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.

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988 mb hitting the lesser antilles..
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144
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Trof over the east is better defined and 94L is already showing a WNW movement.
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Quoting 954FtLCane:


132 hrs, I noticed this map includes shear in it.


Now this is more pleasant to look at. Yes, that is the shear map which is right below the other model on the Tropical section.
Member Since: December 31, 1969 Posts: Comments:
132 hours and west
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Quoting GTcooliebai:
00z GFS 120 hrs.



18z GFS 120 hrs.



pretty much identical o_O


GFS with consistency= near 100% certainty. I seriously think they gave the model Mother Nature's calender and itenerary this year. GFS this year has scored higher on track and intensity this year than any other model. Hopefully GFS will be be able to predict her two month period for atlantic hurricanes accurately before an 8 month menopause. (metaphorically speaking)
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132 hrs, I noticed this map includes shear in it.
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816. ryang
Quoting 954FtLCane:


for us olden ones


My poor house!
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Looks like the GFS basically just kills off Helene (eventually) this run. Beginning to doubt anything significant ever comes from her.
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Barbados would be the first to feel Isaac's effects, could even talk a direct hit!
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Quoting stormchaser19:
114 hours and here comes the ugly part of the history
Isaac and Joyce brother and sister like 2000 they really want to be together.
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Barbados look out, wow
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Quoting washingtonian115:
I think we all knew Isaac was more thank likely going to be the bad one of the season :(.
Maybe Isaac don`t want to be on the list anymore as the other veteran had gone.
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for us olden ones
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Somehow, this run will be stronger than the 18z and more than likely further west based on what I'm seeing.

Still should get plucked out of the Caribbean.
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114 hours and here comes the ugly part of the history
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Member Since: December 31, 1969 Posts: Comments:
00z GFS 120 hrs.



18z GFS 120 hrs.



pretty much identical o_O
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Quoting JLPR2:


By 114hrs still a mirror. :\ I'm thinking buying supplies after a second identical run might not be a bad idea. XD
Still a week to watch but could be those systems than just play by the book and dont change much.
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114 hours
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Quoting TropicalAnalystwx13:
Wind shear forecast for 94L.

SHEAR (KT) 20 23 21 16 14 8 7 4 6 6 1 6 3

As low as 1 knot of Shear, under 8 knots past 3 days. rising SST's and TCHP over predicted track
Gulp
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Back to 0Z.

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And the frames went screwy...

I realize the image changed to 12z.
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798. JLPR2
Quoting TropicalAnalystwx13:
A mirror of the 18z GFS so far.



By 114hrs still a mirror. :\ I'm thinking buying supplies after a second identical run might not be a bad idea. XD
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102 hours and west
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Quoting RTSplayer:


That's a little complicated, because I don't have pen and paper copies of tracking maps, and this site no longer keeps storm history on an per-update basis in the public archives, so finding the exact ones I had in mind would be pretty hard, and probably take me several days to sort through my memories and the resources on wikipedia to find them.

It's not like you're going to find a phrase "hurricane center re-positions storm coordinates," because when they do it, it's usually in a veiled manner, i.e. attempting to smooth it out.

Why they don't just come out and admit it is beyond me sometimes. Although a few times they actually have admitted it.

You typically get about one every season or two though, and some are more obvious than others.


You can probably start with TDs and TS which have strangely jerky tracks, or in a few cases discontinuities in the track, although again, you'll have to pay close attention to notice them.


And no I don't have them memorized, I just know for a fact I've seen it happen several times on both the NHC and TWC.
the nhc has archives check it out
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A mirror of the 18z GFS so far.

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I think we all knew Isaac was more thank likely going to be the bad one of the season :(.
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793. JLPR2
By 105hrs Joyce absorbed the 3rd low.
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Quoting stormchaser19:
84 hours, helene in the gulf again?

yes it has been there sitting and slowly strengthening
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Four days and Helene is still spinning in the Gulf.

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Wind shear forecast for 94L.

SHEAR (KT) 20 23 21 16 14 8 7 4 6 6 1 6 3
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789. JLPR2
Quoting Grothar:


TA, please stop posting that disgusting map. The colors are getting me stomach sick. It looks like someone poured Pepto Bismol over a purple icicle pop!!!


Haha! <--- Just had to waste a post like that, it was that good. :D
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Quoting Grothar:


TA, please stop posting that disgusting map. The colors are getting me stomach sick. It looks like someone poured Pepto Bismol over a purple icicle pop!!!


I like the green/yellow one better.
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Quoting Grothar:


TA, please stop posting that disgusting map. The colors are getting me stomach sick. It looks like someone poured Pepto Bismol over a purple icicle pop!!!


that version loads quicker..
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84 hours, helene in the gulf again?
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No not Ernesto part 3! That's getting boring
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784. JLPR2
Quoting TropicalAnalystwx13:
This is probably not going to turn out well.



On another note, the two lows behind 94L are doing the Fujiwara. :P
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Quoting TropicalAnalystwx13:


TA, please stop posting that disgusting map. The colors are getting me stomach sick. It looks like someone poured Pepto Bismol over a purple icicle pop!!!
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Quoting TropicalAnalystwx13:
This is probably not going to turn out well.



Not good at all.
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Quoting TropicalAnalystwx13:
lol
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This is probably not going to turn out well.

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Quoting scott39:
Yes, its still works very well. Do you have someone in mind?


Now that everyone has embarrassed me on the open blog and corrected my spelling, I may just use it. :)
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Quoting TXCaneCrasher:


Please tell me the storms they were off by 50-100 miles before? I would really like to know.


That's a little complicated, because I don't have pen and paper copies of tracking maps, and this site no longer keeps storm history on an per-update basis in the public archives, so finding the exact ones I had in mind would be pretty hard, and probably take me several days to sort through my memories and the resources on wikipedia to find them.

It's not like you're going to find a phrase "hurricane center re-positions storm coordinates," because when they do it, it's usually in a veiled manner, i.e. attempting to smooth it out.

Why they don't just come out and admit it is beyond me sometimes. Although a few times they actually have admitted it.

You typically get about one every season or two though, and some are more obvious than others.


You can probably start with TDs and TS which have strangely jerky tracks, or in a few cases discontinuities in the track, although again, you'll have to pay close attention to notice them.


And no I don't have them memorized, I just know for a fact I've seen it happen several times on both the NHC and TWC.
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The 00z Bams were updated a few minutes ago as they didn't do that earlier.

WHXX01 KWBC 180349
CHGHUR
TROPICAL CYCLONE GUIDANCE MESSAGE
NWS NATIONAL HURRICANE CENTER MIAMI FL
0349 UTC SAT AUG 18 2012

DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.
PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE
AND SUBTROPICAL CYCLONE INFORMATION.

ATLANTIC OBJECTIVE AIDS FOR

DISTURBANCE INVEST (AL942012) 20120818 0000 UTC

...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...
120818 0000 120818 1200 120819 0000 120819 1200

LAT LON LAT LON LAT LON LAT LON
BAMS 11.1N 25.5W 11.5N 27.5W 12.2N 29.2W 12.8N 31.5W
BAMD 11.1N 25.5W 11.4N 28.1W 11.9N 30.3W 12.4N 32.5W
BAMM 11.1N 25.5W 11.6N 28.3W 12.3N 30.6W 12.9N 33.0W
LBAR 11.1N 25.5W 11.4N 28.8W 11.9N 32.3W 12.3N 35.8W
SHIP 20KTS 25KTS 32KTS 43KTS
DSHP 20KTS 25KTS 32KTS 43KTS

...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...
120820 0000 120821 0000 120822 0000 120823 0000

LAT LON LAT LON LAT LON LAT LON
BAMS 13.4N 34.2W 14.7N 42.3W 15.1N 51.8W 13.4N 60.4W
BAMD 13.0N 34.7W 14.4N 39.8W 15.6N 45.2W 16.8N 49.6W
BAMM 13.5N 35.6W 14.7N 42.4W 15.2N 50.4W 14.7N 58.6W
LBAR 12.8N 39.3W 13.5N 46.3W 13.2N 51.3W .0N .0W
SHIP 51KTS 66KTS 82KTS 100KTS
DSHP 51KTS 66KTS 82KTS 100KTS

...INITIAL CONDITIONS...
LATCUR = 11.1N LONCUR = 25.5W DIRCUR = 270DEG SPDCUR = 17KT
LATM12 = 11.2N LONM12 = 22.0W DIRM12 = 270DEG SPDM12 = 17KT
LATM24 = 11.1N LONM24 = 17.3W
WNDCUR = 20KT RMAXWD = 50NM WNDM12 = 20KT
CENPRS = 1009MB OUTPRS = 1012MB OUTRAD = 150NM SDEPTH = S
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM
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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