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 KoritheMan:


Where in north California, Taz?



hi can you check sonora CA
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Quoting KoritheMan:


Yes, but the long-term average for US hits is 4. I read that somewhere, though I'm not quite sure where. Lately we've been lucky to exceed 2. Last year we came close, but Don was so pathetic it shouldn't even be considered.

If that wasn't scott's point, it is at least mine.
You hit the nail right on the head.
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Quoting Hurricanes101:
uh oh, armchair mets chastize the NHC lol


to me this is a TS that is being impacted by Dmin, nothing more. I have seen a lot worse looking storms have a name

she will come back tomorrow morning, and I think she will not make landfall in Mexico

Couldn't say it any better than this.Completely agree!
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Quoting Tazmanian:
can some one check the hrr and see what it shows for N CA i got t-storms fourming all a round and i want too see what it shows for the net few hrs or so


Where in north California, Taz?
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African dust rules...and fools drool.
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Quoting clwstmchasr:


Not sure what you mean by that. Florida has been hit by 2 tropical storms that busted the drought.


Yes, but the long-term average for US hits is 4. I read that somewhere, though I'm not quite sure where. Lately we've been lucky to exceed 2. Last year we came close, but Don was so pathetic it shouldn't even be considered.

If that wasn't scott's point, it is at least mine.
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can some one check the hrr and see what it shows for N CA i got t-storms fourming all a round and i want too see what it shows for the net few hrs or so
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It was close to mexico already,so they went ahead and named it.Like I said what matters now is its northerly drift! Keep an eye on that.
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Quoting MAweatherboy1:

Personally I'd say she's looking rather gross.


Gross.
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Quoting VAbeachhurricanes:
When did consistency lose its qualification for TC formation? Finding 40 mph for 5 minutes? Thats a afternoon thunderstorm. The HH were in there for 5 hours and found 5 mins of TS winds in the first hour and never again.

They had to get in Helene before landfall in order to not miss two MX cyclones in two weeks.
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uh oh, armchair mets chastize the NHC lol


to me this is a TS that is being impacted by Dmin, nothing more. I have seen a lot worse looking storms have a name

she will come back tomorrow morning, and I think she will not make landfall in Mexico
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Current steering

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Quoting TomTaylor:
lol, it's just so I can make the animation. The website that I got the images from is the same old NCEP Model Analysis site. Just click the region you want and then hit "GEFS-SPAG" and then pick the variables you want to plot.


No! You hurted my feelings!

*cries*
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I still can't believe they named a thunderstorm.

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Not Gross! :)
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Is Helene playing hide and go seek.
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When did consistency lose its qualification for TC formation? Finding 40 mph for 5 minutes? Thats a afternoon thunderstorm. The HH were in there for 5 hours and found 5 mins of TS winds in the first hour and never again.
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All it matters is that northerly drift right now
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Quoting STXHurricanes2012:
It just needs convection geez...I told you naked swirls are worser!!


my grammerz are worser than urs lolololo
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For those twiddling their thumbs waiting for 00z run,
here is an interesting link to a video from
Impact Weather about a correlation between wet July's in SE Texas Coast(like this year) and increased risk of hurricanes in the NW Gulf.Link
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Quoting WeatherNerdPR:

Gross.
Speaking of gross, Helene ain't looking so good right now.

Personally I'd say she's looking rather gross.

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It just needs convection geez...I told you naked swirls are worser!!
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Quoting KEEPEROFTHEGATE:

This scenario depends on a radical center relocation, which the GFS is handy with.
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Quoting STXHurricanes2012:
Can you stop saying gross!!! lol

Gross.
Speaking of gross, Helene ain't looking so good right now.
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Quoting Felix2007:


That is 15 days out. When I see it for real...then I wont be so negative! Tracking the last 3 seasons have made me bah humbug! Lol
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Yuck?
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Quoting KoritheMan:


Why do people keep masking the URLs to cool websites that I want? You just like to troll me don't you Tom? :(
lol, it's just so I can make the animation. The website that I got the images from is the same old NCEP Model Analysis site. Just click the region you want and then hit "GEFS-SPAG" and then pick the variables you want to plot.
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Naked Swirl TS's are more gross than this lol!
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Quoting STXHurricanes2012:
Can you stop saying gross!!! lol




gross
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Can you stop saying gross!!! lol
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Quoting scott39:
So far its just another mexico...out to sea season. Time will tell if this boring pattern continues.


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Quoting TomTaylor:
People have already pointed this out, but here's another look at the shift from the 12z ensemble run to the 18z ensemble run. We shouldn't be surprised to see such a shift, however, since this is 12 days out. Expect another model shift at the 0z run.

12z Ensemble vs 18z Ensemble at 276 Hours



Why do people keep masking the URLs to cool websites that I want? You just like to troll me don't you Tom? :(
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Quoting floridaboy14:
Just Curious. who think we are in el nino RIGHT NOW meaning the atmosphere is behaving like an el nino.?


Don't know about others but, FL is rather mute on the effects during the summer.

South Florida winters are usually dry and warm during La Niña conditions, while El Niño conditions usually bring cool and wet conditions to our region. ENSO effects on South Florida are rather minimal during the summer months, with the exception of tropical cyclone activity in the Atlantic Basin.
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So far its just another mexico...out to sea season. Time will tell if this boring pattern continues.
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Quoting PlazaRed:
I can't help but find this interesting in a sort of secretive sarcastic way!
33. SLU
Year 2000's Hurricane Isaac and Joyce

Now then? What is significant about this apart from it being a very interesting close encounter of the Cyclonic kind?

Well not to keep the suspense going too long but this happened on SEPTEMBER the 27th.( Issac and Joyce.)
A quick check of the calender reveals that we are only at the 18th of August about 6 weeks "Avant Garde," not that we want to sag into French but this season could become serious. Avant Garde.
Any news on the Arctic ice?



Melting, Meeelllting...

Sea Ice Heads for Record Low

ahem.



DOOM
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Quoting RTSplayer:
Helene = toast.

Official center fix is probably wrong.



So your saying that based off of a satellite wind field when we have recon telling us it's still over water?
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17/2315 UTC 20.7N 96.7W T1.0/1.5 HELENE -- Atlantic gross
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I wonder if perhaps 94L can resist the urge to recurve? Time will tell.

Regardless if it does or doesn't, I sure hope Isaac lives up to its notoriety as the "storm of the season" (sans the retirement, which is difficult to avoid anytime a major threatens land...).
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Quoting stormchaser19:


in what coordinate you think 94l will recurve
Honestly, the potential recurve is so far out in time that any coordinates thrown out are just guesses. I do think the storm will recurve (recurve as in turn to the NE in the westerlies) as ensemble runs do show a weakness in the 500mb heights off the east coast. And I like Levi's prediction, but again...look at the coordinates in his prediction...it's between 65N and 80N. Just goes to show that at this point in time there is a lot of uncertainty.
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Quoting PensacolaDoug:
Helene looks like a glorified thunderstorm. The NHC is slow to name some things that are obviously worth naming, and then they name things that are very marginal. There is no consistancy that I can discern.


Sadly I agree. In general they still do pretty good, though.
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Quoting VAbeachhurricanes:
Okay, so seriously... what did the NHC look at and say "looks 5mph stronger than 530"

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 17th day of the month at 23:31Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Tropical Depression: Number 7 (flight in the North Atlantic basin)
Mission Number: 2
Observation Number: 16
A. Time of Center Fix: 17th day of the month at 23:20:00Z
B. Center Fix Coordinates: 20°47'N 96°01'W (20.7833N 96.0167W)
B. Center Fix Location: 154 miles (249 km) to the SE (130°) from Tampico, Tamaulipas, México.
C. Minimum Height at Standard Level: Not Available
D. Estimated (by SFMR or visually) Maximum Surface Wind: 8kts (~ 9.2mph)
E. Location of the Estimated Maximum Surface Wind: 4 nautical miles (5 statute miles) to the NW (319°) of center fix
F. Maximum Flight Level Wind Inbound: From 50° at 15kts (From the NE at ~ 17.3mph)
G. Location of Maximum Flight Level Wind Inbound: 4 nautical miles (5 statute miles) to the NW (319°) of center fix
H. Minimum Sea Level Pressure: 1006mb (29.71 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 24°C (75°F) at a pressure alt. of 303m (994ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 26°C (79°F) at a pressure alt. of 290m (951ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 24°C (75°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 1,500 feet
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 3 nautical miles
Remarks Section:
Maximum Flight Level Wind: 30kts (~ 34.5mph) in the south quadrant at 22:28:00Z
Sea Level Pressure Extrapolation From: Below 1,500 feet


well first off it was 45mph at 5pm, so it was not 5mph higher, secondly, even in the vortex messages sometimes they do not get the accurate readings
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Helene looks like a glorified thunderstorm. The NHC is slow to name some things that are obviously worth naming, and then they name things that are very marginal. There is no consistancy that I can discern.
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I can't help but find this interesting in a sort of secretive sarcastic way!
33. SLU
Year 2000's Hurricane Isaac and Joyce

Now then? What is significant about this apart from it being a very interesting close encounter of the Cyclonic kind?

Well not to keep the suspense going too long but this happened on SEPTEMBER the 27th.( Issac and Joyce.)
A quick check of the calender reveals that we are only at the 18th of August about 6 weeks "Avant Garde," not that we want to sag into French but this season could become serious. Avant Garde.
Any news on the Arctic ice?

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Okay, so seriously... what did the NHC look at and say "looks 5mph stronger than 530"

Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 17th day of the month at 23:31Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 303)
Tropical Depression: Number 7 (flight in the North Atlantic basin)
Mission Number: 2
Observation Number: 16
A. Time of Center Fix: 17th day of the month at 23:20:00Z
B. Center Fix Coordinates: 20°47'N 96°01'W (20.7833N 96.0167W)
B. Center Fix Location: 154 miles (249 km) to the SE (130°) from Tampico, Tamaulipas, México.
C. Minimum Height at Standard Level: Not Available
D. Estimated (by SFMR or visually) Maximum Surface Wind: 8kts (~ 9.2mph)
E. Location of the Estimated Maximum Surface Wind: 4 nautical miles (5 statute miles) to the NW (319°) of center fix
F. Maximum Flight Level Wind Inbound: From 50° at 15kts (From the NE at ~ 17.3mph)
G. Location of Maximum Flight Level Wind Inbound: 4 nautical miles (5 statute miles) to the NW (319°) of center fix
H. Minimum Sea Level Pressure: 1006mb (29.71 inHg) - Extrapolated
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 24°C (75°F) at a pressure alt. of 303m (994ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 26°C (79°F) at a pressure alt. of 290m (951ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 24°C (75°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Not Available
M. Eye Shape: Not Available
N. Fix Determined By: Penetration, Wind, Pressure and Temperature
N. Fix Level: 1,500 feet
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 3 nautical miles
Remarks Section:
Maximum Flight Level Wind: 30kts (~ 34.5mph) in the south quadrant at 22:28:00Z
Sea Level Pressure Extrapolation From: Below 1,500 feet
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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