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 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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somebody who isn't Kori didn't learn from Ernesto...

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.
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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.


so in other words, she is over water?
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523. JLPR2
Could that possibly be an eye on Gordon?

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Quoting RTSplayer:
Helene is moving WSW and is about 50 to 60 miles inland.



The HH may have been in some sort of ejected LLC earlier, but it's just not consistent with the radars in mexico, nor the radar in Brownsville, nor the satellites.



Looks can be deceiving...
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Quoting RTSplayer:
Helene is moving WSW and is about 50 to 60 miles inland.



The HH may have been in some sort of ejected LLC earlier, but it's just not consistent with the radars in mexico, nor the radar in Brownsville, nor the satellites.


disagreed, but I will wait to see what the NHC says
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Quoting RTSplayer:
Helene is moving WSW and is about 50 to 60 miles inland.



The HH may have been in some sort of ejected LLC earlier, but it's just not consistent with the radars in mexico, nor the radar in Brownsville, nor the satellites.
We will see what the next advisory says.
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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 ?
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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.
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Quoting redwagon:



You can see siamese twins here, too. Although it looks like the absorption has begun.


A lot of models missed that 2nd vortike. You can see them plainly there.
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Quoting ncstorm:
That storm will be huge enough to create it's own moisture field to the point where dry air won't be a problem for it like it has for so many other storms this year.
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Quoting Gearsts:
lol Already did, keeping them inform and they think im annoying.


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....
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514. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #1
TROPICAL DEPRESSION 16
9:00 AM JST August 18 2012
====================================

SUBJECT: Tropical Depression In Sea East Of The Philippines

At 0:00 AM UTC, Tropical Depression (1008 hPa) located at 19.0N 126.0E has 10 minute sustained winds of 30 knots with gusts of 45 knots. The depression is reported as moving south at 6 knots.

Dvorak Intensity: T2.0

Forecast and Intensity
========================

24 HRS: 18.5N 124.5E - 35 knots (CAT 1/Tropical Storm)
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Oh yup, agree after the newest maps you guys have posted, Helenes center looks just offshore still.

We must be having some of that pineapple express going on here...it's just after 3am, about 70' and 95% humidity.....70' is usually the high this time of year, not the nightly low! Thought might get a thunderstorm out of it...maybe tomorrow as it's supposed to be a bit warmer yet. If there was one after I got home from work will try and get a few images. But the few times there have been thinderstorms at night here, lightening is few and far between. I grew up in 110' heat, and this is too much for me now! haha I can't imagine being in the S/E US when I can't even cope with this! I'm def a cold weather person LOL
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Helene is moving WSW and is about 50 to 60 miles inland.



The HH may have been in some sort of ejected LLC earlier, but it's just not consistent with the radars in mexico, nor the radar in Brownsville, nor the satellites.
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Quoting ncstorm:


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

HairBear.


LOL.
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Quoting Tropicalupdate:
When is HH going in to TS Helene again?


12z tomorrow. Or about 8 AM eastern.
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Quoting stormchaser19:


Lol when she enter in the gulf again ,if enter


Once again, Helene has not made landfall
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Quoting BahaHurican:
Wait; are these from the same run?




YES! YES! YES! A thousand times YES! j/k
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Quoting BahaHurican:
Wait; are these from the same run?


Apparently !!
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Until 94L starts to loose the extra spin to the west and south of it don't expect development soon.We should start to see development late Sunday into Monday.
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Quoting Tropicsweatherpr:


You can see a faint S type in the cloud pattern there.


The best situation would be that it vanishes.... But that is not going to happen... Big low that looks organizing... Then the best situation would be that it reaches storm or hurricane status fast... models are more accurate forecasting developed systems...
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Quoting BahaHurican:
This is prolly the cleanest, easiest to read view of the GFS people post on here. Everything else is too colour-hectic or monochromatic.... Thanks, Grothar.


Thank you, Baha. My motto is keep it simple.
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Quoting Grothar:
GFS at 168 hours amd 180 hours one on the 24th and one on the 25th.






Wait; are these from the same run?

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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. :)

HairBear.
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Quoting Tropicalupdate:
When is HH going in to TS Helene again?


Lol when she enter in the gulf again ,if enter
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Quoting gustavcane:

Grothar, 94L passes right thru the first Hebert Box. this may be bad for South Florida if it takes this route.Link
http://upload.wikimedia.org/wikipedia/commons/a/a 7/Hebert_boxes.jpg


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. :)
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Quoting Grothar:


What I was doing in that entry was trying to explain why some models had it going more to the NW while others do not. There is a low to the east of 94L. If they were to interact, it could cause a type of Fujiwhara effect and perhaps move 94L more to the North if there is a weakness in the high.

Most of the other models do not appear to be using that scenario, which is why many have 94L moving further west at this time, and perhaps moving WNW as the system approaches the Antilles. Just an observation, a forecast.



You can see siamese twins here, too. Although it looks like the absorption has begun.
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Quoting Grothar:
GFS at 168 hours amd 180 hours one on the 24th and one on the 25th.






This is prolly the cleanest, easiest to read view of the GFS people post on here. Everything else is too colour-hectic or monochromatic.... Thanks, Grothar.
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Quoting KoritheMan:
0000 UTC microwave data for Helene:



This should put to rest the "she's inland" crowd.
When HH going into Helene again?
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Quoting Grothar:


It is also expected to be a rather large system.

... generating 30' waves at it's centre.
The swells from that would be substantial and destructive.
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492. JLPR2
Quoting Grothar:


Look closely at the dates, JL. One is for the 24th and the other is the 25th. It is from a loop run.


Eh? 18z has it crossing DR or the Mona Passage on the 25th.

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0000 UTC microwave data for Helene:



This should put to rest the "she's inland" crowd.
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Quoting sunlinepr:


Still a long way to go... Preventive preparation, call family and friends to be alert and we can only wait...
lol Already did, keeping them inform and they think im annoying.
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Quoting pottery:

If that's so, it puts the storm in the Caribbean sea on 24th, and back in the Atlantic on 25th.

It would have to cross the islands twice.

Sounds rather unpleasant.......


It is also expected to be a rather large system.
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488. wxmod
Quoting 954FtLCane:

That is some psychedelic african dust man!


That's a NASA rendition of dust.
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Quoting stormchaser19:
we are about a hour and half to see with what GFS comes.....lets see if the trends continues
When is HH going in to TS Helene again?
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Quoting BahaHurican:
Right... back from my weekly politics fix... lol

Not on this blog... lol

And I am sticking around until the 00Zs come out... want to see where the GFS ends up w/ 94L. I as skeptical as CyberTeddy about that massive swing in the GFS, and I want to see if it shows up for more than one run. Given the fact that we've had a couple of Caribbean runners already, I would not be surprised if we end up with such a track, but some consistency has to be shown.

What time would that be in Central time?
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Quoting redwagon:
Quoting Chicklit, Grothar:




You can see two distinct entities here. As Gro said, if the Eastern one gobbles up the Western one, the Fujuwharic effect will likely send the consolidated storm more North. If the Western one just slows down and absorbs the Eastern one and captures it, more likely to resume Westward movement after a hiccup or two.


What I was doing in that entry was trying to explain why some models had it going more to the NW while others do not. There is a low to the east of 94L. If they were to interact, it could cause a type of Fujiwhara effect and perhaps move 94L more to the North if there is a weakness in the high.

Most of the other models do not appear to be using that scenario, which is why many have 94L moving further west at this time, and perhaps moving WNW as the system approaches the Antilles. Just an observation, a forecast.
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Quoting sunlinepr:


You can see a faint S type in the cloud pattern there.
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Quoting JLPR2:


Even passing that far the GFS shows PR covered with hurricane force winds.


Yeah I see that.
Lets hope the models are wrong here......

But the high is strong, and this looks like a big one, with good conditions.
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Quoting washingtonian115:
Yes.I wasn't going down without a fight.However there were other fights reported in the area including robberies.
That is sad.
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Quoting Gearsts:
VERY bad because i live in Aguadilla.


Still a long way to go... Preventive preparation, call family and friends to be alert and then... only wait... keep on bloging.
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Quoting Tropicsweatherpr:
wash115, I am already preparing for anything that whatever this system may bring to PR if it comes to the Eastern Caribbean. I went today to a hardware store and bought panels,flashlights,candles and a power plant. I am avoiding the big rush when watches and warnings are issued.
It's not like they're going to go bad if you don't use them right away... early purchase also gives more time to figure out how to use them properly expecially the power plant, so that when you do need them, they work for you.

Multiple plusses...

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we are about a hour and half to see with what GFS comes.....lets see if the trends continues
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Quoting Grothar:


Look closely at the dates, JL. One is for the 24th and the other is the 25th. It is from a loop run.

If that's so, it puts the storm in the Caribbean sea on 24th, and back in the Atlantic on 25th.

It would have to cross the islands twice.

Sounds rather unpleasant.......
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476. JLPR2
Quoting pottery:

Check the wind-barbs there.
That's a really big system anticipated.


Even passing that far the GFS shows PR covered with hurricane force winds.

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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