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

By: Dr. Jeff Masters , 2:02 PM GMT en Agosto 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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Quoting weatherfan92:


I've been getting that too. Is anyone else getting an error message that closes the webpage?


I have been as well. I haven't logged in for most of the season, and I did two days ago, right after that my computer started going ape sh**. Not sure!
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282. jipmg
Quoting extreme236:


These numbers represent the organization of a system and the intensity is based off of organization. I will give you some examples.

A T1.0 signifies a system with primitive organization not yet of the requirement to be a TD. Winds of 25kts or less.

T1.5 to T2.0 can be a tropical depression with winds of 25 knots and 30 knots respectively.

T2.5 through T3.5 is a tropical storm.

T4.0 and higher is a hurricane. Here is the chart link: Link


oh ok thanks for the information
Quoting weatherfan92:


I've been getting that too. Is anyone else getting an error message that closes the webpage?

I get it all the time... I just refresh the page again.
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Quoting weatherfan92:


I've been getting that too. Is anyone else getting an error message that closes the webpage?



yes
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Quoting Drakoen:
Good thing JFV isn't here. He would go into cardiac arrest looking at that long-range CMC
ROFLMAO!!! I live in Miami and a lot of models are pointing here im not worried, i dunno what is his problem, lol.
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Quoting hurricanehanna:
I know this is off topic, but why does this keep happening when I refresh? Is it part of the virus from a few days ago? Thanks.

JeffMasters does not have any blog entries.


I've been getting that too. Is anyone else getting an error message that closes the webpage?
Quoting jipmg:


what do those numbers mean? I know the position, but T1.0/1.0 what does that mean?


These numbers represent the organization of a system and the intensity is based off of organization. I will give you some examples.

A T1.0 signifies a system with primitive organization not yet of the requirement to be a TD. Winds of 25kts or less.

T1.5 to T2.0 can be a tropical depression with winds of 25 knots and 30 knots respectively.

T2.5 through T3.5 is a tropical storm.

T4.0 and higher is a hurricane. Here is the chart link: Link
Member Since: Agosto 2, 2007 Posts: 19 Comments: 19234
Quoting jipmg:


what do those numbers mean? I know the position, but T1.0/1.0 what does that mean?
Link
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Good thing JFV isn't here. He would go into cardiac arrest looking at that long-range CMC
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253 Drakoen ---->249. Ditto
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Look how many runs of the GFS ensemble take it down near or below 10°, even to 8°. A little S is one thing, but from 12° to 8°, this far west, doesn't seem very typical. Is there really Atlantic ridging that strong?
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Quoting jipmg:


yea it means its less likely to steer north based on the current forecasts


ok, thanks
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I know this is off topic, but why does this keep happening when I refresh? Is it part of the virus from a few days ago? Thanks.

JeffMasters does not have any blog entries.
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.
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Quoting TexasHurricane:


what does that mean? Trough less potent? Meaning it won't steer it north, it will continue a westerly track?


When it get though the Bahamas or Greater Antilles there may not be anything to recurve it out to sea. Florida would be the first to be affected. It still a ways out though. A long ways out.
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next week looking pretty interesting here in pr going to start prepairing tomorrow
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Quoting weathersp:


Where are you getting the Dvorak T#'s when they arn't on the CMISS site yet?


Its from the SSD site...also can be found in the ATCF file.
Member Since: Agosto 2, 2007 Posts: 19 Comments: 19234
Quoting canesrule1:
14/1145 UTC 14.6N 41.7W T1.0/1.0 02L


Current Time is 15:33
Quoting Drakoen:


Long range GFS and to some extent the CMC. The trough is looking less potent


Thanks Drak. :)
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261. jipmg
Quoting TexasHurricane:


what does that mean? Trough less potent? Meaning it won't steer it north, it will continue a westerly track?


yea it means its less likely to steer north based on the current forecasts
260. JRRP
if this train continue we could see td3 at 5 pm or 11 pm
Link
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Quoting weathersp:


Where are you getting the Dvorak T#'s when they arn't on the CMISS site yet?
Link
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Quoting NEwxguy:
It looks like pick your model to decide where in the US this would hit,but to be expected when its not even a TD yet.


We stick to the dynamic operational models for now
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257. jipmg
Quoting canesrule1:
14/1145 UTC 14.6N 41.7W T1.0/1.0 02L


what do those numbers mean? I know the position, but T1.0/1.0 what does that mean?
Quoting canesrule1:
14/1145 UTC 14.6N 41.7W T1.0/1.0 02L


Where are you getting the Dvorak T#'s when they arn't on the CMISS site yet?
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Quoting Drakoen:


Long range GFS and to some extent the CMC. The trough is looking less potent


what does that mean? Trough less potent? Meaning it won't steer it north, it will continue a westerly track?
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Quoting TheCaneWhisperer:


Convection holds I would look for re-gen of 02L at 5pm.


yep
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The ensembles are all over the place lol. You draw line down the middle and you get your mean
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It looks like pick your model to decide where in the US this would hit,but to be expected when its not even a TD yet.
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Quoting wunderkidcayman:

what dose it says about ex-TD2



yep
14/1145 UTC 14.6N 41.7W T1.0/1.0 02L
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Quoting StormW:


The scenarios are what we've been discussing here. I don't think at this time former TD2 should gave an effect. If it doesn't get out of the way...90L may eat it! LOL!


Cue Jaws music.

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Progs last week for transition for ( ) NAO (if memory serves)didn't occur & keep getting pushed into the future.Link
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Quoting wunderkidcayman:

what dose it says about ex-TD2



yep


02L came in at T1.0
Member Since: Agosto 2, 2007 Posts: 19 Comments: 19234


Quite the spread.
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Quoting OSUWXGUY:
I think the ADT is a little confused at where the centers at...

I mean...we have visible so we "know" where it is at...and it isn't that far EAST

This is also probably why the ADT number is not responding to the recent convection.



Well there have been no new information from the NHC so it doesn't really work probably. You just gotta watch the subjective numbers.
Member Since: Agosto 2, 2007 Posts: 19 Comments: 19234
Quoting CaneAddict17:
if it doesn't work try this address:

http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_late2.png
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Quoting leftovers:
looked more north to me acklee seemed to consolidated accu is centered at penn state


Right outside of State College, its not at the university.
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Am worried about a northern gulf track as my area (big bend) is overdue.
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12Z GFS Running... FYI.
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Quoting canesrule1:
90L could be a TD:

14/1145 UTC 12.1N 27.9W T1.5/1.5 90L

what dose it says about ex-TD2

Quoting jipmg:
TD 2 looking good with each satellite image..


yep
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Convection holds I would look for re-gen of 02L at 5pm.
Quoting CaneAddict17:
if it doesn't work try this address:

http://euler.atmos.colostate.edu/~vigh/guidance/northatlantic/track_late2.png
k
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Quoting homelesswanderer:
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
957 AM CDT FRI AUG 14 2009


LONGER RANGE MODELS DEPICT THE BERMUDA HIGH RIDGING OVER THE
REGION AS A MID TO UPPER LEVEL HIGH DEVELOPS OVER THE SERN
STATES.
HAVE TAPERED POPS FROM CHC CATEGORY TUESDAY TO SLT CHC
THURSDAY AS UPPER RIDGE BUILDS OVER THE REGION WITH TEMPS EXPECTED
TO GRADUALLY INCREASE.

Ok. This from the western GOM. What models show this?? And if thats true then is the high supposed to retreat back east before 90l could get in the gulf? Just curious because as far west as i have seen the models was N.O.



Long range GFS and to some extent the CMC. The trough is looking less potent
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I think the ADT is a little confused at where the centers at...

I mean...we have visible so we "know" where it is at...and it isn't that far EAST

This is also probably why the ADT number is not responding to the recent convection.

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I'm kind of concerned about 90L because it looks like it could hit the Caribbean Islands around Cat.3 intensity.
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90L looks like a classic cape verde wave that could be well on its way to tropical storm status by sunday.
Member Since: Agosto 31, 2008 Posts: 0 Comments: 833

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About JeffMasters

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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