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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Closed circulation? You obviously weren't looking at visible loops today. How much clearer can westerly winds on the south side of a low center be?
As for convection it had it easily last night, and it doesn't have to be this big circular CDO like people keep claiming. It's only a TD. Anyone looking at a sat loop of the Atlantic with no memory of 92L's prior past would think it was a tropical cyclone, hands down. It has the appearance of a struggling tropical cyclone on satellite imagery, and that's what it is and has been since last night.
I know half the blog will fight me on that....but it's ok.
Yeah!
What he said...
Global warming.
TORNADO WARNING
KYC037-OHC061-150300-
/O.NEW.KILN.TO.W.0014.100615T0234Z-100615T0300Z/
BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE WILMINGTON OH
1034 PM EDT MON JUN 14 2010
THE NATIONAL WEATHER SERVICE IN WILMINGTON HAS ISSUED A
* TORNADO WARNING FOR...
EXTREME NORTHERN CAMPBELL COUNTY IN NORTHERN KENTUCKY...
SOUTHERN HAMILTON COUNTY IN SOUTHWEST OHIO...
* UNTIL 1100 PM EDT.
* AT 1033 PM EDT...RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF
PRODUCING A TORNADO. THIS DANGEROUS STORM WAS LOCATED NEAR
LUDLOW...MOVING EAST AT 35 MPH.
* LOCATIONS IMPACTED INCLUDE...
CINCINNATI...
NEWPORT...
BELLEVUE...
DAYTON...
NORWOOD...
MARIEMONT...
IN ADDITION...WOODLAWN...FAIRFAX...SILVERTON AND TURPIN HILLS ARE
NEAR THE PATH OF THIS DANGEROUS THUNDERSTORM.
THIS INCLUDES INTERSTATE 71 IN OHIO BETWEEN MILE MARKERS 1 AND 12.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A
STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR
OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT
YOURSELF FROM FLYING DEBRIS.
PLEASE REPORT TORNADOES...FUNNEL CLOUDS...STRONG WINDS OR HAIL TO THE
NATIONAL WEATHER SERVICE BY CALLING TOLL FREE...877-633-6772...WHEN
YOU CAN DO SO SAFELY.
A SEVERE THUNDERSTORM WATCH REMAINS IN EFFECT UNTIL 200 AM EDT
TUESDAY MORNING FOR NORTHEASTERN KENTUCKY AND SOUTHWESTERN OHIO. A
SEVERE THUNDERSTORM WATCH ALSO REMAINS IN EFFECT UNTIL 1100 PM EDT
MONDAY EVENING FOR SOUTHEASTERN INDIANA AND NORTHERN KENTUCKY AND
SOUTHWESTERN OHIO.
&&
LAT...LON 3913 8462 3920 8438 3909 8436 3909 8451
3909 8452 3909 8454 3909 8455 3908 8457
3908 8461
TIME...MOT...LOC 0235Z 258DEG 29KT 3911 8456
$$
HAWBLITZEL
You just dumped my whole area into really hot water... Not very nice!
Come on Jeff, this whole subject is lunacy!!
Perhaps this will better explain it. From the NHC's initial advisory on Tropical Depression Fifteen:
ZCZC MIATCDAT5 ALL
TTAA00 KNHC DDHHMM
TROPICAL DEPRESSION FIFTEEN DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL152007
500 PM EDT THU OCT 11 2007
THE AREA OF LOW PRESSURE IN THE CENTRAL ATLANTIC EAST OF BERMUDA HAS
BEEN MAINTAINING STEADY DEEP CONVECTION NEAR THE CENTER FOR ABOUT
12 HOURS OR SO...AND DVORAK CLASSIFICATIONS FROM TAFB AND SAB AT
18Z HAVE RISEN TO T1.5. ON THIS BASIS...ADVISORIES ARE INITIATED ON
TROPICAL DEPRESSION FIFTEEN. AN ASCAT PASS NEAR 14Z SUGGESTS THAT
MAXIMUM WINDS ARE NEAR 30 KT.
THE INITIAL MOTION IS 075/14. THE CYCLONE IS LOCATED TO THE EAST OF
AN UPPER LOW THAT IS PRODUCING STRONG SOUTHWESTERLY FLOW OVER THE
CENTER. GLOBAL MODELS SUGGEST THAT THE SOUTHWESTERLY FLOW WILL BE
REPLACED BY EVEN STRONGER NORTHERLIES OVER THE NEXT 24-36 HOURS.
IN THIS STRONG SHEAR ENVIRONMENT...THE MOTION OF THE CYCLONE WILL
DEPEND ON HOW MUCH CONNECTION THE CENTER MAINTAINS WITH THE FLOW
ALOFT. THE 12Z RUNS OF THE GLOBAL MODELS SEEM TO HAVE ALREADY
SEPARATED THE CENTER FROM THE DEEP CONVECTION...WHICH OF COURSE
HASN'T HAPPENED YET. AS A RESULT...MY FORECAST TAKES THE CYCLONE A
LITTLE FARTHER EAST THAN MOST OF THE OBJECTIVE GUIDANCE. BEFORE
TOO LONG...HOWEVER...THE SHEAR SHOULD PREVAIL...LEAVING THE
LOW-LEVEL CIRCULATION BEHIND TO MEANDER UNTIL THE NEXT FRONTAL
SYSTEM ARRIVES IN THE AREA IN ABOUT TWO DAYS.
WITH STRONG SHEAR FORECAST TO PERSIST OVER THE CYCLONE...LITTLE OR
NO STRENGTHENING IS EXPECTED. THE OFFICICAL FORECAST IS IN GOOD
AGREEMENT WITH THE SHIPS AND HWRF GUIDANCE. THE GFDL DOES BRING
THE DEPRESSION TO STORM STRENGTH...BUT THERE IS ONLY A VERY SHORT
WINDOW OF OPPORTUNITY FOR THIS TO OCCUR.
IT IS POSSIBLE THAT SOME OF THE LOW-LEVEL VORTICITY FROM KAREN'S
REMNANTS HAS PLAYED A ROLE IN THE GENESIS OF THIS CYCLONE.
HOWEVER...THE EVIDENCE IS NOT STRONG ENOUGH TO ATTACH THAT NAME TO
THIS SYSTEM.
AL, 92, 2010061312, , BEST, 0, 71N, 349W, 25, 1011, DB, 0, , 0, 0, 0, 0, 1014, 200, 45, 0, 0, L, 0, , 0, 0, INVEST, D,
AL, 92, 2010061318, , BEST, 0, 77N, 363W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1012, 200, 50, 0, 0, L, 0, , 0, 0, INVEST, D,
AL, 92, 2010061400, , BEST, 0, 84N, 376W, 25, 1010, DB, 0, , 0, 0, 0, 0, 1013, 240, 60, 35, 0, L, 0, , 0, 0, INVEST, D,
AL, 92, 2010061406, , BEST, 0, 90N, 388W, 25, 1010, DB, 0, , 0, 0, 0, 0,
Read that comment again, very closely look at the word "IF"!!!! I wish you guys would stop bashing the guts out of me. No one is right.
Ah I see.
I'll support you on that one. Everything I've seen or analyzed (which I presented with data and imagery to support) suggests that indeed.
Looks like 92L is on a westward path again.
LMAO!! memories
Interesting definitions ?
Tropical Depression:
A tropical cyclone in which the maximum sustained surface wind speed (using the U.S. 1-minute average) is 33 kt (38 mph or 62 km/hr) or less.
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. Once formed, a tropical cyclone is maintained by the extraction of heat energy from the ocean at high temperature and heat export at the low temperatures of the upper troposphere. In this they differ from extratropical cyclones, which derive their energy from horizontal temperature contrasts in the atmosphere (baroclinic effects).
I looked at a lot of loops and stills today but one thing I have learned over the years is that a satellite image does not confirm a closed surface low. Go back into the archives and look at pre Dolly that had TS force winds, looked like a TS but did not have a closed low.
The winds you were seeing could just as easily have been at the mid levels.
Believe what you want but show me precisely where this ever had a closed low.
I am not a down-caster, but I have seen bigger waves in my bathtub. Let us wait a little and she what it does. We will be here all season.
You are a downcaster! (Sorry, I'm just kidding.)
You just had to do it... didn't you... Jeff bad
Oh my...you just never know what to expect on this blog.
Well thats not what I was referring to...
The NHC wont classify the system just because it looks nice due to a diurnal phase. They'll wait at least another 6-12 hours and take it from there like they have been doing for the past 72 hours. Again, if 92L can sustain convection in all quadrants tomorrow, it has a decent shot. If it doesnt do so...it'll probably die out in a few days.
And no one has bashed you. Just having a "debate".
AOI/BOC
The entire idea behind it, I think, is the persistence behind Karen's remnant vorticity.
Not really sure how it's funny either, but to each their own.
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