New African disturbance 96L likely to develop

By: Dr. Jeff Masters , 2:55 PM GMT on September 07, 2009

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A tropical wave (96L) that emerged off the coast of Africa yesterday has organized rather quickly, and will likely become a tropical depression by Tuesday night. Satellite imagery from the European satellite shows a well-organized circulation, but not enough heavy thunderstorm activity near the center of circulation to be considered a tropical depression. The storm is far enough south that the dry air of the Saharan Air Layer is not a major impediment to development. Wind shear is moderate, 10 - 15 knots, and ocean temperatures are 1 - 2°C above the threshold needed for tropical cyclone formation.


Figure 1. Morning satellite image of 96L, off the coast of Africa. The remains of disturbance 95L, which are under 30 - 40 knots of wind shear, can be seen at upper left.

The forecast for 96L
Most of the models develop 96L, and the chances are that this disturbance will become Tropical Storm Fred later this week. The system will initially move west-northwest, but by Thursday, a strong trough of low pressure passing to 96L's north will pull the storm to the northwest, and may be capable of fully recurving the storm to the northeast. However, most of the models foresee that 96L will not move far enough north for this to happen, and that the storm will have to wait for the next trough of low pressure. With the steering pattern for this year continuing to feature plenty of deep troughs of low pressure moving off the U.S. East Coast, the odds of 96L making it all the way across the Atlantic to threaten land areas appear low. Still, much that is unexpected can and does happen in the world of tropical meteorology, and 96L bears watching.

North Carolina low
An area of concentrated thunderstorms has developed off the North Carolina coast in association with the remains of an old cold front. This system is under about 20 - 30 knots of shear, and is not tropical. However, it will bring heavy rain to eastern North Carolina today and Tuesday, as the storm slides north-northeastward along the coast.

I'll have an update Tuesday.

Jeff Masters

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885. TheDawnAwakening
10:26 PM GMT on September 07, 2009
Wow TD7 looks like TS Fred now. I think the strongest systems go from invest to TD to TS. I mean look at Danny and Erika this year. They went from Invest to TS but did not do much afterwards. If you look at the archives of the category five hurricanes for the most part they all started slowly and then went through rapid intensification.
Member Since: October 21, 2008 Posts: 245 Comments: 3898
884. laflastormtracker
10:25 PM GMT on September 07, 2009
Cool - me too! I'll have to watch Rob at 6 - missed the 5.

Def he is fairly accurate and is a very smart man. He was discussing potential for development and looked serious this evening. I was thinking uh-oh, similar expressions I remember from last summer:(. i want BLUE skies ahead:)
883. Patrap
10:25 PM GMT on September 07, 2009
NEXRAD Radar
Wilmington, Storm Relative Mean Radial Velocity 1.45 Degree Elevation Range 124 NMI

Member Since: July 3, 2005 Posts: 424 Comments: 128273
882. Cavin Rawlins
10:24 PM GMT on September 07, 2009
Quoting JLPR:


definitely
looking better than a typical depression


I posted a comment earlier today for you.

The 00Z GFS had a hurricane hitting the Leeward Islands on the 20 September 2009, around the exact time as Georges. Coincidently, September 2009 and 1998 has the same calender dates and days; as Georges hit Saint Kitts during the night of Sunday 20 September 1998.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
881. Patrap
10:23 PM GMT on September 07, 2009
Member Since: July 3, 2005 Posts: 424 Comments: 128273
880. Cavin Rawlins
10:22 PM GMT on September 07, 2009
Quoting centex:
This says it all, like Erika they said same thing but everyone was so sure of most likly track. THE HIGHLY UNCERTAIN INITIAL MOTION. Take it to mean no one knows and watch.


dude, the NHC said the initial motion is uncertain not the forecast motion

THE HIGHLY UNCERTAIN INITIAL MOTION ESTIMATE IS 280/14. THE
DEPRESSION IS CURRENTLY LOCATED SOUTH OF A NARROW EAST-TO-WEST
ORIENTED RIDGE. THE RIDGE IS FORECAST TO WEAKEN AS A MID-LEVEL
TROUGH MOVES INTO THE EASTERN ATLANTIC AND AN UPPER-LEVEL LOW
CUTS-OFF NEAR 27N40W DURING THE NEXT DAY OR TWO. THIS IS EXPECTED
TO ALLOW THE CYCLONE TO TURN NORTHWESTWARD IN A COUPLE OF DAYS...
FOLLOWED BY A TURN TO THE NORTH THEREAFTER. THE TRACK GUIDANCE IS IN
REASONABLY GOOD AGREEMENT ON THIS SOLUTION
...AND THE OFFICIAL
FORECAST IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
879. hurricanehanna
10:21 PM GMT on September 07, 2009
Quoting laflastormtracker:
Lafayette was watching Perillo. Hes forecasting 60 percent both Sat and Sun due to disturbance in Gulf moving north.
Quoting laflastormtracker:
Lafayette was watching Perillo. Hes forecasting 60 percent both Sat and Sun due to disturbance in Gulf moving north.


Cool - me too! I'll have to watch Rob at 6 - missed the 5.
Member Since: September 5, 2007 Posts: 0 Comments: 3487
878. JLPR
10:20 PM GMT on September 07, 2009
Quoting Weather456:
I'm thinking Fred at 11PM or 5AM





definitely
looking better than a typical depression
Member Since: September 4, 2007 Posts: 36 Comments: 5223
877. Cavin Rawlins
10:19 PM GMT on September 07, 2009
I'm thinking Fred at 11PM or 5AM



Member Since: July 24, 2005 Posts: 407 Comments: 19076
876. laflastormtracker
10:18 PM GMT on September 07, 2009
Lafayette was watching Perillo. Hes forecasting 60 percent both Sat and Sun due to disturbance in Gulf moving north.
875. centex
10:18 PM GMT on September 07, 2009
This says it all, like Erika they said same thing but everyone was so sure of most likly track. THE HIGHLY UNCERTAIN INITIAL MOTION. Take it to mean no one knows and watch.
Member Since: August 10, 2007 Posts: 0 Comments: 3233
874. Cavin Rawlins
10:17 PM GMT on September 07, 2009
Member Since: July 24, 2005 Posts: 407 Comments: 19076
873. Cavin Rawlins
10:15 PM GMT on September 07, 2009
Quoting centex:
Please explain why east of 35W looks like N track? That is the part I have a problem with.


a weakness

NHC

THE HIGHLY UNCERTAIN INITIAL MOTION ESTIMATE IS 280/14. THE
DEPRESSION IS CURRENTLY LOCATED SOUTH OF A NARROW EAST-TO-WEST
ORIENTED RIDGE. THE RIDGE IS FORECAST TO WEAKEN AS A MID-LEVEL
TROUGH MOVES INTO THE EASTERN ATLANTIC AND AN UPPER-LEVEL LOW
CUTS-OFF NEAR 27N40W DURING THE NEXT DAY OR TWO. THIS IS EXPECTED
TO ALLOW THE CYCLONE TO TURN NORTHWESTWARD IN A COUPLE OF DAYS...
FOLLOWED BY A TURN TO THE NORTH THEREAFTER. THE TRACK GUIDANCE IS IN
REASONABLY GOOD AGREEMENT ON THIS SOLUTION...AND THE OFFICIAL
FORECAST IS NEAR THE MIDDLE OF THE GUIDANCE ENVELOPE.


My Blog

Tropical Invest 96L is moving off towards the west under the influence of the Azores side of the subtropical ridge and this motion is expected for at least the next 3 days. Through day 4, a deep frontal trough digs across the Atlantic and breaks down the ridge enough to create a weakness which pulls 96L more towards the northwest and then north-northwest.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
872. hurricanehanna
10:15 PM GMT on September 07, 2009
Quoting laflastormtracker:
Local Chief Met is billboarding increased rain chances nxt wkend. Noooooooo!

Where are you located?
Member Since: September 5, 2007 Posts: 0 Comments: 3487
870. Cavin Rawlins
10:10 PM GMT on September 07, 2009
Quoting hurricaneseason2006:
Weather456,

In that image you posted with Invest 95L and TD 7, was that west-northwest turn by 95L forecasted, I believe you did but was it for sure?


yes, I think you meant yesterday's update

As the weakness closes, 95L hits the high-pressure bridge and begin to move more towards the west-northwest and this is already indicated on the last few frames satellite imagery.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
869. centex
10:10 PM GMT on September 07, 2009
Quoting Weather456:



there are several things that dont add up

1. Though TD 7 is further south than 95L, becuz its following the same direction as 95L, the difference is minute

2. The trough is deep enough, its affecting the shallow layer flow, that is why 95L was able to pull north even through it did not deepen.

3. Troughs 1 and 2 are coming from the Eastern Canada near the Icelandic low, not the East Coast of the USA. Trough 1 is currently in the mid-Atlantic per satellite imagery.

4. I do agree than TD 7 will shift back west but that is due to alternating trough and ridges through the forecast period as was forecast for 95L. As to whether it continues west and miss the troughs or re-curve is a 30-70 chance to me








Please explain why east of 35W looks like N track? That is the part I have a problem with.
Member Since: August 10, 2007 Posts: 0 Comments: 3233
867. Cavin Rawlins
10:04 PM GMT on September 07, 2009
Quoting TheDawnAwakening:
Where do we get those quickly update satellite images of the E Atlantic?


LINK
Member Since: July 24, 2005 Posts: 407 Comments: 19076
866. Cavin Rawlins
10:03 PM GMT on September 07, 2009
Quoting TheDawnAwakening:
TD7 is much lower in latitude then 95L ever was in its lifetime. Also I don't expect rapid intensification given that SSTs are lower around 28C just below the threshold for such intensification at this time. Also it has been pretty quiet here in the Northeast for late summer weather with no real signs of troughs across the US at this time. Also the trough off the Eastern US coastline is expected to move soon.



there are several things that dont add up

1. Though TD 7 is further south than 95L, becuz its following the same direction as 95L, the difference is minute

2. The trough is deep enough, its affecting the shallow layer flow, that is why 95L was able to pull north even through it did not deepen.

3. Troughs 1 and 2 are coming from the Eastern Canada near the Icelandic low, not the East Coast of the USA. Trough 1 is currently in the mid-Atlantic per satellite imagery.

4. I do agree than TD 7 will shift back west but that is due to alternating trough and ridges through the forecast period as was forecast for 95L. As to whether it continues west and miss the troughs or re-curve is a 30-70 chance to me








Member Since: July 24, 2005 Posts: 407 Comments: 19076
865. laflastormtracker
9:58 PM GMT on September 07, 2009
Local Chief Met is billboarding increased rain chances nxt wkend. Noooooooo!
864. futuremet
9:58 PM GMT on September 07, 2009
Quoting Weather456:
Usually when the MJO is at an upward pulse it means vertical velocity is upward. When that air hits the tropopause it spreads out (outflow) with such an upper pattern, wind shear may not end the season so quickly as 2006. It may linger a few weeks into October especially if anything develops in the NW Caribbean which is typical of October.


And troughs are usually not our friend in October.
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863. TheDawnAwakening
9:52 PM GMT on September 07, 2009
Where do we get those quickly update satellite images of the E Atlantic?
Member Since: October 21, 2008 Posts: 245 Comments: 3898
862. Cavin Rawlins
9:51 PM GMT on September 07, 2009
Usually when the MJO is at an upward pulse it means vertical velocity is upward. When that air hits the tropopause it spreads out (outflow) with such an upper pattern, wind shear may not end the season so quickly as 2006. It may linger a few weeks into October especially if anything develops in the NW Caribbean which is typical of October.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
861. TheDawnAwakening
9:50 PM GMT on September 07, 2009
TD7 is much lower in latitude then 95L ever was in its lifetime. Also I don't expect rapid intensification given that SSTs are lower around 28C just below the threshold for such intensification at this time. Also it has been pretty quiet here in the Northeast for late summer weather with no real signs of troughs across the US at this time. Also the trough off the Eastern US coastline is expected to move soon.
Member Since: October 21, 2008 Posts: 245 Comments: 3898
860. centex
9:48 PM GMT on September 07, 2009
Quoting extreme236:


Pattern really isn't different. In fact it favors more troughing than before. Not sure what your looking at.
Ok, not an expert but IMO is it misses first trough, even Doc suggested this, I guess based on earlier models. I find the water vapor images interesting because they seem to show a change, flip flop or oscillation in flow after the last low clears out. I'm not trying to forecast it out more than 48 hours.
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859. Tazmanian
9:45 PM GMT on September 07, 2009
my bad i mean too say no name storms in octer in a EL nino year this take a look back too 2006 too see what i mean
Member Since: May 21, 2006 Posts: 5091 Comments: 115084
858. futuremet
9:45 PM GMT on September 07, 2009
Quoting BurnedAfterPosting:
I disagree about all that shear, I think we will see close to home activity at the end of September and into October

It is definitely possible


You may be right. The CFS' forecast flip-flops a lot like other models do.
Member Since: July 19, 2008 Posts: 43 Comments: 4051
857. Orcasystems
9:45 PM GMT on September 07, 2009
Quoting Tazmanian:
we may have no name storms in a EL Nino year


take a look at 2006


Member Since: October 1, 2007 Posts: 81 Comments: 26511
856. extreme236
9:44 PM GMT on September 07, 2009
Quoting Tazmanian:
we may have no name storms in a EL Nino year


take a look at 2006


El Nino years can be unpredictable though. El Nino isn't an end-all, but it makes it rougher for systems to form after September, yes.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
855. futuremet
9:44 PM GMT on September 07, 2009
Quoting Tazmanian:
we may have no name storms in a EL Nino year


take a look at 2006


It had named storms.
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854. BurnedAfterPosting
9:43 PM GMT on September 07, 2009
I disagree about all that shear, I think we will see close to home activity at the end of September and into October

It is definitely possible
853. futuremet
9:43 PM GMT on September 07, 2009
Quoting extreme236:


Maybe some non-tropical lows in the central Atlantic could spin up with favorable conditions or a late GOMEX/SEUS storm with more favorable conditions there in Nov if that forecast pans out. But it seems it isn't very reliable more than a month out at best.


The CFS is expecting shear to be 4kts above average in the Caribbean.....which isn't all....that bad.
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852. Tazmanian
9:42 PM GMT on September 07, 2009
we may have no name storms in a EL Nino year


take a look at 2006
Member Since: May 21, 2006 Posts: 5091 Comments: 115084
851. extreme236
9:42 PM GMT on September 07, 2009
Raw T-numbers are above TS strength already:

ADVANCED DVORAK TECHNIQUE
ADT-Version 7.2.3
Tropical Cyclone Intensity Algorithm

----- Current Analysis -----
Date : 07 SEP 2009 Time : 211500 UTC
Lat : 12:30:24 N Lon : 24:33:05 W


CI# /Pressure/ Vmax
2.1 /1008.2mb/ 31.0kt


Final T# Adj T# Raw T#
(3hr avg)
2.1 2.2 2.9

Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting centex:
This thing still very weak. May not go rapid to TS and too me looks like will trend west. Pattern is differnt from last system. IMO.


Pattern really isn't different. In fact it favors more troughing than before. Not sure what your looking at.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting futuremet:


Activity will likely shut down in the MDR and the GOM during October, as a result of increased shear and cooler SSTs. These anomalously high SSTs we have seen in the GOM this summer will likely propagate southward to the SW Caribbean. Upper level troughs will also kink farther south, and depending on where the jet streak is located, upper level anticyclones might form over these regions.

Hopefully the CFS' forecast is correct with the above wind shear in the Caribbean. However, it has been slightly decreasing the anomalous shear values over the past cycles.





Maybe some non-tropical lows in the central Atlantic could spin up with favorable conditions or a late GOMEX/SEUS storm with more favorable conditions there in Nov if that forecast pans out. But it seems it isn't very reliable more than a month out at best.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
This thing still very weak. May not go rapid to TS and too me looks like will trend west. Pattern is differnt from last system. IMO.
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Quoting centex:
More complicated than that.


Perhaps, but you didn't really give me an explanation to why you say that.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting BurnedAfterPosting:


yea futuremet and to me this season will not end in September like so many claim it will. MJO shows a pretty strong upward motion for the GOM, Caribbean and West Atlantic starting during the last week of September and going through mid-October; to me in this time we could get 3 or 4 storms to form in that area with all those undisturbed waters.

For people who think this season is over, you are dead wrong.


Activity will likely shut down in the MDR and the GOM during October, as a result of increased shear and cooler SSTs. These anomalously high SSTs we have seen in the GOM this summer will likely propagate southward to the SW Caribbean. Upper level troughs will also kink farther south, and depending on where the jet streak is located, upper level anticyclones might form over these regions--providing favorable conditions for tropical cyclone formation.

Hopefully the CFS' forecast is correct with the above wind shear in the Caribbean. However, it has been slightly decreasing the anomalous shear values over the past cycles.



Member Since: July 19, 2008 Posts: 43 Comments: 4051
Repost

6. Weather456 10:32 AM AST on September 07, 2009
Regarding development in GOM,

a possible low pressure forming over the BOC and drifting north into Texas or Louisiana in 1 week. I'm not 100% sold on development but as the low pressure appears weak and close to land. Just have to see what happens but 20% chance for now.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Wow! The trough that's suppose to turn TD 7 to the north must be a deep one,considering that the TD is not really that far north at 12.5W.Sort of unusual for just the first week of Sept to have something digging that deep.
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Quoting extreme236:


Then all your watching is the spreading of convection and movement in the clouds. You gotta watch the center for movements. A center isn't very likely to relocate when there is deep convection over it and with a favorable environment.
More complicated than that.
Member Since: August 10, 2007 Posts: 0 Comments: 3233
Quoting btwntx08:

Here is part of the Short Term Forecast for NWS Brownsville, TX:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BROWNSVILLE TX
112 PM CDT MON SEP 7 2009

.DISCUSSION...DYNAMIC MID LEVEL FLOW WILL STAY WELL NORTH OF DEEP
SOUTH TEXAS THIS FORECAST...LEAVING LOCAL CONDITIONS PRETTY MUCH
TO THEIR OWN DEVICES. MID LEVEL H5 TROUGHING EXTENDING SOUTH ALONG
THE MISSISSIPPI VALLEY WILL MIND ITS OWN BUSINESS AND WILL NOT DIG
VERY DEEP INTO THE GULF OF MEXICO. THIS WILL ALLOW UNSETTLED
WEATHER TO CONTINUE OFFSHORE...AND WILL ALLOW LOWER PRESSURE IN
THE SOUTHWEST GULF TO PERSIST.
THURSDAY WILL BE INTERESTING. THE GFS EXTENDS COASTAL TROUGHING
NORTH FROM THE BAY OF CAMPECHE TO THE LOWER TEXAS COAST. THE RESULT
IS A BULLSEYE OF HEAVY QPF RIGHT OVER BROWNSVILLE AND THE NEARBY
MARINE AREAS. THE HEAVY RAIN IS FORECAST TO PERSIST RIGHT THROUGH
FRIDAY. WHILE OTHER MODELS DO NOT CONCUR WITH SUCH LARGE QPF
SIGNALS...THE COASTAL TROUGH SCENARIO WILL BE A FACTOR...AND COULD
TIP THE SCALES TOWARD A WETTER COUPLE OF DAYS...AT LEAST NEAR THE
COAST. IN FACT...WEAK CONVERGENCE AND CYCLONIC CIRCULATION APPEAR TO
BE OFFSHORE NOW...BUT ARE JUST NOT WELL DEVELOPED OR NEAR ENOUGH TO
TRIGGER THE JUICE READILY AVAILABLE.
No real mention from local meteorlogist to suggest Tropical Low development!!
Member Since: August 25, 2009 Posts: 20 Comments: 6785
Quoting Weather456:
I'm thinking my September Outlook of 4-5 named storms will verify...its been 1 week so far and I'm half way there (if Fred is named this week)


I agree completely, I say 5 named storms and 2-3 more in October
Quoting centex:
I don't pay too much attention to official coordinate in developing systems. They relocate, I follow the larger system to get idea of trend.


Then all your watching is the spreading of convection and movement in the clouds. You gotta watch the center for movements. A center isn't very likely to relocate when there is deep convection over it and with a favorable environment.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting BurnedAfterPosting:


right now its just scattered convection, nothing imminent at this point. If anything were to form it would likely to take 4-5 days


That's good, thank you.
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My public advisory on Dujuan at 5PM
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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.