First tropical depression of the season may form from 92L
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
Reader Comments
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when you posted them and they were moving so fast I felt like my eyeballs were going to pop out of my head lol
Stay safe this season, your first TD is heading for you so you know what that means! Buckle up, it's going to be a wild ride!
Question for Levi, how much do you agree with the change in the GFS upper analysis as indicated by 456?
We have a young teen-age blogger that blogs and forecasts like a meteorologist. We have a few
grown adults who wanna argue, over 92L.
92L is developing in a region of the MDR, about 1-1 1/2 months early. The SST are near 83-87F, about 2 degrees above normal, wind shear is light, at the moment.
I don't believe this will become a major storm. I don't believe anyone does, however, according to SHIPS model, it is a remote possibility. It is just interesting to see any tropical development near 7N/35W..
Just look at the definition of a tropical cyclone:
Tropical Cyclone:
A warm-core non-frontal synoptic-scale cyclone, originating over tropical or subtropical waters, with organized deep convection and a closed surface wind circulation about a well-defined center.
Usually the subjective "organized deep convection" and "about a well-defined center" are what is lacking in NHCs opinion with marginal systems.
Closed low: http://forecast.weather.gov/glossary.php?word=CLOSED%20LOW
Thanks for the answer IpswichWeatherCenter. I guess that's why they get paid and I don't. I would have already called it. Thanks Weather456 also.
Apocalypse
The banding pattern suggests that the structure of this system is well organized. Now, it just needs to put some meat on the bones...
It wasn't an unexpected change on the GFS for me. I figured if 92L took off it would drag the upper anticyclone with it and help push the TUTT out. So far it looks pretty good on the 200mb forecast. It has been handling these first TUTTs of the year pretty well.
...SPECIAL FEATURES...
A BROAD AREA OF CYCLONIC CIRCULATION IS IN THE CENTRAL TROPICAL
ATLANTIC EMBEDDED WITHIN THE ITCZ...FOCUSED ON A 1012 MB SURFACE
LOW CENTERED NEAR 7N35W IN. THE MOISTURE AND INSTABILITY
SURROUNDING THE LOW IS GENERATING SCATTERED MODERATE TO STRONG
CONVECTION FROM THE EQUATOR TO 13N BETWEEN 30W AND 44W. THIS
SYSTEM IS EMBEDDED IN A LARGE AREA OF DEEP LAYER MOISTURE NOTED
IN THE TOTAL PRECIPITABLE WATER IMAGERY. UPPER LEVEL DIFFLUENCE
ASSOCIATED WITH AN UPPER LEVEL RIDGE OVER NORTHEASTERN SOUTH
AMERICA IS HELPING TO VENTILATE CONVECTION AND SUSTAIN LIFT IN
THE SURFACE TO MID-LEVEL CYCLONIC CIRCULATION. THE UPPER AND
LOWER LEVEL ATMOSPHERIC CONDITIONS IN THE VICINITY OF THE LOW
APPEAR NOT TO BE FAVORABLE FOR CONTINUED ORGANIZATION OVER THE
NEXT COUPLE OF DAYS.
That's strange.
Not alot of rain for such a large storm - especially seeing as thats the centre of 92L
I second that...does not make the NHC look good if they have conflicting reports like that. But we know better.
Just one? I reckon theres quite a few of us.
Maybe they put the word "NOT" in by accident. Take that word out and it reads like the TWO.
LOL
Link
How quickly thinks can evolve with weather. Yesterday at this time, I was like everyone else in how impressed our wave was out in the Eastern Atlantic. It was designated to 92L a bit quicker than I anticipated. However, this large system has quickly organized much more than expected as well. This is very impressive indeed for this time of year to have a system like this out there. If this is a harbinger of things to come, my goodness we are for one long, long season of potentially potent and deadly storms out there.
92L looks very impressive on the satellite imagery and it appears that it is right on the threshold of being classified as a TD, and it may already be at that now. Plenty of time to monitor the system of course, and hopefully, a more hostile wind shear pattern within 96 hours will cripple this system as it approaches the Lesser Antilles.
Meanwhile, another very impressive wave is about to emerge off the coast of Africa within the next 24 hours and that will need to be watched in the coming days as well.
that is more likely
I think it's a typo as well
Lol...I guess we can unload on them now. MSLP difference of 1mb isn't that big of a deal, but makes you wonder how the communications between agencies are going.
then why would they say the opposite in the TWO they released not 30 minutes earlier?
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