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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Quoting kmanislander:


I posted about the topographic effects even before the first discussion came out. If it had not been that far South and close to the coast it may never have developed a closed low.
is there any history of a storm forming there then going north or north east?
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heres a link for the 18z gfs
Link
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Quoting wxmobilejim:
The Cone and track for Helene keeps it more along the coast instend of way inland Could it never go in Mexico and stay in gulf?
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Maybe here will be easier to see

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Helene was never what it appeared to be.



I think we see a lot of that around here....

: )
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Quoting floridaT:
just like dr masters talked about with ernesto last week


I posted about the topographic effects even before the first discussion came out. If it had not been that far South and close to the coast it may never have developed a closed low.
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Quoting Grothar:


A lot of bad ones have passed through those boxes. My question is, how many people are going to provide the correct pronunciation of the name Hebert this season. :)

lol yes Grothar that is always a big question. we must watch Tropical Storm Helene very closely because these storms tend to spin up very fast in the Bay of Campeche.
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i see the cmc also has helen eventually coming over the Louisiana coast..... another note what are the odds of 94L taking a due north turn just before the caribbean
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Quoting kmanislander:


The storm's apparent robustness was the result of forcing from the topography on the SW side of the BOC.
Helene was never what it appeared to be.
just like dr masters talked about with ernesto last week
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Quoting Stormchaser2007:


Oooh. That`s not so good. Didn`t realise the SSTs around Nova Scotia were so far above normal. Hardly rocket fuel, but worrying just the same.
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Quoting JLPR2:


That is all. :)

Well, yes!
That will be a challenge.
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Quoting Grothar:


I must have been napping.


I imagine so, you were up with the chickens doing a blog this morning..

Nogaps run
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Quoting floridaT:
most moist environment we have seen from an african wave so far this year.


I believe it is.
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Quoting ILOVESTORMS23:
94L fizzle or fish?


neither...to early to tell
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Quoting KEEPEROFTHEGATE:
i guess you could call it a quickie bubbles

lol


The storm's apparent robustness was the result of forcing from the topography on the SW side of the BOC.
Helene was never what it appeared to be.
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Quoting KoritheMan:
Station LMBV4 off the coast of Mexico north of Veracruz is reporting west winds as of 0200 UTC, and a buoy near 22N 94W, quite a bit east of Helene's center, is reporting east winds. Tell me, if this thing was inland, wouldn't we be seeing the winds veer? I thought so.


No, not necessarily.

The system is so weak and poorly organized you shouldn't expect buoy 2.5 to 3 degrees away to observe relative cyclonic motion...

When you look in IR and RGB and all the other tools, including radar, you can see inside and see how torn up the system is...

The buoy could be reporting thunderstorm winds, or an outflow boundary.

If you're talking about the national data buoy center's buoy out over open water, that buoy was 9 miles per hour, and in the wrong direction when I checked it about 30 minutes ago...Currently the wind is east at 9.7 with Gust to 11...so...it's trade winds...seriously, you think 9.7kts matters?

The wind at Veracruze is from the west a ONE kts...

You realize that means either it's inside the CoC and getting some break, or else, more likely, it's inside a lull on the NE quadrant between the first and second band, and is experiencing some turbulence...



I will concede that the mexican radar loops SUCK, but this storm should be downgraded to a remnant low. Even IF the CoC is still over water, it has no vertical alignment whatsoever and maximum sustained winds of 10mph at any of the buoys? Seriously.

This is a joke at this point...
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Quoting wxmobilejim:
000
WTNT42 KNHC 180232
TCDAT2

TROPICAL STORM HELENE DISCUSSION NUMBER 10
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072012
1000 PM CDT FRI AUG 17 2012

A HURRICANE HUNTER PLANE INVESTIGATED HELENE FOR SEVERAL HOURS THIS
EVENING AND FOUND THAT THE DEVELOPMENT TREND OBSERVED EARLIER TODAY
IS NO LONGER OCCURRING. HELENE IS EITHER WEAKER OR ON A STEADY
STATE WITH MAXIMUM WINDS OF 35 KNOTS. THE CYCLONE STILL HAS A WELL
DEFINED CIRCULATION AS INDICATED BY THE RECONNAISSANCE PLANE BEFORE
IT LEFT THE AREA...AND ALTHOUGH THE SATELLITE PRESENTATION HAS
DETERIORATED...ENVIRONMENTAL CONDITIONS ARE SOMEWHAT FAVORABLE FOR
HELENE TO REGAIN SOME STRENGTH BEFORE IT MOVES INLAND IN ABOUT 24
HOURS OR EARLIER. AFTER LANDFALL...A STEADY WEAKENING IS
ANTICIPATED.

FIXES FROM THE RECONNAISSANCE PLANE INDICATE THAT HELENE WAS
MEANDERING OR DRIFTING NORTHWARD DURING THE PAST COUPLE OF HOURS.
HOWEVER...THERE IS ENOUGH RIDGING TO THE NORTH OF THE CYCLONE TO
FORCE HELENE SLOWLY NORTHWESTWARD AT ABOUT 6 KNOTS TOWARD THE COAST
OF MEXICO. ALTHOUGH THIS IS THE MOST LIKELY SCENARIO AS INDICATED IN
THE OFFICIAL FORECAST...ONE SHOULD NOTE THAT VARIOUS MODELS
INCLUDING THE GFS AND THE ECMWF KEEP A LOW...OR PERHAPS THE MODEL
REPRESENTATION OF HELENE DRIFTING NORTHWARD VERY CLOSE TO THE COAST
OF MEXICO FOR SEVERAL DAYS...AND IN FACT...THE GFS RESTRENGTHENS
THIS FEATURE.

NEVERTHELESS...THE MAIN THREAT FROM HELENE WILL BE HEAVY
RAINFALL...WHICH WILL CONTINUE EVEN AS THE CYCLONE SLOWLY MOVES
INLAND AND WEAKENS.


FORECAST POSITIONS AND MAX WINDS

INIT 18/0300Z 21.0N 96.4W 35 KT 40 MPH
12H 18/1200Z 21.7N 97.2W 40 KT 45 MPH
24H 19/0000Z 22.2N 97.8W 45 KT 50 MPH...ON THE COAST
36H 19/1200Z 23.0N 98.0W 30 KT 35 MPH...INLAND
48H 20/0000Z 24.0N 98.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 21/0000Z...DISSIPATED

$$
FORECASTER AVILA



So if I get this right, the NHC is discounting the GFS AND the Euro on the potential regeneration of Helene. WTH?!?
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Quoting KEEPEROFTHEGATE:
i guess you could call it a quickie bubbles

lol
I wont say it almost got in trouble last week
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Quoting unknowncomic:
Healthy waves behind 94L.



Yep. This is the little feature you have seen on some of the maps following 94L.



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Quoting Grothar:


I believe it is one of the reasons they believe it will be large. I really don't know. Even though there is a lot of SAL showing on the maps, there seems to be an abundant amount of moisture at the lower levels. It if can get strong enough, the outflow should moisten the environment around and ahead of it.
most moist environment we have seen from an african wave so far this year.
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interesting that this track shows a turn northward just inland for Helene - a trend maybe?
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552. JLPR2


That is all. :)
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Quoting floridaT:
good evening Helene has got to be the weakest ts ive ever seen. and not long lasting either.
i guess you could call it a quickie bubbles

lol
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It's pronounced he-bear.
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000
WTNT42 KNHC 180232
TCDAT2

TROPICAL STORM HELENE DISCUSSION NUMBER 10
NWS NATIONAL HURRICANE CENTER MIAMI FL AL072012
1000 PM CDT FRI AUG 17 2012

A HURRICANE HUNTER PLANE INVESTIGATED HELENE FOR SEVERAL HOURS THIS
EVENING AND FOUND THAT THE DEVELOPMENT TREND OBSERVED EARLIER TODAY
IS NO LONGER OCCURRING. HELENE IS EITHER WEAKER OR ON A STEADY
STATE WITH MAXIMUM WINDS OF 35 KNOTS. THE CYCLONE STILL HAS A WELL
DEFINED CIRCULATION AS INDICATED BY THE RECONNAISSANCE PLANE BEFORE
IT LEFT THE AREA...AND ALTHOUGH THE SATELLITE PRESENTATION HAS
DETERIORATED...ENVIRONMENTAL CONDITIONS ARE SOMEWHAT FAVORABLE FOR
HELENE TO REGAIN SOME STRENGTH BEFORE IT MOVES INLAND IN ABOUT 24
HOURS OR EARLIER. AFTER LANDFALL...A STEADY WEAKENING IS
ANTICIPATED.

FIXES FROM THE RECONNAISSANCE PLANE INDICATE THAT HELENE WAS
MEANDERING OR DRIFTING NORTHWARD DURING THE PAST COUPLE OF HOURS.
HOWEVER...THERE IS ENOUGH RIDGING TO THE NORTH OF THE CYCLONE TO
FORCE HELENE SLOWLY NORTHWESTWARD AT ABOUT 6 KNOTS TOWARD THE COAST
OF MEXICO. ALTHOUGH THIS IS THE MOST LIKELY SCENARIO AS INDICATED IN
THE OFFICIAL FORECAST...ONE SHOULD NOTE THAT VARIOUS MODELS
INCLUDING THE GFS AND THE ECMWF KEEP A LOW...OR PERHAPS THE MODEL
REPRESENTATION OF HELENE DRIFTING NORTHWARD VERY CLOSE TO THE COAST
OF MEXICO FOR SEVERAL DAYS...AND IN FACT...THE GFS RESTRENGTHENS
THIS FEATURE.

NEVERTHELESS...THE MAIN THREAT FROM HELENE WILL BE HEAVY
RAINFALL...WHICH WILL CONTINUE EVEN AS THE CYCLONE SLOWLY MOVES
INLAND AND WEAKENS.


FORECAST POSITIONS AND MAX WINDS

INIT 18/0300Z 21.0N 96.4W 35 KT 40 MPH
12H 18/1200Z 21.7N 97.2W 40 KT 45 MPH
24H 19/0000Z 22.2N 97.8W 45 KT 50 MPH...ON THE COAST
36H 19/1200Z 23.0N 98.0W 30 KT 35 MPH...INLAND
48H 20/0000Z 24.0N 98.0W 25 KT 30 MPH...POST-TROP/REMNT LOW
72H 21/0000Z...DISSIPATED

$$
FORECASTER AVILA

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Quoting Grothar:


I believe it is one of the reasons they believe it will be large. I really don't know. Even though there is a lot of SAL showing on the maps, there seems to be an abundant amount of moisture at the lower levels. It if can get strong enough, the outflow should moisten the environment around and ahead of it.

SAL is there, but not very dense.
And as you say, moisture south.
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Quoting Grothar:


It is also expected to be a rather large system.


Don't tell me it's coming here Gro, I got plans the weekend after if it does.
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Quoting ncstorm:
I posted an old run today from the Nogaps where it was showing 94L doing a fujiwhara with another system right off of Africa


I must have been napping.
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544. THL3
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good evening Helene has got to be the weakest ts ive ever seen. and not long lasting either.
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Quoting redwagon:
The combined ACE when absorption is complete explains the monstrous size the models are portraying. This almost has to be a fish storm for that reason alone.


I believe it is one of the reasons they believe it will be large. I really don't know. Even though there is a lot of SAL showing on the maps, there seems to be an abundant amount of moisture at the lower levels. It if can get strong enough, the outflow should moisten the environment around and ahead of it.
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I posted an old run today from the Nogaps where it was showing 94L doing a fujiwhara with another system right off of Africa
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Quoting sunlinepr:


Post 495 is for the 25th...

So the post at 509 is wrong, then.
It can't make all that distance in 48 hrs (23rd-25th)
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Quoting wxmobilejim:
10:00 PM CDT Fri Aug 17
Location: 21.0°N 96.4°W
Moving: NW at 7 mph
Min pressure: 1006 mb
Max sustained: 40 mph


but....but...I thought it had moved inland
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Major shift to the north in track with Helene.
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Quoting Hurricanes101:


I think observations are a better tool than looking at a satellite image lol

I agree, Helene has not made landfall


Satellite imagery is just one medium we can use to determine center fixes. It is not uncommon for satellite and radar data to be in disagreement with recon fixes or surface observations.
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Healthy waves behind 94L.

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10:00 PM CDT Fri Aug 17
Location: 21.0°N 96.4°W
Moving: NW at 7 mph
Min pressure: 1006 mb
Max sustained: 40 mph
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Learn from the past or be doomed to repeat it...
Unfortunately many don't heed that lesson XD

Quoting KoritheMan:


I meant it when I said I learned from Ernesto. I will never be so humiliated in a forecast again. lol
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Quoting KoritheMan:


Who would've thought...


I think observations are a better tool than looking at a satellite image lol

I agree, Helene has not made landfall
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532. THL3
Texas radar link:
Link
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Quoting evilpenguinshan:
somebody who isn't Kori didn't learn from Ernesto...



I meant it when I said I learned from Ernesto. I will never be so humiliated in a forecast again. lol
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Quoting Grothar:


A lot of models missed that 2nd vortike. You can see them plainly there.
The combined ACE when absorption is complete explains the monstrous size the models are portraying. This almost has to be a fish storm for that reason alone.
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Quoting pottery:
Post 509...
That's for Aug. 23. Still a long way from the islands.
Earlier the forecast was for crossing the islands around 23rd.
A big slow-down predicted ?


Post 492 is for the 25th...
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Quoting Hurricanes101:


so in other words, she is over water?


Who would've thought...
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Quoting sunlinepr:


I don't know if that happens to you bloggers but we are better informed than the average person...

When we give information to friends or family, they usually think that we are obsessed and are fanatics....


I resemble that remark.
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Quoting Grothar:


I really like those, nc. Just the right touch of pastel to off-set the main event. They look scary, too!


um humm..yes, me and GT actually had a conversation today about the choice of "colors" in some of these images..
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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