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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Member Since: Posts: Comments:
Quoting SLU:
Very little doubt in my mind that 94L is already a TD. At this current trend, we could have a TD declared by 5pm ...

Maybe tomorrow morning.
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Quoting SLU:
Very little doubt in my mind that 94L is already a TD. At this current trend, we could have a TD declared by 5pm ...


Not there yet. But low-level rotation is becoming visible in visible satellite loops, which is the NHC usually gives a Code Red.
Member Since: Posts: Comments:
Quoting SLU:
Very little doubt in my mind that 94L is already a TD. At this current trend, we could have a TD declared by 5pm ...



Love that image. Helene, Gordon and 94L all in one frame.
Member Since: Posts: Comments:
iam fine

chillin as always

cooler now better
Member Since: July 15, 2006 Posts: 174 Comments: 54449
Quoting LargoFl:
Wow Largo...you are getting tons of rain today huh...
We had some early coasties this morn down here.
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Quoting Bayside:
They say the best place to be ten days out is under the eye, guess I'll find out. Going to Germany for two weeks, this is really making me nervous.


I don't think it will hit Gemany.
Member Since: July 17, 2009 Posts: 71 Comments: 26520
Quoting KEEPEROFTHEGATE:


its safe for a while anyway maybe more than a week

lol

how are ya press don't see ya much


Hey mon!!! All is well...been knocking out a bunch of work this summer...You good?
Member Since: Posts: Comments:
Intensity and track wise this can be a good analog track to Bertha 1996.

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268. SLU
Very little doubt in my mind that 94L is already a TD. At this current trend, we could have a TD declared by 5pm ...

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Quoting hydrus:
Reminds me of Donna, just further south..


That is one of the Analog comparison storms
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Dr. Neil Frank (one of the best) always stated that he did not start to pay close attention (US wise) until a storm reached the Antilles; that was close enough in time to get a better handle on the trof and ridging pattens 2-3 days out. Also, the models were not as sophisticated then as they are now. My point is, disregard the current long-term models showing a potential US impact; we will not have any real idea until the is storm is at the Antilles and the models recalculate all of the variables at that time.

No need to worry(if you are in the US) at this juncture.
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Gordon Dvorak
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Quoting presslord:


Does that mean we're safe from you posting photos of me in drag for a while?!


its safe for a while anyway maybe more than a week

lol

how are ya press don't see ya much
Member Since: July 15, 2006 Posts: 174 Comments: 54449
„ 1900: Galveston, TX, hurricane, resulted in more than 8,000 deaths, most by storm tide.
„ 1969: Hurricane Camille produced a 24-foot storm tide in Mississippi.
„ 1989: Hurricane Hugo generated a 20-foot storm tide in South Carolina.
„ 1992: Hurricane Iniki produced a 6-foot storm tide on the island of Kauai in Hawaii.
„ 2005: Hurricane Katrina generated a 27-foot storm tide in Mississippi.
„ 2008: Hurricane Ike produced a 20-foot storm tide in Texas.
Member Since: August 6, 2011 Posts: 4 Comments: 39276
I think Gordon is a Category 2 hurricane.

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Quoting emcf30:
East Coast DOOM Run

GFS 12Z

Reminds me of Donna, just further south..
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Quoting presslord:


Does that mean we're safe from you posting photos of me in drag for a while?!



LOL am not even going too be posting photos of you for a while



there is a time and place too post off topic photos and a time and place when its not and when we have storms out there now it is not the time too posting off topic photos
Member Since: May 21, 2006 Posts: 5091 Comments: 115244
Meanwhile... Gordon.

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This is the rigged SST:

Remember, yellow and green are less than 1C anomaly, so "near normal"...

Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting 7544:
interesting how strong is that while the approch on so fla and up the east coast tia 7days out and counting
by monday we should have abetter idea
Member Since: August 6, 2011 Posts: 4 Comments: 39276
Quoting Tazmanian:
with the blog geting vary busy now with 94L now is not the time too be posting off topic photos not un less you want a 24hr bannd for doing it




WHATS KILL WITH THE OFF TOPIC PHOTOS PLZS


Does that mean we're safe from you posting photos of me in drag for a while?!
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Member Since: August 6, 2011 Posts: 4 Comments: 39276
254. 7544
interesting how strong is that while the approch on so fla and up the east coast tia 7days out and counting
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Quoting LargoFl:
oh time to prepare folks, IF it dont come ok you are prepared for the one behind 94L..but if it does come..your ready way beforehand..unlike most of your neighbors who will be flying to the stores and finding out..they are OUT of what they need


What? Way too early for that....
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Quoting emcf30:
East Coast DOOM Run

GFS 12Z



looks like its heading to eastern end of lake ontario
lol

too far out to mean anything
Member Since: July 15, 2006 Posts: 174 Comments: 54449
Quoting RTSplayer:

Thanks. Other than Dean and Felix, and Wilma, whose RI was *after* they were established cyclones, I don't think storms just born could defy physics to go from 0 to 4 in 5 days. 'For entertainment purposes only', indeed.
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Quoting emcf30:
East Coast DOOM Run

GFS 12Z




Am I seeing that right, because that's a near repeat of Irene, except the model hooks 94L to the West, stalls for a day, and then it turns south west back into the mainland US...or else it merged with something I missed between frames...

Either way, that's a lot of rain.

Fortunately, the heaviest rains in the model run is off-shore always, but S. of PR and Hispaniola it was accumulation off the scale in 48 hours, so presumably at least 10 inches.

On land I think it got to 5 inches in Hispaniola. Not sure what it takes to be dangerous in Haiti, but it's vegetation free mountains, so that's gotta suck in the valley regions below...
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting emcf30:


And almost the entire Eastern seaboard. Thank goodness the track will change a gizzilion time from now to then, but, I believe the thinking is right...
oh time to prepare folks, IF it dont come ok you are prepared for the one behind 94L..but if it does come..your ready way beforehand..unlike most of your neighbors who will be flying to the stores and finding out..they are OUT of what they need
Member Since: August 6, 2011 Posts: 4 Comments: 39276
Quoting Stormchaser2007:


No thank you. I am done after Isabel and Irene!
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Quoting WxGeekVA:


Hey, I was about to do that!


I stole my Macaulay Culkin back. LOL
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#232: Oh No Baha, not that one!
We've got beach erosion bad enough now.
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Quoting MAweatherboy1:
New storm in the picture as we get to fantasy land:



I do not like that image... that is a strong TS sitting right over me.
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Quoting VAbeachhurricanes:


I'll hold down the fort while you are gone :p


Thanks, I really wanted to go after hurricane season, but wife's grandmother is really sick, so we were told to hurry. I'll do what I can prep wise and hope for the best I guess...
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Yikes!

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Quoting LargoFl:
in THAT run it would ruin alot of florida..oh boy


And almost the entire Eastern seaboard. Thank goodness the track will change a gizzilion time from now to then, but, I believe the thinking is right...
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Good Afternoon. Reading Dr. M's blog and looking at the latest model runs for 94L, looking like the pre-season is over and it is the start of game time. 94L is going to be a slow burner but the growing moisture envelope and persistent convection (which was not as prevalent yesterday) is most impressive. Classic pre-storm CV signature but still moving at a relatively fast clip of 15-12 mph.......Need to see when/if it slows downs a little more before reaching the vicinity of Antilles.
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Quoting emcf30:
East Coast DOOM Run

GFS 12Z



Hey, I was about to do that!
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Member Since: August 6, 2011 Posts: 4 Comments: 39276
with the blog geting vary busy now with 94L now is not the time too be posting off topic photos not un less you want a 24hr bannd for doing it




WHATS KILL WITH THE OFF TOPIC PHOTOS PLZS
Member Since: May 21, 2006 Posts: 5091 Comments: 115244




hope this doesn't verify. Don't like the rainfall potential with this
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Quoting Bayside:
They say the best place to be ten days out is under the eye, guess I'll find out. Going to Germany for two weeks, this is really making me nervous.


I'll hold down the fort while you are gone :p
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Quoting emcf30:
East Coast DOOM Run

GFS 12Z

in THAT run it would ruin alot of florida..oh boy
Member Since: August 6, 2011 Posts: 4 Comments: 39276
They say the best place to be ten days out is under the eye, guess I'll find out. Going to Germany for two weeks, this is really making me nervous.
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Hi DC while I'm here I though I'd visit the White House at 336 hrs
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Quoting mcluvincane:
Dare i say floyd part deux
More like this:

Member Since: October 25, 2005 Posts: 19 Comments: 22322

324 hrs....visiting Norfolk and VA Beach....

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Quoting 954FtLCane:


300 hrs, 981 mb

Looks to be around the Jacksonville, NC area..nothing is set in stone and models are trending west..if it keeps doing that, this might end up being a texas storm
Member Since: August 19, 2006 Posts: 13 Comments: 15688
Quoting MAweatherboy1:
New storm in the picture as we get to fantasy land:

Joyce could play a major part in Isaac's track and keep him pinned up against the coastline and perhaps further west. What the GFS is showing is a similar situation to what occurred between Hurricane Dog and Easy in 1950.



Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting redwagon:

I know, by then the mystery of how the models created such a monster so quick will be irrelevant by then. Cat 4 in 5 days.. harrumph.


The mystery is solved by this:



That graphic attempts to show the max potential intensity based on maximum thermodynamic potential between the ocean and the anticipated outflow in the upper levels of a hypothetical storm. The hotter the water, the higher the clouds will rise, and the higher they rise, the cooler the atmosphere.

Plus, if the atmosphere is already cooler anyway for some reason, it makes the potential intensity even higher.

For example, some storms make -90C cloud tops very easy, because they are probably under a cold pocket anyway, while other storms in seemingly similar surface conditions may struggle to get beyond -60C clouds.

Anyway, this shows the maximum theoretical limit for TODAY, it's not valid 5 days from now, so some areas will come down slightly, while others will continue to rise.

I wouldn't expect much change in the Gulf except maybe slightly larger numbers, since nothing significant is moving across it right now, but the area east of the L. Antilles and pretty much the whole Caribbean can easily make category 5 pressures (so small category 5 storms, or big category 4 storms).


The models have this data input in it's raw form in the form of TCHP and other values, which is why some of them like to take this thing to high cat 3 or low cat 4.
Member Since: January 25, 2012 Posts: 33 Comments: 1520

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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.

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