Little change to 90L; new African tropical wave is worth watching

By: Dr. Jeff Masters , 8:53 PM GMT on July 30, 2010

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Invest 90L is a tropical wave in the eastern Atlantic near 10N 33W with a very limited amount of heavy thunderstorm activity but a decent amount of spin. It does not have a well-defined surface circulation, and has shown little change in organization today. CIMMS wind-shear analyses show a low amount of wind shear (5 - 10 knots) over 90L, and sea surface temperatures are a record warm 29°C. The wave currently is in a moist environment and is not being affected by the dry Saharan Air Layer (SAL) to its northwest. The disturbance has moved far enough away from the Equator to leverage the Earth's spin to help it develop. The Saharan Air Layer with its dust and dry air lurks just to the north of 90L, but the SHIPS model predicts 90L will remain far enough from the dry air over the next five days so that it will not interfere with development.


Figure 1. Afternoon visible satellite image from 2pm EDT 7/30/10 of the relatively tiny 90L, and the large new tropical wave that moved off the coast of Africa yesterday.

Forecast for 90L
One factor inhibiting development of 90L this week will be the Madden-Julian Oscillation (MJO.) The MJO currently favors downward motion over the tropical Atlantic, which will act to decrease the chances of tropical storm formation. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased.

Perhaps the main factor interfering with 90L's development will be the presence of the large tropical wave to the east of 90L that moved off the coast of Africa yesterday. This new wave is large enough and close enough to 90L that it will probably begin to dominate regional weather patterns this weekend, stealing away 90L's inflow of low-level moist air. The new wave may also act to bring sinking air over 90L that will tend to suppress 90L's thunderstorm activity. It may turn out that the new wave will also steal some of 90L's spin, and end up being a threat to develop itself later on this weekend.

The latest 8am EDT (12Z) model runs for 90L show very little in the way of development of the storm. The predominant track forecast takes 90L into or just north of the northern Lesser Antilles Islands about 6 - 8 days from now. Looking at climatology based on research done by Dr. Bob Hart at Florida State University,, 90L has a 19% chance of developing into a tropical cyclone by 2pm Sunday. NHC is putting these odds at 20%. Dr. Hart also has an experimental product showing that historically, about 30% of all tropical cyclones that develop at 90L's current position eventually hit land as a hurricane. Of course, 90L is not yet a tropical cyclone, and I think that the large tropical wave off the coast of Africa will kill 90L this weekend.

Tropical wave in the eastern Caribbean
A tropical wave in the eastern Caribbean, south of the Dominican Republic, is moving west at 15 - 20 mph with no signs of development. The wave is under a high 20 knots of wind shear, due to strong upper-level westerly winds from an upper level low centered north of Puerto Rico. This shear is expected to remain remain high through Saturday. By Sunday, when the wave will be approaching Nicaragua, the wave will be far enough away from the upper level low that shear should fall to the moderate range, 10 - 20 knots. Some development is possible on Sunday, but the wave will have only about a 1-day window to develop before its westerly motion brings it inland over Nicaragua on Monday. NHC is giving this wave a 10% chance of developing into a tropical depression by 2pm Sunday.

Extreme cold records for 2010
In my post yesterday, I reported that fourteen countries had set their all-time hottest temperature record this year. I neglected to mention that one country has also set its coldest temperature in recorded history mark in 2010. Guinea had its coldest temperature in its history on January 9, 2010, when the mercury hit 1.4°C (34.5°F) at Mali-ville in the Labe region. Of the 229 countries with extreme coldest temperature records, 14 of these records have occurred in the past ten years (6% of all countries). There have been five times as many (74) extreme hottest temperature records in the past ten years (33% of all countries.) My source for extreme weather records is Chris Burt, author of Extreme Weather.

New study finds huge drop in the plants that form the base of the oceanic food chain
A study published this week in the journal Nature documents that microscopic marine phytoplankton, which form the basis of the marine food chain, have declined by 40% globally since 1950. Joe Romm at climateprogress.org discusses the implications, using this headline:

Scientists may have found the most devastating impact yet of human-caused global warming — a 40% decline in phytoplankton since 1950 linked to the rise in ocean sea surface temperatures. If confirmed, it may represent the single most important finding of the year in climate science.

I plan to discuss this paper next week.

Next update
I'll have an update this weekend, probably by 8pm EDT Saturday.

Jeff Masters

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Quoting AllStar17:


What do you think of this analysis?
Visible Loop
Definitely has acquired some banding, and where you put the circle looks about right to me. Good call there.
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Quoting MiamiHurricanes09:
Indeed. Telling from the location of the strongest 850mb vorticity, an area of low pressure may be trying to develop near 10N and 31W. However with all that latent heat being released by the convection to its west we might end up with several vorticies.



Where can I find the sat image with the vorticity overlay?
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Quoting MiamiHurricanes09:
Indeed. Telling from the location of the strongest 850mb vorticity, an area of low pressure may be trying to develop near 10N and 31W. However with all that latent heat being released by the convection to its west we might end up with several vorticies.



What do you think of this analysis?
Visible Loop
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1387. bappit
Cool stuff.

From a footnote:

Surface winds from scatterometry are indisputably valuable, but it is unnecessary for such images (as from QuikSCAT or ASCAT) to display a closed circulation in order for a closed circulation to exist in a Lagrangian sense (see Appendix D). A morphed animation of total precipitable water from microwave imagery (beginning in 2006) is proving very helpful for analysis and prediction of moist tropical waves in the lower troposphere (http://cimss.ssec.wisc.edu/tropic2). Forecasters are now using this product to detect, locate and extrapolate the position of wave troughs. By viewing the sequence of frames, the viewer obtains a sense of Lagrangian horizontal motions weighted by the vertical profile of moisture, together with the impacts of convective moistening and horizontal entrainment. Extraction of quantitative Lagrangian information from sequential imagery is far from trivial, but a worthwhile goal. When it comes to closed circulations in propagating waves, the difference between Eulerian and Lagrangian flow is critically important, as will become clear in this paper. Forecasters deal simultaneously with both viewpoints in their arsenal of observations, yet (to our knowledge) without a clear differentiation between them.
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Quoting CyclonicVoyage:
Re #1381

Surely ITCZ enhanced. The area is breathing well though and in low shear so I don't think it will take long to regen a surface low now that 90L is out of the picture.
Indeed. Telling from the location of the strongest 850mb vorticity, an area of low pressure may be trying to develop near 10N and 31W. However with all that latent heat being released by the convection to its west we might end up with several vorticies.

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Man this season has been a tease...lol
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Re #1381

Surely ITCZ enhanced. The area is breathing well though and in low shear so I don't think it will take long to regen a surface low now that 90L is out of the picture.
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Plenty of "Vortical" hot towers/overshooting tops.

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Quoting CyclonicVoyage:
Morning All.

I see 90L all but dissipated.

We'll need to monitor both waves for regeneration of a surface low. My opinion is the wave that spawned 90L along 37.5W

Both the GFS and CMC are showing an eventual re-curve now. Way to far out to speculate though as the pressure pattern thus far has been that of High Pressure along the east coast.

Yep, all that remains of 90L is a surface trough. According to the NHC what is left of 90L is mixed inside of all that convection extending from 43W to 32W or so.

THE 1010 MB LOW PRESSURE CENTER THAT WAS NEAR 10N34W SIX HOURS
AGO HAS DISSIPATED. A SURFACE TROUGH REMAINS ALONG 34W/35W
FROM 7N TO 13N. ANY OF THE PRECIPITATION THAT JUST IS RELATED TO
THIS TROPICAL WAVE UNDOUBTEDLY IS MIXED WITH THE ITCZ SCATTERED
STRONG SHOWERS AND THUNDERSTORMS THAT ARE FROM 2N TO 10N BETWEEN
32W AND 43W.
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Quoting StormW:


Getting ready to head to Busch Gardens!


good morning! well you have fun and enjoy :)
Member Since: July 3, 2010 Posts: 0 Comments: 427
1379. Patrap
The wunderblogs only use 3-4 % of the server on a Busy Landfalling Day.

There is much more traffic to the site for General and Business weather interests than the blogs.

Everyday,..and always.
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Quoting CybrTeddy:


It doesn't look terrible. Good amount of convection. I just don't know what's going on, nor does the models which is probably why the ECMWF lost 90L because its just as much as in the dark as we are.


im new to this I am prob looking at the wrong thing... can someone put up somthing and show me what you are seeing? I really love to learn :)
Member Since: July 3, 2010 Posts: 0 Comments: 427
1375. msphar
Somewhere in the world, its already August 1st. Let the show begin...oh wait, it already has.
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i am new how do i get an avatar to show up
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testing 123
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Morning All.

I see 90L all but dissipated.

We'll need to monitor both waves for regeneration of a surface low. My opinion is the wave that spawned 90L along 37.5W

Both the GFS and CMC are showing an eventual re-curve now. Way to far out to speculate though as the pressure pattern thus far has been that of High Pressure along the east coast.

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1371. NASA101
Quoting jasoniscoolman2010x:
Quoting jasoniscoolman2010x:



There is some good amount of turning around 30-35 W and 8N - lots of convection stating to fire around it... look at the loops - it's obvious!
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Latest satellite image overlayed with 850mb vorticity.

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1367. NASA101
Nonsense!

There is some good amount of turning around 30-35 W and 8N - lots of convection stating to fire around it... look at the loops - it's obvious!
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Quoting MiamiHurricanes09:
I left early last night and no I have no clue about what's going on, lol. I see two tropical waves...which one is the one that sucked in 90L?


It's gotta be the one on the right. It can't be that close to SA yet can it? It only came off of Africa like 2 days ago, looks like the one on right to me, or the one posted in 1336.
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testing testing
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Quoting CybrTeddy:


Okay, have fun. Don't bring it here.
LOL
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long watch on this system,but still looks pretty disorganized
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90L is no longer on the Navy site but the floater is still up.
Member Since: July 11, 2006 Posts: 14 Comments: 11358
Quoting Snowlover123:
I'm bored. I'm going to a Global Warming Forum and talk about that instead of the 'tropics.' See you.


Okay, have fun. Don't bring it here.
Member Since: July 8, 2005 Posts: 259 Comments: 24249
I say ex-90L is making pre-91L kinda reminds me of the Fujiwhara effect except with invests
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Quoting ho77yw00d:


but if it did why does it look so bad? idk I am with you guys....LOST!!


It doesn't look terrible. Good amount of convection. I just don't know what's going on, nor does the models which is probably why the ECMWF lost 90L because its just as much as in the dark as we are.
Member Since: July 8, 2005 Posts: 259 Comments: 24249
I'm bored. I'm going to a Global Warming Forum and talk about that instead of the 'tropics.' See you.
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Quoting CybrTeddy:


I'm confused too. I think what's happened is the large tropical wave merged with 90L.
Quoting DaytonaBeachWatcher:


The one to the east of it
I looked at surface analysis, the TWO, and the TWD and one thing I know for sure is that the area of low pressure that 90L had dissipated and turned into a surface trough. Telling from surface analysis the surface trough looks to be in between both tropical waves. However, the NHC is saying that that surface trough is associated with the tropical wave just off of the African coast/Cape Verde islands.



From the TWD:

"THE 1010 MB LOW PRESSURE CENTER THAT WAS NEAR 10N34W SIX HOURS
AGO HAS DISSIPATED. A SURFACE TROUGH REMAINS ALONG 34W/35W
FROM 7N TO 13N. ANY OF THE PRECIPITATION THAT JUST IS RELATED TO
THIS TROPICAL WAVE UNDOUBTEDLY IS MIXED WITH THE ITCZ SCATTERED
STRONG SHOWERS AND THUNDERSTORMS THAT ARE FROM 2N TO 10N BETWEEN
32W AND 43W.
"
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Quoting CybrTeddy:


I'm confused too. I think what's happened is the large tropical wave merged with 90L.


but if it did why does it look so bad? idk I am with you guys....LOST!!
Member Since: July 3, 2010 Posts: 0 Comments: 427
Well I guess that answers our question from a day ago about what would happen to 90L if it merged with the other wave. 91L if it holds itself together! Do you think we will get 91L today? I'm probably going to say tomorrow.
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http://cimss.ssec.wisc.edu/tropic/real-time/tpw2/natl/anim/latest72hrs.gif

It looks like there may be the start of circulation just leaving the coast of Africa.
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Quoting MiamiHurricanes09:
I left early last night and no I have no clue about what's going on, lol. I see two tropical waves...which one is the one that sucked in 90L?


The one to the east of it
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Quoting MiamiHurricanes09:
I left early last night and no I have no clue about what's going on, lol. I see two tropical waves...which one is the one that sucked in 90L?


I'm confused too. I think what's happened is the large tropical wave merged with 90L.
Member Since: July 8, 2005 Posts: 259 Comments: 24249
I know you guys love the tropics and stuff but I am ready for winter, sorry i cannot take the heat and humidity.
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Quoting CybrTeddy:


Your going to be changing your tune shortly.

I hope so.
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Quoting CybrTeddy:

I left early last night and no I have no clue about what's going on, lol. I see two tropical waves...which one is the one that sucked in 90L?
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yes Tropicsweatherpr I see it very well seems to be near 12-13N 23-23W moving west
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My best guess they'll hold at 20% for ex-90L.
Member Since: July 8, 2005 Posts: 259 Comments: 24249
where is storm when you need him...lol
Member Since: July 3, 2010 Posts: 0 Comments: 427

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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.