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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Ex-TD2 had some really well stacked vorticity from 850-500mb early this morning that was barely visible at 200mb....I'm not surprised by the new reports at all *shrugs*
Member Since: Posts: Comments:
Quoting jipmg:
TD 2 is getting fairly impressive at a fast pace..


just like it got very un-impressive at an extremely high rate... lol
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well there are 2 things that we can agree on both are going west and atleast something well develope
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Quoting IKE:


You are addicted to this blog...just like the rest of us...lol.


I think im addicted to my computer in general. Got one window open with all my tropical weather stuff and one with my facebook window open lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
1980. jipmg
I definately see TD 2 and TD 3 at 11, 90L is getting alot better organized, and TD2 is looking like its rapidly gathering strength
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1979. Relix
Worst Case Scenario: PR gets hit by both Ana and Bill. Unlikely and has never happened before but entirely possible. Would be a disaster though.
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1978. Patrap
"Hebert in a Box"


Member Since: July 3, 2005 Posts: 423 Comments: 127807
Quoting IKE:


I thought what 456 posted was the 18Z. I'm in need of a good nights sleep.


18Z HWRF

HOUR: 126.0 LONG: -63.10 LAT: 16.90 MIN PRESS (hPa): 929.00 MAX SURF WIND (KNOTS): 102.00


18Z GFDL

HOUR:126.0 LONG: -64.24 LAT: 16.98 MIN PRESS (hPa): 960.93 MAX SURF WIND (KNOTS): 99.34
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Quoting IKE:


You are addicted to this blog...just like the rest of us...lol.


Entertainment and education all in one place!
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Sounds like the NHC may be keeping an eye on that area just north of Cuba once it gets into the Gulf. Claudette maybe? We'll see.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
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this is going to be fun


whats see what storm make land fall 1st


this kinding
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1972. IKE
Quoting CaneWarning:


Oh no!


You are addicted to this blog...just like the rest of us...lol.
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1971. DDR
Quoting Weather456:


well basically all folks have to do at this time, is make sure you have a plan or its up to date. 90L may miss us but what about storms later in the hurricane season, we still have September to go. So its better to be safe and not hit you than to dont prepare and somethings hit you.


Hurricane shelters are schools, health centers, etc. I know example set, exmaple follow, but I'm not going to a shelter unless if its cat 3 or less. lol

Very true,Our Odpm says our home is our first shelter.
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TWO REDS
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1932. cchsweatherman
Very excellently thought out and written on all counts.
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1968. Patrap
Member Since: July 3, 2005 Posts: 423 Comments: 127807
Quoting extreme236:
Back to watching the ATCF page during the next hour or so. Could seeing some renumbering and a race to become Ana.


So exciting.
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Quoting cjswilmingtoneye:
456 are there any benchmarks that stand out to you that need to be reached, before we know in what direction this will go in the long term. For example the "herbert box"? or any others.


a define circulation can really help tell where 90L is going

Herbert boxes are also good

and speed of motion
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1964. IKE
Quoting Chiggy007:
18z gfdl is out and it is futher south than its 12Z run!!


I thought what 456 posted was the 18Z. I'm in need of a good nights sleep.
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1963. 7544
looks like we might just might be seeing 2 td by 11pm tonight if thier not there already the race for ana ias on again
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Back to watching the ATCF page during the next hour or so. Could seeing some renumbering and a race to become Ana.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Grothar:
TO: SavannahStorm

I did enjoy the view. Thank you. Where do you find these sites? I have seen you post others and never seem to find them. It is a spectacular sight. Do you have information on how strong the building high pressure is going to be; or how far down it is projected?


I get those images from the EUMETSAT page. The most impressive images are usually in the RGB Composite section. That satellite gets a good angle to show the height of cloudtops in the visible spectrum.

As for the high pressure ridge, my thought is this: While there is a spread in the model runs, it appears the ridge will be in place long enough to threaten somewhere on the North American continent. Whether that's Mexico, the Gulf Coast, Florida, or the East Coast is uncertain at this point. The biggest variable I see is TD2. If it can strengthen into a tropical storm, it may create enough weakness in the ridge to start turning 90L WNW while it is east of the Lesser Antilles. If this occurs, then I think 90L will be an East Coast event. If TD2 dissipates, then I don't think enough of a weakness will remain and 90L will continue west.

TD2 is the key to 90L's track beyond 5 days.
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1959. Patrap
Quoting mobilegirl81:
Patrap, what is your opinion with the entity moving into the gulf?


Bears watching, as anything can Happen with the SSt's and things can and do usually change fast in these situ's.Monitor the NHC and your Local NWS for anything that changes
Member Since: July 3, 2005 Posts: 423 Comments: 127807
We could see TD2 again soon...code red!
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1957. sctonya
We have yellow, yellow, red, and red on the NHC page. (for those that don't know)
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1956. DDR
Quoting JRRP:
Link

Hey hows it going,
Are you from the Dominican Republic or PR?
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000
ABNT20 KNHC 142325
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT FRI AUG 14 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

SATELLITE IMAGES AND DROPSONDE DATA FROM A NOAA HIGH ALTITUDE JET
INDICATE THAT FORMER TROPICAL DEPRESSION TWO LOCATED ABOUT 1000
MILES EAST OF THE LESSER ANTILLES IS REGENERATING AND COULD BECOME
ONCE AGAIN A TROPICAL CYCLONE TONIGHT OR EARLY SATURDAY. UPPER-
LEVEL WINDS ARE MARGINALLY FAVORABLE FOR ADDITIONAL DEVELOPMENT AS
THE SYSTEM MOVES WESTWARD AT 12 TO 15 MPH. THERE IS A HIGH
CHANCE ...GREATER THAN 50 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

THE BROAD AREA OF LOW PRESSURE CENTERED ABOUT 400 MILES SOUTHWEST OF
THE WESTERNMOST CAPE VERDE ISLANDS IS ACCOMPANIED BY A LARGE AREA
OF CLOUDINESS AND THUNDERSTORMS. THIS SYSTEM IS GRADUALLY BECOMING
BETTER ORGANIZED AND A TROPICAL DEPRESSION COULD ALSO FORM TONIGHT
OR SATURDAY. THE LOW IS EXPECTED TO MOVE WESTWARD AT 15 MPH. THERE
IS A HIGH CHANCE...GREATER THAN 50 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.


A TROPICAL WAVE INTERACTING WITH AN UPPER-LEVEL LOW IS PRODUCING
DISORGANIZED CLOUDINESS AND SHOWERS OVER THE WESTERN CARIBBEAN
NORTHWARD ACROSS CUBA AND THE BAHAMAS. THE ACTIVITY IS MORE
CONCENTRATED JUST NORTH OF THE COAST OF CENTRAL CUBA AND IS
EXPECTED TO SPREAD WEST-NORTHWESTWARD OVER SOUTH FLORIDA AND THE
SOUTHEASTERN GULF OF MEXICO DURING THE NEXT COUPLE OF DAYS.
THERE
IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A
TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

DISORGANIZED SHOWERS AND THUNDERSTORMS OVER THE NORTHEASTERN GULF OF
MEXICO ARE ASSOCIATED WITH A WEAK TROUGH OF LOW PRESSURE. SURFACE
PRESSURES ARE RELATIVELY HIGH IN THIS AREA. THERE IS A LOW
CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER AVILA

Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting Chiggy007:
GFDL 18Z run: Well, it's on the Wunderground graphics - the blue line :)


Thats currently the interpolated run, the actual run should be up soon.
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the mode runs are worth less at this point in time
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that is old trough is not going to be that strong
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Quoting DDR:

I hope you are prepared,is there a hurricane shelter near your house.


well basically all folks have to do at this time, is make sure you have a plan or its up to date. 90L may miss us but what about storms later in the hurricane season, we still have September to go. So its better to be safe and not hit you than to dont prepare and somethings hit you.


Hurricane shelters are schools, health centers, etc. I know example set, exmaple follow, but I'm not going to a shelter unless if its cat 3 or less. lol
Member Since: Posts: Comments:
Quoting nrtiwlnvragn:


Typically with storms in the Atlantic/Carribean, the hurricane hunter planes are stationed in the Virgin Islands, they will probably send several planes.
They fly out of Grand Cayman quite often when the storm is heading west towards the Yucatan.
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1948. Patrap
TD 2/remnant AL022009 - Tropical Depression TWO,RAAMB

TD 2/remnant AL022009 - Tropical Depression TWO,RAAMB
Member Since: July 3, 2005 Posts: 423 Comments: 127807
Quoting WeatherStudent:
Dude, honestly, IDK. However, if it gets into the GOM, then it could certainly threaten Tampa, FL.


Oh no!
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1946. mkmand
Quoting Tazmanian:
i wounder if we have TD 3 yet

I would say we do. We should also have TD2 back again.
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I'm wondering if this thing might turn out to be a Dean and it just misses everybody in the U.S.
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Quoting mobilegirl81:
Keep a close eye on the gulf situation
why, pressures are far too high
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i wounder if we have TD 3 yet
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Patrap, what is your opinion with the entity moving into the gulf?
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1939. JRRP
Link
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Quoting wunderkidcayman:

I think it is too


what please tell more


Typically with storms in the Atlantic/Carribean, the hurricane hunter planes are stationed in the Virgin Islands, they will probably send several planes.
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Hey Ike? Look what I found.....

(Atlanta AFD)

.LONG TERM /MONDAY THROUGH FRIDAY/...
UPPER-LEVEL RIDGE BEGINS TO BUILD BACK INTO THE SOUTHEASTERN
UNITED STATES FROM THE ATLANTIC ON MONDAY. WHILE DEEP MOISTURE
WILL REMAIN IN PLACE ACROSS THE REGION...SUBSIDENCE FROM THE UPPER-
RIDGE MAY CAUSE CONVECTION TO BECOME MORE LIMITED BY THE MIDDLE TO
END OF NEXT WEEK. BOTH THE GFS AND THE ECMWF DEVELOP A LARGE FALL-
LIKE TROUGH ACROSS THE GREAT LAKES REGION LATE NEXT WEEK..WHICH
WOULD RESULT IN ANOTHER FRONTAL BOUNDARY AFFECTING GEORGIA BY
FRIDAY OR SATURDAY. THE POSITION AND AMPLITUDE OF THIS TROUGH WILL
ALSO PLAY AN IMPORTANT ROLE IN THE TRACK OF ANY POTENTIAL TROPICAL
SYSTEMS THAT MAY APPROACH THE SOUTHEASTERN UNITED STATES DURING
THIS PERIOD.


And B'ham.....

AS WE HEAD TOWARDS THE END OF NEXT WEEK...UNCERTAINTY IN THE
FORECAST BEGINS TO INCREASE. A LONG WAVE TROF IN THE UPPER LEVEL
WILL BEGIN TO APPROACH THE AREA ALONG WITH A TRAILING SURFACE
FRONT. THE 12Z RUN OF THE GFS HAS A MORE AMPLIFIED SYSTEM COMPARED
TO THE 06Z RUN. THIS IS A VERY INTERESTING FEATURE THAT WILL NEED
TO BE CLOSELY MONITORED AS THIS FEATURE WILL PLAY A ROLE ON A
POSSIBLE TROPICAL SYSTEM IN THE ATLANTIC. THIS IS STILL WAY OUT
THERE IN TIME AND THUS A HIGH DEGREE OF UNCERTAINTY IS TO BE
EXPECTED. HOWEVER...SINCE WE ARE SLOWLY APPROACHING PEAK TIME
FOR TROPICAL ACTIVITY...IT IS SOMETHING WORTH WATCHING.

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Quoting Weather456:
this weekend is crucial
456 are there any benchmarks that stand out to you that need to be reached, before we know in what direction this will go in the long term. For example the "herbert box"? or any others.
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1935. jipmg
TD 2 is getting fairly impressive at a fast pace..
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1934. DDR
Quoting Weather456:
this weekend is crucial

I hope you are prepared,is there a hurricane shelter near your house?
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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.

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