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

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Quoting KoritheMan:
Not really sure why everyone is impressed? The deepest convection isn't even over the center...
Nonetheless, there is still convection over the center and a closed low. I thought those were the requirements for a TD. Well they used to be at least.....
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2740. KEEPEROFTHEGATE (Mod)
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2739. EricSFL
You guys remember 97L last year... Boy that thing looked like a strong TS in the middle of the Atlantic, yet it never even got a red circle. lol
Member Since: May 26, 2010 Posts: 0 Comments: 821
2738. xcool
WHAT ABOUT ANA 2009
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2737. xcool
Acemmett90 .I Try not
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Quoting Acemmett90:
i spy an eye

PINHOLE EYE ...
Oh .. it's just a spot absent of convection? .. well that's less than exciting ..... uhmm ..
PINHOLE SPOT ABSENT OF CONVECTION!!!
MUCH better
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Quoting SouthDadeFish:
Someone take a look at this, and tell me you don't see the lower-level black clouds swirling about a center. It's very well defined. I don't understand.


It needs to be classified. It is so much better organized than Tropical Storm Danny or Erica ever was last year.
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1234 Levi32 "Supposedly the highest ever recorded sea-surface temperature was 95 degrees fahrenheit..."

I think it was in the Gulf of Aqaba.
Member Since: August 21, 2007 Posts: 0 Comments: 4860
2731. xcool
Gustav OMG
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Not really sure why everyone is impressed? The deepest convection isn't even over the center...
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2727. xcool
TD HERE.IMO..
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That "eye" feature really reminds me of Gustav back in '08 when it was a TD. Then it rapidly intensified into a cane. Lol not saying that will happen this time.
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2724. xcool
Acemmett90 he look at you
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2723. KEEPEROFTHEGATE (Mod)
Quoting WindDamage:


night, lev. sweet dreams.
maybe ya should give him a kiss
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2721. EricSFL
Quoting SouthDadeFish:
Shortwave imagery shows clear cyclonic turning at the low levels.


true
Member Since: May 26, 2010 Posts: 0 Comments: 821
This should definitely be classified at 5 AM, although I really doubt they will. :( Really am looking forward to reading the NHC's thoughts on survivability and forecast track.
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2719. xcool
. JLPR2bye .lol
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Quoting Houstonia:


Thanks SouthALWX!

you got it :)
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2717. JLPR2
Quoting KoritheMan:
Looks like convection is attempting, once again, to wrap cyclonically into the center.

Not overly impressed though, as convection has actually waned in recent frames.


yeah...
well, 92L has officially pissed me off, if its going to develop it should do it already and if its going to die it should already, I'm tired of looking at it firing just enough convection to survive ¬¬

Well, off to bed, lets see what 92L did tonight tomorrow morning,
night! :D
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Quoting EricSFL:
I also think it is a depression. But maybe we're seeing the "wrap-around" of convection in the mid-levels and not a well defined circulation at the surface.
Shortwave imagery shows clear cyclonic turning at the low levels.
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2715. xcool
SouthDadeFish.nice defined center
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2714. EricSFL
I also think it is a depression. But maybe we're seeing the "wrap-around" of convection in the mid-levels and not a well defined circulation at the surface.
Member Since: May 26, 2010 Posts: 0 Comments: 821
Someone take a look at this, and tell me you don't see the lower-level black clouds swirling about a center. It's very well defined. I don't understand.
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Quoting SouthALWX:

he's saying seabreeze storms may start firing after the middle of the week, but if you are smart you'd bet on the oppressive heat and drought to continue.


Thanks SouthALWX!
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2711. xcool
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Looks like convection is attempting, once again, to wrap cyclonically into the center.

Not overly impressed though, as convection has actually waned in recent frames.
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I honestly think this is a depression now. Idk what the NHC is waiting for. Looking at satellite, there must be a closed center. I understand it may die, but as of right now this thing looks much better than many depressions I've seen.
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2708. xcool
come on 92L YOU CAN DODODO
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Quoting xcool:
wrapping around nowwwww woww


It's not exploding or wrapping around. Holding its own and convection has weakened a touch. Nothing big happening right now
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Quoting melwerle:


I'm in San Diego...and we have no idea if it's a precursor...


Thanks. Just wondering b/c I have family members in L.A.
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Quoting Houstonia:
Can someone translate this into regular English for me and tell me what our local forecaster is saying in this Houston/Galveston discussion?

Synoptic gradient across state appears to relax enough past middle-week to allow the mesoscale to become more of a player (sea breeze)...but smart Money is on subsidence. If this does continue to win out...this will be an unfortunate circumstance for US. On average...it is drier at this time this year than last year. Iah rainfall is at a 1.59" deficit...7.96" at hou...in relation to 2009's year-to-date rainfall.
In contrast...our northerly neighbors in cll are on the other side of it...with a surplus of 5.09"! 31

he's saying seabreeze storms may start firing after the middle of the week, but if you are smart you'd bet on the oppressive heat and drought to continue.
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2702. EricSFL
Hi btw!
Member Since: May 26, 2010 Posts: 0 Comments: 821
2701. xcool
lol
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2699. EricSFL
Good night Levi, thanks.
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Quoting tennisgirl08:


where are you in Cali? is this a precursor to a larger quake?


I'm in San Diego...and we have no idea if it's a precursor...
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2697. xcool
yep
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2696. 7544
Quoting xcool:
wrapping around nowwwww woww


yeap in dmax soon
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2695. Levi32
I'm out too, night all.
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Can someone translate this into regular English for me and tell me what our local forecaster is saying in this Houston/Galveston discussion?

Synoptic gradient across state appears to relax enough past middle-week to allow the mesoscale to become more of a player (sea breeze)...but smart Money is on subsidence. If this does continue to win out...this will be an unfortunate circumstance for US. On average...it is drier at this time this year than last year. Iah rainfall is at a 1.59" deficit...7.96" at hou...in relation to 2009's year-to-date rainfall.
In contrast...our northerly neighbors in cll are on the other side of it...with a surplus of 5.09"! 31
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Quoting melwerle:
GT...I listen to my bird now. The dogs started to bark and i kind of blew them off tonight.


where are you in Cali? is this a precursor to a larger quake?
Member Since: July 17, 2008 Posts: 0 Comments: 1242
2692. Levi32
Quoting EricSFL:
Levi, according to the run, would the storm in the Gulf come from 92L or is it from the wave behind it?


The storm depicted is 92L but this is 10 days out on a model that likes to blow things up. It should not be taken seriously at this point....92L first needs to survive and be an intact system at the islands before we can even begin to think about anything specific beyond that.
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Quoting winter123:


Ah, gotta love CMC doomcasts. I cannot believe anyone takes that model seriously. But maybe it's ok for canada weather, eh?

Its good for midlatitudes and therfor is sometimes useful when looking at a trough picking up a TC ... outside of that? HA HA HA!
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Dr. Masters co-founded wunderground in 1995. He flew with the NOAA Hurricane Hunters 1986-1990. Co-blogging with him: Bob Henson, @bhensonweather

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