Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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90L is also displaying banding features
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How can 90L not be a Depression.....WOW its looking very healthy..
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When do the next run of the models come out?
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wow just wow

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Advisorys on TD3 at 11 is likely. We could have Bill later today.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting StormW:


Morning StormW! I have a question that I hope you can answer...Now that 90L has a deepening system to the west, does that mean that 90L's future motion will be determined by where Ana goes? Will one follow the other? Thanks in advance.
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Quoting 954FtLCane:
good morning all, anyone have any idea why Ana is forecasted to remain a tropical storm & not a hurricane?


Upper level conditions, wind shear magnitude and direction.
Member Since: September 23, 2005 Posts: 14 Comments: 11053
Quoting StormW:


good pic. 2 very healthy looking storms atm
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Is it just me or is the northen end of the wave SE of Fl beginning to rotate. Could that system become better organized so close to land? Could it pass into the GOM and blow up? Weather for the keys: A large area of moderate rainfall with embedded scattered showers and isolated thunderstorms will impact almost all of the offshore waters 25 to 60 nm offshore of the Upper Keys. The strongest showers and storms will produce wind gusts near 30 knots...heavy downpours accompanied by visibility less than 2 nm...and occasional cloud to water lightning strikes.
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4372. bcn
More water around 90L than around Ana:

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4371. Prgal
AFK for a while...
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4370. jipmg
Lets see what happens
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its funny how TDs work 1st we had a TD then it die out then it comes back to TD 2 then we get are 1st name storm
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Quoting 954FtLCane:
good morning all, anyone have any idea why Ana is forecasted to remain a tropical storm & not a hurricane?


uncertainties in the forecasted upper level enviroment
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Quoting 954FtLCane:
good morning all, anyone have any idea why Ana is forecasted to remain a tropical storm & not a hurricane?


Mostly dry air I'd say, wind shear might increase periodically but probably won't become as destructive as the force that destroyed TD #2 Mark I.
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4365. Walshy
Quoting 954FtLCane:
good morning all, anyone have any idea why Ana is forecasted to remain a tropical storm & not a hurricane?



because the models said so....
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Quoting WPBHurricane05:
Umm...is this some type of joke? First the CMC now the GFS...


Yikes, again.
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good morning all, anyone have any idea why Ana is forecasted to remain a tropical storm & not a hurricane?
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Quoting WPBHurricane05:
Umm...is this some type of joke? First the CMC now the GFS...


Yeah I was laughing when I saw the GFS this morning, although I have to admit it would be real cool to see something like that happen.
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4361. Prgal
Quoting JRRP:

buenos dias jejeje..
gracias por el link

Your welcome!
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4360. KBH
Hi all
first time I am back since last yearand loks like we have a pint size one called Anna trying to do some damage
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4357. JRRP
Quoting Prgal:

Buenos dias (good morning) desde Carolina. JRRP, I used this page to convert from knots to mph: http://www.militaryfactory.com/conversioncalculators/speed_knots_to_miles_per_hour.asp Hope it helps.

buenos dias jejeje..
gracias por el link
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Quoting Prgal:

I hope we dont end up like the guys in "LOST" lol (in reference of your avatar).


hehe
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Umm...is this some type of joke? First the CMC now the GFS...
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Morning everyone!

TRMM made a scan earlier this morning and caught both Ana and most of the developing depression. Ana clearly has banding while 90L looks to be developing a heavy band SE of its center.

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4353. Prgal
Quoting WPBHurricane05:


Hmm...landfall 30 miles north of me. It will change I guess. But now I see the models are back with a Puerto Rico track with TD 3/90L and I'm getting kind of nervous.

This could be a wild week for those in the Leeward Islands, Puerto Rico, and the Bahamas.

I hope we dont end up like the guys in "LOST" lol (in reference of your avatar).
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Quoting TampaSpin:
ANA is born.........


Thank God...though I don't like where she plans on going. LOL
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Quoting StormW:


They're all with KerryinNOLA and stormno signing up for Meteorology 101 when school starts back.


"dude the gom thats were you guys should be focusing and the real action is you sphaghetti model readers"

lol
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Morning all
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Quoting Prgal:

Buenos dias (good morning) desde Carolina. JRRP, I used this page to convert from knots to mph: http://www.militaryfactory.com/conversioncalculators/speed_knots_to_miles_per_hour.asp Hope it helps.
Just multiply kts times 1.15 equals mph
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ANA is born.........
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GFDL seems like its confused. Although, no one really knows how the ridges will work out in 3-4 days.
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Quoting Weather456:
From the NWS in Puerto Rico - 90L

IF THE SYSTEM MOVE
SLOWER...IT WILL REACH THE WEAKNESS BY THAT TIME...AND WILL TEND
TO MOVE MORE ON A NORTHWESTERLY COMPONENT. HOWEVER...IF THE SYSTEM
MOVE FASTER THAN INDICATED BY THE MODELS...THE RIDGE WILL BE
INTACT AND MORE STRONGER WHICH WILL ALLOW THE SYSTEM TO MOVE
CLOSER TO THE LOCAL AREA.

DUE TO THIS UNCERTAINTY IN THE FUTURE TRACKS OF BOTH SYSTEMS...RESIDENTS
OF PR AND THE USVI ARE ENCOURAGED TO MONITOR LATEST FORECASTS FROM
THE NATIONAL HURRICANE CENTER OVER THE WEEKEND AND GO OVER THEIR
HURRICANE DISASTER PLANS IN CASE THE THREAT FROM THESE TWO
TROPICAL SYSTEMS BECOMES MORE REAL.


Did Daddy Yankee write this?
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4345. IKE
Quoting StormW:
Part of fcst discussion for Ana

THE 0000 UTC GLOBAL MODELS GENERALLY FORECAST A MORE CONDUCIVE
ENVIRONMENT FOR STRENGTHENING THAN PREVIOUS CYCLES...SHOWING A
WEAKER MID-OCEANIC TROUGH AFFECTING THE SYSTEM. IN PARTICULAR...THE
UKMET AND NOGAPS BUILD UPPER-RIDGING NEAR THE CYCLONE WITH LIGHT
SHEAR THROUGH THE PERIOD. HOWEVER...THE ECMWF SHOWS SOME WESTERLY
SHEAR DEVELOPING IN ABOUT A DAY...BUT EVEN THAT MODEL HAS LIGHTER
SHEAR CONDITIONS IN A FEW DAYS. THE INTENSITY GUIDANCE RUNS THE
FULL SPECTRUM THIS MORNING...WITH THE GFDL DISSIPATING THE
SYSTEM...WHILE THE HWRF SHOWS A CATEGORY TWO HURRICANE BY THE END
OF THE FORECAST PERIOD. GIVEN THE UNCERTAINTY IN THE UPPER-LEVEL
ENVIRONMENT LATER IN THE FORECAST PERIOD...THE OFFICIAL INTENSITY
FORECAST IS INCREASED CONSERVATIVELY...IN BEST AGREEMENT WITH THE
SHIPS MODEL BUT BELOW THE INTENSITY CONSENSUS.

A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THE LEEWARD
ISLANDS LATER TODAY.


6Z GFDL now puts it as a TS on the western tip of Cuba...
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well let me get to the supermarket i need to fill up my car see you guys later buenos dias a todos
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Quoting StormW:
Part of fcst discussion for Ana

THE 0000 UTC GLOBAL MODELS GENERALLY FORECAST A MORE CONDUCIVE
ENVIRONMENT FOR STRENGTHENING THAN PREVIOUS CYCLES...SHOWING A
WEAKER MID-OCEANIC TROUGH AFFECTING THE SYSTEM. IN PARTICULAR...THE
UKMET AND NOGAPS BUILD UPPER-RIDGING NEAR THE CYCLONE WITH LIGHT
SHEAR THROUGH THE PERIOD. HOWEVER...THE ECMWF SHOWS SOME WESTERLY
SHEAR DEVELOPING IN ABOUT A DAY...BUT EVEN THAT MODEL HAS LIGHTER
SHEAR CONDITIONS IN A FEW DAYS. THE INTENSITY GUIDANCE RUNS THE
FULL SPECTRUM THIS MORNING...WITH THE GFDL DISSIPATING THE
SYSTEM...WHILE THE HWRF SHOWS A CATEGORY TWO HURRICANE BY THE END
OF THE FORECAST PERIOD. GIVEN THE UNCERTAINTY IN THE UPPER-LEVEL
ENVIRONMENT LATER IN THE FORECAST PERIOD...THE OFFICIAL INTENSITY
FORECAST IS INCREASED CONSERVATIVELY...IN BEST AGREEMENT WITH THE
SHIPS MODEL BUT BELOW THE INTENSITY CONSENSUS.

A TROPICAL STORM WATCH MAY BE REQUIRED FOR PORTIONS OF THE LEEWARD
ISLANDS LATER TODAY.


storm, you got links on shear animation models? tyia
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4342. cg2916
Quoting IKE:
pronounced....AH-na....

I think it's pronounced like the A in and, but I'll check... nope, it's Ah-nah.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Miami forecast discussion

EXTENDED FORECAST...
HERE IS WHERE THE FUN BEGINS WITH THE FORECAST. THE NATIONAL
HURRICANE CENTER HAS TROPICAL STORM ANA LOCATED OVER THE CENTRAL
BAHAMA ISLANDS TUESDAY NIGHT WHICH IS DAY 5. BEYOND THAT
POINT...THE UNCERTAINTY INCREASES WITH THE ECMWF MODEL TAKING THE
SYSTEM INTO CENTRAL FLORIDA...WHILE THE OTHER GFS KEEPS THE SYSTEM
AS AN OPEN TROPICAL WAVE.

THE 00Z ECMWF MODEL IS THE ONLY MODEL THAT INITIALIZED A LOW
PRESSURE SYSTEM WHERE THE TROPICAL STORM ANA IS NOW...WHILE THE GFS
MODEL HAS IT AS A OPEN WAVE. SO WILL LEAN TO ECMWF MODEL AT THIS
TIME FOR MIDDLE OF NEXT WEEK. THIS WILL ALLOW FOR THE WINDS OVER
THE CWA TO BE MORE NORTHERLY MIDDLE OF NEXT WEEK. SOUTH FLORIDA
WILL ALSO BE DRIER...AS THE AREA WILL BE ON THE DRIER SIDE OF THE
SYSTEM.

THE ECMWF MODEL CONTINUES TO MOVE THE LOW PRESSURE SYSTEM
NORTHWEST INTO NORTH FLORIDA BY NEXT WEEKEND...AND TAKES THE
STRONG TROPICAL WAVE IN THE FAR EASTERN ATLANTIC WATERS NORTHWEST
INTO THE CENTRAL ATLANTIC WATERS BY NEXT WEEKEND. HOWEVER...THE
00Z GFS MODEL TAKES THE SYSTEM THAT IS TROPICAL STORM ANA NORTHWEST
INTO THE CENTRAL GULF OF MEXICO BY NEXT WEEKEND...AND THE STRONG
TROPICAL WAVE WEST-NORTHWEST TOWARD SOUTH FLORIDA BY NEXT WEEKEND.

AT THIS TIME WILL CONTINUE TO FOLLOW THE ECMWF MODEL FOR LATE
THIS WEEK INTO NEXT WEEKEND FOR SOUTH FLORIDA...SINCE IT IS THE ONLY
MODEL THAT INITIALIZED A LOW PRESSURE WHERE TROPICAL STORM ANA IS
NOW...THEREFORE CONFIDENCE LEVEL IS HIGHER WITH THIS MODEL. SO
WILL SHOW A SOUTH TO SOUTHWEST STEERING FLOW OVER THE CWA FOR LATE
THIS WEEK INTO NEXT WEEKEND WITH THE HIGHEST POPS OVER THE
INTERIOR AND EAST COAST METRO AREAS.

HOWEVER...EVERYONE NEEDS TO KEEP UPDATED WITH THE LATEST
INFORMATION FROM THE NATIONAL HURRICANE CENTER ON TROPICAL STORM ANA
AND THE STRONG TROPICAL WAVE OVER THE FAR EASTERN ATLANTIC WATERS.

Member Since: September 23, 2005 Posts: 14 Comments: 11053
4339. JRRP
Link
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Quoting IKE:
pronounced....AH-na....


like hanna montana...lol
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Quoting nrtiwlnvragn:
HPC preliminary forecast for thursday Aug 20




Hmm...landfall 30 miles north of me. It will change I guess. But now I see the models are back with a Puerto Rico track with TD 3/90L and I'm getting kind of nervous.

This could be a wild week for those in the Leeward Islands, Puerto Rico, and the Bahamas.
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Quoting InTheCone:


GFDL


I see GDFL brings it over PR. is this model partial to latinos? >:(
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4335. IKE
pronounced....AH-na....
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4334. JRRP
Quoting Weather456:


slow

Quoting Prgal:

Carolina :)

JRRP, that's 11.508mph

Quoting serialteg:


thats like 13mph... not that fast, definitely not slow, typical for waves (15-20kt) and hurricanes out there in the open at'l i'd say...

ok thanks
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.