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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Area Forecast Discussion
Issued by NWS San Juan, PR

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
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000
FXCA62 TJSJ 301912
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
312 PM AST FRI JUL 30 2010

.SYNOPSIS...GENERALLY FAIR WEATHER IS EXPECTED ACROSS THE LOCAL
ISLANDS THROUGH THE UPCOMING WEEKEND WITH LIMITED AFTERNOON
CONVECTION EXPECTED TO DEVELOP EACH AFTERNOON OVER THE INTERIOR
AND WESTERN SECTIONS OF PUERTO RICO. INCREASING MOISTURE AND
INSTABILITY ARE EXPECTED BY EARLY NEXT WEEK...WITH AN INCREASE IN
SHOWER ACTIVITY EXPECTED FOR LATE MONDAY AND TUESDAY...AND A
POTENTIALLY STRONG TROPICAL WAVE EXPECTED TO REACH THE LOCAL
ISLANDS BY WEDNESDAY OR THURSDAY.

&&

.DISCUSSION...A TROPICAL WAVE PASSING SOUTH OF THE LOCAL ISLANDS
IS HAVING LITTLE IMPACT ON THE LOCAL WEATHER AS DRIER AIR HAS
ADVECTED ACROSS THE REGION AND A STRONG SUBSIDENCE CAP HAS KEPT
SHOWER ACTIVITY TO A MINIMUM ACROSS THE LOCAL ISLANDS TODAY.
CONTINUED GENERALLY DRY AND FAIR WEATHER IS EXPECTED TO PREVAIL
THROUGH THE UPCOMING WEEKEND...WITH AN ISOLATED SHOWER OR
THUNDERSTORM POSSIBLY BREAKING THROUGH THE CAP ACROSS WESTERN
SECTIONS OF THE ISLAND DURING THE AFTERNOON HOURS EACH DAY.


THE TUTT LOW TO OUR NORTHEAST IS EXPECTED TO RETROGRADE WESTWARD
EARLY NEXT WEEK...WITH A LOW LEVEL TROUGH OR REFLECTION OF THIS
TUTT EXPECTED TO BRING AN INCREASE IN MOISTURE ACROSS THE VI AND
SECTIONS OF PUERTO RICO BY MONDAY AFTERNOON AND TUESDAY. THE MOST
INTERESTING FEATURE OVER THE NEXT SEVEN DAYS IS THE POTENTIALLY
STRONG TROPICAL WAVE...THAT AT THIS TIME HAS A LOW CHANCE OF
DEVELOPING INTO A TROPICAL CYCLONE...EXPECTED TO REACH THE LOCAL
ISLANDS TOWARD THE MIDDLE TO END OF NEXT WEEK. STILL MUCH
UNCERTAINTY...BUT EITHER WAY...EXPECT A SIGNIFICANT INCREASE IN
SHOWER AND THUNDERSTORM ACTIVITY ACROSS THE LOCAL ISLANDS BY NEXT
WEDNESDAY OR THURSDAY AS THIS WAVE APPROACHES THE LOCAL ISLANDS.

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Blog Information," A massive hurricane that formed in early August!"
Link
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71 WeatherNerdPR "Dare I ask again, What is that thing NE of the Bahamas?"

No, What is on second base.
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ATL sat pic looks like JB's "whack-a-mole" pattern!
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Quoting WeatherNerdPR:

Levi, can you tell me what is that area of Cloudiness North of the Bahamas?

I'm not levi, but it's a disturbed area of thunderstorms that has formed off of a decaying front...
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USS Alabama Webcams
Member Since: July 3, 2005 Posts: 426 Comments: 129093
What do you all make of this?
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Quoting Patrap:
When ya see the Battleship Alabama Turrets drooping..ya know itsa hot one.


Dere noses in da bay right now
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Quoting Levi32:
This can take a long time to update....but the June PDO came in recently and the number finally plummeted and is now below zero for the first time this year.

2010** 0.83 0.82 0.44 0.78 0.62 -0.22

Levi, can you tell me what is that area of Cloudiness North of the Bahamas?
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Return of the.. MJO?
Member Since: July 8, 2005 Posts: 259 Comments: 24485
When ya see the Battleship Alabama Turrets drooping..ya know itsa hot one.
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Dangerous heat this weekend too.

We may hit da beach in Gulfport..leave late and stay till Sunset and then some.
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting dmdhdms:
Sorry about the wrong button hit on the previous post.

Gulfport, MS.....NWS .... 99F.....heat index 112F at 1639 CDT.

It is hot.


yeah, tell me about it. Try being out in it delivering the mail all day...Think I'm gonna pass out!
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Quoting dmdhdms:
Sorry about the wrong button hit on the previous post.

Gulfport, MS.....NWS .... 99F.....heat index 112F at 1639 CDT.

It is hot.




Mobile is stoopid hot. Hear dat Pat? Stoopid hot!!!
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Sorry about the wrong button hit on the previous post.

Gulfport, MS.....NWS .... 99F.....heat index 112F at 1639 CDT.

It is hot.


Quoting Patrap:


Heat Advisory

Statement as of 3:09 PM CDT on July 30, 2010

... Heat advisory remains in effect until 8 PM CDT this evening...
... Heat advisory in effect from noon to 8 PM CDT Saturday...

The National Weather Service in New Orleans has issued a heat
advisory... which is in effect from noon to 8 PM CDT Saturday. A
heat advisory remains in effect until 8 PM CDT this evening.

Heat indicies remain in the 105-110 range this afternoon and
should begin to drop during the late evening hours. On
Saturday... temperatures will climb into the mid to upper 90s.
These warm temperatures will combine with high humidity levels to
create heat index values between 105 and 110 degrees. The greatest
threat for heat related illnesses will be during the mid to late
afternoon hours. The warm and moist airmass will remain across the
region through the weekend... with temperatures topping out in the
upper 90s on Sunday as well.

Precautionary/preparedness actions...

A heat advisory means that a period of hot temperatures is
expected. The combination of hot temperatures and high humidity
will combine to create a situation in which heat illnesses are
possible. Drink plenty of fluids... stay in an air-conditioned
room... stay out of the sun... and check up on relatives and
neighbors.
Member Since: Posts: Comments:
Latest CIMSS vorticity product suggests that PGI21L is accompanied by a fairly vigorous MLC, it also appears to be trying to work its way down to the lower levels. Satellite imagery suggests that it is accompanied by some broad cyclonic curvature.
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This can take a long time to update....but the June PDO came in recently and the number finally plummeted and is now below zero for the first time this year.

2010** 0.83 0.82 0.44 0.78 0.62 -0.22
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Quoting Patrap:


Heat Advisory

Statement as of 3:09 PM CDT on July 30, 2010

... Heat advisory remains in effect until 8 PM CDT this evening...
... Heat advisory in effect from noon to 8 PM CDT Saturday...

The National Weather Service in New Orleans has issued a heat
advisory... which is in effect from noon to 8 PM CDT Saturday. A
heat advisory remains in effect until 8 PM CDT this evening.

Heat indicies remain in the 105-110 range this afternoon and
should begin to drop during the late evening hours. On
Saturday... temperatures will climb into the mid to upper 90s.
These warm temperatures will combine with high humidity levels to
create heat index values between 105 and 110 degrees. The greatest
threat for heat related illnesses will be during the mid to late
afternoon hours. The warm and moist airmass will remain across the
region through the weekend... with temperatures topping out in the
upper 90s on Sunday as well.

Precautionary/preparedness actions...

A heat advisory means that a period of hot temperatures is
expected. The combination of hot temperatures and high humidity
will combine to create a situation in which heat illnesses are
possible. Drink plenty of fluids... stay in an air-conditioned
room... stay out of the sun... and check up on relatives and
neighbors.
Member Since: Posts: Comments:
I'm gonna be conservative here and say it develops Monday as well
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Dare I ask again, What is that thing NE of the Bahamas?
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Quoting MiamiHurricanes09:
Why don't you reread that comment a few more times...I think you understood it incorrectly.


Okay, I read it as saying that the wave will absord the invest into it's circulation. The wave has no circulation at this point in my humble opinion.

Where is the confusion, especially if it is mine!

And trust me, I have been wrong before!
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Considering the excellent upper-air conditions that the system should have in front of it for quite some time, it's tempting to go with an early date for TD formation, but the "circulation" of 90L does not go down to the surface (at least not "well-defined" as per Dr. M.). So even if the wave pulls it in, it will still have to make its way down. I do think that the wave will "steal" 90L, because frankly there is not enough time for something with minimal vorticity to develop any circulation of its own before it starts to have 90L pulled up under it, but we would still have the usual wait for a surface spin.
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Heat Advisory

Statement as of 3:09 PM CDT on July 30, 2010

... Heat advisory remains in effect until 8 PM CDT this evening...
... Heat advisory in effect from noon to 8 PM CDT Saturday...

The National Weather Service in New Orleans has issued a heat
advisory... which is in effect from noon to 8 PM CDT Saturday. A
heat advisory remains in effect until 8 PM CDT this evening.

Heat indicies remain in the 105-110 range this afternoon and
should begin to drop during the late evening hours. On
Saturday... temperatures will climb into the mid to upper 90s.
These warm temperatures will combine with high humidity levels to
create heat index values between 105 and 110 degrees. The greatest
threat for heat related illnesses will be during the mid to late
afternoon hours. The warm and moist airmass will remain across the
region through the weekend... with temperatures topping out in the
upper 90s on Sunday as well.

Precautionary/preparedness actions...

A heat advisory means that a period of hot temperatures is
expected. The combination of hot temperatures and high humidity
will combine to create a situation in which heat illnesses are
possible. Drink plenty of fluids... stay in an air-conditioned
room... stay out of the sun... and check up on relatives and
neighbors.
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting Caribbeanislands101:

Thanks Patrap, How's the weather in the Big Easy?



Current Conditions

Uptown, New Orleans, Louisiana (PWS)

Updated: 30 sec ago

Scattered
Clouds

94.9 °F

Scattered Clouds
Humidity: 51%
Dew Point: 74 °F
Wind: Calm
Wind Gust: 3.6 mph
Pressure: 29.97 in (Falling)

Heat Index: 106 °F

Visibility: 10.0 miles
UV: 7 out of 16
Pollen: 2.60 out of 12
Pollen Forecast new!
Clouds:
Scattered Clouds 4900 ft
Scattered Clouds 25000 ft
(Above Ground Level)
Elevation: 20 ft
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting Patrap:
ATCF images (Hurricane Track Models)

Current Storms:
Invest90

wow, great links, thanks
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Quoting asgolfr999:


It has no circulation
Why don't you reread that comment a few more times...I think you understood it incorrectly.
Member Since: Posts: Comments:
Met Service of Jamaica

July 30, 2010 at 4:00 p.m.

LOCAL WEATHER FORECAST

SIGNIFICANT FEATURE… .

Comment
Trough will remain across the central Caribbean, gradually moving west by Monday.


24-HOURS FORECAST
Tonight… becoming fair.
Tomorrow… Mainly fair morning .Scattered showers and isolated thunderstorms mainly across sections of western parishes,
during the afternoon.


3-DAYS FORECAST (after tomorrow)

Sun.. Scattered showers and thunderstorms across
southern and northwestern parishes.
Mon/Tues.. Scattered afternoon showers and
thunderstorms across most parishes.

Regionally… Another Tropical Wave moving across the
eastern Caribbean will move across Jamaica early Sunday.

pef
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Really slows down here after 5pm EST!
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Quoting Patrap:
ATCF images (Hurricane Track Models)

Current Storms:
Invest90

Thanks Patrap, How's the weather in the Big Easy?
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This hurricane season is a bust!! lol not really,
Who's JFV or whoever that is? He's really famous!!
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Quoting CybrTeddy:
I suspect the wave off Africa will absorb 90L into its massive circulation and then it will develop.


It has no circulation
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Quoting CybrTeddy:


Monday, at the earliest IMO.
I'm going with tropical depression on Sunday. Monday sounds like a safer bet, but I'll take my chances. :)
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ATCF images (Hurricane Track Models)

Current Storms:
Invest90
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Quoting jasoniscoolman2010x:
new African tropical wave WILL BE INVEST 91L THIS WEEKEND.

I don't know why, but your post or comments are always hidden they never ever show up on this blog, but your info is great, I agree with you by the way!
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Quoting Patrap:

Record Events for Fri Jul 23, 2010 through Thu Jul 29, 2010


Total Records: 3060
Rainfall: 807
High Temperatures: 453
Low Temperatures: 71
Lowest Max Temperatures: 222
Highest Min Temperatures: 1507


Thank you for the information. Considering it's July, and those are U.S. figures, it does add some information to consider.
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Quoting extreme236:


I'd say Sunday


Monday, at the earliest IMO.
Member Since: July 8, 2005 Posts: 259 Comments: 24485
Quoting SouthALWX:
Let me rephrase .. as long as the AOIs stay relatively open on the south side and remain inverted troughs of lower pressure, they act as waves (hence the term "trough") and can possibly merge ... If one becomes more established it is more likely that that one destroys or eats the other as waves of comparable amplitude are more likely to constructively combine than waves of greatly differing amplitude.
Ok that makes more sense.
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Most of the time, waves have to create their own closed circulations in order to develop. Cannibalism of another system's circulation center seems to be far less common in the deep tropics, and I rather look forward to watching it unfold.
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Quoting Patrap:
18z Early Cycle NHC model tracks
Invest90
Statistical/Simple Models (CLIPER,BAMs,LBAR,other Statistical Models)




Dynamic Models (More sophisticated models)




Hey, could put in link of where you got those models? I' ve been looking but can't find them
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Let me rephrase .. as long as the AOIs stay relatively open on the south side and remain inverted troughs of lower pressure, they act as waves (hence the term "trough") and can possibly merge ... If one becomes more established it is more likely that that one destroys or eats the other as waves of comparable amplitude are more likely to constructively combine than waves of greatly differing amplitude.
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Quoting CybrTeddy:
I suspect the wave off Africa will absorb 90L into its massive circulation and then it will develop.

It seems that way.
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Quoting StormSystems:

It looks that way, you think will be a TD soon?
well in my opinin the lager circulations take longer to develop and if this occurs 90l might be the one wrapping up soon
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Quoting NoNamePub:
hmmm Last one to know apparently....NEW BLOG

Aww man... I think I'm the last one...
Anyway, the African wave looks VERY potent.
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Quoting MiamiHurricanes09:
We aren't talking about tropical waves it seems since the area of low pressure associated with 90L was left behind by the actual tropical wave. It just looks like the area of low pressure that 90L has will move under PGI21L's convection.

No but they are troughs and troughs are wave form.
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Quoting StormSystems:

It looks that way, you think will be a TD soon?


I'd say Sunday
Member Since: August 2, 2007 Posts: 19 Comments: 19234

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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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