Tropical update

By: Dr. Jeff Masters , 9:02 PM GMT on September 26, 2007

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Tropical Storm Karen is now suffering the effects of 15-20 knots of winds shear, and has stopped intensifying. The latest satellite loops show a large and expanding cloud pattern with good outflow to the north, but no eye. The wind shear affecting Karen is expected to stay at 15-20 knots the next four days, and Karen will probably not change much in strength during that period. The long range outlook for Karen remains unchanged. The models are all fairly unified in taking Karen to a latitude north of the Lesser Antilles Islands. However, the trough of low pressure expected to steer Karen to the northwest is unlikely to be strong enough to recurve Karen out to sea. A new ridge of high pressure may build in, forcing Karen westwards towards the U.S., just north of the Lesser Antilles Islands. This scenario, favored by the UKMET model, would put Karen in a position to threaten the U.S. East Coast late next week. The GFS model does not build in such a strong ridge, and instead forecasts that Karen will stall for 2-4 days a few hundred miles north of the Lesser Antilles Islands, and eventually recurve out to sea when the next strong trough of low pressure comes along. This scenario would put Bermuda at risk from Karen. It is too early to speculate which of these scenarios is more likely, and how much of a risk Karen may present to Bermuda or the U.S. East Coast.

Tropical Depression 13
Tropical Depression 13 remains nearly stationary in the far southwestern Gulf of Mexico. Satellite imagery show a well-organized system that should be a tropical storm, but this is not supported by Hurricane Hunter reports. The top winds found this afternoon at the surface by the airplane were less than 30 mph. Wind shear is about 10 knots over the disturbance, and is expected to remain 10 knots or below for the next three days. This should allow Tropical Depression 13 to develop into a strong tropical storm--possibly a Category 1 hurricane--before it makes landfall along the Mexican coast 2-3 days from now. Steering currents are weak in the southwest Gulf of Mexico, and the storm will move slowly and erratically. This storm is primarily a threat to Mexico, due to a very strong ridge of high pressure that will prevent the storm from turning northwards.

Tropical wave 97L grows disorganized
A tropical wave (97L) has brought heavy rains of up to 2-4" to Puerto Rico today. Satellite imagery and Puerto Rico long range radar show that this wave has degenerated. High wind shear of 20-30 knots has seriously disrupted the wave, and this will be my last mention of it.

Tropical disturbance 98L near South Florida and the Bahamas
A surface low pressure area (98L) formed near Key West this morning, and has moved northeast to a position off the SW coast of Florida south of Naples. The rotation of the low is clearly evident on long range radar out of Miami. However, there are no organized spiral bands, and winds measured throughout South Florida this afternoon have been 12 mph or less. The system is under about 10-20 knots of wind shear, which should keep any development slow today. This disturbance has brought rains of up to four inches to portions of the Florida Keys and the western Bahamas as seen on Miami radar.

The disturbance is lifting northeastward in response to a strong trough of low pressure swinging off the U.S. East Coast. On Thursday, when 98L will be over the warm waters of the Gulf Stream approaching North Carolina, the system has the potential to organize into a tropical depression, as wind shear is expected to fall to 10 knots. The GFDL develops 98L very rapidly, and predicts it will approach Category 1 hurricane status as it passes about 200 miles east of Cape Hatteras on Friday night. This is too aggressive a forecast, and I prefer the HWRF forecast, which forecasts top winds of 35-40 mph by Friday night. A very strong band of wind shear associated with the jet stream will affecting 98L by Friday night, and could rapidly destroy the storm. 98L or its remnants may then move rapidly northeastward past Cape Cod, Massachusetts, or may stall off the coast of North Carolina and wander erratically for several days. The models are split on this matter.

Coast of Africa wave
A tropical wave a few hundred miles south-southeast of the Cape Verdes Islands is under about 10 knots of wind shear, and has some potential for development over the next few days.


Figure 1. Tropical Storm Karen and the latest tropical wave coming off the coast of Africa at 8:45 am EDT Sep 26, 2007. Image credit: NOAA Visualization Program.

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 Thursday morning.

Jeff Masters

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1403. beell
2:07 PM GMT on September 27, 2007
fact is it will take days and days of this kind of shear to kill that circulation

I agree. Not too much will quickly kill a llc at that latitude. Imagine, a band of winds spinning at 30-50 kts at least 5,000 feet high. A huge amount of energy. It won't just stop. Karen's increased forward speed allows a good opportunity to stay w/the ridge.
Member Since: September 11, 2007 Posts: 143 Comments: 16735
1401. ncsmiles
1:59 PM GMT on September 27, 2007
Dr. Masters has a new blog
1400. hurricane23
1:58 PM GMT on September 27, 2007
This year has really been to much to be honest with to Category 5 hurricanes and bunch of invest falling apart in the face of unfavorable conditions.

Thankfully the one real signifcant threat that developed with humberto did not end up being a real significant problem as far as lives lost and damage.My heart goes out to those folks down there were they really took it hard with dean and felix.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1399. SEFL
1:58 PM GMT on September 27, 2007
"Posted By: jphurricane2006 at 1:54 PM GMT on September 27, 2007.

Adrian has spoken


Karen is dead folks, season is dead folks, see you next year

lol"

That's a little over the top...lie down on the couch and tell me why it bothers you so much. :)
1397. Tazmanian
1:57 PM GMT on September 27, 2007
55kt 1002mbs not bad at all for no t-storms with it

lol
Member Since: May 21, 2006 Posts: 5091 Comments: 115244
1396. IKE
1:57 PM GMT on September 27, 2007
Posted By: jphurricane2006 at 8:56 AM CDT on September 27, 2007.
no im not IKE, karen is dead based on the situation, oh well

next


I hope it is dying. The odds of it ever affecting the US are less than 1%. It's almost October...look closer to home. The GFS has been consistent in developing a system in the central GOM the middle of next week.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1394. NEwxguy
1:56 PM GMT on September 27, 2007
I'm curious 23,do you see an active October?
Member Since: September 6, 2007 Posts: 881 Comments: 15840
1393. IKE
1:55 PM GMT on September 27, 2007
Posted By: jphurricane2006 at 8:54 AM CDT on September 27, 2007.
Adrian has spoken


Karen is dead folks, season is dead folks, see you next year

lol


He didn't say that...he was stating what the NHC told him...now you're jumping to conclusions.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
1392. msphar
1:55 PM GMT on September 27, 2007
Karen's appears to be on life support, I wish her dead. She seems to be following in Ingrid's footsteps.
Member Since: August 20, 2006 Posts: 0 Comments: 289
1391. IKE
1:54 PM GMT on September 27, 2007
Posted By: hurricane23 at 8:52 AM CDT on September 27, 2007.
Ive spoken to several at the NHC in the past few days and trust me there is little concern on this system even coming close to the U.S. as of right now.

Iam looking at the overall situation with karen and its future is clearly not bright if the LLC runs away from the thunderstorm activity.Its being decoupled from the mid and upper levels as the NHC states in there discussion..welll see what they have to say at 11am.


That's great news....and looking at it...shear rules!!!!!

Member Since: June 9, 2005 Posts: 23 Comments: 37858
1389. NEwxguy
1:53 PM GMT on September 27, 2007
It would be crazy to write her off this early,we'll see by the end of the weekend
Member Since: September 6, 2007 Posts: 881 Comments: 15840
1387. hurricane23
1:52 PM GMT on September 27, 2007
Ive spoken to several at the NHC in the past few days and trust me there is little concern on this system even coming close to the U.S. as of right now.

Iam looking at the overall situation with karen and its future is clearly not bright if the LLC runs away from the thunderstorm activity.Its being decoupled from the mid and upper levels as the NHC states in there discussion..we'll see what they have to say at 11am.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1385. CJ5
1:51 PM GMT on September 27, 2007
Ouch...Karen took a hit overnight. There is a very visible and well defined COC, though. Shear will be tough for at least the next 24 hours. I would not call her dead yet. We saw Ingrid maintain her naked coc for three days in heavy shear before she finally gave up. Karen is a much more vigorous storm so I would expect at least a few days of life left in her.

It seems everything else; TD13, 98L and 97L is going away also. It was a flurry of activity here in the last week of Sept.
Member Since: July 4, 2007 Posts: 0 Comments: 1755
1383. FitzRoy
1:50 PM GMT on September 27, 2007
Posted By: thelmores at 1:38 PM GMT on September 27, 2007.


Any prediction at this point would be little more than an educated guess......

Might I suggest that those prognosticators of Karen's demise display rather an uneducated attitude. The educated position is to watch and wait. I'm not having a pop at you thel - I'm agreeing with what you and JP are saying, although it may be inelegantly expressed - lol!
1382. SEFL
1:49 PM GMT on September 27, 2007
"Posted By: HouseofGryffindor at 1:45 PM GMT on September 27, 2007.

SEFL, 23 didn't really give any facts either, just stated an opinion. If you look at the shear maps, it seems to me that shear should lessen earlier than 3 days like the NHC says. Shear came on quicker than they thought, and will end quicker too."

I guess you read what he says differently than I do. What I see is the evidence he backs up with images showing the exposed center and the tilt or split of the upper levels from the lower. You say since the shear arrrived before it was expected I think it will leave before expected. What is the basis for that other than your "guess"? We all know that hurricanes can be very unpredictable, but observations about what is happeneing and why explain more than just saying...oh well, it just has to change. That's what I read.
1380. rareaire
1:47 PM GMT on September 27, 2007
ok i think Karen will survive cause JP said it would!!
Member Since: August 19, 2007 Posts: 0 Comments: 1601
1379. Squid28
1:47 PM GMT on September 27, 2007
Question, I know that a TD/TS can have a couple of centers during formation and they will basically duke it out until on of them wins or the whole thing falls apart. But once a TD/TS has formed can it by itself (after becoming a dominant center) spawn another center and basically repeat the same cycle and if so how far away could it potentially form the new center?I'm not speaking in terms of something like an ERC, I'm looking for much larger in distance.... TIA
Member Since: May 23, 2006 Posts: 0 Comments: 343
1378. flzepher
1:46 PM GMT on September 27, 2007
If Karen continues moveing on a more westerly direction, will she get out of the shear enviorment faster than if she moved NW? I feel that she can survive a couple of days of this shear. I also feel for every hour she is moving more west, the greater the chances are that she will rebuild and affect a land mass somewhere. Not saying the East coast. There are to many varables at this point, should she survive. Still way to early to write her off or build her to a hurrincane. I have noticed alittle jog to the NW. We shall see if this persist.
1377. A4Guy
1:45 PM GMT on September 27, 2007
No expert by any means...but I would have to say that after looking at the shortwave IR, Karen is in trouble...at least for the short-term.
Member Since: June 23, 2006 Posts: 0 Comments: 668
1374. hurricane23
1:45 PM GMT on September 27, 2007
Here's one more large close-up visible shot of karen in the face of some unfavorable conditions.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1372. miamihurricane12
1:43 PM GMT on September 27, 2007
i dont know if this has been mentioned, for i have not read through the blog....but there is this one preservering tropical storm which made history


tropical storm andrew back in 1992, was being sheared and was void of all convection yet maintained a very vigourous circulation and kept winds at 60-70 mph...heading northwest into the open sea...a high pressure built back in and sent andrew to the west very fast and in a no shear environment...and we all know what happened after that

I am not saying that this will happen, just pointing out the similarities between the two
1371. FitzRoy
1:42 PM GMT on September 27, 2007
HoG, you wanted some links to stuff on T#'s:

Current

and

Dvorak Intensity Chart

Hope these help.
1370. SEFL
1:41 PM GMT on September 27, 2007
"Posted By: HouseofGryffindor at 1:35 PM GMT on September 27, 2007.

But 23, what if this shear doesn't last as long as they expect? I really don't think it will."

I would respectfully suggest that if you disagree with the analysis by h23 that you provide some support for your "i really don't think it will". Discussion of possibilities is good for all of us as long as there is some support for the differences. :)
1369. hurricane23
1:42 PM GMT on September 27, 2007
Here's a close-up visible shot from Mcidas which shows the LLC becoming exposed.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1368. Squid28
1:41 PM GMT on September 27, 2007
Posted By: underthunder at 1:21 PM GMT on September 27, 2007.

will someone please address the blob above 13...

Nice flare up in the last couple of frames, looks to be in the outer circulation on the visible sat. Guess I'll keep an eye on it....
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1367. NEwxguy
1:40 PM GMT on September 27, 2007
Well,if the shear doesn't last as long as predicted,that would aid Karen in staying alive,but who knows
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1365. thelmores
1:38 PM GMT on September 27, 2007
Yesterday Karen was almost a Hurricane, and today people are writing off Karen....

some people on this blog are so Fickle! LOL

Karen has a strong enough circulation to stick around a couple days in the face of even the highest shear. After stating that, can you honestly predict with reasonable certainty that Karen will not survive.

Any prediction at this point would be little more than an educated guess......

So for those that insist that things are "obvious", Karen is dead, Karen is fish, etc.... are just "guesses" at this point!

You are entitled to your opinion, and I encourage you to share it, but be careful to make "written in stone" type comments.....

If "anybody" tells you they know Karen's fate, they are bit arrogant imho!
Member Since: September 8, 2005 Posts: 0 Comments: 3805
1364. hurricane23
1:37 PM GMT on September 27, 2007
Besides a WNW-NW on satelitte you can see how the LLC is moving away from the thunderstorms which is not good if you looking for intensification.

Ramsdis visible loop
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1363. Tazmanian
1:35 PM GMT on September 27, 2007
Posted By: Sfloridacat5 at 6:09 AM PDT on September 27, 2007.

Any chance of 97l coming back? I think I see some rotation that has come off of Dom. Haiti.

NO
Member Since: May 21, 2006 Posts: 5091 Comments: 115244
1361. hurricane23
1:32 PM GMT on September 27, 2007
Posted By: HouseofGryffindor at 9:18 AM EDT on September 27, 2007.

hurricane23, I don't think anything is obvious with Karen at this point, except the fact that she is under heavy shear.

Without thunderstorm activity over the LLC no development will take place if anything karen will weaken even at a faster rate.The LLC should gradually spin down without thunderstorms over it.In the face of 30-40kt shear its unlikely anything will be left as these conditions are forcasted to be in place for about 2-3 days as per the NHC.
Member Since: May 14, 2006 Posts: 8 Comments: 13804
1360. decimus785
1:31 PM GMT on September 27, 2007
TheCaneWhisperer at 1:26 PM GMT on September 27, 2007.

Morning All!

Karen should be arrested for indecent exposure :-b

Possibly bad news for the US as she will move further west than anticipated. To early to speculate any US impact.


I think the shear has to be arrested,he's tearing Karen's clothes apart and wants to kill her.
1359. TheCaneWhisperer
1:31 PM GMT on September 27, 2007
1358. NEwxguy
1:29 PM GMT on September 27, 2007
Karen is going to have a hard time surviving.
Member Since: September 6, 2007 Posts: 881 Comments: 15840
1356. TheCaneWhisperer
1:26 PM GMT on September 27, 2007
Morning All!

Karen should be arrested for indecent exposure :-b

Possibly bad news for the US as she will move further west than anticipated. To early to speculate any US impact though.
1355. Hurricane1956
1:25 PM GMT on September 27, 2007
I DON'T SEE THIS NEW AREA OF LOW PRESSURE FORMING ON THE EAST COST OF FLORIDA MENTION IN THE BELOW NHC STATEMENT,ANY BODY SEE THIS????

For the North Atlantic...Caribbean Sea and the Gulf of Mexico...
The National Hurricane Center is issuing advisories on Tropical
Storm Karen...located about 970 miles east of the Windward Islands
and on Tropical Depression Thirteen....located about 150 miles
east of Tuxpan Mexico.
A trough of low pressure extending from The Straits of Florida to
the South Carolina coast is accompanied by a large area of
cloudiness and showers stretching from the northwestern Bahamas
northward for several hundred miles. A new area of low pressure
could be developing off the Florida east-central coast...and slow
development of this system is possible during the next couple of
days as it moves northeastward
.

Shower and thunderstorm activity over portions of Hispaniola...
associated with a tropical wave...has diminished.
A tropical wave over the eastern Atlantic just south of the Cape
Verde Islands has become a little better organized this morning.
Some slow development of this system is possible over the next
couple of days as it moves westward at about 15 mph.
Elsewhere...tropical cyclone formation is not expected during the
next 48 hours.
$$
Forecaster Mainelli/Beven
Member Since: August 28, 2006 Posts: 0 Comments: 624
1354. underthunder
1:21 PM GMT on September 27, 2007
will someone please address the blob above 13...
Member Since: August 9, 2006 Posts: 0 Comments: 96

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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.