First tropical depression of the season may form from 92L

By: Dr. Jeff Masters , 3:38 PM GMT on June 13, 2010

An unusually large and well-developed African tropical wave for so early in the season has developed midway between the coast of Africa and South America. The storm was designated Invest 92L by the National Hurricane Center yesterday, and has a good chance of becoming the first tropical depression of the Atlantic hurricane season. Surface winds measured by the 8:23am EDT pass of the European ASCAT satellite revealed that 92L already has a closed surface circulation, though the circulation is large and elongated. Top winds seen by ASCAT were about 25 mph. METEOSAT visible satellite loops show a large and impressive circulation that is steadily consolidating, with spiral bands building inward towards center, and upper-level outflow beginning to be established to the northwest and north.


Figure 1. Morning satellite image of Invest 92L.

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 - 30°C, which is warmer than the temperatures reached during the peak of hurricane season last year, in August - September. 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.) While 92L will cross over a 1°C cooler patch of water on Monday, the storm will encounter very warm SSTs of 28-29°C again by Tuesday.

The disturbance doesn't have to worry about dry air--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 300 - 400 miles from any substantial areas of dry air. The 60-day cycle of enhanced thunderstorm activity called the Madden-Jullian 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.

The forecast for 92L
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 is currently located at 7°N, well south of this band of high shear, and is only experiencing 5 - 15 knots of shear. This moderate amount of shear should allow for some steady development of 92L over the next few days as it tracks west-northwest at 10 - 15 mph. The National Hurricane Center is giving 92L a medium (30% chance) of developing into a tropical depression by Tuesday morning. Based on visible satellite imagery over the past few hours, I believe this forecast is not aggressive enough, and that 92L has a 50% chance of developing into a tropical depression by Tuesday morning. Another factor holding 92L back is its proximity to the Equator. I would give 92L higher chances of developing if it were not so close to the Equator. The system is organizing at about 7°N latitude, which is so close to the Equator that it cannot leverage the Earth's spin much to help it get spinning. It is quite unusual for a tropical depression to form south of 8°N latitude.

The farther south 92L stays, the better chance it has at survival. With the system's steady west-northwest movement this week, 92L should begin encountering hostile wind shear in excess of 30 knots by Thursday, which should be able to greatly weaken or entirely destroy the storm before it gets to the Lesser Antilles Islands. However, 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 by Saturday or Sunday next weekend. The GFDL and HWRF models are predicting that 92L will develop into a moderate strength tropical storm that will then be weakened or destroyed by the end of the week, before it reaches the islands. This looks like a reasonable forecast.


Figure 3. The departure of sea surface temperature (SST) from average for June 10, 2010. Image credit: NOAA/NESDIS.

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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3897. leo305
2:36 PM GMT on June 14, 2010
Quoting CaribBoy:
92L looks like those shered systems having most of weather on the their Northern side.


there is no shear over 92L right now
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3896. cg2916
2:26 PM GMT on June 14, 2010
NEW BLOG!!!
Member Since: December 21, 2007 Posts: 13 Comments: 3047
3895. SCwannabe
2:24 PM GMT on June 14, 2010
Quoting TropicalNonsense:
Surprize! ....



I think that is just convection associated with an ULL?? Looks impressive though!!
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3894. GeoffreyWPB
2:24 PM GMT on June 14, 2010
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3893. reedzone
2:21 PM GMT on June 14, 2010
This scenario is quite familiar to Karen (2007), Once Karen hit the wall of 40-50 knot shear, she dissipated, slowly, but also stalled do to the wind shear pushing her back and forth. It was a very gory death (tropical wise).
Member Since: July 1, 2008 Posts: 13 Comments: 7732
3892. CaribBoy
2:21 PM GMT on June 14, 2010
92L looks like those shered systems having most of weather on the their Northern side.
Member Since: October 6, 2007 Posts: 0 Comments: 8757
3891. extreme236
2:19 PM GMT on June 14, 2010
Quoting MiamiHurricanes09:
Yeah, I was about to say the same thing.



NHC surface map says its closed.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
3890. Patrap
2:19 PM GMT on June 14, 2010
Tropical Cyclone Heat Potential

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3888. MiamiHurricanes09
2:19 PM GMT on June 14, 2010
New Blog!
Member Since: September 2, 2009 Posts: 131 Comments: 21573
3887. Dropsonde
2:19 PM GMT on June 14, 2010
Based on the Windsat, it took quite the jog north overnight. (I have difficulty reading B&W visible sats for storms like this one, and the NOAA RGB that I prefer to use is still way off center.) The Windsat fix also indicates that it is definitely NOT decoupled from the convection and with the anticyclone aloft is not in danger of that. It just needs to put on some weight in its lower half.
Member Since: August 22, 2006 Posts: 10 Comments: 414
3886. reedzone
2:18 PM GMT on June 14, 2010
MiamiHurricanes09, though it will most likely change, notice the light wind shear currently from north of the islands to Florida?
Member Since: July 1, 2008 Posts: 13 Comments: 7732
3885. Drakoen
2:18 PM GMT on June 14, 2010
Quoting kmanislander:


Not closed as there are ENE winds on the South side of the circulation where West winds should be in order to have a closed low. No TD for now.


I wouldn't make judgements on whether it is closed or not based on the Windsat. Also that pass was 6 hours ago.
Member Since: October 28, 2006 Posts: 57 Comments: 32762
3884. beell
2:18 PM GMT on June 14, 2010
Quoting Skyepony:


I was unimpressed by the pressure but kinda far west too. The shift in wind made me sit up..


I think the ULL or at least some very sharp upper troughing will sit there for at least a couple of days. It will be hard to ignore-blob-wise!
Member Since: September 11, 2007 Posts: 158 Comments: 19999
3883. FLWeatherFreak91
2:18 PM GMT on June 14, 2010
In my opinion, 92l isn't a threat to anyone at all at this point. The islands are blocked by a wall of some intense shear. 92l will be torn to shreds and sent in the form of cirrus clouds to the north atlantic in about a day.
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3882. SavannahStorm
2:17 PM GMT on June 14, 2010
New blog is up.
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3881. MiamiHurricanes09
2:17 PM GMT on June 14, 2010
Quoting kmanislander:


Not closed as there are ENE winds on the South side of the circulation where West winds should be in order to have a closed low. No TD for now.
Yeah, I was about to say the same thing.

Member Since: September 2, 2009 Posts: 131 Comments: 21573
3880. CaribBoy
2:16 PM GMT on June 14, 2010
Quoting hurricane23:
Updated atl anomaly map is insane.



Lol wasn't it supposed to cool!?? Once again reality is way different.
Member Since: October 6, 2007 Posts: 0 Comments: 8757
3879. kmanislander
2:15 PM GMT on June 14, 2010
Quoting cg2916:
Do you guys think the ASCAT and Windsat show a closed low?


Not closed as there are ENE winds on the South side of the circulation where West winds should be in order to have a closed low. No TD for now.
Member Since: August 19, 2006 Posts: 0 Comments: 16723
3878. FLWeatherFreak91
2:14 PM GMT on June 14, 2010
oh man... someone should tell 92l that if he keeps going that direction he's screwed. This is going to be sad to see when it hits that shear.
Member Since: December 1, 2006 Posts: 2 Comments: 3779
3877. reedzone
2:14 PM GMT on June 14, 2010
Quoting robert88:
Looks like 92L has a small window of 24-48 hours and then it most likely reaches it's death. Trying not to be a downcaster. It's getting ready to hit the shear zone near 50W. 92L is a lot smaller system now too. It does appear right now it's trying to develop a CDO structure possibly. It hasn't given up completely just yet.


Early this morning, it looked like a classic Cape Verde Depression, now it still looks good but I hear some people on here say the circulation is exposed, but I see it right south of the deep convection. I believe a TD can form any moment. Your not a downcaster, you say "I think", not "this is how it will be". I agree, this is most likely going to get sheared. but a 40-50 mph. TS is not out of the question in my opinion.
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3876. SavannahStorm
2:14 PM GMT on June 14, 2010
Quoting hurricane23:
Updated atl anomaly map is insane.



Quite insane. Looks like the Pacific is rapidly transitioning to La Nina as well.
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3875. MiamiHurricanes09
2:14 PM GMT on June 14, 2010
Quoting DestinJeff:
There is a ULL situation in the NW GOM. The counter-clockwise flow around the ULL is creating between 20- 30 knts of westerly shear over the BOC.
.


This shear creates divergent flow aloft, which allows for air to rise and you get the thunderstorm blob seen on IR images.


However there is no low level spin associated with this blob ... no convergence or vorticty. This is strictly an upper-level dynamic taking place
Exactly.
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3874. Skyepony (Mod)
2:13 PM GMT on June 14, 2010
Quoting beell:
3837. Not too much happening at the surface, Skye. We'll see. Rising pressure/2knot west wind.

Pressure at the same buoy:


Link


I was unimpressed by the pressure but kinda far west too. The shift in wind made me sit up..
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3873. MiamiHurricanes09
2:13 PM GMT on June 14, 2010
Quoting kmanislander:


That is not 92L. Too far West. ASCAT missed it but see Windsat pass
I don't trust WindSAT as much as I trust the ASCAT. But regardless I would like to see what it shows.
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3872. cg2916
2:13 PM GMT on June 14, 2010
We have 92E, BTW.
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3870. charlottefl
2:13 PM GMT on June 14, 2010
Morning Everyone. When that subtropical jet lifts this season we're going to have problems. Shear over the tropical Atlantic is almost non-existent.
Member Since: December 18, 2006 Posts: 8 Comments: 2752
3868. MiamiHurricanes09
2:12 PM GMT on June 14, 2010
Quoting HouGalv08:
The monsters are coming alive out there. Take a look at the satellite loops of the G.O.M. There was NOTHING out there in the B.o.C yesterday, and today, BOOM!
There is nothing in the BOC, it just an area of divergence enhanced by the ULL to the north. Expect the convection to increase steadily throughout the evening and plummet when the sun sets. Anyways its a mid to upper level feature so no development is expected.
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3867. belizeit
2:12 PM GMT on June 14, 2010
Quoting cg2916:


That doesn't look closed.
i TOLD ascat thank you for missing it
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3866. hurricane23
2:12 PM GMT on June 14, 2010
Updated atl anomaly map is insane.

Member Since: May 14, 2006 Posts: 8 Comments: 13872
3865. kmanislander
2:12 PM GMT on June 14, 2010
Quoting belizeit:
Thank you ASCAT


That is not 92L. Too far West. ASCAT missed it but see Windsat pass
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3864. ElConando
2:12 PM GMT on June 14, 2010
Quoting cg2916:
Do you guys think the ASCAT and Windsat show a closed low?


ASCAT missed 92L they can tell you about Windsat.
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3863. Skyepony (Mod)
2:11 PM GMT on June 14, 2010
Compare sheer, steering, precip here.
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3862. ElConando
2:11 PM GMT on June 14, 2010
Quoting kmanislander:
92L windsat




Now that got it.
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3861. cg2916
2:11 PM GMT on June 14, 2010
Do you guys think the ASCAT and Windsat show a closed low?
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3860. ElConando
2:10 PM GMT on June 14, 2010
Quoting cg2916:


That doesn't look closed.


That's because it missed it.
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3858. beell
2:10 PM GMT on June 14, 2010
3837. Not too much happening at the surface, Skye. We'll see. Rising pressure/2knot west wind.

Pressure at the same buoy:


Link
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3857. SLU
2:09 PM GMT on June 14, 2010
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3856. kmanislander
2:09 PM GMT on June 14, 2010
92L windsat


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3855. nrtiwlnvragn
2:08 PM GMT on June 14, 2010
New East Pacific Invest


EP 92 2010061418 BEST 0 134N 1037W 20 1008 DB
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3854. cg2916
2:08 PM GMT on June 14, 2010
Quoting belizeit:
Thank you ASCAT


That doesn't look closed.
Member Since: December 21, 2007 Posts: 13 Comments: 3047
3853. Skyepony (Mod)
2:08 PM GMT on June 14, 2010
Quoting cg2916:


It's a shear-enhanced divergence area, once the shear goes away, it'll die. It can't develop into a TD.


ULL is giving it some a difluence aloft but it's found a sweet spot of shear of ~5kts..

Current steering is going to want to take it to an area of high shear, it's short on time but water temps like that & how it's tried over land the last few days, I'll give it an outside chance.
Member Since: August 10, 2005 Posts: 412 Comments: 43694
3852. MiamiHurricanes09
2:07 PM GMT on June 14, 2010
A track similar to #1 would optimize the length of 92L's existence, while a track similar to #2, would take 92L into the Caribbean and dissipate rapidly. Keep in mind, this is with current conditions, models do forecast a decrease in shear in the Caribbean.

Member Since: September 2, 2009 Posts: 131 Comments: 21573
3851. CaneWarning
2:07 PM GMT on June 14, 2010
Quoting ElConando:


On CNBC? Shouldn't they be talking about stocks?


They were, specifically oil stocks and rigs in the Gulf.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
3850. ElConando
2:06 PM GMT on June 14, 2010
Quoting leo305:


tropical wave reacting to an upper level low..


That's pretty much is what it is.
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3849. SavannahStorm
2:06 PM GMT on June 14, 2010
I blew my forecast because the diurnal orographic stratification was miscalculated or overlooked.
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3848. belizeit
2:06 PM GMT on June 14, 2010
Thank you ASCAT
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3847. robert88
2:06 PM GMT on June 14, 2010
Looks like 92L has a small window of 24-48 hours and then it most likely reaches it's death. Trying not to be a downcaster. It's getting ready to hit the shear zone near 50W. 92L is a lot smaller system now too. It does appear right now it's trying to develop a CDO structure possibly. It hasn't given up completely just yet.
Member Since: May 22, 2010 Posts: 0 Comments: 958

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