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 ncstorm:


TWC is salivating right now..
So is the major media networks..they just can't wait...Someone's Labor day plans are going to be ruined.
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GFS 18Z: Very bad news for the Islands and the East coast while gulf coast residents' hurricane kits are still collecting dust
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Quoting Hurricanes4life:
From a nova scotian perspective it looks like an Earl track on 18z. still fantasy land though haha, lots still to change!


I was thinking the same thing (from a NC perspective). Man was that a stressful one... hope Isaac doesn't follow suit. Good thing is if the models are predicting it this far in advance, it probably won't happen
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Quoting Felix2007:
Newfoundland's next


As rigged/ridiculous as that looks, the SST anomaly probably supports it easily...

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So hybrid of Dean and Earl?
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Quoting ncstorm:
from the previous blog..

Joe Bastardi is going to have a field day with that run..


JFV is probably crying
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From a nova scotian perspective it looks like an Earl track on 18z. still fantasy land though haha, lots still to change!
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Quoting washingtonian115:
GFS basically says to hell with the north east and wipes NYC off the map..


TWC is salivating right now..
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Quoting washingtonian115:
GFS basically says to hell with the north east and wipes NYC off the map..


I'm sorry that situation is not funny at all, but the way you said it definitely made me lol
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from the previous blog..

Joe Bastardi is going to have a field day with that run..
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the last frame and oh, next player up to bat at Africa
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GFS basically says to hell with the north east and wipes NYC off the map..
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Quoting Levi32:
18z GFS makes much more sense with 94L's long-term track, more in line with my thoughts from earlier. Still a long time to work on this one.


Don't say that....
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Newfoundland's next
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Most of this year's storms have been weak, though

Yea, but most of them have been unique unlike in 2011. None of them where below 60mph for example, Beryl plowed into Florida in May as a near hurricane for another example. Ernesto was probably a Category 2 based on the many sub 975mb pressure readings and 100mph sustained winds recorded. This season is a lot more interesting than 2011.

Isaac could be a bad one I'm afraid if (big emphasis on the if) it manages to not recurve as it reaches the islands.
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Quoting Levi32:
18z GFS makes much more sense with 94L's long-term track, more in line with my thoughts from earlier. Still a long time to work on this one.
Levi, is the east coast in danger of 94L?
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With the models changing their tune drastically from run to run

um no kidding..the 18z run..WOW!!!
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18z GFS makes much more sense with 94L's long-term track, more in line with my thoughts from earlier. Still a long time to work on this one.
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Thanks, Doc.
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Things are gonna get ugly.

Thanks for the new blog Doc.
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Thanks Doc.Your going to be a busy man over these coming weeks...
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ugh dr this had too do a new blog right when the mode run where comeing out
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Thanks doc
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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