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: 1415 - 1365

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

1415. Patrap
Member Since: Posts: Comments:
Quoting moonlightcowboy:


I'd prefer that you were correct, but I think you're missing this one, Adrian, and being overly conservative as usual.

97L is in an area of little or no inhibiting shear in the present, or near present, for miles yet. It is better organized, imagery suggests it is trying to form an llc. Certainly, it has a good strong, mid-level circ, but convection was diminished through dmin as any system would respond usually. Now, when it has the greater opportunity to create more t'storm activity with a greater chance of lift between the differences in sfc and atmospheric temps, you want to assume that it won't increase convection. I don't understand that, because it should.


Agreed.
Member Since: Posts: Comments:
1413. KEEPEROFTHEGATE (Mod)
Quoting RufusBaker:
POOF
in your picture it looks like you have a small brain that must be the reason for your nonsense all the time
Member Since: Posts: Comments:
Quoting hurricane23:


What? Thought it was depression already lol.


Now this is where your tone starts to seem condescending
1410. IKE
I'll say A with the NHC answer.

Member Since: Posts: Comments:
1409. IKE
Quoting weathersp:
Start your F5 engines on the NHC site...


They are.

I see everyone is still in place arguing over 97L.

I'm on the right blog.
Member Since: Posts: Comments:
Quoting RufusBaker:
POOF


What? Thought it was depression already lol.
Member Since: May 14, 2006 Posts: 8 Comments: 13636
Quoting hurricane23:


You'll be looking at a naked swirl soon lol.No suprise there with the GFDL if you ask me.


I'd prefer that you were correct, but I think you're missing this one, Adrian, and being overly conservative as usual.

97L is in an area of little or no inhibiting shear in the present, or near present, for miles yet. It is better organized, imagery suggests it is trying to form an llc. Certainly, it has a good strong, mid-level circ, but convection was diminished through dmin as any system would respond usually. Now, when it has the greater opportunity to create more t'storm activity with a greater chance of lift between the differences in sfc and atmospheric temps, you want to assume that it won't increase convection. I don't understand that, because it should.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
000
AXNT20 KNHC 192334
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT SUN JUL 19 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY
THROUGH 2245 UTC.

...TROPICAL WAVES...
A TROPICAL WAVE IS ALONG 41W/42W S OF 19N MOVG W NEAR 20 KT.
THIS WAVE COINCIDES WITH A DEEP LAYER MOISTURE MAXIMUM OBSERVED
IN TOTAL PRECIPITABLE WATER IMAGERY. THIS WAVE IS JUST W OF A
DRY SAHARAN AIR LAYER. DUE TO THE PRESENCE OF THIS DRY AIR...NO
DEEP CONVECTION IS CURRENTLY ASSOCIATED WITH THE WAVE.

A TROPICAL WAVE IS ALONG 52W S OF 18N MOVG W NEAR 15 KT. THIS
WAVE COINCIDES WITH A LOW TO MIDDLE LEVEL CYCLONIC CIRCULATION
NEAR THE WAVE AXIS AT 13N. SCATTERED MODERATE CONVECTION IS FROM
12N-15N BETWEEN 51W-54W.

A HIGH AMPLITUDE TROPICAL WAVE IS ALONG 71W S OF 26N MOVG W
20-25 KT. THIS WAVE COINCIDES WITH A HIGH AMPLITUDE MOISTURE
MAXIMUM OBSERVED ON TOTAL PRECIPITABLE WATER IMAGERY. AN
INVERTED-V PATTERN OF LOW CLOUDS IS ALSO EVIDENT ON VISIBLE
SATELLITE IMAGERY. SCATTERED MODERATE/ISOLATED STRONG CONVECTION
IS FROM 16N-20N BETWEEN 69W-72W INCLUDING PORTIONS OF CUBA. THIS
WAVE MAY FRACTURE OVER THE NEXT DAY WITH THE N PORTION OF THE
WAVE FORMING A TROUGH THAT WILL CONTINUE TO THE NW...WHILE THE S
PORTION OF THE WAVE CONTINUES TO PROPAGATE WWD.

...THE ITCZ...
ITCZ AXIS IS CENTERED ALONG 12N15W 7N27W 10N40W 10N51W 9N62W.
SCATTERED MODERATE CONVECTION IS FROM 9N-13N BETWEEN 13W-17W. A
CLUSTER OF NUMEROUS MODERATE/SCATTERED STRONG CONVECTION IS FROM
5N-9N BETWEEN 26W-29W. SCATTERED MODERATE CONVECTION IS FROM
7N-14N BETWEEN 60W-64W.

...DISCUSSION...

THE GULF OF MEXICO...
A STATIONARY FRONT IS OVER THE NRN GULF OF MEXICO ALONG 31N81W
28N88W 29N96W. AN UPPER LEVEL TROUGH EXTENDING DOWN THE ERN
CONUS INTO THE GULF TO NEAR 26N90W SUPPORTS THE FRONT. SURFACE
CONVERGENCE AHEAD OF THE FRONT ALONG WITH UPPER LEVEL DIFFLUENCE
ARE SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS FROM 24N-29N E OF
96W. THE REMAINDER OF THE GULF IS UNDER A BROAD SURFACE RIDGE
ANCHORED BY A 1020 MB SURFACE HIGH NEAR 26N87W BRINGING
GENERALLY FAIR WEATHER S OF 24N. A MID-LEVEL DRY SAHARAN AIR
LAYER IS ACROSS THE SRN GULF OF MEXICO SUPPORTING THE NOTED FAIR
WEATHER. LIGHT ANTICYCLONIC FLOW IS AROUND THE SURFACE RIDGE
WITH E-SE WINDS UP TO 15 KT PRESENT ACROSS THE SRN GULF...EXCEPT
FOR A SMALL PORTION OF NE WINDS UP TO 20 KT NEAR THE YUCATAN
PENINSULA COAST. EXPECT THE FRONT TO STALL TONIGHT AND BECOME
DIFFUSE TOMORROW.

THE CARIBBEAN SEA...
FAIR WEATHER IS NOTED IN THE FAR NW PORTION OF THE CARIBBEAN AS
IT IS UNDER THE INFLUENCE OF A MID-LEVEL DRY SAHARAN AIR LAYER.
HOWEVER...ATMOSPHERIC INSTABILITY IS CAUSING A FEW ISOLATED
SHOWERS TO FLARE UP OVER CUBA AND THE YUCATAN PENINSULA. AN
UPPER LEVEL RIDGE DOMINATES THE MAJORITY OF THE CARIBBEAN
CENTERED NEAR 14N75W. UPPER LEVEL DIFFLUENCE AND THE PROXIMITY
OF THE E PACIFIC ITCZ ARE SUPPORTING SCATTERED
SHOWERS/THUNDERSTORMS OVER CENTRAL AMERICA S OF 14N W OF 80W
INCLUDING PORTIONS OF NICARAGUA...COSTA RICA...AND PANAMA.
SURFACE CONVERGENCE AROUND A 1008 MB SURFACE LOW OVER COLUMBIA
NEAR 8N76W IS SUPPORTING SCATTERED SHOWER/THUNDERSTORMS S OF 10N
BETWEEN 75W-78W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER LEVEL
RIDGE OVER THE CARIBBEAN AND AN UPPER LEVEL LOW IN THE ATLC NEAR
27N55W IS SUPPORTING SCATTERED SHOWERS/THUNDERSTORMS OVER THE
ERN CARIBBEAN N OF 14N BETWEEN 63W-69W. THIS SHOWER ACTIVITY IS
PROBABLY BEING ENHANCED BY THE TROPICAL WAVE ALONG 71W.
SCATTERED SHOWERS/THUNDERSTORMS ARE ALSO AFFECTING THE SRN
LESSER ANTILLES S OF 14N W OF 62W DUE TO UPPER LEVEL DIFFLUENCE
AND THE PROXIMITY OF THE ATLC ITCZ. EXPECT A SECOND TROPICAL
WAVE TO REACH THE ERN CARIBBEAN EARLY TUE.

THE ATLANTIC OCEAN...
SCATTERED SHOWERS/THUNDERSTORMS ARE ACROSS S FLORIDA ENTERING
THE ATLC AND APPROACHING THE BAHAMAS FROM 25N-29N W OF 79W. THIS
SHOWER ACTIVITY IS SUPPORTED BY A SMALL UPPER LEVEL LOW OVER THE
BAHAMAS NEAR 25N77W. UPPER LEVEL DIFFLUENCE BETWEEN THE UPPER
LEVEL TROUGH OVER THE ERN CONUS AND AN UPPER LEVEL RIDGE
CENTERED AROUND 39N54W IS SUPPORTING ISOLATED
SHOWERS/THUNDERSTORMS ACROSS THE SW NORTH ATLC N OF 24N BETWEEN
68W-75W. THE REMAINDER OF THE ATLC IS DOMINATED BY A BROAD RIDGE
ANCHORED BY A 1029 MB SURFACE HIGH N OF THE DISCUSSION AREA NEAR
35N46W BRINGING GENERALLY FAIR WEATHER ACROSS THE MAJORITY OF
THE CENTRAL AND ERN ATLC. HOWEVER...A LINE OF SHOWERS ARE FROM
17N58W TO 24N50W DUE TO UPPER LEVEL DIFFLUENCE BETWEEN AN UPPER
LEVEL HIGH NEAR 15N50W AND AN UPPER LEVEL LOW NEAR 27N55W.

$$
WALTON

Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Nolehead:
do any of the models suggest anything developing from this frontal boundary that's draped in the GOM right now?? weird front for July...very hot waters right now..things might start popping up before we know it...

Wondered that myself. Have to watch the shear line. The clouds down here have been weird lately. Still having a hard time setting up a solid sea breeze which is odd for this time of year.
Member Since: Posts: Comments:
WS we said shear was affecting it, doesnt meant to forget about it and look at a wave 2000 miles to its east that will take days and days to develop

Start your F5 engines on the NHC site...
Member Since: January 14, 2007 Posts: 17 Comments: 4140
POOF
Member Since: Posts: Comments:
no recon scheduled yet, if they thought this had a chance they would be getting ready to go.
Member Since: Posts: Comments:
Quoting WaterWitch11:


don't mean to be a pain in the butt. could you provide the link?

Sure. No problem.
Link
Member Since: May 16, 2009 Posts: 1 Comments: 1231
do any of the models suggest anything developing from this frontal boundary that's draped in the GOM right now?? weird front for July...very hot waters right now..things might start popping up before we know it...
Member Since: Posts: Comments:
Quoting Patrap:
Early-cycle track guidance AL97



access denied on this link baby doll
Member Since: Posts: Comments:
WISHYGUESTCASTING!
Member Since: Posts: Comments:
As a famous news anchor would say "And thats the way it is."

Thank you Walter Kronkite.
Member Since: Posts: Comments:
Quoting weatherwatcher12:

The Satellite Services decision's. Tropical Formation branch


don't mean to be a pain in the butt. could you provide the link?
Member Since: Posts: Comments:
1392. Drakoen
Member Since: October 28, 2006 Posts: 57 Comments: 29925
Quoting ArmyWifeInGa:
I just have 1 question for the moment. Didn't Faye do the same thing? People thought the same thing about Faye, saying she was RIP and she wasn't.

Fay was a big rain making and not much else. 97L will bring lots of rain to someone. It wont just disappear off the face of the map but it wont go tropical. fay was impressive though, if it was 2 degrees south of the panhandle, the Gulf Coast would have gotten hammered instead of just some showers. Florida is probably still dumping water back out to sea after that one.
Member Since: Posts: Comments:
Quoting moonlightcowboy:
I don't think anyone is saying that we're going to have Ana in the next 12-24 hours, but 97L isn't going away anytime soon either. The little shear in the immediate area to speak of won't kill it. The approaching winds from the trough won't be as prominent either if the trough continues to lift out. The westerly flow is still very visible and dominant which is where 97L is and trying to get a good llc going. The easterly flow from the trough is not as strong as it was, dissipating and is lifting - it won't kill it. 97L, if it stays on a westerly course, as all steering suggests, it'll come in under most of the resistance from the trough anyway. It may not get to TD status until it gets past the islands, but writing it off - at this time isn't going to happen.
DEAD BLOB OF CLOUDS!
Member Since: Posts: Comments:
Quoting hurricane23:
Thats the main issue many seem not to understand without a well defind surface circulation theres nothing to support deep thunderstorm activity.


Hey H23! You're right. It's still a wave with a very ill defined low level center (assuming there is one, we don't have a QS pass yet), and tropical waves by nature are unable to sustain convection by themselves.
Member Since: Posts: Comments:
Quoting moonlightcowboy:

Dismal, where? Further west 200-300 miles or better?


You'll be looking at a naked swirl soon lol.No suprise there with the GFDL if you ask me.
Member Since: May 14, 2006 Posts: 8 Comments: 13636
1387. Patrap

RAMMB AL972009 - INVEST
Member Since: Posts: Comments:
What's also interesting is that the GFDL, in addition to the GFS, CMC, and ECMWF, attempt to spin something up off the US SE coast and have it moving N or NE. It's in the medium range and the global models, especially the ECMWF and CMC, have been showing something trying to break off a frontal boundary towards the end of the week. As far as I can tell it's not directly associated with 97L.
Member Since: Posts: Comments:
I just have 1 question for the moment. Didn't Faye do the same thing? People thought the same thing about Faye, saying she was RIP and she wasn't.
Member Since: Posts: Comments:
Quoting hurricane23:


Not when upper environment is dismal.

Dismal, where? Further west 200-300 miles or better?
Member Since: July 9, 2006 Posts: 184 Comments: 29594
WS you took a complete 180 in the last 5 minutes lol
Quoting nrtiwlnvragn:


One source, CIMSS. Description

These are based on satellite derived winds, using the microwave sounder on the GOES satellite.

Thanks for the info. i appreciate it.
Member Since: Posts: Comments:
Quoting Mikla:
Pic of the storm that just rolled in (Merritt Island, FL)...


Thats a beautiful wall cloud there.
Member Since: Posts: Comments:
Ya, been watching it creep onto my screen. That one looks very far south...but its embedded a decent moisture surge it looks like. Maybe something to watch over the coming days.
Member Since: Posts: Comments:
ATTENTION...NATIONAL HURRICANE CENTER

NCEP COUPLED HWRF HURRICANE MODEL FORECAST MADE FOR

TROPICAL DEPRESSION INVEST 97L

INITIAL TIME 18Z JUL 19

FORECAST POSITIONS (FROM STATS.SHORT FILE...)

HOUR LATITUDE LONGITUDE MIN PRESS (hPa) MAX SFC WIND (KTS)

HOUR: 0.0 LONG: -52.50 LAT: 12.00 MIN PRESS (hPa): 1012.00 MAX SURF WIND (KNOTS): 31.00
HOUR: 6.0 LONG: -54.20 LAT: 12.30 MIN PRESS (hPa): 1008.00 MAX SURF WIND (KNOTS): 35.00
HOUR: 12.0 LONG: -56.00 LAT: 12.40 MIN PRESS (hPa): 1007.00 MAX SURF WIND (KNOTS): 35.00
HOUR: 18.0 LONG: -58.00 LAT: 13.00 MIN PRESS (hPa): 1008.00 MAX SURF WIND (KNOTS): 36.00
HOUR: 24.0 LONG: -59.90 LAT: 13.50 MIN PRESS (hPa): 1008.00 MAX SURF WIND (KNOTS): 33.00
HOUR: 30.0 LONG: -61.70 LAT: 14.20 MIN PRESS (hPa): 1010.00 MAX SURF WIND (KNOTS): 34.00
HOUR: 36.0 LONG: -63.40 LAT: 14.90 MIN PRESS (hPa): 1009.00 MAX SURF WIND (KNOTS): 32.00
HOUR: 42.0 LONG: -64.90 LAT: 15.60 MIN PRESS (hPa): 1011.00 MAX SURF WIND (KNOTS): 26.00
HOUR: 48.0 LONG: -66.30 LAT: 16.40 MIN PRESS (hPa): 1010.00 MAX SURF WIND (KNOTS): 28.00
STORM DISSIPATED AT 48.0 HOURS AT ABOVE POSITION.
Member Since: September 23, 2005 Posts: 14 Comments: 10909
Quoting reedzone:
The HWRF and GFDL dissipate the storm less then 1 day... hmmm.

The global dynamic models are basically useless, especially the GFDL, when it comes to forecasting cyclogenesis.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
1377. Patrap
Floater 1 - Water Vapor Loop

Member Since: Posts: Comments:
Quoting missmaxi:
Does anyone think that this might come towards Miami?


I think south florida has a bigger risk right now with the convection overhead!
Member Since: Posts: Comments:
Quoting moonlightcowboy:

Good point, but it's in the warmest water its found yet, best organized it been and should benefit from the greatest lift from the difference between sfc and atmospheric temps through dmax. That should aid t'storm activity and lower pressure as well.


Not when upper environment is dismal.
Member Since: May 14, 2006 Posts: 8 Comments: 13636
Quoting KoritheMan:


Want me to get on AIM now, then?


Yep
Member Since: Posts: Comments:
Quoting hurricane23:
Thats the main issue many seem not to understand without a well defind surface circulation theres nothing to support deep thunderstorm activity.

Good point, but it's in the warmest water its found yet, best organized it been and should benefit from the greatest lift from the difference between sfc and atmospheric temps through dmax. That should aid t'storm activity and lower pressure as well.
Member Since: July 9, 2006 Posts: 184 Comments: 29594
Quoting FloridaTigers:


Yep


Want me to get on AIM now, then?
Member Since: Posts: Comments:
Quoting HaboobsRsweet:
Can someone tell me what the source is of these magically shear maps? Are they just model data or are they based off of soundings lauched over water? If thye are just model data or estimated shear maps then why are we all so quick to think shear is def going to decrease?


One source, CIMSS. Description

These are based on satellite derived winds, using the microwave sounder on the GOES satellite.
Member Since: September 23, 2005 Posts: 14 Comments: 10909
Quoting KoritheMan:


Are you Zappa?


Yep
Member Since: Posts: Comments:
Quoting BurnedAfterPosting:


we dont even know if it will survive the night

It will survive barely tonight and go away tomorrow for sure.
Member Since: Posts: Comments:
1367. Mikla
Pic of the storm that just rolled in (Merritt Island, FL)...
Member Since: Posts: Comments:
Quoting cjswilmingtoneye:
Here's the deal. No matter what someone says on this blog, or what the computer models say; Mother nature will always decide what is going to happen. Everyone needs to just relax a little bit, and OBSERVE. How many times in the last hour or two has someone said that the invest is currently in the diurnal minimum? So isn't it expected that the system not look as good as it did several hours ago? Maybe I'm a little confused. I don't think that the shear has such swift swings from one hour to the next. It looks to me like a normal diurnal pattern is what is unfolding with 97 L right now. This will happen EVERY DAY with ANY tropical system. So why should someone say at one part of the day, "oh... this system looks great and is going to survivie", and then a few hours later, "oh... this system looks ragged and soon will go POOF"? why is that?


Thank you!!
Member Since: Posts: Comments:
Quoting KYhomeboy:
Convection beginning to refire near the center. I don't understand why people jump on the "it's dead" bandwagon the second heavy convection subsides. Developing systems typically do through day to day phases/ pulses like this. The shear will be this invests biggest enemy for now.


I have seen systems have the top's sheared completely off, leaving only a surface circulation. This can then fire up again when shear subsides.

Member Since: Posts: Comments:

Viewing: 1415 - 1365

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

Overcast
60 °F
Overcast