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Unusually well-organized 92L disturbance may become a tropical depression

By: Dr. Jeff Masters , 2:14 PM GMT on June 14, 2010

Invest 92L, a remarkably well-developed African tropical wave for so early in the season, is midway between Africa and the Lesser Antilles Islands. Infrared satellite loops show a modest area of heavy thunderstorms along the north side of 92L's center of circulation, and the storm's heavy thunderstorms activity appears to be slowly increasing in intensity and areal coverage. Upper-level outflow is apparent to the west and north of 92L, and the outflow has been gradually improving this morning. Visible satellite loops do not show much in the way of low-level spiral bands, and my current take from the satellite imagery is that 92L is slowly organizing, and will not become a tropical depression any earlier than 11pm EDT tonight (Monday.) A 4:27 am EDT pass from the WINDSAT satellite saw a partially closed circulation at the surface (open on the south side), with top surface winds of 25 - 30 mph north of the center.


Figure 1. Morning satellite image of Invest 92L (left side of image) and a vigorous new tropical wave that has moved off the coast of Africa (right side.) None of models develop the new tropical wave, but it bears watching.

Sea surface temperatures
Climatology argues against development of 92L, since only one named storm has ever formed between Africa and the Lesser Antilles Islands in the month of June--Tropical Storm Ana of 1979 (Figure 2). However, sea surface temperatures (SSTs) underneath 92L are an extremely high 28°C, and will increase to 29°C by Thursday. In fact, with summer not even here, and three more months of heating remaining until we reach peak SSTs in the Atlantic, ocean temperatures across the entire Caribbean and waters between Africa and the Lesser Antilles are about the same as they were during the peak week for water temperatures in 2009 (mid-September.)

Dry air not a problem for 92L until Wednesday
The disturbance doesn't have to worry about dry air today or Tuesday--Total Precipitable Water (TPW) loops show a very moist plume of air accompanies 92L, and water vapor satellite loops show that the center of 92L is at least 200 - 300 miles from any substantial areas of dry air. As 92L continues to push northwest, though, the SHIPS model is predicting that relative humidity at middle levels of the atmosphere will fall from the current value of about 70%, to 60% on Wednesday. This dry air may begin to cause problems for 92L on Wednesday, especially since wind shear will be increasing at the same time. Tropical cyclones are more vulnerable to dry air when there is substantial wind shear, since the strong winds causing the shear are able to inject the dry air deep into the core of the storm.

Madden-Julian Oscillation
The 60-day cycle of enhanced thunderstorm activity called the Madden-Julian Oscillation is currently favoring upward motion over eastern tropical Atlantic, and this enhanced upward motion helps create stronger updrafts and higher chances of tropical cyclone development.


Figure 2. Tropical Storm Ana of 1979 was the only June named storm on record to form between Africa and the Lesser Antilles Islands.

Wind shear
A major issue for 92L, like it is for most June disturbances, is wind shear. The subtropical jet stream has a branch flowing through the Caribbean and tropical Atlantic north of 10° N that is bringing 20 - 40 knots of wind shear to the region. Our disturbance was located near 10°N, 40°W at 8am EDT this morning, a few hundred miles south of this band of high shear, and is currently only experiencing 5 - 10 knots of shear. This low amount of shear should allow for some steady development of 92L over the next two days as it tracks west-northwest or northwest at 15 mph. The latest run of the SHIPS model is predicting the shear will rise to 20 knots on Wednesday, which may start to cause problems for 92L.

The forecast for 92L
The National Hurricane Center is giving 92L a high (60% chance) of developing into a tropical depression by Wednesday morning, which is a reasonable forecast. The odds of development have increased since yesterday, as the storm has moved considerably to the northwest, away from the Equator. Now it can leverage the Earth's spin to a much greater degree to help get it get spinning. It is quite unusual for a tropical depression to form south of 8°N latitude.

I expect that 92L's best chance to become a tropical depression will come on Tuesday, and the storm could strengthen enough by Wednesday to be named Tropical Storm Alex. The farther south 92L stays, the better chance it has at survival. With the system's steady west-northwest movement this week, 92L will probably begin encountering hostile wind shear in excess of 20 knots by Wednesday, which should interfere with continued development. Several of our reliable models do develop 92L into a tropical storm with 40 - 55 mph winds, but all of the models foresee weakening by Thursday or Friday as 92L approaches the Lesser Antilles Islands and encounters high shear and dry air. I doubt 92L will be anything stronger than a 45 mph tropical storm when it moves through the northern Lesser Antilles Islands on Friday and Saturday, and it would be no surprise if wind shear has destroyed the storm by then. However, as usual, surprises can happen, and the GFS and the SHIPS model (which is based upon the GFS) do indicate that more modest levels of wind shear in the 15 - 20 mph range late this week may allow 92L to stay stronger than I'm expecting. Residents of the islands--particularly the northern Lesser Antilles--should follow the progress of 92L closely, and anticipate heavy rains and high winds moving through the islands as early as Thursday night.

Oil spill wind forecast
There is little change to the oil spill wind forecast for the coming two weeks. Light winds of 5 - 10 knots mostly out of the south or southeast will blow in the northern Gulf of Mexico all week, according to the latest marine forecast from NOAA. These winds will keep oil near the coast of Louisiana, Alabama, Mississippi, and the extreme western Florida Panhandle, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range 8 - 16 day forecast from the GFS model indicates a typical summertime light wind regime, with winds mostly blowing out of the south or southeast. This wind regime will likely keep oil close to the coastal areas that have already seen oil impacts over the past two weeks.

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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Quoting Orcasystems:


tell the truth, you were on facebook... harvesting your crop before ranger Rick shows up.
Hey was you watching me????

LMAO
The sad part is.... "That's what I was Doing"
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2390. scott39
Quoting Levi32:


It will be on the edge....we shall have to see. It has a lot to deal with right now.
Thanks
Member Since: December 31, 1969 Posts: Comments:
I don't know if I expressed it right, but I am in agreement with you Kman. It's just some can not let it go. You can state your opinion but after awhile it starts to sound like a broken record.
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2388. Levi32
Quoting scott39:
If it stays more W than WNW or NW for the next 48 hours, will it avoid strong ripping apart shear?


It will be on the edge....we shall have to see. It has a lot to deal with right now.
Member Since: December 31, 1969 Posts: Comments:
2386. scott39
Quoting Levi32:


Not a massive change, but there has been a westward shift in heading during the last few hours.
If it stays more W than WNW or NW for the next 48 hours, will it avoid strong ripping apart shear?
Member Since: December 31, 1969 Posts: Comments:
well weathersp yes the caribbean has shear but it is also becoming weak
Member Since: December 31, 1969 Posts: Comments:
2383. MZV
We have learned before that the NHC forecasters themseleves don't agree on things. There may have been quite a lot of debate behind the scenes how to classify this ... (after all there isn't that much else to watch right now and it's been such a knife-edge choice how to call it.)

I suspect, just like among ourselves, the junior forecasters feel more inclined to "call it" and the senior forecasters say wait for the proof.
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Quoting taco2me61:
yelp and I need to stay off of Facebook because when I come back I lose more post like the last 50 LOL

Taco:o)

Oh Yea from what I see in the GOM is ULL with a T-Wave going into the E-Pac


tell the truth, you were on facebook... harvesting your crop before ranger Rick shows up.
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Quoting galvestongal:
What is that in the BOC?


Bay of Campeche in the GOM.
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2379. Levi32
Quoting galvestongal:
What is that in the BOC?


A portion of a tropical wave interacting with a 200mb low. It is not a threat to develop.
Member Since: December 31, 1969 Posts: Comments:
since Levi mentioned it, i came across this site. Most of you probably know about it.
Link

http://www.usno.navy.mil/USNO/astronomical-applications/data-services/rs-one-day-us
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2377. Levi32
Quoting scott39:
Levi do you see a big shift of W motion with 92L?


Not a massive change, but there has been a westward shift in heading during the last few hours.
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Quoting Acemmett90:
ahhh i see i left and all hell has broken lose
yelp and I need to stay off of Facebook because when I come back I lose more post like the last 50 LOL

Taco:o)

Oh Yea from what I see in the GOM is ULL with a T-Wave going into the E-Pac
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Quoting gordydunnot:
Kman I am sure some of the premiere blogger s here don't bother to read the Doc's blog first, before they post on it.Or they must believe he is a little to old now and losing it. It's alright to have an opinion but please defer to knowledge if not age.Stop beating A DEAD HORSE.


I thought I had
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2373. scott39
Levi do you see a big shift of W motion with 92L?
Member Since: December 31, 1969 Posts: Comments:
Reviewing recent satellite imagery from the past few hours or so, Invest 92L has begun moving on a more westward course as most models had been indicating. Will be very interesting to see what this does overnight and how the overall upper level environment changes.
Member Since: Posts: Comments:
Kman I am sure some of the premiere blogger s here don't bother to read the Doc's blog first, before they post on it.Or they must believe he is a little to old now and losing it. It's alright to have an opinion but please defer to knowledge if not age.Stop beating A DEAD HORSE.
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2368. Levi32
Quoting btwntx08:
we got so much proof and i believe ur still wrong k and levi is correct


It's not a slam-dunk either way...just a difference of opinion, which happens a lot in this field.
Member Since: December 31, 1969 Posts: Comments:
Quoting Levi32:


11:27pm tonight. Currently 21 hours 53 minutes of daylight per day.

Levi you know your stuff
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Quoting wunderkidcayman:
the system is moving west and I expet all the models to shift into the Caribbean I expect shear to decrease and we could have TS ALEX
While the models don't always have it right. The Caribbean sill has shear...
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Quoting btwntx08:
we got so much proof and i believe ur still wrong k and levi is correct


That's ok. I don't mind.
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2362. xcool
lol rob..
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the system is moving west and I expet all the models to shift into the Caribbean I expect shear to decrease and we could have TS ALEX
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2358. Levi32
Quoting RitaEvac:
Levi, what time does the sun set up there where your at?


11:27pm tonight. Currently 21 hours 53 minutes of daylight per day.
Member Since: December 31, 1969 Posts: Comments:
my thoughts on 92L feel free to leave comments or questions!!!
Member Since: December 31, 1969 Posts: Comments:
What is that in the BOC?
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2354. Levi32
Quoting Orcasystems:


As the crow flys (no pun intended) your what, about 40 miles from it?


60-70 miles.
Member Since: December 31, 1969 Posts: Comments:
Quoting CosmicEvents:
Normally, these African land-canes hit the water and go poof. This year, with the ocean water at RECORD highs they're exploding more when they hit the water.
.
.
In all seriousness I think we may see sometime this year the African continent plopping a system that gets classified as a TS/Hurricane before it's 400 miles from the African coast.


Didn't that actually happen a couple years ago?
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Quoting btwntx08:
we had a CLOSED LOW period lol


wow
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2350. 7544
u can see it spining now
Member Since: December 31, 1969 Posts: Comments:
Quoting CosmicEvents:
Normally, these African land-canes hit the water and go poof. This year, with the ocean water at RECORD highs they're exploding more when they hit the water.
.
.
In all seriousness I think we may see sometime this year the African continent plopping a system that gets classified as a TS/Hurricane before it's 400 miles from the African coast.

LOL
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2348. K8eCane
Lots of differing opinions tonight and we all know that opinions are like bleep bleep. We all have one
Member Since: Posts: Comments:
Normally, these African land-canes hit the water and go poof. This year, with the ocean water at RECORD highs they're exploding more when they hit the water.
.
.
In all seriousness I think we may see sometime this year the African continent plopping a system that gets classified as a TS/Hurricane before it's 400 miles from the African coast.
Member Since: Posts: Comments:
Quoting Levi32:


Lol, coincidence I assure you. I haven't heard from it in quite a while. It's back to being a beautiful site, and nothing more.


As the crow flys (no pun intended) your what, about 40 miles from it?
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2345. Ossqss
Quoting Orcasystems:


Good to see you back JFV :)
Jeff has your shower curtain :)


LoL, not mine! You trouble maker :)

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Levi, what time does the sun set up there where your at?
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2342. MZV
I always say: "West of 55 and they come alive" - 92L does not need to do much for the next day or two, other than hang together.
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Quoting kmanislander:
For the very last time, a closed low is not the only yardstick to determine whether to classify a TD. You can have a closed low but insufficient convection or vice versa. When we have had one we have not had the other.

What's the point ?. You never had a TD.


Yup, your right.. it is the last time I will see
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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

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