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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1276. trey33
Quoting LargoFl:
..if it makes it to This point..it could be dangerous for us, me i hope it recurves before that point but we'll see, half the models bring it here, half recurve..too early to tell just yet


Largo,
what is the timing if it does?
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Quoting CybrTeddy:
06z GFS showed a nasty hurricane hitting the US. 3rd run in a row that something might happen like this, starting to show consistency. Lost the ECMWF model support, but the UKMET is developing this which is rare for the two to disagree so sharply. 00z ECMWF run should be discounted.
I was just about to ask about the 00Z GFS... did it still show the system going through the NE Car and up towards the US coast?
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1274. SLU
.... and I must agree with you Teddy. This season is far more interesting than last year at this same stage.
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1273. SLU
Quoting CybrTeddy:
Meanwhile, Hurricane Gordon is putting on a show. ADT thinks it's already a Category 2.

CI# /Pressure/ Vmax
5.0 / 964.9mb/ 90.0kt


Gordon could pass for a 100mph hurricane in my books.

Meanwhile pre-Isaac seems to be getting its act together.
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Quoting MAweatherboy1:
Looks like it should miss the US this run:

Nothing about the high in this image suggests a northward track....
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Check out the Windsat Coriolis for 94L
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Quoting LargoFl:
if it just stays right there half on the coast half off..and continues northward, might be a good thing for the parched area's of southern texas, most of the models have this down to a Low again sooner than later, for now something to watch,wait and see what happens

Good Morning, if you click on GOM WV Loop and then click on Trop Points, you see it is forecast to become a low as it strafes the coast.
Ya never know. Especially with the front coming into the GOM. Stranger things have happened.
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Gordon's eye is huge. Nearly a degree wide.
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Good morning. Here is the San Juan NWS take on this.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
506 AM AST SAT AUG 18 2012


THE ELEPHANT IN THE KITCHEN...SO TO SPEAK...IS THE GFS FORECAST OF A
HURRICANE PASSING BETWEEN CULEBRA AND SAINT THOMAS LATE SATURDAY.
THIS CAUSES NORTHEAST FLOW AT THE SURFACE TO BEGIN THURSDAY AND
STRENGTHEN FRIDAY AND SATURDAY. ENSEMBLE SOLUTIONS SHOW A WIDE
RANGE OF TRACKS AND THE GFS LIKELY HAS NOT STABILIZED SUFFICIENTLY.
THE GFS TRACK SOLUTION WAS WELL TO THE NORTHEAST OF THE ISLANDS 24
HOURS AGO AND THE 18Z RUN SHOWED THE STORM PASSING TO THE SOUTH A
LITTLE EARLIER...BUT AM UNABLE TO LOAD MOST OF THE PARAMETERS FROM
THIS...18/00Z...MODEL FORECAST PACKAGE DUE TO THE UNCERTAINTY YET IN THE
FORECAST AND THE SEVERITY OF THE CONDITIONS FORECAST...EVEN FOR A
SYNOPTIC SCALE MODEL. SOME CHANGE TO THE TRACK IS LIKELY AND IT IS
IMPOSSIBLE TO TELL IF THIS WOULD TAKE THE CYCLONE NORTH OR SOUTH
OF THE AREA...ALTHOUGH FORMATION IN THE NEXT 72 HOURS SEEMS MORE
LIKELY THAN IT WAS YESTERDAY. THEREFORE WILL SIMPLY SAY THAT THIS
SOLUTION IS PLAUSIBLE AND PRELIMINARY SEASONAL PREPARATIONS SHOULD
BE COMPLETED AND DOUBLE CHECKED...BUT NO CONFIDENCE CAN BE GIVEN
TO THE CLOSE-PASSAGE SCENARIO YET.
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Morning everybody.... I see Gordon did go to hurricane overnight... as I expected... and 94L is up to 30%....

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CMC:


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Meanwhile, Hurricane Gordon is putting on a show. ADT thinks it's already a Category 2.

CI# /Pressure/ Vmax
5.0 / 964.9mb/ 90.0kt
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06z GFS showed a nasty hurricane hitting the US. 3rd run in a row that something might happen like this, starting to show consistency. Lost the ECMWF model support, but the UKMET is developing this which is rare for the two to disagree so sharply. 00z ECMWF run should be discounted.
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folks im not buying the end of the operation run of the GFS. it will come down to how much it erodes the ridge and how deep it digs out. if it lifts out fast, then the system could turn back west
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1259. VR46L
Quoting MAweatherboy1:

Or not. Weakens it for some reason and brings it west:



It weakens it because it is affected by the land on the Islands in my opinion ... and dont forget the large stalled front could act as a magnet Just my opinion... I dont want that scenario but the way everything is getting set up It could be a very dangerous time .Helena was to go west but is going North
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CI# /Pressure/ Vmax
5.0 / 964.9mb/ 90.0kt
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Quoting MAweatherboy1:
Ouch.




Damn!!! Right over Boston!!
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Ouch.



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Awfully close to our North Carolina friends

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Going between Bermuda and the US:

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Gordon might be more than 75mph:

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1251. LargoFl
..................well coffee time..see you all later..happy hunting lol
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Hard right:

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Quoting MAweatherboy1:
Looks like it should miss the US this run:


Or not. Weakens it for some reason and brings it west:

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1248. LargoFl
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Looks like it should miss the US this run:

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1245. LargoFl
Quoting AtHomeInTX:
Ouch Puerto Rico

..if it makes it to This point..it could be dangerous for us, me i hope it recurves before that point but we'll see, half the models bring it here, half recurve..too early to tell just yet
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1244. LargoFl
Quoting MAweatherboy1:
Good morning! The 6z GFS is coming in. 180 hours:

good morning, yep an interesting week for sure coming up
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Good morning! The 6z GFS is coming in. 180 hours:

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Ouch Puerto Rico

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1241. LargoFl
south Texas can sure use Helene to cool things off a bit huh..............
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1240. VR46L
Gordon sure is the most beautiful Atlantic storm this season so far

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1239. LargoFl
gee alabama has been getting whacked pretty hard these last few days.....................BULLETIN - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WARNING
NATIONAL WEATHER SERVICE BIRMINGHAM AL
504 AM CDT SAT AUG 18 2012

THE NATIONAL WEATHER SERVICE IN BIRMINGHAM HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...
CENTRAL PICKENS COUNTY IN WEST CENTRAL ALABAMA...

* UNTIL 530 AM CDT

* AT 504 AM CDT...THE NATIONAL WEATHER SERVICE INDICATED A SEVERE
THUNDERSTORM CAPABLE OF PRODUCING DAMAGING WINDS IN EXCESS OF 60
MPH. THIS STORM WAS LOCATED NEAR PICKENSVILLE...AND MOVING EAST AT
45 MPH.

* LOCATIONS IMPACTED INCLUDE...
CARROLLTON...GORDO...DILLBURG...OWENS AND KIRK.

WINDS OF 60 TO 70 MPH WILL BREAK LARGE TREE LIMBS AND CAUSE SOME
DAMAGE...ESPECIALLY TO SMALLER STRUCTURES.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

FOR YOUR PROTECTION...MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF
YOUR HOME OR BUSINESS.
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Scene Type : EYE
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1237. LargoFl
Quoting STXHurricanes2012:
Basically the gfs kills helene cause of possible upswelling and being stationary at that spot! I like it that it takes back out over water but disagree dissipating it though but will see!
yeah i kinda agree, this system does not want to die lol..been around for weeks now huh, if it gets back over water again, could rebuild once again..gee we'll see what happens and where it is tomorrow
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It would be nice if Helene's center appear on radar to track. It would be something to watch!
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Basically the gfs kills helene cause of possible upswelling and being stationary at that spot! I like it that it takes back out over water but disagree dissipating it though but will see!
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Finally starts to feel the trough here

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1233. LargoFl
GMZ001-182030-
SYNOPSIS FOR THE GULF OF MEXICO
524 AM EDT SAT AUG 18 2012


.SYNOPSIS...TROPICAL STORM HELENE NEAR 21.6N 97.0W AT 18/0900 UTC
MOVING NW AT 6 KT WITH MAXIMUM SUSTAINED WINDS 35 KT GUSTS TO 45
KT. HELENE IS FORECAST TO MOVE TO 21.9N 97.6W NEAR THE COAST THIS
AFTERNOON...THEN INLAND TO 22.4N 98.1W SAT NIGHT...THEN WILL
BECOME A REMNANT LOW OVER MEXICO THEREAFTER. OTHERWISE A RIDGE
ALONG 27N/28N WILL PERSIST THROUGH THE WEEKEND. A COLD FRONT MAY
ENTER THE NW GULF MON...SLOWLY DRIFTING E ACROSS THE NORTHERN
WATERS THROUGH WED.

$$
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Quoting rmbjoe1954:


I do not think 94L will dissipate.


Not if it does that no. :(
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Gordon RAW T#

Final T# Adj T# Raw T#
3.4 3.9 5.4
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1230. LargoFl
Quoting AtHomeInTX:
GFS dissipates Helene in a few days basically where she is now. And though I was hoping it would drop it it still shows 94l.

yes helene wont be a big deal, just a rain maker, 94L is the one to watch this coming week, especially if it makes it to the Islands, might recurve before that, we will see
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Quoting AtHomeInTX:
GFS dissipates Helene in a few days basically where she is now. And though I was hoping it would drop it it still shows 94l.



I do not think 94L will dissipate.
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GFS dissipates Helene in a few days basically where she is now. And though I was hoping it would drop it it still shows 94l.

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1227. LargoFl
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Quoting LargoFl:
if it just stays right there half on the coast half off..and continues northward, might be a good thing for the parched area's of southern texas, most of the models have this down to a Low again sooner than later, for now something to watch,wait and see what happens


Yep if she could ride the coast up and pump some rain into those areas it would help. As long as it's not too much in one place.
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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