Two African waves worth mentioning

By: Dr. Jeff Masters , 3:51 PM GMT on July 18, 2009

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There are two African tropical waves worth mentioning today, though neither looks particularly threatening. A tropical wave near 12N 45W, about 1200 miles east of the Lesser Antilles Islands (97 L), is moving west at 15 - 20 mph. This wave is now surrounded by an area of very dry air from the Sahara Desert. The dry air has disrupted most of the wave's heavy thunderstorm activity, and will continue to make it difficult for this system to develop over the next 2 - 3 days. Wind shear is a modest 10 knots over the disturbance, and should remain in the moderate 10 - 15 knot range over the next 2 - 3 days. Thereafter, shear is expected to rise to 20 - 30 knots. This morning's QuikSCAT pass showed no evidence of a surface circulation, and only a modest wind shift associated with 97L. The National Hurricane Center is giving this system a low (less than 30% chance) of developing into a tropical depression in the next 48 hours.

A second tropical wave now approaching the northern Lesser Antilles Islands is under 30 knots of wind shear, and has little prospect of development due to the high shear. However, the wave will bring heavy rain to the islands over the next two days.

None of the computer models are forecasting tropical storm development over the next seven days, and I don't expect either of the two African waves mentioned today to develop over at least the next three days.


Figure 1. Current satellite image of African wave 97L, 1200 miles east of the Lesser Antilles Islands.

I'll have an update Sunday afternoon.
Jeff Masters

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Quoting JRRP:
RIP 97L ?


yep
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Quoting JRRP:
RIP 97L ?


Not even close..
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Quoting VAbeachhurricanes:


its 4:31 where the wave is and Dmax is around 6 or 7 therefore it is near and approaching DMAX. thank you


Dmin
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Quoting jrweatherman:
All models except for the NOGAPS form a low pressure out of one of these waves in 100 hours north of the Carribean near Florida. I think this is why the NHC has not de-activated 97L. In A few days, it might just do something. The East Coast needs to watch out for a possible weak Tropical Storm later next week.

Just jumped on and I'm confused. You says that all models expect one develop low pressure in 4 days. However, in Dr. Masters blog he says that none of the models develop a storm over the next 7 days. Which is correct?



He is correct...
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All models except for the NOGAPS form a low pressure out of one of these waves in 100 hours north of the Carribean near Florida. I think this is why the NHC has not de-activated 97L. In A few days, it might just do something. The East Coast needs to watch out for a possible weak Tropical Storm later next week.

Just jumped on and I'm confused. You says that all models expect one develop low pressure in 4 days. However, in Dr. Masters blog he says that none of the models develop a storm over the next 7 days. Which is correct?

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345. JRRP
RIP 97L ?
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Quoting errantlythought:


We are nowhere remotely near Dmax.


its 4:31 where the wave is and Dmax is around 6 or 7 therefore it is near and approaching DMAX. thank you
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Good Afternoon,
I am amazed that 97L stayed so far south. Appears to be moving straight west since last night. Also the wave ahead of it getting smashed apart in the shear. Should be interesting to see what happens, if anything, once 97L catches up with at least the southern end of convection.
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342. CUBWF
Hello everybody. First time I post. Reading the blog for a time. Learning something new every season. Sorry for my english. I know is not the best. I'll try to understand. Please, be patient on my questions. LOL
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Quoting BurnedAfterPosting:
lol canes then why is it that the wave you say "we wouldnt care about" is an Invest, yet the big blow up is not?

its an invest because it has a low, i said if it didn't have a low we wouldn't care about this because its just a couple clouds, right
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Quoting VAbeachhurricanes:


DMAX jeez its just a wave stop waiting for each new satitlite loop They fluctuate.


We are nowhere remotely near Dmax.
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Quoting VAbeachhurricanes:


oh thought u were talking about the antillies wave, im sorry.
oh my bad sorry, didn't want to be mean, thought you where talking about 97L
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Central Atlantic - AVN Color Infrared Loop
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lol canes then why is it that the wave you say "we wouldnt care about" is an Invest, yet the big blow up is not?

Quoting canesrule1:
They fluctuate but this one is just a couple clouds with a shower or two and a spin if this didn't have a low we wouldn't care about this.


oh thought u were talking about the antillies wave, im sorry.
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Dvorak

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Quoting VAbeachhurricanes:


DMAX jeez its just a wave stop waiting for each new satitlite loop They fluctuate.
They fluctuate but this one is just a couple clouds with a shower or two and a spin if this didn't have a low we wouldn't care about this.
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333. CUBWF
test
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JSL channel


Rainbow
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the shear is what is creating the "outflow"
Quoting HurricaneSwirl:


my psychic powers tell me...
another explosion today similar to yesterdays..
and tomorrow..
and monday.......

sigh


but not on tuesday because there will be no one left to get anything going lol
Member Since: July 7, 2008 Posts: 2 Comments: 3237
Quoting Acemmett90:
it has good outflow even with the shear


The shear is what causing the good outflow and the intense convection. However the shear is what also preventing the formation of a closed LLC.
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its really starting to spin
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ALL models except for the NOGAPS form a low pressure out of one of these waves in 100 hours north of the Carribean near Florida. I think this is why the NHC has not de-activated 97L. In A few days, it might just do something. The East Coast needs to watch out for a possible weak Tropical Storm later next week.
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Quoting amd:
there is no surface low forming near Guadeloupe. After checking the latest surface observations both to the north and south of Guadeloupe, there is no evidence of a west, or north wind.

Also, pressure is still around 1016 mb at all locations that I checked, and the pressure needs to be around 1010 mb to suggest that a low may be forming.

One interesting thing to note is that 97L is still moving around 20 mph to the west, while the blob just east of the islands continues to be stationary. If the two interact, a tropical system can develop.
yeah that is what i think will be the most likely scenario, i think they are going to combine, and then we will have convection and a low, aka a TD
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Seems like we have forgot about 97L due to the Antilles wave, but 97L still does have a good structure, and you can still clearly see spin. While now it looks very meager at best, look for thunderstorms to flare up tonight and tomorrow as the wave gets into a more favorable environment. (Less African Dust, favorable shear). The Antilles wave we are keeping an eye on looked even worse than 97L when it was where our invest is now. So, 97L certainly is not dead, and as it enters the "sweet spot" near the islands, look for a rebound of the convection, and look for some gradual development.
Member Since: June 29, 2009 Posts: 13 Comments: 5238
Quoting canesrule1:
13 minutes ago... 97L visible, starting to fade, imo.
Link


DMAX jeez its just a wave stop waiting for each new satitlite loop They fluctuate.
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Dust..the choker of Waves..

ack,coff,spit.


Central Atlantic - Water Vapor Loop
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321. Vero1
000
AXNT20 KNHC 181758
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SAT JUL 18 2009

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST
FROM THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED
ON SATELLITE IMAGERY...METEOROLOGICAL ANALYSIS...WEATHER
OBSERVATIONS...AND RADAR.

BASED ON 1200 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1715 UTC.

...TROPICAL WAVES...

A TROPICAL WAVE IS ALONG 31W S OF 19N MOVING W NEAR 15 KT.
ALTHOUGH THE WAVE LACKS ANY SIGNIFICANT DEEP CONVECTION DUE TO
THE PRESENCE OF SAHARAN DUST TO THE NORTH AND EAST OF THE WAVE
AXIS...SLIGHT LOW TO MIDDLE LEVEL CYCLONIC TURNING OF THE CLOUD
FIELD IS NOTED IN THE SATELLITE CLOUD DRIFT WINDS WITH THIS WAVE.

A TROPICAL WAVE IS ALONG 44W S OF 16N MOVING W NEAR 20 KT. THIS
WAVE COINCIDES WITH A LOW TO MIDDLE LEVEL CYCLONIC CIRCULATION
ALONG THE WAVE AXIS NEAR 12N. SCATTERED MODERATE CONVECTION IS
FROM 10N-14N BETWEEN 43W-47W.

A TROPICAL WAVE EXTENDS ALONG 21N58W 15N61W TO 10N62W MOVING
W NEAR 18 KT. THIS WAVE COINCIDES WITH A MAXIMUM IN DEEP LAYER
MOISTURE BASED ON THE TOTAL PRECIPITABLE WATER PRODUCT FROM
CIMSS. WATER VAPOR IMAGERY INDICATES THE WAVE IS BEGINNING TO
MOVE BENEATH AN UPPER LEVEL RIDGE ACROSS THE ERN CARIBBEAN AND
THE NRN PORTION OF THE WAVE IS COMING UNDER THE IMPACTS OF AN
UPPER LOW CENTERED NE OF PUERTO RICO NEAR 23N58W. UPPER LEVEL
DIFFLUENCE BETWEEN THESE TWO FEATURES ARE ENHANCING SCATTERED
MODERATE CONVECTION FROM 13N-18N BETWEEN 55W-62W.

...ITCZ...
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13 minutes ago... 97L visible, starting to fade, imo.
Link
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319. amd
there is no surface low forming near Guadeloupe. After checking the latest surface observations both to the north and south of Guadeloupe, there is no evidence of a west, or north wind.

Also, pressure is still around 1016 mb at all locations that I checked, and the pressure needs to be around 1010 mb to suggest that a low may be forming.

One interesting thing to note is that 97L is still moving around 20 mph to the west, while the blob just east of the islands continues to be stationary. If the two interact, a tropical system can develop.
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Video caught by W456



Winds seem to be increasing near the Antilles wave...that is mostly gradient wind, however.
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If the latest El Nino 2 (modicko?) no longer has a viable set of parameters, then could this mean we may see an increase in projections for this hurricane season?
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18 minutes ago...Satellite imagery...
Link
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Buoy east of Martinique (Owned and maintained by Meteo France
14.600 N 56.201 W)

Wind Direction (WDIR): ESE ( 110 deg true )
Wind Speed (WSPD): 9.9 kts
Wave Height (WVHT): 5.6 ft
Dominant Wave Period (DPD): 8 sec
Atmospheric Pressure (PRES): 30.03 in
Pressure Tendency (PTDY): -0.02 in ( Falling )
Air Temperature (ATMP): 77.7 °F
Water Temperature (WTMP): 81.7 °F
Dew Point (DEWP): 75.9 °F
Heat Index (HEAT): 79.9 °F
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Quoting VAbeachhurricanes:




shear continues to decrease over the lessar antillies wave
agreed, over 20 knots!
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Current Conditions for Princess Juliana International Airport, Netherlands Antilles


84°F
Partly Cloudy Feels Like
92°F

UV Index: 10 Very High
Dew Point: 75°F
Humidity: 74%
Visibility: 6.2 miles
Pressure: 30.00 inches and falling
Wind: From the East at 16 gusting to 35 mph
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Tropical wave - I wanna be like my hero Barry (2007) and build in these conditions :D

97L - Me to, me to, wait for me... (chugging along)
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2009's been downcasted half to heck imo.
2008 was the exact opposite.
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shear continues to decrease over the lessar antillies wave
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309. SLU
Quoting hunkerdown:
Sorry, don't see a low forming nor do I see this as being an invest in the very near future. Also, winds accompanied in tstorms/rain/showers are not actual as they are deemed "rain caused".


Which is why I was careful to mention "in heavy showers"
Member Since: July 13, 2006 Posts: 12 Comments: 4733
Current Conditions for Antigua, Antigua And Barbuda


79°F
Light Rain Shower Feels Like
83°F

UV Index: 6 High
Dew Point: 73°F
Humidity: 83%
Visibility: 6.2 miles
Pressure: 30.03 inches and falling
Wind: From the East Northeast at 23 mph
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waning
latest enhance wv image 157 pm est
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Central Atlantic - Water Vapor Loop
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Quikscat only has so wide a swath in Degrees ,so its field of View is Limited to the whims of Orbital Mechanics.

QuikSCAT Storm Page
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what radar?

that link from SLU was horrible, it is only a 3 frame loop and it skipped between the 2nd and 3rd frame

you cant tell anything from that
303. SLU
Quoting BurnedAfterPosting:


After looking I agree with you


Animate the radar and look near Guadeloupe. It is certainly not a high. Sorry if you can't see it.
Member Since: July 13, 2006 Posts: 12 Comments: 4733
Quoting BurnedAfterPosting:


stop being weird lol
i know right, not normal rufus
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Quoting BurnedAfterPosting:
the shear at the right angle can make it look like a low is forming, when it really isnt

im looking at that perfect circle that looks like an eye on radar.
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Where's the quikscat when you need it.
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About JeffMasters

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