm. However, tomorrow you could see chances go up as we approach the small window. The COL area is to remain with fluctuation between it and the ATL Ridge with respect to the Peninsula. Never know.
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C
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1842. nigel20
Have a good night everyone!
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Oh yeah my answer is B
Member Since: March 16, 2012 Posts: 127 Comments: 7972
Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+


B)
Member Since: June 20, 2012 Posts: 0 Comments: 2169
At 4:15 utc, looks like the convection is starting again?
Member Since: June 20, 2012 Posts: 0 Comments: 2169
Quoting wxchaser97:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+


B
Member Since: Posts: Comments:
For anyone that does a late night pole, poll time.
Q: What do you guys think 99L percentage of development will be at 2am EDT?
A: a)20%-40%
b)same(50%)
or
c)60%+
Member Since: March 16, 2012 Posts: 127 Comments: 7972
Quoting ProgressivePulse:


Typically that means a new low pressure system.


Well that's a heck of a good answer to my earlier question about 0% circles. There is a reason! NHC does know what they are doing. Well signing out for the night, that's the most comments I have posted in a long time.
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Quoting ilovehurricanes13:
someone help me out what is the x mean next to miami


Correction

The "X" marks a 500mb "Vort Max" and not a surface low.
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Quoting KoritheMan:


That's what I was thinking as well. With a low pressure field north of the Greater Antilles, the ridge would remain strong to the north of 99L.


Just goes to show that 0% circles are not there for no reason. With the GFS picking up on it now, it has my interest for sure.
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Quoting RussianWinter:


Prolly low pressure.

Nothing serious, a rainy day at best.


Is that what the "x" means? Must admit I have seen them before and not entirely sure.
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Quoting ProgressivePulse:
Hey, at least it has a shred of model support now, lol. NAM has been good in the past on weak systems. More curious due to the fact that it could have track implications for 99L. Looks like the ridge traps the AOI in the Bahamas at the end of the run.


That's what I was thinking as well. With a low pressure field north of the Greater Antilles and east of the Bahamas, the ridge would remain strong to the north of 99L.
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Quoting KoritheMan:


This season was never analogous to 2004.

2004:



2012:



Modiki El Nino guys. Gotta love it.


Thanks, that's a very clear graphic! Big difference in the location of the cold water areas.
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Quoting ilovehurricanes13:
someone help me out what is the x mean next to miami


Prolly low pressure.

Nothing serious, a rainy day at best.
Member Since: August 21, 2011 Posts: 0 Comments: 666
Hey, at least it has a shred of model support now, lol. NAM has been good in the past on weak systems. More curious due to the fact that it could have track implications for 99L. Looks like the ridge traps the AOI in the Bahamas at the end of the run.
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Quoting GTcooliebai:
Boy if this thing develops rapidly, I'm looking at the large scale synoptic pattern across the CONUS and it shows a trough coming down from the Great Lakes and moving towards the Southeast, if the system has gained enough latitude it could get caught and brought up into the GOM.
i concur,as stated previos.temps in the gulf,un believable.it will be an interesting experiment.
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Blog update on 99L

Member Since: March 16, 2012 Posts: 127 Comments: 7972
Quoting Huracaneer:


Last time I started comparing this year to 2004 (a weak el nino starting) and making doom predictions the activity shut down and I have been sulking since (right after Debby when we had a bunch of yellow circles). So I am not making any new doom predictions until I see the white of their eyes! (hurricanes that is).


This season was never analogous to 2004.

2004:



2012:



Modiki El Nino guys. Gotta love it.
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1823. nigel20
Quoting GTcooliebai:
So of the past storms that you have been through which one gave you the worst weather?

I've only seen Ivan and Dean, but Gilbert would have been worst as it traversed the entire island causing damage in excess of $3 billion dollars.
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Quoting ilovehurricanes13:
where did that dry air come from!!

what dry air
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Quoting ProgressivePulse:


Actually starts to close it off at 36hrs



Does @ 60hrs



Looks like a developing low east of TCI. Should be taking shape pretty quickly if the NAM has a low trying to close off in 36hrs.
NAM is not the only one picking up on it, check out the GFS:

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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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