97L growing more organized, will bring heavy rain to the Lesser Antilles

By: Dr. Jeff Masters , 3:55 PM GMT on July 19, 2009

Share this Blog
1
+

The tropical wave near 12N 52W, about 600 miles east of the Lesser Antilles Islands (97 L), has grown more organized this morning as it tracks west at about 20 mph. This wave is surrounded by an area of very dry air from the Sahara Desert, but 97L has been able to steadily moisten a large region of the atmosphere over the past day, insulating itself from the dry air. This moistening process has been aided by sea surface temperatures (SSTs) that have steadily increased from 26.5°C to 27.5°C, plus the presence of only 10 knots of wind shear. The system now has a small area of intense thunderstorms near its center, with some rotation of the cloud pattern evident at mid-levels of the atmosphere. An upper-level outflow channel has opened to the north, and there is evidence that surface spiral bands are beginning to form. This morning's QuikSCAT pass missed 97L, so we don't know what is happening at the surface.

Wind shear is a modest 10 knots over the disturbance, and is forecast to remain in the moderate 10 - 15 knot range through Monday morning. This should allow further development to occur today, and 97L could be approaching tropical depression strength on Monday as it moves through the central Lesser Antilles Islands. Monday night, shear is expected to rise to 20 - 30 knots, thanks to the presence of a trough of low pressure at upper levels of the atmosphere over the eastern Caribbean. Since 97L is a relatively small system, it is very vulnerable to wind shear. This shear may be able to drive some of the dry air west of 97L deep into its interior, significantly disrupting the disturbance. Shear will remain high along 97L's path through Thursday, when the storm should be in the western Caribbean near Cuba. If there is anything left of 97L by then, some development is possible. The National Hurricane Center gave 97L a low (less than 30% chance) of developing into a tropical depression in the next 48 hours in their 8am Tropical Weather Outlook. However, I'd say the odds are now in the medium range (30 - 50%).

None of the computer models are forecasting tropical storm development over the next seven days.


Figure 1. Current satellite image of African wave 97L.

I'll have an update Monday morning. As 97L approaches the islands, you may want to follow local observations there using our wundermap for 97L.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 915 - 865

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48Blog Index

Quoting yamil20:
based on recent visible images, is me or the system is creating some hot towers?


I've been noticing them, too. However, the angle of the sun is getting low in the sky, so it may just be shadows cast by lower cloudtops.
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:
well we could do the same poll question again

Poll closes at 7pm EDT

What will the circle look like for the 8pm TWO?

A) Yellow
B) Orange
C) Red
D) Circle will be removed

VOTE NOW!!


B
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:
well we could do the same poll question again

Poll closes at 7pm EDT

What will the circle look like for the 8pm TWO?

A) Yellow
B) Orange
C) Red
D) Circle will be removed

VOTE NOW!!

orange orange orange !!!!!!
Member Since: June 13, 2009 Posts: 2 Comments: 11991
Quoting Weather456:
97L pass just south of here


That buoy dropped like a rock
Member Since: May 16, 2009 Posts: 1 Comments: 1231
910. eye
I know everyone is longing for the first TD or storm and are trying to make the best possible conditions (shear is going away, YAY!) for it to develop...but listen to the experts, NHC doesnt give it much of a chance...sorry, there is always the next wave....
Member Since: August 21, 2006 Posts: 0 Comments: 147
Quoting yamil20:
based on recent visible images, is me or the system is creating some hot towers?


ROFL...Its an invest. Only major hurricanes can create hot towers.
Member Since: Posts: Comments:
Quoting WeatherStudent:
Gang, any early stabs on what the 8pm TWO from the NHC will read? Just for jokes.


1. THERE HAS BEEN LITTLE CHANGE TO SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE
LOCATED ABOUT 600 MILES EAST OF THE WINDWARD ISLANDS. ENVIRONMENTAL
CONDITIONS ARE CURRENTLY FAVORABLE FOR SOME DEVELOPMENT OF THIS
SYSTEM...UPPER-LEVEL WINDS ARE EXPECTED TO BECOME LESS FAVORABLE
TONIGHT. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINFALL AND
GUSTY WINDS COULD AFFECT THE WINDWARD ISLANDS ON MONDAY AS THE WAVE
MOVES WESTWARD AT 15 TO 20 MPH. THERE IS A LOW CHANCE...LESS THAN
30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.
Member Since: Posts: Comments:
The circle should be red, but at the rate the nhc is going it will probably be gone.
Member Since: Posts: Comments:
That's about as close as a disturbance can get to being designated at T.D.
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:
well we could do the same poll question again

Poll closes at 7pm EDT

What will the circle look like for the 8pm TWO?

A) Yellow
B) Orange
C) Red
D) Circle will be removed

VOTE NOW!!


B with 60% confidence.
Member Since: Posts: Comments:
Quoting Weather456:


I also did a TCFC:

Total Points of Invest 97L - 34
Total Need for Issuance of a TCFA - 35-38

Highlights:

A circulation is evident on visible, shortwave infrared, microwave imagery or QuikSCAT [check]

Winds associated with system are at least 25 knots [check]

A weather station reported a pressure drop of 2 mb [check]

The estimated MSLp is less than 1008 mb [uncheck]

Westerly flow above disturbance less than 15 knots [check]

SSTs are above 26C [check]

System has persisted for 24 hrs [uncheck]

Dvorak Classification of 1.5 or greater [check]

NWP genesis considerations (NOGAPS, GFS, UKMET, ECMWF) [uncheck]



The persistence qualification is what is killing it right now.
Member Since: Posts: Comments:
Quoting WeatherStudent:
Gang, any early stabs on what the 8pm TWO from the NHC will read? Just for jokes.


FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. SHOWER AND THUNDERSTORM ACTIVITY ASSOCIATED WITH A TROPICAL WAVE
LOCATED ABOUT 600 MILES EAST OF THE WINDWARD ISLANDS HAS PERSISTED OVER THE PAST SEVERAL HOURS. WHILE ENVIRONMENTAL
CONDITIONS ARE CURRENTLY FAVORABLE FOR SOME DEVELOPMENT OF THIS
SYSTEM...UPPER-LEVEL WINDS ARE EXPECTED TO BECOME LESS FAVORABLE
TONIGHT. REGARDLESS OF DEVELOPMENT...LOCALLY HEAVY RAINFALL AND
GUSTY WINDS COULD AFFECT THE WINDWARD ISLANDS ON MONDAY AS THE WAVE
MOVES WESTWARD AT 15 TO 20 MPH. THERE IS A LOW CHANCE...LESS THAN
30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

Member Since: Posts: Comments:
based on recent visible images, is me or the system is creating some hot towers?
Member Since: Posts: Comments:
well we could do the same poll question again

Poll closes at 7pm EDT

What will the circle look like for the 8pm TWO?

A) Yellow
B) Orange
C) Red
D) Circle will be removed

VOTE NOW!!
Member Since: Posts: Comments:
Member Since: October 28, 2006 Posts: 57 Comments: 30489
97L pass just south of here

Member Since: July 24, 2005 Posts: 407 Comments: 19076
how can one tell (on the radar pictures) when the convection is increasing? is it the presence of cool tops or more precip? or looking for circulation?
Member Since: Posts: Comments:
Quoting eddye:
why dude


Do I really need to provide an explanation?
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting louisianaweatherguy:
WOW... haven;t been on this site in a while... 97L does look impressive... NONE of the models think it will develop? that's strange. something tells me that will change by tomorrow...


Models are doing HORRIBLE this year.
Member Since: July 8, 2005 Posts: 259 Comments: 24017
895. amd
Quoting BurnedAfterPosting:


just seems to me everyone is ignoring the increasing shear that is occuring east of the Islands, that shear is dipping southward


i see the same thing. looks like unless something dramatic changes, the nhc will be correct as usual.
Member Since: Posts: Comments:
Quoting GeoffreyWPB:
Wow Keeper...never saw that before...Okay, whose going to add up the points for 97?
its on my blog and 456 is right 34 1 away from a possible T.C.F.A. being issued got to watch numbers see if dvork goes up if so a T.C.F.A. may be issued
Member Since: Posts: Comments:
I don't agree with downcasting this system. To put it simply: When I see a comma shaped tropical wave at around 12N 53W, obviously spinning with ample convection near the center, over 28-29C degree waters heading W toward the Caribbean it gets my attention. There is shear around it, but the shear won't affect it until early tomorrow. Plus there are still questions on how much shear will actually be occurring by tomorrow and Tuesday.
Member Since: Posts: Comments:
Quoting sporteguy03:

Interesting too is looking at all the sat pictures throughout the day if this was falling apart why does convection still keep firing, so if shear is effecting it what should we be looking for?


Just thought I'd ask again.. if someone can answer it would be great :)
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:


456 already did, came to 34 points, just short of a TCFA being issued


I also did a TCFC:

Total Points of Invest 97L - 34
Total Need for Issuance of a TCFA - 35-38

Highlights:

A circulation is evident on visible, shortwave infrared, microwave imagery or QuikSCAT [check]

Winds associated with system are at least 25 knots [check]

A weather station reported a pressure drop of 2 mb [check]

The estimated MSLp is less than 1008 mb [uncheck]

Westerly flow above disturbance less than 15 knots [check]

SSTs are above 26C [check]

System has persisted for 24 hrs [uncheck]

Dvorak Classification of 1.5 or greater [check]

NWP genesis considerations (NOGAPS, GFS, UKMET, ECMWF) [uncheck]

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting cchsweatherman:


Thats because I removed you as a friend on Facebook.


LOL
Member Since: Posts: Comments:
WOW... haven;t been on this site in a while... 97L does look impressive... NONE of the models think it will develop? that's strange. something tells me that will change by tomorrow...
Member Since: Posts: Comments:
Spiral bands now appear to be propogating from all quadrants of the invest judging by the most recent visible loop. Strong convective bands are developing on the NW and attempting to wrap around the center. There is also a clearly closed low. We just might TS Ana soon!
Member Since: Posts: Comments:
Quoting Weather456:
Allstar and WS,

we are in limbo with shear here. the NHC sees one solution and we see the other. I do believe 97L has what it takes to become our next depression based on what I'm seeing all day. I'm rather confused with the NHC this year since they have been inconsistent. They thought 93L would develop in the GOM due to favorable upper pattern and the opposite occur, how ironic that we a similiar situation here. They could be right, but for now it seems 97L stands more than 30% of becoming a TD.



Thank you and I do agree. I always look for your opinion, as well as Storm W's, etc. because I am pretty new to this blog.
Member Since: Posts: Comments:
In other news the remnants of Carlos looked to have triggered an invest 91C in the Central Pacific
Member Since: Posts: Comments:
Allstar and WS,

we are in limbo with shear here. the NHC sees one solution and we see the other. I do believe 97L has what it takes to become our next depression based on what I'm seeing all day. I'm rather confused with the NHC this year since they have been inconsistent. They thought 93L would develop in the GOM due to favorable upper pattern and the opposite occur, how ironic that we a similiar situation here. They could be right, but for now it seems 97L stands more than 30% of becoming a TD.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Name's Andrew (but that name is banned here...)
Member Since: Posts: Comments:
Weaker convection already re-firing.

Member Since: Posts: Comments:
Quoting GeoffreyWPB:
Wow Keeper...never saw that before...Okay, whose going to add up the points for 97?


456 already did, came to 34 points, just short of a TCFA being issued
Member Since: Posts: Comments:
877. eddye
why dude
Member Since: August 12, 2008 Posts: 0 Comments: 1272
Quoting KEEPEROFTHEGATE:
REQUIREMENTS FOR Tropical Cyclone Formation Alert

If a system gets 35 to 38 points, a TCFA may be issued depending on Dvorak trends, and if a system gets 39 points or more a TCFA should be issued.

Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities 3 points
A circulation has been evident for at least 24 hours 5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance 5 points
Any wind associated with the system is at least 20 kt 2 points
Any wind associated with the system is at least 25 kt 3 points
Any wind associated with the system is at least 30 kt 4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours 3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours 4 points
The estimated MSLP of the system is less than 1010 to 1009 mb 3 points
The estimated MSLP of the system is 1008 mb or less 4 points

500 mb height
Condition Points
There is evidence of at least an inverted trough 2 points
There is evidence of a closed circulation in the system 4 points

200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance -4 points
There is evidence of anticyclonic outflow over the centre of the disturbance 4 points
Easterly flow of at most 20 kt over the disturbance 3 points

Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher 3 points

Satellite data
Condition Points
The system has persisted for at least 24 hours 3 points
The system has persisted for at least 48 hours 4 points
The system has persisted for at least 72 hours 5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA) 3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies 5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies -2 points

Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude 3 points
The tropical system is within 72 hours of reaching a Department of Defense resource 3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other 2 points
**********************************************************


I was optimistic, and I came up with 30 points.
Member Since: Posts: Comments:
Wow Keeper...never saw that before...Okay, whose going to add up the points for 97?
Member Since: Posts: Comments:
Quoting eddye:
dude i dont see you on right now man cchsweatherman


Thats because I removed you as a friend on Facebook.
Member Since: April 14, 2007 Posts: 8 Comments: 5169
Quoting Stormchaser2007:
CMC develops two tropical storms off the East coast and bombs one out...what a surprise.

That front will be hanging around the Gulf for the next couple of days...
Member Since: Posts: Comments:
Quoting BaltOCane:


my bad. I need glasses


nah its all good, its easy to see how you got mixed up
Member Since: Posts: Comments:
Quoting weatherwatcher12:

I was talking about the NOGAPS shear forecast


NOGAPS 200 hPa Strmlns ; |850-200 Wind Shear| ; 850 (Red) and 200 (Green) Wind Barbs

Darker green is better for shear. The lightest green is 20-30kt shear, which is too high, especially for a small system.
Member Since: Posts: Comments:
868. eddye
dude i dont see you on right now man cchsweatherman
Member Since: August 12, 2008 Posts: 0 Comments: 1272
Quoting BurnedAfterPosting:


that one is Edith, that one with the loop by the Bahamas is Betsy


my bad. I need glasses
Member Since: Posts: Comments:
REQUIREMENTS FOR Tropical Cyclone Formation Alert

If a system gets 35 to 38 points, a TCFA may be issued depending on Dvorak trends, and if a system gets 39 points or more a TCFA should be issued.

Surface
Condition Points
A circulation is evident using visible satellite, shortwave infrared, microwave imagery or QuikSCAT/Windsat ambiguities 3 points
A circulation has been evident for at least 24 hours 5 points
A westerly surface- or gradient-level wind of 5 kt that is within 200 nm (370 km, 230 mi) south of the centre of the disturbance 5 points
Any wind associated with the system is at least 20 kt 2 points
Any wind associated with the system is at least 25 kt 3 points
Any wind associated with the system is at least 30 kt 4 points
A weather station within 200 nm of the system has reported had a pressure drop of 2 mb over 24 hours 3 points
A weather station within 200 nm of the system has had a pressure drop of 3 mb over 24 hours 4 points
The estimated MSLP of the system is less than 1010 to 1009 mb 3 points
The estimated MSLP of the system is 1008 mb or less 4 points

500 mb height
Condition Points
There is evidence of at least an inverted trough 2 points
There is evidence of a closed circulation in the system 4 points

200 mb height
Condition Points
Westerly flow of at least 15 kt over the disturbance -4 points
There is evidence of anticyclonic outflow over the centre of the disturbance 4 points
Easterly flow of at most 20 kt over the disturbance 3 points

Sea surface temperature
Condition Points
The sea surface temperature is 26 Celsius (78.8 Fahrenheit) or higher 3 points

Satellite data
Condition Points
The system has persisted for at least 24 hours 3 points
The system has persisted for at least 48 hours 4 points
The system has persisted for at least 72 hours 5 points
The system has a Dvorak classification of T1.0 to T1.5 from all three agencies (TAFB, SAB, AFWA) 3 points
The system has a Dvorak classification of T1.5 to T2.0 from all three agencies 5 points
The Dvorak final-T number has decreased by T0.5 to T1.0 from two or more agencies -2 points

Miscellaneous
Condition Points
The cloud system is north (or south) of 5 degrees latitude 3 points
The tropical system is within 72 hours of reaching a Department of Defense resource 3 points
The cloud system center and the satellite centre fixes for the system are within 2 degrees of each other 2 points
**********************************************************
Member Since: Posts: Comments:

Viewing: 915 - 865

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48Blog Index

Top of Page

About

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

Local Weather

Mostly Cloudy
73 °F
Mostly Cloudy