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 weatherwatcher12:
Approaching DMAX


What is DMAX?
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Good night. We will see what is happening with our invest in the morning.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:

Yeah, and so does that ship report


yep.
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Quoting homelesswanderer:
Sheap Comparisons. Depending on which you choose. It may get better or worse. Lol. Didn't realize they were so different.

http://www.meteo.psu.edu/~gadomski/COMPSHEARATL_0z/comploop.html

That wind/pressure chart sre shows that pressure tanking. Kinda hard to deny that.

Yeah, and so does that ship report
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Sheap Lol. I mean shear. Comparisons. Depending on which you choose. It may get better or worse. Lol. Didn't realize they were so different.

http://www.meteo.psu.edu/~gadomski/COMPSHEARATL_0z/comploop.html

That wind/pressure chart sre shows that pressure tanking. Kinda hard to deny that.
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Approaching DMAX
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TampaSpin:
its pouring at the house

That was a pretty big shower
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Member Since: May 16, 2009 Posts: 1 Comments: 1231
its pouring at the house
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A ship just reported a pressure of 1010 millibars near the invest
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Member Since: May 16, 2009 Posts: 1 Comments: 1231
We got a buoy dropping like a rock just wnw of our invest:
Wind Direction (WDIR): ENE ( 70 deg true )
24-hour plot - Wind Speed Wind Speed (WSPD): 22.9 kts
24-hour plot - Wave Height Wave Height (WVHT): 7.9 ft
24-hour plot - Dominant Wave Period Dominant Wave Period (DPD): 8 sec
24-hour plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.88 in
24-hour plot - Pressure Tendency Pressure Tendency (PTDY): -0.04 in ( Falling )
24-hour plot - Air Temperature Air Temperature (ATMP): 80.8 F
24-hour plot - Water Temperature Water Temperature (WTMP): 81.1 F
24-hour plot - Dew Point Dew Point (DEWP): 75.7 F
24-hour plot - Heat Index Heat Index (HEAT): 86.7 F
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TheWeatherMan504:


The increase in convergence is likely diurnal.

Probably, but last time we had none so it must be improving
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:
The convergence has increased too


The increase in convergence is likely diurnal.
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The convergence has increased too
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Look the divergence flow has been cut off from the ULL
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Quoting weatherwatcher12:
New shear map. Any thoughts.


NO surprises.....you can see the shear increasing the past 24hours.....i won't change too much the next 24 either.
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Another view. On this it doesn't appear to be pulling to the north.

Link
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New shear map. Any thoughts.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
well im out guys, we'll know more of 97s future very soon no reason to jump to RIP/apoco-cane yet =] Vorticity is consolidated and I've seen waves survive worse so we'll see. Of course I've seen waves die in what seemed perfect conditions too. It remains to be seen, what we do know is that the convection tonight is of little consequence to 97's future. I could be wrong, but that's my take =]
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2144. HadesGodWyvern (Mod)
India Meteorological Department
Tropical Cyclone Bulletin Number ONE
DEPRESSION BOB03-2009
8:30 AM IST July 20 2009
=====================================

Sub: Depression over northwest Bay of Bengal

At 3:00 AM UTC, Latest satellite imageries and coastal observation indicate that a depression has formed over northwest Bay of Bengal and lays centered near 21.0N 88.5E or about 120 kms southeast of Digha, 160 kms east-southeast of Balasore, and 200 kms southwest of Khepupara.

Satellite imagery indicates gradual organization of convection during past 12 hours. The Dvorak intensity of the system is T1.5. Associated broken intense to very intense convection lies over Bay of Bengal between 18.5N and 21.5N and to the west of 89.5E. The lowest cloud top temperature due to convection is around -70C.

Maximum 3 minute sustained winds near the center is 25 knots with a central pressure of 992 hPa. The state of the sea is rough to very rough around the system's center.

Vertical wind shear of horizontal wind over the region is low to moderate (around 10-20 knots). Sea surface temperature is about 29C. The system is supported by upper level divergence and lower level convergence. Strong east-southeasterly winds prevail over the region in the upper tropospheric level. As observed at 3:00am UTC, the 24 hours pressure fall is higher in the west-northwesterly direction and is maximum (-3.6 hPa) over Digha.

Considering all the above, the system is likely to intensify further and move in a west-northwesterly direction and cross north Orissa-West Bengal coast between Balasore and Digha around 1200 PM UTC.
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a key here is to follow the shape of convection .. it's following the divergence as it fans out forming a left facing "V" shape.
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I think I see what could be an anti-cyclone forming in the central Caribbean
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:

Even if the convection is just ULL there is still a high 850mb vorticity associated with it.


correct, and that vorticity is what will be watched in the carribean should it be maintained to any extent.
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Quoting weatherwatcher12:

Even if the convection is just ULL there is still a high 850mb vorticity associated with it.

So if it can detach itself from the divergence and fire it's own convection it has a fair chance.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting SouthALWX:
Have to disagree, convergence may be increasing but if you look at the divergent upper air pattern it's clear to see the culprit is the ULL. Reminds of a month or so ago when divergent upper flow created a "blob" that was talked about on here for two nights ... Once the divergence shut down so did the blob ... Nothing to really look at now imo until a few days out when 97 emerges (if) in the western to central carribean.

Even if the convection is just ULL there is still a high 850mb vorticity associated with it.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting SouthALWX:
Have to disagree, convergence may be increasing but if you look at the divergent upper air pattern it's clear to see the culprit is the ULL. Reminds of a month or so ago when divergent upper flow created a "blob" that was talked about on here for two nights ... Once the divergence shut down so did the blob ... Nothing to really look at now imo until a few days out when 97 emerges (if) in the western to central carribean.


Dido.....well said!
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Agree with TS on this, though dmax will play a role, this is a case of divergence.
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Have to disagree, convergence may be increasing but if you look at the divergent upper air pattern it's clear to see the culprit is the ULL. Reminds of a month or so ago when divergent upper flow created a "blob" that was talked about on here for two nights ... Once the divergence shut down so did the blob .I think it was over haiti for a few days you guys may remember I don't remember who but there was a detailed explanation concerning the divergent factors given that I found to be spot on.. Nothing to really look at now imo until a few days out when 97 emerges (if) in the western to central carribean.
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Yeah it does have to get through the SAL. I don't know if either of these will survive. But if this is any indication of what the actual CV season will be like I think it may be a lot busier than people think. This is my first season tracking the storms. But the SOI looks like its not doing what was expected of it either.
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Quoting weatherwatcher12:

That's the whole point of DMAX. To flare up and there is also improved convergence


The flare up is from the ULL causing uplift...
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Quoting SouthALWX:
looks to me like a big part of the convection flare up is more from DMAX and divergence created by the ULL that anything else.

That's the whole point of DMAX. To flare up and there is also improved convergence. It's taking advantage of DMAX.
Member Since: May 16, 2009 Posts: 1 Comments: 1231
looks to me like a big part of the convection flare up is more from DMAX and divergence created by the ULL that anything else.
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Has some SAL to get through
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting homelesswanderer:
The other little guy at 30W flaring up pretty good too.
Quoting FloridaTigers:
Approaching Dmax.

Yes to both of these
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The other little guy at 30W flaring up pretty good too.
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Approaching Dmax.
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Looks to be trying to fire some heavy convection
Member Since: May 16, 2009 Posts: 1 Comments: 1231


Member Since: May 16, 2009 Posts: 1 Comments: 1231
Couldnt sleep and finished my book. :( The CMC takes this smack into central Louisiana. Yea I know, I know. IF it survives, too early, etc. Just found that a little too close for comfort.
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Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TampaSpin:


Cybr know you for a long time......if i came across that to everyone i apologize...it was only intended to just a hand full..


I know man, its not your forecasting though thats off (pretty darn accurate) its the little end comments that tend to well.. rall up the blog.
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The ULL to the North is causing alot of the Shear.....it too is moving nearly due West and might start moving more WSW......Shear won't be relaxing anytime in the next couple of days.
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the shear doesnt look as bad
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Buoy to the west also reporting falling pressure:
Wind Direction (WDIR): E ( 80 deg true )
24-hour plot - Wind Speed Wind Speed (WSPD): 22.0 kts
24-hour plot - Wave Height Wave Height (WVHT): 7.2 ft
24-hour plot - Dominant Wave Period Dominant Wave Period (DPD): 8 sec
24-hour plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.90 in
24-hour plot - Pressure Tendency Pressure Tendency (PTDY): -0.05 in ( Falling )
24-hour plot - Air Temperature Air Temperature (ATMP): 81.7 F
24-hour plot - Water Temperature Water Temperature (WTMP): 81.5 F
24-hour plot - Dew Point Dew Point (DEWP): 75.7 F
24-hour plot - Heat Index Heat Index (HEAT): 88.5 F
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Pressure dropping at a buoy just east of the invest:
Wind Direction (WDIR): E ( 80 deg true )
5-day plot - Wind Speed Wind Speed (WSPD): 19.4 kts
5-day plot - Wind Gust Wind Gust (GST): 23.3 kts
5-day plot - Wave Height Wave Height (WVHT): 9.2 ft
5-day plot - Dominant Wave Period Dominant Wave Period (DPD): 8 sec
5-day plot - Average Period Average Period (APD): 5.8 sec
5-day plot - Atmospheric Pressure Atmospheric Pressure (PRES): 29.91 in
5-day plot - Pressure Tendency Pressure Tendency (PTDY): -0.05 in ( Falling )
5-day plot - Air Temperature Air Temperature (ATMP): 81.3 °F
5-day plot - Water Temperature Water Temperature (WTMP): 81.9 °F
5-day plot - Dew Point Dew Point (DEWP): 76.8 °F
5-day plot - Heat Index Heat Index (HEAT): 88.5 °F
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Funkadelic:


You do have to admit pressure is falling and getting convection again... Maybe 97l won't be destroyed after all


10% chance maybe....I don't see it making it.
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Quoting Relix:
97L is like the brave little toaster!! Haha, holding out against shear. Is it me or is there more of a noticeable WNW component right now, or is it the mess of convection messing with my eyes?

I think it's an illusion from the upper level shear blowing the tops off 97L. I believe it's still holding basically true to the westerly steering patterns. And, unless mine are deceiving me, there may actually be a small swesterly movement.
Member Since: July 9, 2006 Posts: 184 Comments: 29610
Quoting Relix:
97L is like the brave little toaster!! Haha, holding out against shear. Is it me or is there more of a noticeable WNW component right now, or is it the mess of convection messing with my eyes?

It could be the convection expanding
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Pressure (MSLP): 1011 mb (29.85 inHg | 1011 hPa)
Sustained wind speed (1 min. avg.): 25 knots (29 mph | 13 m/s)
Member Since: May 16, 2009 Posts: 1 Comments: 1231

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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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