Karen, TD 13, Florida disturbance 98L, and African disturbance

By: Dr. Jeff Masters , 1:57 PM GMT on September 27, 2007

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Tropical Storm Karen is being ripped apart by 20-40 knots of wind shear, thanks to strong southwesterly winds aloft (Figure 1). Satellite loops show that these strong winds have exposed the center of circulation, now visible as a swirl of low clouds, and pushed the remaining heavy thunderstorm activity to the storm's northeast side.

Karen was probably a hurricane yesterday morning, since a NOAA hurricane hunter aircraft that arrived at the storm during the afternoon found winds near hurricane force. These winds were much stronger than the storm's satellite presentation suggested. This flight occurred after Karen had already peaked in intensity, so it is likely Karen was a hurricane for a few hours. The storm may be upgraded to a hurricane in post-storm analysis. It looks right now that Karen does not have much chance to regain hurricane status over the next five days, and may not survive at all. Wind shear over the next five days is predicted to range between 20-30 knots, and there is at least a 30% chance Karen will be destroyed by this. None of the computer models forecast total destruction, though.


Figure 1. This morning's visible satellite image, with yellow contour lines showing the amount of wind shear (in knots) superimposed. Strong upper winds winds blowing from the southwest (shown by the large white arrow) were creating 20-40 knots of wind shear over Karen. These strong winds pushed Karen's heavy thunderstorm activity to the downwind (northeast) side of Karen, exposing the low-level center of circulation to view. Image credit: University of Wisconsin CIMSS.

A severely weakened Karen will not turn to the north as much as the models have been predicting, since the storm will not extend as high in the atmosphere. Shallow storms respond to the wind field closer to the surface. These surface winds are blowing more east-to-west, and Karen is expected to follow a more westerly track to a point a few hundred miles north of the Lesser Antilles Islands five days from now. Steering currents will weaken then, and Karen will move slowly for a few days. It appears likely now that a ridge of high pressure will then build in and force Karen (or its remnants) to the west towards the U.S. East Coast late next week.

Tropical Depression 13
Tropical Depression 13 remains virtually unchanged from a day ago. Satellite imagery shows a small, compact storm that is affecting a very limited portion of the Mexican coast. Wind shear is a low 5 knots, and TD 13 could still strengthen to a 50-55 mph tropical storm before its expected landfall in Mexico on Saturday, between Poza Rica and Tampico. TD 13 will not affect Texas, due to the storm's small size. The next Hurricane Hunter mission is scheduled to arrive at 2 pm EDT today.

Tropical disturbance 98L near the east coast of Florida
A surface low pressure area (98L) moved over South Florida last night, and now appears to be reforming about 100 miles southeast of Cape Canaveral. The system is bringing heavy rain to the waters offshore Florida and the northern Bahama Islands, as seen on long range radar out of Miami. However, there are no organized spiral bands, and winds measured throughout Florida this morning have been 8 mph or less. The system is under about 10-15 knots of wind shear, which may allow some development today. This disturbance has brought rains of up to four inches to portions of South Florida and the western Bahamas, as seen on Miami radar. The center is forming far enough off the coast that 98L will probably not be a big rainmaker for Florida.

The disturbance is lifting northeastward in response to a strong trough of low pressure swinging off the U.S. East Coast. The system has the potential to organize into a tropical depression today or tomorrow, and 98L will pass several hundred miles east of Cape Hatteras, North Carolina Saturday. The system is expected to accelerate to the northeast and could bring heavy rain and high wind gusts to the Canadian Maritime provinces early next week. It is unlikely 98L will have time to become any stronger than a 45 mph tropical storm, and any effects on the U.S. will be minimal.

Coast of Africa wave
A tropical wave about 150 miles south of the Cape Verdes Islands is under about 10-20 knots of wind shear, and has some potential for development over the next few days. This morning's QuikSCAT pass showed an elongated circulation, with top winds of 35 mph to the storm's northeast side.

Wind shear tutorial
For those interested, I've posted a wind shear tutorial. This page is permanently linked on our tropical page.

I'll have an update Friday morning at the latest.

Jeff Masters

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2984. Tazmanian
1:35 PM GMT on October 01, 2007
bump
Member Since: May 21, 2006 Posts: 5091 Comments: 115430
2983. CandiBarr
3:39 PM GMT on September 28, 2007
I dont know why we are all still looking at the models, it seems as though they have been postcasting instead of forecasting. karen seems to outrun them :o
2982. CandiBarr
3:37 PM GMT on September 28, 2007
Woot.

I posted this yesterday if the sheer is ripping mositure away from the storm isn't it possible that "new moisture" could replace it and cause a huge jump in the westward direction of karen?

okay so the storm jumped south, but it jumped none the less.

paperfrog, I think your right it is difficult to converse on this blog. also, I think the shear is whats going to make karen take a wierd jump later today. there are two smaller "wet" areas that are going to be pulled into her, plus she jumped into warmer water on her west side of the convention. I look for karen to pull through.
2981. TampaSpin
2:45 PM GMT on September 28, 2007
Gang i'm looking at the satellite and it seems the shear will start relaxing very soon. Look at the Islands, it seems that the cut off of shear is starting.
Member Since: September 2, 2007 Posts: 179 Comments: 20448
2980. paperfrog
2:42 PM GMT on September 28, 2007
Wunderground does a great job, but this really needs to be a forum with threaded conversations. Gets kinda ponderous after 24 hours of prognostications and graphics, and I'm on a robust computer.

A very weird late season. I'm also in Florida (Pensacola), and it's still summer here. We've still got a month to go -- at the least -- before the Gulf starts cooling down appreciably. Maybe longer.

Go, shear, go!
Member Since: May 16, 2005 Posts: 0 Comments: 37
2979. Crawls
2:41 PM GMT on September 28, 2007
DRAK,

You posted earlier (spagetti models) that you were inclined to go with the BAMS model - unless Karen got stronger.

My question is - What is your prediction on track with "stronger"?
Member Since: August 17, 2007 Posts: 0 Comments: 272
2978. Chucktown
2:40 PM GMT on September 28, 2007
Posted By: presslord at 2:36 PM GMT on September 28, 2007.

Chucktown...that's a pretty bold forecast...Ya gonna say that on the air?


If I had more than 3 minutes I would...LOL
Member Since: August 27, 2006 Posts: 0 Comments: 1780
2977. wxguru1
2:40 PM GMT on September 28, 2007
jphurricane, are you talking about the LLC being around 14N 52W?
2976. OSUWXGUY
2:40 PM GMT on September 28, 2007
Karen continues to try to fight through the shear this morning. I'm of the thinking that it will weaken into a broad low level circulation (TD for another 24-36 hours or so), and will track mostly west-northwest or nortwest before bending back to the west in 3-4 days.

The GFS 200mb flow does not look particularly favorable at any time in the next week, with even stronger shear expected over the next 36 hours.

I'll certainly continue to watch this system with the path that I expect it to take in case the model is wrong and it can reorganize, but as of right now, I'd say the chances of Karen threatening the US as a major hurricane are remote.



but if you look at the GFS 200mb flow through the next 10 days, I'm pretty confi
2975. StormJunkie
2:38 PM GMT on September 28, 2007
DR M has a new blog up.
Member Since: August 17, 2005 Posts: 26 Comments: 16874
2973. Chucktown
2:36 PM GMT on September 28, 2007
Posted By: STSUCKS at 2:29 PM GMT on September 28, 2007.

Chucktown I would love for you to share your knowledge on the occasional CV October East Coast storm


The two that quickly come to mind is Hurricane Hazel in 1954 and Hurricane Gloria in 1985. These were both Cape Verde storms. But again the pattern late next week is not favorable for an east coast strike, unless Karen can "beat" the weakness by speeding up dramatically and at the same time get her act together. Too many ifs, but we'll just have to wait and see.
Member Since: August 27, 2006 Posts: 0 Comments: 1780
2972. presslord
2:36 PM GMT on September 28, 2007
Chucktown...that's a pretty bold forecast...Ya gonna say that on the air?
Member Since: August 13, 2007 Posts: 0 Comments: 10492
2971. Tazmanian
2:35 PM GMT on September 28, 2007
99L came out of no where TD 14 came out of no where LOL
Member Since: May 21, 2006 Posts: 5091 Comments: 115430
2970. littlefish
2:34 PM GMT on September 28, 2007
KAREN GOIN' NORTH AND WEAK... Can she survive? Can she turn west in a big way to threaten US? Stay tuned, episode 2 next week.
2969. thelmores
2:34 PM GMT on September 28, 2007
"The UKMET is only run fully on the 0z and 12z runs. Its not really run on the 6Z or 18Z runs."

WELL THATS STUPID! LOL
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2967. jpritch
2:34 PM GMT on September 28, 2007
Karen will start to jet W again in a little while. The northern part of her lower level circulation caught the speedy east-west flow in that high shear zone ahead of her and her center hasn't quite caught up to it yet. You can see it best on the RGB.
Member Since: June 28, 2007 Posts: 0 Comments: 291
2966. mississippiwx23
2:34 PM GMT on September 28, 2007
I just looked at the 200mb GFS model and it looks like the jet stream is going to be very far north over the next two weeks. The front to move off the coast as Karen approaches looks weak and zonal flow dominates after that front. I am sorry, but I dont see your high 200mb winds in the tropics.
Member Since: August 20, 2007 Posts: 3 Comments: 683
2965. SavannahStorm
2:34 PM GMT on September 28, 2007
new blog
Member Since: September 22, 2005 Posts: 18 Comments: 2343
2963. TheCaneWhisperer
2:33 PM GMT on September 28, 2007
<-----Rubs Eyes.

That is the mid-level circulation and your correct NASH, the LLC is bare and moving WNW.
2962. STSUCKS
2:33 PM GMT on September 28, 2007
I could understand you guys saying we need to watch TD 14 if this was late Aug. or Early to mid Sept. and yes JP I heard your La Nina talk...but I'm sticking to my climatology talk and I'm banking on TD 14 heading out to sea...but if I'm wrong I'll be the first to say I was!!
Member Since: August 8, 2006 Posts: 0 Comments: 9
2961. SomeRandomTexan
2:32 PM GMT on September 28, 2007
are the GFS models still showing development in the gulf next week?
Member Since: August 30, 2007 Posts: 0 Comments: 1857
2960. thelmores
2:31 PM GMT on September 28, 2007
"Posted By: Drakoen
I don't have the patience for this blog anymore LOL."


Don't make threats! LOL
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2959. Crisis57
2:31 PM GMT on September 28, 2007
Posted By: jphurricane2006 at 2:30 PM GMT on September 28, 2007.

but once again I state for you that this late La Nina pattern has pushed these conditions back a month, it is still baking here in Florida, all the fronts have fizzled before they get here

this is more like a late August pattern than a late September pattern and that includes the steering, how do you think we got TD 14 out by the CV Islands on Sept 28th? That wouldnt have happened in a "normal" year


and i must give you credit for calling it a couple of weeks agao and saying things might get rolling later in the yr
2958. tampabayfish
2:31 PM GMT on September 28, 2007
Naaahh, thats gotta be the LLC on visible. ALL clouds/convection are responding to that center, must be surface... heading frickin NNE, weird.
2957. Drakoen
2:31 PM GMT on September 28, 2007
thelmores where are the reliable models in that mess.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
2956. STSUCKS
2:30 PM GMT on September 28, 2007
Well Drak I'm just saying...pull up any archive year and look at storms near the CV and see where they end up...sure we could watch TD 14 but its most likely going to end up out to sea
Member Since: August 8, 2006 Posts: 0 Comments: 9
2955. Drakoen
2:30 PM GMT on September 28, 2007
Posted By: thelmores at 2:29 PM GMT on September 28, 2007.
somebody have a link to the UKMET that goes out past 48hrs?


The UKMET is only run fully on the 0z and 12z runs. Its not really run on the 6Z or 18Z runs.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
2954. thelmores
2:30 PM GMT on September 28, 2007
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2951. Tazmanian
2:29 PM GMT on September 28, 2007
huh? this is way too soon to be calling this a fish storm give this a few days and by sunday we sould no where its going
Member Since: May 21, 2006 Posts: 5091 Comments: 115430
2949. STSUCKS
2:29 PM GMT on September 28, 2007
Chucktown I would love for you to share your knowledge on the occasional CV October East Coast storm
Member Since: August 8, 2006 Posts: 0 Comments: 9
2948. thelmores
2:29 PM GMT on September 28, 2007
somebody have a link to the UKMET that goes out past 48hrs?
Member Since: September 8, 2005 Posts: 0 Comments: 3805
2947. mississippiwx23
2:28 PM GMT on September 28, 2007
If that circulation I see on satellite is NOT the LLC, than Karen is dead. I do not see any other circulation near her except for the northward moving one.
Member Since: August 20, 2007 Posts: 3 Comments: 683
2946. Drakoen
2:28 PM GMT on September 28, 2007
I don't have the patience for this blog anymore LOL.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
2945. Chucktown
2:28 PM GMT on September 28, 2007
Not only that STSUCKS, as you gain in latitude this time of the year, the wsterlies become increasingly faster. While there has been the occasional Cape Verde storm to reach the East Coast in October, the models are predicting a very fast west to east flow by late next week. Just take a look at some the jet streaks moving along at 200 mb. Nothing will move in from the east if this holds true. Karen had better take the low road or else is just gonna be a "fish storm."
Member Since: August 27, 2006 Posts: 0 Comments: 1780
2943. sporteguy03
2:27 PM GMT on September 28, 2007
Isn't it ironic that just a few days ago Karen was suppose to be in the CATL now it heading West, but it is still going to sea, the WATL:)
Member Since: July 7, 2005 Posts: 0 Comments: 5417
2941. STSUCKS
2:26 PM GMT on September 28, 2007
Posted By: Drakoen at 9:25 AM CDT on September 28, 2007.

None of the reliable computer models even developed TD 14. Whether or not you guys think it will be a fish storm we still need to watch it.


Watch it go out to sea...unless youre talking about the Azores
Member Since: August 8, 2006 Posts: 0 Comments: 9
2940. Crisis57
2:26 PM GMT on September 28, 2007
Good morning all just checking in whats the latest with the tropics?
2939. Drakoen
2:26 PM GMT on September 28, 2007
Posted By: nash28 at 2:24 PM GMT on September 28, 2007.
Guys-

I may be wrong, but I believe this NEWD drift is a seperate circulation in the mid levels, while the LLC is moving WNW.

Also wanted to remind everyone that Karen looked like chewed up hell yesterday as well and look how well she did beginning in the early afternoon. She is currently pulsing some strong convection, so again, she will not die.


Thats what i have been saying all morning LOL. More reliable blogger agreement LOL.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
2938. sporteguy03
2:26 PM GMT on September 28, 2007
JP,
remember the comments this is just like 2006, lol sure is just add a few more storms and throw two cat 5's in there:)
Member Since: July 7, 2005 Posts: 0 Comments: 5417
2937. wxguru1
2:25 PM GMT on September 28, 2007
Nash28, let's just say you are right, which I don't think you are. But if you were, then Karen has degenerated into an open wave. And again, I don't think that has happened.... YET!!!
2936. Drakoen
2:25 PM GMT on September 28, 2007
None of the reliable computer models even developed TD 14. Whether or not you guys think it will be a fish storm we still need to watch it.
Member Since: October 28, 2006 Posts: 57 Comments: 30670
2934. decimus785
2:24 PM GMT on September 28, 2007
I really don't like this forecast path for florida.

karen

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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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