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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1833. Patrap
For my Bud Ike,and Hopefully we wont be breaking this one out in a weeks time..
Member Since: July 3, 2005 Posts: 415 Comments: 125628
Quoting BiloxiIsle:

Yes, he does.
He's too young to remember Andrew.
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ex TD 2 is firing real good thunderstorms over the center but 90L just needs a tad more organization and it will be on its way to TD Status, just curious why is there so much shear over 90L was there suppose to be shear there
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I've decided that I'm not concerned about the two blobs out there. I will not be reviewing my hurricane plan this weekend.
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1827. Ldog74
Quoting extreme236:


SHIPs RI index for 25kt increase in 24 hours suggests only a 12% chance for rapid intensification.


I was referring more to individuals' comments on the possibility of rapid intensification than what the models are showing. But it seems to me that the SHIPS is being a little bullish, topping out just below Cat 3 strength in 5 days. Thats based on 90L being a mid range TS by this time tomorrow, which I am just not seeing.
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Quoting adjusterx:


I think that makes him Ingloreous


Don't tell me the knatzees have their own group.
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Well kids, I am headed out for the evening. Keep an eye on our two swirling blobs out in the Atlantic, make sure nobody has a heart attack in SE FL, and.. PLAY NICE!
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1823. IKE
Quoting DestinJeff:


howdy, ike. nothing here, but as you noted maybe some sort of tropical-ish moisture in store for us soon


I just had 30-45 minutes of moderate to heavy rain. Red blob on radar was right over me. I've had just under 1 1/2 FEET of rain in the last 6 weeks.
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Quoting FloridaTigers:
WS, do you want S. Fla to get hit by a hurricane? Just curious.

Yes, he does.
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Quoting weatherboykris:
OMG...everyone lay off Patrap...he posted a pic of Nazis...big deal.


I think that makes him Ingloreous
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A local Met was showing a Tropical Future Scan model ( which he's never used on the news before).
It showed the wave moving into South Florida tomorrow becoming a pretty well developed low by the time it moves into Mississippi the beginning of next week?

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Extreme and DRak:
I see what you are saying but please have a look at the sat loops and let me know!
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guys why are you all posting image that is not posting material not relevant to the discussion of tropical weather, or the topic of the blog entry itself ????


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Quoting chevycanes:

all the runs also take it very close or over S. FL.

it can very easily hit both.
True, it is a very common track historically.
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1814. Patrap
GOM 60 Hour Wave Forecast (using WaveWatch 3)
Member Since: July 3, 2005 Posts: 415 Comments: 125628
1813. IKE
Quoting FloridaTigers:
WS, do you want S. Fla to get hit by a hurricane? Just curious.


I can answer that...sure he does. Or he thinks he does.

It's no secret...that's how he feels. I'm not the smartest egg in the basket and even I know that.
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1812. ackee
it looks like TD#2is back to me any thoughts
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I just talked to a friend who is a met and he thinks former TD2 is the one to worry about. He also thinks 90L will curve out to sea after a close call with the Carolina coast.
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GFS 18z run back in the GOM.
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Quoting Grothar:
I have just been in contact with my friend who is a meteorologist. She said that both systems have an excellent chance of passing over the Northern Antilles and should pass through the Bahamas and be close to the South Florida coast. Depending upon the speed of both and where the low shall be when they reach that area; it should be of concern to Florida. 2D will be passing through an area of dry air and be pushed quickly by a building high pressure by tomorow. I would assume as with all these systems, speculation does not help but observation is important. Does anyone have information as to how strong the high pressure will be in the coming week.


Umm, your met friend just speculated.
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18z GFDL is not out yet...
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1804. IKE
It's a wonder this blog survives.

I just had another 1+ inch of rain here in the inland area of the Florida panhandle....more to come this weekend. Likely probabilities of rain.
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Quoting Chiggy007:
Well, then 90L has more than one LLC competing.. I clearly see "one of the LLCs" around 11.5N - 30W in the NHC sat loops...


There is only one center as shown on QS and microwave images.
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1802. Grothar
I have just been in contact with my friend who is a meteorologist. She said that both systems have an excellent chance of passing over the Northern Antilles and should pass through the Bahamas and be close to the South Florida coast. Depending upon the speed of both and where the low shall be when they reach that area; it should be of concern to Florida. 2D will be passing through an area of dry air and be pushed quickly by a building high pressure by tomorow. I would assume as with all these systems, speculation does not help but observation is important. Does anyone have information as to how strong the high pressure will be in the coming week.
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1801. jipmg
Convection continues to wrap around the center of 90L, TD 2 might be reinstated soon
18Z GFDL is even further SOUTH now...
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Quoting Seflhurricane:
max mayfield seemed a bit uptiet this evening i think those disturbances are starting to worry him a little bit

he prolly see's what the models are doing and see's how the steering currents are setting up.
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Quoting SavannahStorm:




I am coming for you, Pat, and your fascist buddies.



Ew.
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Well, then 90L has more than one LLC competing.. I clearly see "one of the LLCs" around 11.5N - 30W in the NHC sat loops...
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WS, do you want S. Fla to get hit by a hurricane? Just curious.
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JFV actually the GFS model takes it to the straits
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OMG...everyone lay off Patrap...he posted a pic of Nazis...big deal.
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Quoting DDR:

What does this have to do with weather?
I putting you back where you belong,my S**t list.


What does your post have to do with weather?
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max mayfield seemed a bit uptiet this evening i think those disturbances are starting to worry him a little bit
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1787. jipmg
Quoting RainyEyes:
I don't know if that is a pinhole Taz, but look at the beautiful tails (don't know the technical term...I am new) That looks like one of those perfect little symbols that the weather stations use and put on top of a hurricane. The blender blade look. Awesome view!


feeder bands
Quoting jasoniscoolman10:







Aug. 14, 2009 6:18 pm ET
A juicy but fading front coupled with a tropical disturbance coming out of the Bahamas and Hispaniola with trigger thunderstorms from the Carolinas to the northern Gulf Coast states this weekend. Some of the thunderstorms will contain flash flooding rains.with all his rain from FL TO NC if a big hurricane hit land there will be lots of tree coming down.






why are you posting weather maps from TWC that is called Copyrighting
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Quoting Patrap:



Im hurt,really hurt,..man...a lil humor and the Place goes up In A Glenn Beck Moment

LOL


LMAO...that made me laugh.
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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.