94L a threat to the Lesser Antilles; Gordon a hurricane; Helene hits Mexico

By: Dr. Jeff Masters , 3:24 PM GMT on August 18, 2012

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A large tropical wave that emerged from the coast of Africa Thursday night (Invest 94L) is located a few hundred miles southwest of the Cape Verde Islands off the coast of Africa, and is headed west at 15 - 20 mph. This storm is a threat to develop into a tropical storm that will affect the Lesser Antilles Islands as early as Wednesday. The storm is under moderate wind shear of 10 - 20 knots, and is over waters of 27.5°C. A large area of dry air lies just to the north of 94L, as seen on the latest Saharan Air Layer (SAL) analysis. This morning's 8:15 am EDT ASCAT pass caught the east side of 94L, and showed a partial surface circulation. Satellite images show just a modest amount of heavy thunderstorm activity, and I expect the earliest that 94L could develop into a tropical depression would be Sunday.


Figure 1. Morning satellite image of Invest 94L.

Forecast for 94L
The latest 8 am EDT run of the SHIPS model predicts that wind shear will be low, 5 - 10 knots, and ocean temperatures will gradually warm from 27.5°C to 28.5°C over the next four days, as 94L tracks westwards towards the Lesser Antilles. As is typical with storms making the crossing from Africa to the Antilles, dry air to the north will likely interfere with development. However, with shear expected to be low, dry air may be less of an issue for 94L than it was for Ernesto or TD 7. The storm should maintain a nearly due west track through Monday night, to a point near 50°W, about 700 miles east of the Lesser Antilles. At that point, a trough of low pressure passing to the north of 94L may be able to pull the storm more to the northwest, as suggested by the latest 06Z (2 am EDT) run of the NOGAPS model, and by three members of the GFS model ensemble forecast (Figure 2.) However, the models have been trending more towards a solution where this trough is not strong enough to influence 94L's path. This scenario will be more likely if 94L takes its time to develop, since a weaker storm will be smaller and shallower, and less likely to respond to the trough passing to the north. Our two best performing models, the GFS and ECMFW, both take 94L through the Lesser Antilles. The ECMWF, which predicts that 94L will stay weak and not develop, is faster, bringing the storm through the Lesser Antilles on Wednesday. The GFS model is slower, bringing 94L to the Lesser Antilles on Thursday as a hurricane. The models have shown poor run-to-run consistency in both the timing and the track of 94L, so it is difficult to assess which land areas might be most at risk, and when. A database of historical probabilities of storms in the same location as 94L maintained by Dr. Bob Hart of Florida State University reveals that historically, 45% of storms in this location have eventually hit land, with Canada (13% chance) and North Carolina (15% chance) the most likely targets. In their 8 am EDT Tropical Weather Outlook, NHC gave 94L a 40% chance of developing into a tropical depression by Monday morning.


Figure 2. The 00Z (8 pm EDT) run of the GFS model from August 17, 2012, was done 20 different times at low resolution using slightly different initial conditions to generate an ensemble of forecasts (pink lines.) The high-resolution operational GFS forecast is shown in white.

Gordon becomes a hurricane
Hurricane warnings are flying for the central and eastern Azores Islands as Hurricane Gordon heads eastwards at 18 mph. Gordon became the third hurricane of the 2012 Atlantic hurricane season at 5 am Saturday morning, and is sporting an impressive-looking eye on visible satellite loops. Gordon should be able to maintain hurricane status until Sunday, when wind shear will rise steeply to 30 - 40 knots, and ocean temperatures will drop to 25°C. The combined effects of high wind shear, dry air, and cooler waters will likely act to weaken Gordon to a strong tropical storm by the time it arrives in the Azores Islands Sunday night, but the storm will be strong enough to bring damaging winds and heavy rain to the Azores Islands. Gordon is not a threat to any other land areas, and the extratropical remnants of Gordon will not bring any strong winds or significant rain to Europe. The last time the Azores were affected by a tropical storm was in 2009, when Tropical Storm Grace brought 65 mph winds on October 4. No significant damage was reported. Ironically, the last hurricane to affect the Azores was the 2006 version of Hurricane Gordon, which caused minor damage in the Azores, consisting of mostly fallen trees and power outages. However, after Gordon became an extratropical low, four injuries due to falling debris from high wind were reported in Spain, and Gordon brought high winds and rain that affected practice rounds at the Ryder Cup golf tournament in Ireland. About 126,000 homes were without power after the storm in Northern Ireland and one injury was reported.


Figure 3. Morning satellite image of Hurricane Gordon.

Helene makes landfall in Mexico
Tropical Storm Helene made landfall near 10 am EDT as a tropical storm near Tampico, Mexico, with 40 mph winds. Helene's formation on August 17 ties 2012 with 1933 for the 2nd earliest appearance of the Atlantic's eighth tropical storm. Helene's rains should remain south of Texas, but moisture from Helene may feed into a stalled frontal system over the northern Gulf of Mexico and bring heavy rains to the northern Gulf Coast early next week.

I'll have a new post this afternoon, giving a quick global weather summary for July, the 4th hottest July in Earth's history.

Jeff Masters

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Morning RGB satellite captured all three of the systems we are watching in the Atlantic at various stages of development. Hurricane Gordon, T.D. Helene, and 94L:

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Quoting Tropicsweatherpr:


Trending with the 00z Euro on a weaker solution?

Not really.
Member Since: July 6, 2010 Posts: 113 Comments: 32523
Starting to intensify now:

Member Since: February 11, 2012 Posts: 84 Comments: 7941
does look weaker thusfar.
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Quoting TropicalAnalystwx13:
12z GFS is weaker than the 06Z run somewhat, but shows the same path.


Trending with the 00z Euro on a weaker solution?
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anyone see the 6z ensembles gfs memebers? 3/5 have a US landfall 2 in florida 1 in north carolina the other 2 have it skidding the outter banks
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99 hours. Weaker, but the same path.
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Quoting redwagon:

Huh? not sure how the HHers entered the conversation, but...OK...


If you were a HHer and I handed you this map and said find the center of 94L, what coords would you use for your initial flight plan?

30W, 11N? Thereabouts?

I still don't know what all this has to do with THIS:

Quoting BahaHurican:
I wonder how many remember the GFS long range about 10, 12 days ago spitting out several storms in a row... looks like it had the correct general idea...


It was just such a non sequitur that it caught my eye.
Member Since: October 25, 2005 Posts: 19 Comments: 22563
12z GFS is weaker than the 06Z run somewhat, but shows the same path.
Member Since: July 6, 2010 Posts: 113 Comments: 32523
Quoting wunderkidcayman:


My gut feelings still says Caribbean Hurricane 94L will be


I'm surprised you would say that. Any thoughts on intensity? Cat 3/4
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Quoting wunderkidcayman:


My gut feelings still says Caribbean Hurricane 94L will be


Eastern Caribbean. Too soon to make a call any further West than 63 degrees IMO.
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90 hours:

Member Since: February 11, 2012 Posts: 84 Comments: 7941
Quoting kmanislander:
West it is, even perhaps some short term motion to the WSW not out of the question.



My gut feelings still says Caribbean Hurricane 94L will be
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"This is a future model run and is meant for entertainment purposes only,
follow the NHC and/or your local official weather office for all accurate up to date information regarding your specific area."

This model depicts the possibilities as per the GFS model at 78 hours from 12Z, August 18th 2012.
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Quoting biloxibob:
tampa??


No, Tampa is the forbidden zone :)
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Derived from (NHC) ATCF data for HurricaneGordon for 18August12pmGMT
MinimumPressure decreased from 990millibars to 983millibars
MaxSusWinds increased from 60knots(69mph)111km/h to 70knots(81mph)130km/h
Vector changed from 98.1*East@19.1mph(30.7km/h) to 89.5*East@18.2mph(29.2km/h)

CVU-Corvo :: SMA-SantaMaria :: FNC-Madeira

The westernmost dot marks Gordon's position at the start of its 2nd day as a TropicalStorm
The westernmost dot on the longest line is where TS.Gordon became HurricaneGordon, and it's most recent position

The longest line is a straightline projection through H.Gordon's 2 most recent positions to its closest approach to the nearest coastline
17August12pmGMT: TS.Gordon had been headed for passage 452miles(727kilometres)SSWest of SantaMaria (bottom of the dumbbell beneath the straightline projection)
17August6pmGMT: TS.Gordon had been headed for passage 365miles(587kilometres)SSWest of SantaMaria (bottom of the blob beneath the straightline projection)
18August12amGMT: TS.Gordon had been headed for passage 348miles(559kilometres)SSWest of SantaMaria (top of the blob beneath the straightline projection)
18August6amGMT: TS.Gordon had been headed for passage 413miles(664kilometres)SSWest of SantaMaria (top of the dumbbell beneath the straightline projection)
18August12pmGMT: H.Gordon was heading for passage 267miles(430kilometres)South of SantaMaria in ~1day16hours from now (when this was posted)

Copy&paste cvu, sma, pxo, fnc, 30.71n27.5w, 31.806n26.621w, 32.03n26.46w, spc, vde, 34.3n51.1w-34.6n49.1w, 34.6n49.1w-34.4n47.0w, 34.4n47.0w-34.3n45.0w, 34.3n45.0w-34.2n43.1w, 34.2n43.1w-34.0n41.5w, 34.2n43.1w-31.211n27.162w, 36.928n25.017w-31.211n27.162w, 34.0n41.5w-34.0n39.6w, 34.0n41.5w-33.096n25.71w, 36.928n25.017w-33.096n25.71w into the GreatCircleMapper for a larger-scale map and other information
The previous mapping for comparison
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West it is, even perhaps some short term motion to the WSW not out of the question.

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"This is a future model run and is meant for entertainment purposes only,
follow the NHC and/or your local official weather office for all accurate up to date information regarding your specific area."

This model depicts the possibilities as per the GFS model at 72 hours from 12Z, August 18th 2012.
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Quoting mcluvincane:
Now why did Dr. Masters mention North Carolina? Don't need to be jinxed with this one. Really don't feel like getting the chainsaw and generator out again
Hey, would u rather him not say it and then get surprised???

Member Since: October 25, 2005 Posts: 19 Comments: 22563
Quoting Dakster:


Even a broken clock is correct twice a day.


If it's digital it could be once or none...
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Quoting Jedkins01:


"Remember when I asked your mom to the prom?"

"Shut UP Ted!"
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Quoting WxGeekVA:


Did I call it, or did I call it?
tampa??
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Obviously you wouldn't be posting that [now deleted 49] here.
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Member Since: July 6, 2010 Posts: 113 Comments: 32523


60 hours 12Z... Nothing special yet.
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Quoting WxGeekVA:


True, but somehow I knew that's what he would say...


Just don't let that go to your head. If you are correct time and time again, you get the bragging rights...

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Huh? not sure how the HHers entered the conversation, but...OK...

If you were a HHer and I handed you this map and said find the center of 94L, what coords would you use for your initial flight plan?

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Quoting Tropicsweatherpr:
Who is posting the 12z GFS?


Everybody... :P
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Quoting TropicalAnalystwx13:

It is according to the GFS's 10 meter winds...



Technically, the Saffir-Simpson scale says category 3/Major starts at 111mph, however they forecast and track storms in 5 or 10mph increments, so the lowest value that would get reported is 115mph.

The first barb on a map that would signify a major hurricane is 100kts, which is 115mph.

This would be shown as a double triangle on the barb.

There is nothing currently on any of the model runs for the GFS with a double triangle for any frame... possibly excluding the 1200 run since It's not done yet.

The highest I actually found for any system on the 0600 run was 75kts: Triangle, double hash, half-hash.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
ALTHOUGH THE GFS MODEL SHOWS
HELENE RE-STRENGTHENING OVER WATER IN 2-3 DAYS...THE OFFICIAL
FORECAST FOLLOWS THE OTHER MODELS AND INDICATES DISSIPATION BY 48
HOURS.

From top performer to outlier...can't win em all GFS.
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Who is posting the 12z GFS?
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Quoting Dakster:


Even a broken clock is correct twice a day.


True, but somehow I knew that's what he would say...
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Quoting WxGeekVA:


Did I call it, or did I call it?


Even a broken clock is correct twice a day.
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Quoting TropicalAnalystwx13:
One thing though...



That's a major hurricane, not a strong tropical storm.
Until we improve intensity forecasts, I'm leary about taking these "cat 5 DOOM" scenarios as gospel... more like with a grain or teaspoon of salt...
Member Since: October 25, 2005 Posts: 19 Comments: 22563
In base ball jargon the lesser antilles had two weak stikes in Ernesto and TD7. now this time is third time out with isaac.
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94L could become very interesting to watch in the coming days. My experience, although limited, tells me that the models will continue in their trending away from an out-to-sea solution. We shall see in the coming days.
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Quoting wunderkidcayman:


I'm not back yet I'm just checking in seeing whats going on

so far it is good

Hmm I don't know. but my gut is telling me, this will be a Carib/GOM system and the recurves in the GOM into Fl. not sure about the time frame, but thats what me guts telling


Did I call it, or did I call it?
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Quoting TropicalAnalystwx13:

It is according to the GFS's 10 meter winds...


There is no 100kts wind barb for the GFS on the 0600 run. The highest I found was 75kts, and two other 70kts barbs on the entire run.



Now the 1200 run is starting to be uploaded, so we may see some changes.

100kts shows up as double triangles on a wind barb.

90kts would be a triangle and 4 long hashes.

75kts is one triangle, 2 long hashes, and one short hash.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Not a major. A Category 2 actually.

Still a hurricane. :P

Member Since: July 6, 2010 Posts: 113 Comments: 32523
Also from the last blog...

Quoting stormchaser19:
OMG, my heart is pumping


I remember at the time thinking Georges was about as bad as it could get for a season... then we had Mitch. Pple forgot about Georges altogether for a while...

Quoting LargoFl:
I dunno..looking at 94L in this pic..does not look impressive at all..doesnt even look like its trying to form.....my hope is it stays disorganized..some people might get hurt with this one down the road if it doesnt......................
IIRC, NHC never expected more than slow development before tomorrow anyway... it's why they didn't go right to high. Like H23 and others have said, we have plenty of time to watch this.

Quoting wunderkidcayman:


I'm not back yet I'm just checking in seeing whats going on

so far it is good

Hmm I don't know. but my gut is telling me, this will be a Carib/GOM system and the recurves in the GOM into Fl. not sure about the time frame, but thats what me guts telling
I can see the CAR part of this. I think it's way too early to call anything else right now. There are too many complex relationships out there to resolve, especially if the Twave behind 94L does attempt its own, separate, cyclogenesis. What we might end up with is 94L catapulted off to the NW, while the system behind it meanders into the CAR...

Lots of possibilities out there.

Member Since: October 25, 2005 Posts: 19 Comments: 22563
Quoting LostTomorrows:
\hey, Gordon looks like he's mixing out that bit of dry air quite well. I think he may, in fact, make it to category 2 by day's end. His recurvature towards the Azores should also be happening then.

I should warn a good friend of mine who has taken a vacation to a family villa up there, he's not very attuned to weather, so he probably has no idea that there may be a hurricane barreling towards him. Seems that this Gordon is living up to his namesake's legacy of six years ago after all.

I love this blog... Even in the Azores, we know somebody... lol

Quoting washingtonian115:
Surprised Doc has not made a blog.
Thought about that earlier... maybe he's sleeping in... lol.

Quoting victoria780:
Let the guessing game begin,will Isaac re curve before the windwards >? between Puerto Rico and Hispanola or the trough is not deep enough to move it north and Isaac ends up in the gulf...Remember (Ike)
U mean as in curve up through the ECar, then swing west across The Bahamas and Florida into the GoM?

Or just straight west under the Antilles?

Quoting redwagon:

That last ascat SLU posted depicted the western half of a confused center.. Skyepony should get us the goods as soon as they come in. No need to send the HHs in until one storm gets absorbed by the other.
Huh? not sure how the HHers entered the conversation, but...OK...
Member Since: October 25, 2005 Posts: 19 Comments: 22563
Thank you, Dr. Masters
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THANK you Dr Masters, i have been on that forecast track since friday morning. i have been going with a cat 1 before the system gets to the cental antilles
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One thing though...94L is crossing a portion of water of 29 grades celsius now
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Thanks for the update Dr. Masters...so glad to see that I am probably going to get more rain this coming week..lol...looks like we all will be watching the tropics as 94L rolls across the ATL
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.