Unusually well-organized 92L disturbance may become a tropical depression
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
Reader Comments
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92L is full of tricks I tell you! Full of tricks!
Anything that forms there will pose a threat from Brownsville northward to Corpus Christi.
0z GFS shows unfavorable westerlies for the first couple days, though.
92L looks a little sick to me tonight, as it is still entraining dry air on its SE quadrant. You have to give it credit, though.
What about 92W wave its posibble to developed?
Agree, low-level flow is generally southerly to the SW of surface ridging to the NE and to the SE of that low pressure system over the Central US that wreaked havoc with flooding in Oklahoma today.
Upper flow is also southerly to the E of that dimishing W Gulf of Mexico upper low. Yep, if things thing develops, will track N toward Texas coast. At least it will stay W of the Gulf oil spill.
Agreed with regards to both.
Nothing imminent right now, but it is something I'd keep a wary eye on if I was at the Texas coast. This right now doesn't have a closed low pressure spin, its just the north end of a tropical wave right now, but the atmosphere is gradually becoming more favorable for development. Its got improving outflow to west and east with W Gulf upper low and Caribbean TUTT enhancing the outflow. Plus, shear is reducing as W Gulf upper low fades out. Sort of reminds me of Erin 2007 a little (upper low faded out, then N end of tropical wave spun up).
If the westerlies persist as long as the GFS insists they will (though they do slacken some by 30-36 hours, but still remain at around 20 kt, still not really all that favorable), then the heaviest precipitation will remain offshore in the event that something does form here.
Wouldn't be surprised if this thing persisted and the NHC came on later this morning or afternoon with a yellow circle and said something like "showers and thunderstorms are increasing in the western Gulf of Mexico. Some slow development of this system is possible over the next 48 hours." I wouldn't be surprised either if it stayed as a yellow circle its whole life, this is nothing appearing immenint right now, just keeping a wary eye on it.
This is likely the catalyst for 92L's lack of convection on the east side. No TD as long as it can't wrap around.
yeah I am a little surprised it has maintained its composure throughout the night
DMIN occurs during the day. o_O
All day, but peaks just before sunset.
That it did. We won't be so lucky during the heart of the season.
Last I checked, steering took it predominantly W. Upper-level winds remain conducive for development, and are forecast to continue to be so.
Morning
Well if that's not a TD then let's not play TD for the rest of the season. Look at how tight the circulation is. It has to be generating winds of at least 30mph.
92L 1st visible image of the day.
NATIONAL WEATHER SERVICE SAN JUAN PR
553 AM AST TUE JUN 15 2010
THE LOW PRESSURE CURRENTLY NEAR 12 NORTH AND 43 WEST IS SLIGHTLY
BETTER ORGANIZED THAN IT WAS 24 HOURS AGO AND ROTATION IS STILL
REMARKABLE FOR A SYSTEM THIS TIME OF THE YEAR...NEVERTHELESS THE
MODELS HOLD NO MORE HOPE FOR IT TO DEVELOP INTO A TROPICAL
CYCLONE NOW THAN THEY DID YESTERDAY AND SO EXPECT THIS SYSTEM TO
PASS AS AN OPEN WAVE. INCREASING SHEAR TO THE LOWS NORTHWEST
SUPPORTS THIS SCENARIO. THE LOW MAY ALSO BE INGESTING SOME DRY AIR
ON ITS WESTERN SIDE SINCE VISIBLE IMAGERY YESTERDAY SHOWED SAHARAN
DUST TO THE NORTH OF THE LOW THAT COULD MAKE ITS WAY INTO THE LOW
AND KEEP IT FROM DEVELOPING FURTHER. THE ECMWF SHOWS THIS DRY SLOT
PASSING JUST NORTH OF THE AREA WEDNESDAY EVENING. WITH THE OPEN
WAVE...THE ECMWF BRINGS IN THE HEAVIEST MOISTURE ON SATURDAY...BUT
THE GFS...ALTHOUGH NOT QUITE AS WET...PROLONGS THAT MOISTURE THROUGH
TUESDAY IN A LONG TAIL THAT MAY WELL BE THE REMNANTS OF THE MOST
RECENT WAVE TO HAVE CLEARED THE AFRICAN CONTINENT. EITHER
WAY...EXPECT INCREASED SHOWER AND THUNDERSTORM ACTIVITY BEGINNING
FRIDAY AND PEAKING SATURDAY AND SUNDAY. A THIRD WAVE MAY ARRIVE ON
THE THURSDAY AFTER NEXT.
Pinhole eye! WOOHOO!
NHC update at 2AM could change to RED 60% 92L.
from all appearances looks like a depression
morning Ike, I tend to agree with you but i'm never right much with these storms. It has wrap up nicely.
000
NOUS42 KNHC 141600
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
1200 PM EDT MON 14 JUNE 2010
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 15/1100Z TO 16/1100Z JUNE 2010
TCPOD NUMBER.....10-014
I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK: POSSIBLE LOW LEVEL
INVEST NEAR 14N 53W AT 16/1800Z.
Climotology Rules!!
Still trucking along...
The shear it's going to hit was impressive last night but much less so this morning.
Link
not much to it at all
conditions will become
less favorable as we
progress towards the end of the day
this is done convective wise
refire failed to produce deep convection needed for this system
Buoy 41041/14.4N 46.0W
I think it got choked in dry air. Convection died at a time it should have fired up.
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