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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Stop it with the downcaster crap
I am a realist.
I can't see why the NHC keeps it down to 50%. This thing has a closed, not very elongated LLC, and VERY organized convection. It's been strengthening, and it's currently at 25 knots (28.7 mph) and 1010 MB pressure. IMO, this is definitely a TD, why can't the NHC see that?
If I seem nooby or arrogant to you, I'm normally not like this.
No Taz. All he did was point out the models that dissipate the system.
The NHC likes to take small steps. They aren't going to make a big jump on way or the other very quickly.
N ATL WV Loop
Link
Link
Which I said earlier as well and agree with but, for all intensive purposes, the BAMMS aren't really that much further south. A more southern to central entry would be optimal, similar to the XTRAP.
And yes I know the XTRAP Is not a model.
JFV???
Funny, you sound familiar.
Just back to check the situation==
I see that the track-models are beginning to come together in a tighter cluster for the Islands. Further south than earlier.
I see some Models are doubting that the system will get to the Islands at all.
I see everyone trying to figure out what happens next.
Welcome to Tropical Weather, and particularly to 2010.
Gonna be some fun and games around here.........
The area is rife with surface divergence and high wind shear. If the ridge to the north remains strong enough, it could force this system to move into the Caribbean.
LOL
Wouldn't it be amusing if it turned out to be a really experienced member
That is what some people fail to understand
Looks to be developing a really nice CDO.
That is some high shear.
yea
funny! LOL
really taz....cmon now...your sounding like a wishcaster to me...stop labeling everyone giving their own opinions...especially if they are giving you model data...
Surface winds in the Caribbean is no greater than 15 knots in 5 days.
am this trying too be funny
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
INDICATE A MEDIUM CHANCE...50 PERCENT...OF THIS SYSTEM BECOMING
A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.
they did update the TWD
126 hrs....look closely as the SE Caribbean, notice the bulge in low shear from 92L's upper anticyclone
I've been lurking since 2005 and am very grateful for the blog. I'm not a meteorologist and maybe this is obvious and old hat to you folks but...
I've noticed on the Meteosat East Atlantic AVN Color Infrared satellite imagery that waves just before they exit Africa having a center that goes all the way off the color band into a grey/silver seem to have the greatest potential to develop. You can see it with 92L. The wave behind it had some as well but not as much. The bigger and more centralized the grey/silver, the more likely it seems the wave will have the "oomph" to turn into a tropical storm when it reaches a favorable environment. Am I just seeing things? or is this what the models are focusing on? And what does that grey/silver center really mean?
Thanks. Just curious but I've found it interesting. :)
Link
Yes, much less than they were when the last tropical wave passed through the islands 4 days ago. The strong trades have moved west into the western-central Caribbean.
Yea them and the CMC have been performing the best with this system
Common sense always prevail!
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