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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Quoting HurricaneSwirl:


Shear is supposed to be over 20 knots over this system for nearly the rest of its life.

And so what if i did look at a past one? Shear needed to fall earlier. And it didn't. If it doesn't fall by tonight this thing might get ripped apart.
What are you talking about ? It has many miles to transverse with plenty of time for shear to increase or decrease. And as far as its "lifetime" track, you know what that is going to be ? Please, enlighten us all, and of course, why...
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>Another thing, it's an upper level trough - that does little to effect what's happening at the sfc with 97L imo.

I'm going with the overall satellite presentation to forecast a tropical depression in 48 hours from 5:27p.m. The troughs will not be as strong as normal due to local condition changes presently occuring in adjacent areas.
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Watsoncasters?

LMAO that is awesome lol
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312. IKE
Quoting reedzone:


Hi IKE
Any rain up there? it's really hot over here


Nope...no rain...83 and partly sunny.
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311. DDR
Quoting pottery:
Hey Zoo.
No rain to talk about. Some drizzles overnight. It is a beautiful day here.
Expecting some showers later, but most of the action looks to be north of me.

Hey pottery,how are you?
yea it is.its been raining here since mid-morning.
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Blog Update
Reflector site for those at work, which includes Weather456, daily update.


AOI

AOI

AOI
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Quoting Chicklit:
KmanIslander must be out golfing.
ShortWave
Will be interested to hear what he has to say, too! What d'ya think, Pottery?
Will 97L crash into shear and just give the Cayman Islands golf courses a good drenching?



Kman is in Vancouver going on a cruise although he said he may check in from time to time, Stormno is in San Salavdar for vacation.
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It's lower to mid level. Needs to become more prominent at the surface.
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I realize that there are a lot of Watsoncasters out there but lets just relax and see how this plays out.
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Quoting BurnedAfterPosting:


lol chill out, now you are calling it RIP again? come on now



LOL! I think some people just like RIPing storms...
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Quoting IKE:


That was a 59 yr-old choke job.



It not over he has a 4 hole playoff with Cink
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Quoting IKE:


The drama on this blog.

I'm waiting on the blow-by-blow description of Sunday afternoon DMIN...the every 30 minute update of it falling apart.


Hi IKE
Any rain up there? it's really hot over here
Member Since: July 1, 2008 Posts: 13 Comments: 7423
Quoting IKE:


The drama on this blog.

I'm waiting on the blow-by-blow description of Sunday afternoon DMIN...the every 30 minute update of it falling apart.
You have just crushed their plans by telling them they have to wait for 30 minute intervals...they were so sure they could update the loops by just refreshing.
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Shear was unfavorable over Tom Watson
Member Since: May 17, 2009 Posts: 0 Comments: 559
301. IKE
Quoting hunkerdown:
The SAL was too great for him.


That was a 59 yr-old choke job.

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Quoting HurricaneSwirl:


Shear is supposed to be over 20 knots over this system for nearly the rest of its life.


You are basing that on what?
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Quoting hunkerdown:
You are looking at a tendency over the LAST 24 hours, not a FUTURE tendency/forecast map.


Shear is supposed to be over 20 knots over this system for nearly the rest of its life.

And so what if i did look at a past one? Shear needed to fall earlier. And it didn't. If it doesn't fall by tonight this thing might get ripped apart.
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Quoting hunkerdown:
Actually, isn't that the axis of the TUTT being squeezed out ?


I don't know! Thought I saw a ring of storms trying to form around the center..
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Quoting beell:


True, the trough will not have much influence at the surface. Still at a pretty low latitiude for Coriolis to be much of a factor. It is the trough currently over the CONUS banging on the western edge of the AB ridge that will start to add some weakness and induce the WNW motion in another 24-36 hrs.

Worst case scenario if you don't like landfalling storms would be a due west track under the SA upper ridge. Then another crossing of the westerlies near western Cuba and into the GOM.

Insert standard disclaimer *here* lol


Good post. Beell, I like your steering talents, but this one scares me a bit! UGH!
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting IKE:
Sorry Tom Watson...that looked like a choke on the 18th.
The SAL was too great for him.
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295. IKE
Quoting HurricaneSwirl:
shear is not falling. in fact its rising in the easter caribbean. in the central caribbean its only falling by 10 or so knots. and in the western caribbean, once again, shear is rising. 97L had so much potential :(


The drama on this blog.

I'm waiting on the blow-by-blow description of Sunday afternoon DMIN...the every 30 minute update of it falling apart.
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Yes props to reed, but there were lots of other people who said that.. reed just said it over and over and over. XD but good job, the dmin before it was ineffective because of dry air, but the most recent dmin was much more favorable and had explosive results.. just as you pointed out.
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dang Watson....play-off, sorry guys i know it's off base..but it is unreal!
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Quoting HurricaneSwirl:
shear is not falling. in fact its rising in the easter caribbean. in the central caribbean its only falling by 10 or so knots. and in the western caribbean, once again, shear is rising. 97L had so much potential :(
You are looking at a tendency over the LAST 24 hours, not a FUTURE tendency/forecast map.
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Quoting WeatherStudent:
Indeed, congrats Reed.


Thanks WeatherStudent
I just got out of church and was expecting a bigger invest by now. An orange on the TWO is very possible but I can't rule out a code red by the way it's looking.
Member Since: July 1, 2008 Posts: 13 Comments: 7423
Quoting Chicklit:

Either they're watching the Limey Open or they think shear will R.I.P. it in the Carib.

ShearTendency


WHXX01 KWBC 191217

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

ATTENTION...NATIONAL HURRICANE CENTER

1217 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 1200 UTC



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

090719 1200 090720 0000 090720 1200 090721 0000



LAT LON LAT LON LAT LON LAT LON

BAMS 12.4N 50.2W 13.0N 54.0W 13.9N 58.2W 15.3N 62.2W

BAMD 12.4N 50.2W 12.5N 52.8W 12.7N 55.1W 13.1N 57.6W

BAMM 12.4N 50.2W 12.8N 53.1W 13.3N 56.2W 14.0N 59.2W

LBAR 12.4N 50.2W 12.6N 53.7W 12.9N 57.5W 13.6N 61.3W

SHIP 20KTS 24KTS 29KTS 32KTS

DSHP 20KTS 24KTS 29KTS 32KTS



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

090721 1200 090722 1200 090723 1200 090724 1200



LAT LON LAT LON LAT LON LAT LON

BAMS 16.6N 66.7W 19.8N 74.8W 22.9N 80.3W 25.4N 82.4W

BAMD 13.4N 60.5W 14.0N 67.8W 14.5N 76.1W 14.2N 84.8W

BAMM 14.9N 62.7W 17.1N 70.5W 19.3N 78.1W 20.8N 84.1W

LBAR 14.3N 65.3W 16.1N 72.7W .0N .0W .0N .0W

SHIP 35KTS 37KTS 42KTS 53KTS

DSHP 35KTS 37KTS 42KTS 52KTS



...INITIAL CONDITIONS...

LATCUR = 12.4N LONCUR = 50.2W DIRCUR = 270DEG SPDCUR = 20KT

LATM12 = 12.3N LONM12 = 46.2W DIRM12 = 272DEG SPDM12 = 20KT

LATM24 = 12.0N LONM24 = 42.0W

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

CENPRS = 1013MB OUTPRS = 1014MB OUTRAD = 100NM SDEPTH = S

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



$$

NNNN



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Quoting HurricaneSwirl:
shear is not falling. in fact its rising in the easter caribbean. in the central caribbean its only falling by 10 or so knots. and in the western caribbean, once again, shear is rising. 97L had so much potential :(


lol chill out, now you are calling it RIP again? come on now

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Hey Zoo.
No rain to talk about. Some drizzles overnight. It is a beautiful day here.
Expecting some showers later, but most of the action looks to be north of me.
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287. IKE
Sorry Tom Watson...that looked like a choke on the 18th.
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286. JRRP
TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 PM EDT SUN JUL 19 2009


A TROPICAL WAVE IS ALONG 49W/50W SOUTH OF 17N MOVING WEST 15-20
KT. THIS WAVE COINCIDES WITH A LOW TO MIDDLE LEVEL CYCLONIC
CIRCULATION NEAR THE WAVE AXIS AT 13N51W. SCATTERED MODERATE TO
ISOLATED STRONG CONVECTION IS FROM 11N-14N BETWEEN 50W-53W.
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Satellite imagery confirms low level southwesterlies.
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284. beell
Quoting moonlightcowboy:


Nice obs, beell. Thanks. Yes, I'm not too concerned about the trough, although if 97L gets a little more organized and gains a couple of degrees in latitude from the initial coriolis, I do think it will have some effect on steering eventually - maybe perhaps a bit further north. For now, I'm speculating that it will hold to the westerly steering pattern for the most part until it becomes better organized. Another thing, it's an upper level trough - that does little to effect what's happening at the sfc with 97L imo.


True, the trough will not have much influence at the surface. Still at a pretty low latitiude for Coriolis to be much of a factor. It is the trough currently over the CONUS banging on the western edge of the AB ridge that will start to add some weakness and induce the WNW motion in another 24-36 hrs.

Worst case scenario if you don't like landfalling storms would be a due west track under the SA upper ridge. Then another crossing of the westerlies near western Cuba and into the GOM.

Insert standard disclaimer *here* lol
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Quoting JRRP:

ULL
Actually, isn't that the axis of the TUTT being squeezed out ?
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Quoting SomeRandomTexan:
Props to you REED... you called this yesterday!


Thanks, I just couldn't see how it would fizzle when it was moving into a more favorable environment with less dry air and dust. Now for the future, I dunno.. Shear looks to be a player for this. I think 97L might catch TD status before or IF it gets ripped by shear.
Member Since: July 1, 2008 Posts: 13 Comments: 7423
shear is not falling. in fact its rising in the easter caribbean. in the central caribbean its only falling by 10 or so knots. and in the western caribbean, once again, shear is rising. 97L had so much potential :(
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279. JRRP
Quoting thermoclined:
what is the spin at 27 N 63 W, just west of the ull?

ULL
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Hi Pottery - are you getting some rain out of all this?
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It's sunny and breezy outside right now in south Florida and the beach is waiting for me.See you guys tonight.Peace out.
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Quoting MrSea:
why arent the GFDL and HWRF putting out forecasts for 97L?

Either they're watching the Limey Open or they think shear will R.I.P. it in the Carib.

ShearTendency
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274. IKE
***everyone hitting refresh on the NHC home page***

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Quoting reedzone:
Hey everyone, I told you not to underestimate 97L, it looks like chances will be at medium 30-50% by the next TWO. It's looking good :)

Props to you REED... you called this yesterday!
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Quoting Chicklit:
KmanIslander must be out golfing.
ShortWave
Will be interested to hear what he has to say, too! What d'ya think, Pottery?
Will 97L crash into shear and just give the Cayman Islands golf courses a good drenching?


Hi Chicklit - Kman is on an alaskan cruise this week. He did say in his post yesterday that if the wave survived to 55 it would find the sweet spot, and could change the forecast. Looks like that is what is happening.
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Quoting MrSea:
why arent the GFDL and HWRF putting out forecasts for 97L?


Probably not till this evening if the storm stays together, which has a good chance it will.
Member Since: July 1, 2008 Posts: 13 Comments: 7423
Quoting MrSea:
why arent the GFDL and HWRF putting out forecasts for 97L?


According to 12z the GFS vortex was 0.


CIMSS shows a maxima around 40.
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269. MrSea
why arent the GFDL and HWRF putting out forecasts for 97L?
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what is the spin at 27 N 63 W, just west of the ull?
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Quoting pottery:
Hi Chicklit.
I was never too good at telling the future LOL. A lot of variables in the short/medium term.
Except, I can deffinitely predict, that when I send this post, I will have a cold beer. I am 100% sure of that.

Now THAT's perspective!
Yeah, outthere...will see, won't we?
Conditions are not favorable for another Felix, imo. Which means nothing, but if you look at the satellite I posted, there was no shear breaking that one up.
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See ya guys, BBL... Its sunday, sunny, breezy time to get out the house.
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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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