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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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.
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East Coast DOOM Run

GFS 12Z

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St.Pete is getting hit now.................
Member Since: August 6, 2011 Posts: 4 Comments: 37950
POSS T.C.F.A.
XXL/INV/94/XX
MARK
13.83N/30.31W
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312 hrs, 980 mb.. NC landfall...dare I say Wilmington, NC?

"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 312 hours from 12Z, August 18th 2012.
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300 hrs, 981 mb
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Quoting RTSplayer:
I guess I should have held my comment till the end of the model run...on the 8th day it takes a left-hand turn and goes right over Haiti after drifting around over or near land for nearly a whole day...

That would not be good at all, and I absolute HATE slow moving Hispaniolan Tropical Storms because they tend to kill a lot of people. They'd literally be better off with a fast moving cat 1 or cat 2...


Even tropical storm Debbie killed some people around here...
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288hrs, 984 mb
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Quoting stormchaser19:
GFS is showing
1- A weaker system approaching lesser antilles trends more to the west and late recurve
2- A strong System approaching the lesser antilles trend more to WNW and early recurve

If you look at the current loops the rain field is expanding and it's looking more symmetrical.
Link Wide ATL
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Quoting TropicalAnalystwx13:
What'd I ever do to you?

..IF this pans out,alot of people are going to get hurt, I do hope people up and down the eastern seaboard have their plans and preps ready..NOW is the time to finish up and do so...1-2 days in advance and the stores will be cleaned out of what you need...damn i wish this would recurve OUT into the atlantic and miss the coastline
Member Since: August 6, 2011 Posts: 4 Comments: 37950
Quoting 954FtLCane:


264 hrs @ 992 mb
Jfv is having a heart attack of happiness with these run.
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Quoting MAweatherboy1:
This is just another of about a million scenarios that could happen:

Thanks 4 this... wanted to see if it put the storm in that "sweet" spot I've been talking about all season... lol...

ON a more serious note, everything that's hit that spot this season has blown up and given FL and the NW Bahamas a deluge...
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Quoting mcluvincane:
Dare i say floyd part deux


the entire SE east coast evacuated..yeah good times..
Member Since: August 19, 2006 Posts: 13 Comments: 15091

276hrs, 986 mb....crawling and sippin on the Gulfstream and getting drunk
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Quoting MAweatherboy1:
Looks like DC:



I can see my house under the eye!
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Quoting TropicalAnalystwx13:

984 mb.


Thanks!
Member Since: August 19, 2006 Posts: 13 Comments: 15091
Quoting 1900hurricane:
I'd say Gordon looks pretty good.


It's looking pretty handsome.
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Can you guys post the mb's of those awful color quick plot maps..they are really hard to see..
Member Since: August 19, 2006 Posts: 13 Comments: 15091
Isaac would probably be retire if the Gfs run verifies.
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New storm in the picture as we get to fantasy land:

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264 hrs @ 992 mb
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Dare i say floyd part deux
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Look familiar?

Edit: Of course it does... somebody just posted the track... lol
Member Since: October 25, 2005 Posts: 19 Comments: 21883
Quoting ncstorm:


what mb is that TA?

984 mb.
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Quoting trey33:


Too good. All the mulch we laid yesterday is now washed out and is in the street... ugh
..amazing rain alright
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Quoting Stormchaser2007:
Redeveloping in the southern Bahamas by 228 hours.

Off of SE Florida by 240.
Will u post the 228 hrs pls?

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Oh goodie! GFS just makes me feel great...
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DOOM @240
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Quoting WxGeekVA:




lol ;)
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Quoting RTSplayer:
I guess one good thing about the new GFS is that it has the storm being much weaker, and making landfall on the Dominican side of the island, so at least Haiti would be spared the worst of the rains.

With all the crap they've suffered the past few years, I wouldn't want to see another disaster from rain runoff there.


BTW...

Are there any attempts to re-plant trees, or at least grass or shrubs in Haiti to preserve what's left of the environment, or is it pretty much just doing nothing and being all swept away?!


I kinda take offense since I live IN the Dominican Republic :P ... About forestation in Haiti though the problem is the haitians use wood for fire when cooking (they do not have the facilities to use gas... so they predate whatever trees they get their hands on...
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Quoting LargoFl:
Tampa got it good too after us...........


Too good. All the mulch we laid yesterday is now washed out and is in the street... ugh
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Quoting Jedkins01:



Well really it looks like things are starting to die down now somewhat, the air has stabilized some near us additional, storms have weakened as they reach the coast. we'll see what happens a little later. My street is flooded pretty good so we've had our share, almost 3 inches here.
..oh yeah it Poured here for about an hours or so non stop..im looking at the gulf and the dark clouds and boomers are coming closer..we'll see
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Right over my house @312
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1979 Hurricane David:

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Looks like DC:

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Quoting TropicalAnalystwx13:
What'd I ever do to you?



what mb is that TA?
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Quoting 1900hurricane:
I'd say Gordon looks pretty good.



Considering the location, definitely looking good.

Eye symmetry is ok, I guess, but the SE quadrant has really struggled today with the shear and dry air.


If there had been an anti-cyclone this might be a major hurricane right now, but the dumb westerly shear on the south side is really hindering the south side's convection.
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228 hrs..strengthing between Cuba & FL at 1000mb
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Quoting kmanislander:


New pass for Ascat will not happen until early this evening.

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.
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Yikes.

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Betters the whole East Coast as a strong hurricane.
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What'd I ever do to you?

Member Since: July 6, 2010 Posts: 113 Comments: 31882
Back later
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216hrs. reemerges Cuba at 1002 mb
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Quoting RTSplayer:
I guess I should have held my comment till the end of the model run...on the 8th day it takes a left-hand turn and goes right over Haiti after drifting around over or near land for nearly a whole day...

That would not be good at all, and I absolute HATE slow moving Hispaniolan Tropical Storms because they tend to kill a lot of people. They'd literally be better off with a fast moving cat 1 or cat 2...


No kidding, true the US always rejoices at a weaker storm but still.. that particular scenario would kill a lot of people.
Member Since: July 8, 2005 Posts: 259 Comments: 23880
GFS is showing
1- A weaker system approaching lesser antilles trends more to the west and late recurve
2- A strong System approaching the lesser antilles trend more to WNW and early recurve
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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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