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

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

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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

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1165. CUBWF
B
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Afternoon everyone.
Now I need to go back and catch up on whats going on. I see 97L stayed yellow so those of us that chose B were wrong..lol.
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i am going to go with B for me D looks likely but i want to wait for thunderstorms to be persistent though dmax and throughout tommorow
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1162. KEEPEROFTHEGATE (Mod)
Quoting plywoodstatenative:
someone have the latest model runs that they can uplink on here?


WHXX01 KWBC 191813

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL

1813 UTC SUN JUL 19 2009



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



ATLANTIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (AL972009) 20090719 1800 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

090719 1800 090720 0600 090720 1800 090721 0600



LAT LON LAT LON LAT LON LAT LON

BAMS 12.2N 52.5W 13.0N 56.5W 14.6N 60.5W 16.0N 64.5W

BAMD 12.2N 52.5W 12.5N 54.8W 12.9N 57.2W 13.4N 59.7W

BAMM 12.2N 52.5W 12.7N 55.4W 13.5N 58.4W 14.4N 61.4W

LBAR 12.2N 52.5W 12.4N 56.0W 13.0N 59.8W 13.8N 63.7W

SHIP 25KTS 30KTS 35KTS 38KTS

DSHP 25KTS 30KTS 35KTS 38KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

090721 1800 090722 1800 090723 1800 090724 1800



LAT LON LAT LON LAT LON LAT LON

BAMS 17.8N 68.6W 21.6N 75.7W 24.9N 79.4W 27.5N 79.5W

BAMD 13.9N 62.7W 15.1N 70.0W 16.3N 77.6W 16.6N 84.7W

BAMM 15.4N 64.8W 17.9N 72.3W 20.5N 78.7W 22.1N 83.2W

LBAR 14.9N 67.6W 17.3N 74.6W .0N .0W .0N .0W

SHIP 42KTS 50KTS 56KTS 61KTS

DSHP 42KTS 50KTS 53KTS 58KTS



...INITIAL CONDITIONS...

LATCUR = 12.2N LONCUR = 52.5W DIRCUR = 270DEG SPDCUR = 21KT

LATM12 = 12.4N LONM12 = 48.2W DIRM12 = 270DEG SPDM12 = 20KT

LATM24 = 12.3N LONM24 = 44.2W

WNDCUR = 25KT RMAXWD = 40NM WNDM12 = 20KT

CENPRS = 1012MB OUTPRS = 1014MB OUTRAD = 125NM SDEPTH = M

RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM



$$

NNN

Member Since: July 15, 2006 Posts: 168 Comments: 53285
1161. Ossqss
Quoting Orcasystems:


I think we might get a TD out of it...
If you listen to some.. it should have been dead three days ago from the shear... and then again two days ago.. then again today... etc.

Its a persistent little cuss.


Seems Mother Nature finds a way when she needs to, no matter what.

L8R Happy Sunday all...
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Quoting PSLHokie:
...with eddys...

Not to be confused with Edy's

yum...
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Quoting Orcasystems:


According to TS, this thing was dead three days ago in 12-18 hours.. that would be a couple days ago.

If you want to read weather forecasts.. read 456.


I know I was joking.
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Quoting Drakoen:


There's a lot to look through. Go through the link on Tropical Cyclones.


yeah, looks like it. thanks!
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1157. beell
Still got the southern end of the wave along 72W to watch while we watch 97L. Kinda broad, but there. It is about to get out of the shear and under the ridge.
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Quoting weatherwatcher12:



he is very wrong about that

DMin, and the process of convection waning due to it, occurs between 5-10pm, so no it still has a few hours of dmin and convection does not need to build within the next 2-3 hours for it to have a shot

Dmax is not for another 8 hours or so
1155. 789
789 votes c
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MLC, someone brought up the mention of an Anti-cyclone. Any chance its around when 97L makes it into the area?
Member Since: November 15, 2005 Posts: 16 Comments: 4189
1153. Dar9895
Quoting Seflhurricane:
lets do the same thing as last nights guess game

A) 97L explodes overnight again
B) continues getting better organized and withstands the shear
C) gets torn apart by shear
D) becomes Tropical depression 2 Tomorrow

I'am agree.
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Quoting HaboobsRsweet:
its pretty close to sunset over the storm so we should see more convection in the next 2-3 hours if it has a chance
Quoting HaboobsRsweet:
its pretty close to sunset over the storm so we should see more convection in the next 2-3 hours if it has a chance


Sun has set
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TerraNova:


Afternoon, MLC!

I agree with what you said. 97L is pretty impressive as far as visible wavelenghts go, but it's lacking tall, cold convection near the center (it's had them on and off but hasn't been persistant enough to maintain them, hence the low area near what I assume to be the center), it's still obviously a wave trying to get its act together in the middle of a so-so environment but it's something to watch.


Hey, TN! Good to see you around! I think we'll see that convection build through dmax tonight. It's gotten over some warm water, should create plenty of lift I think. And, yup, while I'd rather see it dissipate, it is indeed interesting to watch. I'd like to see the windward islands prepared for this, though - rains and even low-level gale winds can still be trouble from them.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
Quoting CaneWarning:
All of this speculation would end if everyone would just go read TampaSpin's blog.


According to TS, this thing was dead three days ago in 12-18 hours.. that would be a couple days ago.

If you want to read weather forecasts.. read 456.
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I am going C
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Quoting Seflhurricane:
lets do the same thing as last nights guess game

A) 97L explodes overnight again
B) continues getting better organized and withstands the shear
C) gets torn apart by shear
D) becomes Tropical depression 2 Tomorrow


C
Member Since: March 19, 2009 Posts: 0 Comments: 1421
its pretty close to sunset over the storm so we should see more convection in the next 2-3 hours if it has a chance
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1146. Miami
I go with B... she has been persistent....
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Quoting plywoodstatenative:
someone have the latest model runs that they can uplink on here?

Member Since: May 16, 2009 Posts: 1 Comments: 1231
Really annoying with all the "I think" posts follwed by numbers... i.e. "I think the shear will be 22.75 knotts..."

The atmosphere is turbulent flow, with eddys and vorticies. Without the aid of a computer, it is impossible to mentally forcast anything other than shear is increasing (maybe significantly), or decreasing (maybe significantly).

On a positive note, I really enjoy hearing WHY people think things are going to happen. i.e. ULL interaction, trough interaction, SST influencing storms, etc. There are so many things that we can use to get informaiton from and share with others, why waste my time with Guess-Casting???

Off my soap box, and back to lurking. Otherwise great conversation...
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All of this speculation would end if everyone would just go read TampaSpin's blog.
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someone have the latest model runs that they can uplink on here?
Member Since: November 15, 2005 Posts: 16 Comments: 4189
lets do the same thing as last nights guess game

A) 97L explodes overnight again
B) continues getting better organized and withstands the shear
C) gets torn apart by shear
D) becomes Tropical depression 2 Tomorrow
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:


diurnal Min occurs during late afternoon/early evening (basically right now)

diurnal Max occurs just before sunrise


Hey BAP; thanks for correcting. I've been away from the whole blog/tropics thing since last season.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
Quoting stormsurge39:
The storm is developing right now, but if it doesnt head due west from now until it gets thru the eastern carrb,i dont know how it could stand a chance!! wind shear will tear up a major hurricane. this is still a baby!!

It's going west south west
Member Since: May 16, 2009 Posts: 1 Comments: 1231
1138. KEEPEROFTHEGATE (Mod)


latest as of 601 pm edt
Member Since: July 15, 2006 Posts: 168 Comments: 53285
1137. Drakoen
Quoting BaltOCane:


thanks


There's a lot to look through. Go through the link on Tropical Cyclones.
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Quoting Ossqss:


There are those Dilbert boxes again Orca......LoL

I see nothing in the models on the GOM trough. Considering all the discussion of close and fast developement, what are the chances of the GOM finding developement with the saging trough?


I think we might get a TD out of it...
If you listen to some.. it should have been dead three days ago from the shear... and then again two days ago.. then again today... etc.

Its a persistent little cuss.
Member Since: Posts: Comments:
Quoting moonlightcowboy:
On the contrary, since yesterday 97L has become quite persistent, getting better organized continuously. The winds of the upper level trough will have little effect at the sfc where most of 97L's orgnaization is in the present. Plus, that trough is showing signs of lifting on visibles and dissipating. At best, any upper level winds will serve to knock the tops off of a developing system, or could serve to ventilate the storm more, aiding development as it moves generally west.

Every steering layers mostly shows a westerly guidance into the Caribbean. No steering indicates, at least not any in the present, show any northward movement. And, at this point, I'm not seeing the CONUS trough digging far enough south to show a dramatic northwards tug on the developing system. That upper level steering will only come into play anyways if the storm develops further. I expect a more gradual development and a more gradual wnwest movement. Dissipation - I'm not seeing that all in the present, or in the next day or possibly two. After that, well, we'll have to see what the conditions are.


Afternoon, MLC!

I agree with what you said. 97L is pretty impressive as far as visible wavelenghts go, but it's lacking tall, cold convection near the center (it's had them on and off but hasn't been persistant enough to maintain them, hence the low area near what I assume to be the center), it's still obviously a wave trying to get its act together in the middle of a so-so environment but it's something to watch.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
Quoting Drakoen:

Tutorial


thanks
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The storm is developing right now, but if it doesnt head due west from now until it gets thru the eastern carrb,i dont know how it could stand a chance!! wind shear will tear up a major hurricane. this is still a baby!!
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If 97L develops into anything significant , I sure as hell don't like where the models are taking it, 2 practically direct over the Caymans and if you split the difference of the other models , we'll still be down the center line, lets hope this doesn't amount to much!
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i truly believe that 97L has a very good shot at becoming a TD soon as for the wind shear i have seen countless of tropical storms and TD that have withstanded 20-30 knots of windshear lets wait and see
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97L has gotten more persistent, but DMIN and DMAX still have a heavy effect on it as you can see this morning and right now. its still got a bit to go before a TD if it gets that far, but it is building a LLC looking at Drak's images, and the most recent GFS is showing lower shear than the last run so...
Member Since: July 7, 2008 Posts: 2 Comments: 3237
1128. Ossqss
Quoting Orcasystems:

AOI

AOI

AOI


There are those Dilbert boxes again Orca......LoL

I see nothing in the models on the GOM trough. Considering all the discussion of close and fast developement, what are the chances of the GOM finding developement with the saging trough?
Member Since: Posts: Comments:
Quoting TerraNova:


Basically,
Diurnal Max = convection refires (during evening/night)
Diurnal Min = cloud tops sink, convection diminishes (late morning/noon, if I remember correctly)


diurnal Min occurs during late afternoon/early evening (basically right now)

diurnal Max occurs just before sunrise
1126. Drakoen
Quoting BaltOCane:


How? What am I looking for? I'm asking as a novice...

Tutorial
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If the TUTT wasnt there I could easily see this becoming a hurricane. Although with it in its place I doubt 97L will rise above disturbance levels.
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Quoting stormwatcherCI:
Do you agree with every comment that sounds like a developing storm and disagree with every comment that sounds negative to you ?


some people do that.. earlier today when everyone was saying how good it was doing and everyone was like "it will be orange or red at 2PM" i said shear just *might* prevent development and got bashed halfway to heck..
Member Since: July 7, 2008 Posts: 2 Comments: 3237
The WRF models shear looks like it is current.If it is correct shear will not disrupt 97l
Quoting BenBIogger:


Your seeing it right now


Wow looks like the convection will go poof tonight.Lets see during DMAX if it will be able to refire convection when it encounters 20 knt shear in the morning.
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Quoting StormFreakyisher:
I know what happens during DMAX but what happens during D-MIN?


Basically,
Diurnal Max = convection refires
Diurnal Min = cloud tops sink, convection diminishes
Member Since: July 30, 2007 Posts: 76 Comments: 4063
On the contrary, since yesterday 97L has become quite persistent, getting better organized continuously. The winds of the upper level trough will have little effect at the sfc where most of 97L's orgnaization is in the present. Plus, that trough is showing signs of lifting on visibles and dissipating. At best, any upper level winds will serve to knock the tops off of a developing system, or could serve to ventilate the storm more, aiding development as it moves generally west.

Every steering layer mostly shows a westerly guidance into the Caribbean. No steering indicates, at least not any in the present, show any northward movement. And, at this point, I'm not seeing the CONUS trough digging far enough south to show a dramatic northwards tug on the developing system. That upper level steering will only come into play anyways if the storm develops further. I expect a more gradual development and a more gradual wnwest movement. Dissipation - I'm not seeing that all in the present, or in the next day or possibly two. After that, well, we'll have to see what the conditions are.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
JlPR yES is raining hard west of PR too. This is because the interaction of the famous TUTT and the wave southwest of the island.
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Quoting Drakoen:
Supports the development of a LLC:


How? What am I looking for? I'm asking as a novice...
Storms on 90 degrees around the COC?
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I am gona say it will be 5 to 15kt shear.I will take full blame if i am wrong.
Quoting wunderkidcayman:

I agree
Do you agree with every comment that sounds like a developing storm and disagree with every comment that sounds negative to you ?
Member Since: October 9, 2008 Posts: 0 Comments: 8263

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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.