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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to me i was thinking it was more S
It is the first run though.
but I will check back in at 5pm for the latest update
wonder if it will be a TD by then??? hummm!!!
be nice and keep the info coming.
It may not even have that big of a problem with the TUTT to begin with, but the farther south it goes, the lower the shear it will have to deal with. I'm not sure what you mean by "north of the islands". The TUTT will keep conditions hostile north of the islands.
1. ATLANTIC and NORTHEAST PACIFIC Basins - TPC/NHC (also CPHC)
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5,
T3.0, or T3.5
Hurricane - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher
The point at which regular advisories are initiated is a little
subjective. A system with a Dvorak rating of T1.5 might be upgraded
to a tropical depression if it were in a position to affect a populated
area and/or if it seemed to be rapidly intensifying and its development
potential was considered excellent.
not good enough 1. ATLANTIC and NORTHEAST PACIFIC Basins - TPC/NHC (also CPHC)
MSW Averaging Period: 1 minute
Tropical Cyclone - generic term for systems of all intensities
Tropical Disturbance - distinct area of disturbed weather but
usually with no well-defined low-level circulation apparent/
regular advisories not issued/ usually corresponds to Dvorak
ratings less than T2.0
Tropical Depression - fairly well-defined low-level circulation/
MSW less than 34 kts/ Dvorak rating usually T2.0
Tropical Storm - MSW in range of 34-63 kts/ Dvorak rating T2.5,
T3.0, or T3.5
Hurricane - MSW exceeding 63 kts/ Dvorak rating T4.0 or higher
The point at which regular advisories are initiated is a little
subjective. A system with a Dvorak rating of T1.5 might be upgraded
to a tropical depression if it were in a position to affect a populated
area and/or if it seemed to be rapidly intensifying and its development
potential was considered excellent.
1.0 not high enough for TD status
I know you're alot more learned and skilled when it comes to weather than I am, but I disagree,just watch nature at work in the world today, nearly everything is in defiance of the norm, it's probably just a cycle that we find ourselves living in this time. just my opinion of course, you might be right but I disagree.
No kidding. Apparently that satellite sensor doesn't do well underneath convection.
is this the surface winds ?
Wow....
What the heck is that?
Now, Now!! Dont confuse matters!
It's only June 13th, dont you know!
heheheh
estimated surface winds
Islands????
We have a word for that in England - Fail.
I see 5-10 knots north of the Caribbean, towards the Bahamas.. Wait, is the TUTT causing that, and it can still rip apart anything that goes that direction?
Now I get it, 92L was just a distraction :O
BROAD AREA OF LOW PRES ACROSS THE CNTRL ATLC ALONG 37W IS BECOMING
BETTER ORGANIZED AND APPEARS THIS SYSTEM HAS A VERY GOOD CHANCE IN
BECOMING THE FIRST NAMED STORM OF THE 2010 HURRICANE SEASON. THIS
SYSTEM IS EXPECTED TO TRACK WNW OVR THE NEXT SVRL DAYS WITH MODEL
GUIDANCE INDICATING THIS SYSTEM ENCOUNTERING STRONG SHEAR AS IT
APPROACHES THE WINDWARD ISLANDS LATER IN THE WEEK. 12Z ECMWF AND
CANADIAN GLOBAL MODELS SEEM TO HAVE THE BEST HANDLE ON THIS
DEVELOPING CYCLONE AND BRING THE SYSTEM CLOSE TO THE REGION SAT BUT
AS AN OPEN WAVE. MAIN EFFECT FROM THIS SYSTEM LOOKS TO BE TORRENTIAL
RAINFALL. SO RIGHT NOW IT LOOKS LIKE NEXT WEEKEND COULD BE WET BUT
THIS IS HIGHLY DEPENDENT ON THE TRACK OF THE STORM WHICH HAS YET
TO FORM. GIVEN GOOD TRACK RECORD OF EUROPEAN MODEL WITH TROPICAL
CYCLONES OVER THE LAST FEW YEARS IT APPEARS WILL SEE INCREASING
CHANCES FOR WIDESPREAD RAINFALL NEXT WEEKEND. REGARDLESS OF
WHETHER THIS STORM FORMS OR NOT...BOTTOMLINE IS THAT CONDITIONS IN
THE TROP ATLC ARE ALREADY FAVORABLE FOR TROPICAL CYCLONE FORMATION
AND PEOPLE SHOULD GO OVER THEIR EMERGENCY PLANS AND BE READY FOR
THE NEXT TROPICAL CYCLONE THREAT NO MATTER WHEN IT MIGHT COMING
KNOCKING ON THE DOOR.
Its been there from the beginning, thats how it's so vented.
ok
91L?
Thats pretty darn impressive right there. The African Wave Train continues to amaze for this early in the season.
Ignore.... just jking
JFV DID
that is sick. hwrf picks up on it. wow.
92L is just stunning.
/?
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