Tropical Storm Helene arrives; 94L a potential threat to the Lesser Antilles

By: Dr. Jeff Masters , 10:41 PM GMT on August 17, 2012

After a long path across the Atlantic that mirrored the track of Hurricane Ernesto, Tropical Depression Seven finally got its act together enough over the Bay of Campeche tropical storm breeding grounds to earn the name Helene. Helene's formation on August 17 ties 2012 with 1933 for the 2nd earliest appearance of the Atlantic's eighth tropical storm. Only 2005 had an earlier formation date of the season's eighth storm. Most of this year's storms have been weak, though, so the total Accumulated Cyclone Energy (ACE) of 21 is not that much higher than the normal year-to-date ACE of 15, based on a 1981 - 2010 ACE climatology. The normal yearly ACE for the Atlantic is 104. Helene doesn't have much room to work with before landfall, but has the potential to be a prodigious rainmaker for Mexico, with NHC predicting 5 - 10 inches for portions of Northeast Mexico. This part of the coast is not in drought, so will be prone to heavy flooding. Fortunately, Ernesto's main rains fell to the south of where Helene's rains are falling. Helene's rains should remain south of Texas, though we can't rule out a few thunderstorms bringing 1 - 2 inches of rain to extreme South Texas on Saturday and Sunday.


Figure 1. Afternoon satellite image of Helene.

94L a potential threat to the Lesser Antilles
A large tropical wave emerged from the coast of Africa Thursday night, and was designated Invest 94L by NHC this Friday morning. The models have been impressed this system, and develop it into a tropical storm by the middle of next week. The latest set of 12Z (8 am EDT) model runs are divided on how far west 94L will make it before curving more to the northwest. The ECMWF model keeps 94L weak for the next 5 - 6 days, and has progressively been bringing the storm closer to the Lesser Antilles Islands with each successive run. The ECMWF predicts 94L will pass very close to the northern Lesser Antilles August 24 - 25 as a weak tropical storm. The 12Z GFS model predicted recurvature of 94L well to the east of the Lesser Antilles and Bermuda, but the latest 18Z run has the storm plowing through the Lesser Antilles on Thursday, August 23, as a strong tropical storm, then becoming a hurricane in the Eastern Caribbean. Given that our two top models for forecasting hurricane tracks are increasingly showing a threat to the Lesser Antilles, residents of the islands should pay close attention to the progress of 94L. The eventual track of 94L will depend on the strength of the storm over the next seven days, which is difficult to forecast, since 94L will have the usual trouble with dry air to the north from the Saharan Air Layer (SAL.) With the models changing their tune drastically from run to run, its tough to say what land areas might be most at risk from the storm in the long term. In their 2 pm EDT Tropical Weather Outlook, NHC gave 94L a 10% chance of developing into a tropical depression by Sunday afternoon.


Figure 2. MODIS satellite image of Invest 94L taken at 8 am EDT August 17, 2012, off the coast of Africa. Image credit: NASA.

Jeff Masters


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

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I would put the center of Helene right around 21N 97W.

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Quoting superpete:


EVERY Cape Verde storm does not re-curve, as shown below (DEAN '07).Some of the other experts here will be able to explain better than me why SOME do though...
SP



Many CV storms tend to recurve because they become quite strong having all that ocean to traverse and in the absence of a very strong AB high they have a natural tendency to move poleward. Every CV hurricane that made it far West was steered by a strong ridge of high pressure situated far to the South either initially or one that built in from the N as the hurricane tried to recurve and got blocked..
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I haven't been on my laptop for a few days and I'm currently on my phone, but does anyone care to inform me on what's going on with the whole NNE-moving Helene/Issac thing that the blog's going crazy over please?
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Quoting floridaboy14:
how confident are you 94L recurves? any chance this takes the ECMWF track?


"Recurve" is defined as the storm moving poleward and then into the mid-latitude westerlies. For some reason the blog defines "recurve" as missing the United States. Following the true definition, the storm is very likely to recurve in this pattern, and the vast majority of Cape Verde storms do recurve. My thought so far has been that the recurve will take place between 80W and 65W.
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Quoting Levi32:


We've been consistently over the El Nino threshold for over 8 weeks.



The CPC wants a 3-month average over this threshold in Nino3.4 to declare an "official" El Nino for the historical record.

From the CPC Glossary:

he preliminary CPC definition of El Niño is a phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period), averaged over three months, greater than or equal in magnitude to 0.5oC in a region defined by 120oW-170oW and 5oN-5oS (commonly referred to as Niño 3.4).


thanks Levi..I couldnt find it about how they declare it..but I still dont think we are in an EL Nino..too many inconsistencies with the fluctuating..even the CPC said it in their discussion..
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Quoting RTSplayer:


Don't make plans based on anyone's comments on this blog unless it's the staff.

Pay attention to NWS/NHC discussions.

This is a heavily user-geared blog and a lot of comments and theories on here are just amateurs, myself included.


Thank you, that's good advice. Where can I find NWS / NHC discussions? Do they also provide any sort of forecasts in terms of direction?
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Quoting TropicalAnalystwx13:

El Niño conditions can be felt without one being declared.

The CPC says we aren't feeling it. Waters warmed but the atmosphere has not responded yet.
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Quoting Stormchaser2007:
Have to see if convection can redevelop over that LLC.

Seems to be moving north along 96W

The GFS has recently shown itself to be adept at predicting relocs.
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Quoting evilpenguinshan:
I know everyone is currently riding the Isaac freak-out train, but ya'll might wanna keep your eyes on Helene...
she's definitely moving N/NNE, so I think WU might need to update their forecast cone...


It's a disorganized system, you can't pay much attention to the CoC movement over short time periods because it isn't well defined.

Give it a few more hours to draw conclusions...
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Quoting floridaboy14:
can anyone answer my question. why does EVERY cape verde storm ALWAYS recurve? in 2004 they went right into the coast. ever since then everything either goes out to sea or curves into the coast like irene. now a days, there are so many troughs that nothing can hit the coast DIRECTLY. thoughts and comments?


EVERY Cape Verde storm does not re-curve, as shown below (DEAN '07).Some of the other experts here will be able to explain better than me why SOME do though...
SP

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Quoting belizeit:
Helene is still moving NNE at 7 to 10 MPH NHC will need to shift there cone a lot further north in a couple of Minutes when the next advisory comes out
They don't shift the cone for 8PM they shift for 11PM, 5AM, 11AM, & 5PM.
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12z ensemble comparison shows the ECMWF is further west than the GFS. While it appears the majority of the ECMWF Ensemble solutions show a recurve around 60-70W (to the west of Bermuda) some ensemble members bring the storm into the Bahamas, Florida, and SE US regions. Also note the ridging around the Hudson Bay showing up on the 12z run at 240 hrs. Such a position of anomalous ridging favors landfalls in the SE US, should the storm stay far enough south. Of course, if the storm is further north and east, then it will take the weakness out.

Anyway, something to look at. Still a long way out, but folks on the East Coast need to be ready...



12z ECMWF Ensemble at 10 Days




12z GFS Ensemble at 10 Days

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Quoting Stormchaser2007:


Satellite data also showed that the ridge is a good deal stronger than originally thought.

12z vs 18z



:-)

Forgot that !
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Quoting JLPR2:


I would say we are in a warm neutral, borderline El Nino, though it doesn't need much to finally be declared and would probably be a weak one.


the El Nino Forecast has been pushed back since July..I wouldnt be surprise if they put out another discussion and say October..
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Quoting ncstorm:


if the numbers keep fluctuating, I dont see how this can be an El Nino if one day we in Neutral conditions and the next day as you guys are saying we are experiencing EL Nino conditions..the week a major makes its way across the atlantic with neutral and el nino conditions wont convince me otherwise that we are in an El Nino..and where does it say on the CPC website that it has to be consistent for them to declare it, I tried looking for it but couldnt find it?


We've been consistently over the El Nino threshold for over 8 weeks.



The CPC wants a 3-month average over this threshold in Nino3.4 to declare an "official" El Nino for the historical record.

From the CPC Glossary:

The preliminary CPC definition of El Nino is a phenomenon in the equatorial Pacific Ocean characterized by a positive sea surface temperature departure from normal (for the 1971-2000 base period), averaged over three months, greater than or equal in magnitude to 0.5C in a region defined by 120oW-170oW and 5oN-5oS (commonly referred to as Nino 3.4).
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Quoting kmanislander:


Several of us discussed this likelihood earlier today. The initial motion to the WSW coupled with the fact that cyclogenesis is difficult to get going around 11 N means a generally slow developer in the works. That takes the system farther West before ramping up, hence a potential danger to the Islands and points WNW of there.

No surprise the models have made this shift.


Satellite data also showed that the ridge is a good deal stronger than originally thought.

12z vs 18z

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The history pattern is favorable for a recurve
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I know everyone is currently riding the Isaac freak-out train, but ya'll might wanna keep your eyes on Helene...
she's definitely moving N/NNE, so I think WU might need to update their forecast cone...
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Quoting NativeSun:
Sorry, no nino yet.
Quoting ncstorm:


my point is we arent in an El Nino..you guys are saying that, not NOAA..

Even though we aren't in an El Niño yet, we are already experiencing Niño-like conditions in the Atlantic.

...

In other words, what Cody said.
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Quoting Levi32:


It is here, just not terribly strong.

how confident are you 94L recurves? any chance this takes the ECMWF track?
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Quoting Felix2007:
Looks like Isaac's gonna be the "once in a blue moon" event.
It's not like there hasn't been a "coastal strafer" before...

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Quoting ylibrach:


How often are these model runs wrong? Also, when should I make a final decision? If the models are still showing this on Sunday evening, is it safe to say that's the direction the storm will go in?


Key word: Models. Focus on another word : NHC. You can relax alot more if you follow any info coming out of that office in Miami, FL.
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Quoting ylibrach:
I am about to cry :( .. I am flying out to the Dominican Republic on Monday for 7 days. These latest models have me freaking out. Should I cancel my trip? I am pretty much going to lose all the money I paid for it. How accurate are these models in general?


Don't make plans based on anyone's comments on this blog unless it's the staff.

Pay attention to NWS/NHC discussions.

This is a heavily user-geared blog and a lot of comments and theories on here are just amateurs, myself included.
Member Since: December 31, 1969 Posts: Comments:
Have to see if convection can redevelop over that LLC.

Seems to be moving north along 96W
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Quoting stormchaser19:


Is one run only,but the models are shifting more to the west NOW


Several of us discussed this likelihood earlier today. The initial motion to the WSW coupled with the fact that cyclogenesis is difficult to get going around 11 N means a generally slow developer in the works. That takes the system farther West before ramping up, hence a potential danger to the Islands and points WNW of there.

No surprise the models have made this shift.
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Quoting ylibrach:
I am about to cry :( .. I am flying out to the Dominican Republic on Monday for 7 days. These latest models have me freaking out. Should I cancel my trip? I am pretty much going to lose all the money I paid for it. How accurate are these models in general?


models are meant to be used
for guidance purposes only
things can and will change
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Quoting Hurricanes101:
something of note, vortex fixes show the system is not moving west, but moving north or even a bit east of north

while helene is not all that well organized right now, lets wait and see what happens before we jump the gun either way

I wonder if Helene is considering a center reloc to her N.
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148. JLPR2
Quoting ncstorm:


my point is we arent in an El Nino..you guys are saying that, not NOAA..


I would say we are in a warm neutral, borderline El Nino, though it doesn't need much to finally be declared and would probably be a weak one.
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Quoting bigwes6844:
Levi quick question. is MJO back into theGOM and carribean yet or is it still days off?


It is here, just not terribly strong.

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Quoting ncstorm:


my point is we arent in an El Nino..you guys are saying that, not NOAA..

El Niño conditions can be felt without one being declared.
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Quoting ylibrach:
I am about to cry :( .. I am flying out to the Dominican Republic on Monday for 7 days. These latest models have me freaking out. Should I cancel my trip? I am pretty much going to lose all the money I paid for it. How accurate are these models in general?


No need for panic just yet however, coming into the tropics during cane season, one should always have a back up plan.
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BTW, everybody realizes that once 94L really gets going the twice a day blogs will likely top 4000 posts, right???

LOL

Quoting FLCrackerGirl:


2008: IKE as a Cat 4 had winds of 135mph near the Turk/Caicos and Cuba ... at it's Galveston TX landfall, it was a Cat 2 (not a Major Cat 4).

2005 Wilma was the last Major to US landfall.
Just a semantics point, Ike was still wicked bad & heart-breaking everwhere it passed.

RTSplayer, you beat me to it. LOL :o)
I thought he was just posting highest intensity + eventual outcome, not intensity at US landfall...

Quoting Stormchaser2007:
Looks like a recurve just east of the CONUS.
That could still be GA or the Carolinas, depending on the direction the high is moving...

Like I said earlier today, whatever 94L makes of itself could be anybody's ball game at this point, pretty much.
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something of note, vortex fixes show the system is not moving west, but moving north or even a bit east of north

while helene is not all that well organized right now, lets wait and see what happens before we jump the gun either way
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Quoting TropicalAnalystwx13:

Just watch the storm. This is only one run so far, no reason to panic or change your plans yet.


How often are these model runs wrong? Also, when should I make a final decision? If the models are still showing this on Sunday evening, is it safe to say that's the direction the storm will go in?
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Sorry, no nino yet.
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Quoting TropicalAnalystwx13:

You seem to be under the impression that storms can't make it across the Atlanic during an el niño season, which is not the case. It happened 20 years ago.


my point is we arent in an El Nino..you guys are saying that, not NOAA..
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139. JLPR2
Quoting stormchaser19:


Is one run only,but the models are shifting more to the west NOW


That is what worries me a bit. Last GFS run, eh, it's just one run and it's the 18z. With the GFS seems the best runs are the 00z and 12z
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Quoting ylibrach:
I am about to cry :( .. I am flying out to the Dominican Republic on Monday for 7 days. These latest models have me freaking out. Should I cancel my trip? I am pretty much going to lose all the money I paid for it. How accurate are these models in general?


Never base your plans on forecast models, base it on information from the NHC and right now there is no storm hitting Dominican Republic or forecasted to do so. It does not hurt to buy travel insurance if you can get it.Just in case. Go enjoy your trip.
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Helene really looks like Hel....
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Quoting wxchaser97:
94L at 20%

AN AREA OF DISTURBED WEATHER ASSOCIATED WITH A TROPICAL WAVE IS
LOCATED WELL SOUTH OF THE CAPE VERDE ISLANDS. SOME SLOW DEVELOPMENT
IS POSSIBLE DURING THE NEXT FEW DAYS AS THIS SYSTEM MOVES TOWARD
THE WEST AT 15 TO 20 MPH. THIS SYSTEM HAS A LOW CHANCE...20
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
You better not be a bad storm.
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Florida hurricane Shield lol (18z gfs)

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Quoting Stormchaser2007:
East coast threat

GFS ensembles



Going to have to let this one percolate for a few days, no one is out of the woods ATM. IKE is a good example of that. Re-curve, then FL and ended up into Texas.
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Quoting Cat5hit:


To the simple minded, yes...


Haaaa!!! Meow
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Quoting ncstorm:


if the numbers keep fluctuating, I dont see how this can be an El Nino if one day we in Neutral conditions and the next day as you guys are saying we are experiencing EL Nino conditions..the week a major makes its way across the atlantic with neutral and el nino conditions wont convince me otherwise that we are in an El Nino..and where does it say on the CPC website that it has to be consistent for them to declare it, I tried looking for it but couldnt find it?

You seem to be under the impression that storms can't make it across the Atlanic during an el niño season, which is not the case. It happened 20 years ago.
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This is a ever-lasting thunderstorm
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AN AREA OF DISTURBED WEATHER ASSOCIATED WITH A TROPICAL WAVE IS
LOCATED WELL SOUTH OF THE CAPE VERDE ISLANDS. SOME SLOW DEVELOPMENT
IS POSSIBLE DURING THE NEXT FEW DAYS AS THIS SYSTEM MOVES TOWARD
THE WEST AT 15 TO 20 MPH. THIS SYSTEM HAS A LOW CHANCE...20
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOUR
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Helene is still moving NNE at 7 to 10 MPH NHC will need to shift there cone a lot further north in a couple of Minutes when the next advisory comes out
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Quoting Hurricanes101:


Thanks Taz



you are so welcome
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Quoting ylibrach:
I am about to cry :( .. I am flying out to the Dominican Republic on Monday for 7 days. These latest models have me freaking out. Should I cancel my trip? I am pretty much going to lose all the money I paid for it. How accurate are these models in general?

Just watch the storm. This is only one run so far, no reason to panic or change your plans yet.
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Quoting Levi32:


When forecasting the weather you cannot call this neutral ENSO. It is an El Nino.



If the CPC wants a long-term average to "officially" declare it an El Nino event, that's fine, but that doesn't change the fact that it is already here and affecting the Atlantic this season.


if the numbers keep fluctuating, I dont see how this can be an El Nino if one day we in Neutral conditions and the next day as you guys are saying we are experiencing EL Nino conditions..the week a major makes its way across the atlantic with neutral and el nino conditions wont convince me otherwise that we are in an El Nino..and where does it say on the CPC website that it has to be consistent for them to declare it, I tried looking for it but couldnt find it?
Member Since: December 31, 1969 Posts: Comments:

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Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather