Hurricane Lorenzo blows ashore; Karen continues weakening; TD 14 forms

By: Dr. Jeff Masters , 2:32 PM GMT on September 28, 2007

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Hurricane Lorenzo blew ashore at about midnight local time on the Mexican coast as a Category 1 hurricane with 75 mph winds. Satellite imagery shows that this very small storm is already starting to dissipate, and Lorenzo's effects will be confined to a small area near the coast where the storm made landfall. A pass from NASA's TRMM satellite (Figure 1) showed rainfall amounts of up to one inch per hour from Lorenzo. Lorenzo could dump 5-10 inches of rain over a narrow region extending 50 miles inland from the landfall location. Widespread major flooding is not expected, but some serious local flooding will probably occur.


Figure 1. Rainfall rates estimated by NASA's TRMM satellite as Lorenzo made landfall at 11:26 pm EDT last night. Rainfall amounts as high as one inch per hour (red colors) were estimated in the eyewall and in the spiral band to the west of Lorenzo.

It's not unusual for tropical storms to intensify suddenly where Lorenzo did, in the extreme southwestern Gulf of Mexico's Bay of Campeche. According to a paper presented by NASA's Scott Braun at a hurricane conference in 2006, this may be due to the mountains along shore diverting the low-level winds and helping intensify a tropical storm's vortex. In the case of a model simulation done of 2005's Tropical Storm Gert the authors write:
"The simulation shows an easterly wave and surface trough moving westward over the southern Gulf of Mexico with somewhat disorganized convection occurring in its vicinity. Low-level easterly flow ahead of the trough impinges on the eastern side of the Sierra Madre mountains and leads to flow blocking. Because of the particular shape of the topography, this blocked flow causes northwesterly to westerly flow to occur in the southern Gulf that eventually pinches off the trough to form a closed cyclonic circulation. This topographically forced flow also helps to organize some of the convection in a linear band south of the vortex center. Once the closed cyclonic circulation is formed, convection increases and gradually intensifies the cyclone to tropical storm strength by the time of landfall.

Tropical Storm Karen
Tropical Storm Karen has weakened to a minimal tropical storm, thanks to continued high levels of wind shear. Strong westerly winds aloft are creating about 20-25 knots of wind shear over Karen. This morning's QuikSCAT pass showed a very elongated center of circulation, with winds of minimal tropical storm force to the east of the center. Satellite loops show Karen's exposed low-level center of circulation, now visible as a swirl of low clouds. Most of the heavy thunderstorm activity that was was on the storm's northeast side has died out this morning, and Karen may get downgraded to a tropical depression today. A small area of heavy thunderstorm activity has developed near the center on the east side, but Karen is looking very unhealthy now.

Karen has taken an unexpected jog to the north this morning, which puts the storm closer to a region of higher wind shear. A motion to the west-northwest is expected to resume later today. With Karen's more northerly position, the odds of the storm being torn apart have increased. The GFS model kills Karen by Sunday, and the SHIPS model (which is based on the GFS) is forecasting that 35-40 knots of wind shear will affect the storm tonight through Saturday night. The other models do not kill Karen, but none of them forecasted the northward jog that will bring Karen into higher wind shear sooner. There is about a 50% chance Karen will be gone by Sunday, destroyed by wind shear.

If Karen survives, an ominous possibility arises--a ridge of high pressure is expected to build over the eastern U.S. and western Atlantic, forcing Karen westward towards the U.S. An anticyclone with low wind shear might build over the storm, creating an environment favorable for intensification of Karen into a hurricane. The path Karen might take late next week is highly uncertain. The high pressure ridge expected to build to the north of Karen will be quite strong, which might force Karen westward into Florida, or even west-south-westward through the Bahamas and into Cuba. There will be several small "short wave" troughs moving through the ridge that may be able to turn Karen more northwesterly towards New England, though. Still another uncertainty is the possibility of a new tropical, subtropical, or extratropical cyclone forming off the coast of North Carolina on Sunday or Monday, something now predicted by all of the computer models. Some of the models take this new storm north-eastward out to sea, which would create a weakness in the ridge that would pull Karen northward. However, most of the models predict that the new storm will move west or west-southwest over Georgia or Florida. A storm-storm interaction between Karen and the new storm might ensue, an event the models are poor at handling.

In short, this is a very complicated situation, and we'll just have to wait and see how it unfolds.

Tropical Depression 14
Tropical Depression 14 formed about 50 miles southwest of the Cape Verdes Islands this morning. The storm is under about 10-20 knots of wind shear. This shear should keep any development slow today. This morning's high-resolution QuikSCAT pass showed that the storm down not have a well-organized surface circulation, but rather a crescent-shaped line of converging winds arcing along a 400-mile long line. A few 50-knot wind vectors appeared in squalls on the storm's east side. This system will likely never affect land, since it is starting out too far north and will gain additional latitude in the coming days. The storm is headed northwest towards a region of high wind shear, and may not survive long.

I'll have an update Saturday morning by 10am.

Jeff Masters

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2470. CalvinSimonds
4:07 AM GMT on September 30, 2007
Ok. More on shear and hurricanes. Let's say we look at the vertical column of air outside the eye of a strong hurricane. Let's take a point 50 mi outside the eye and due east of the center. Let's say the hurricane is moving due north at 10 mi per hour. The wind at the surface is 120 miles an hour. Now what happens as we go up the column. My sense is that when we get to the top of the column, the wind is streaming in approximately the opposite direction. The air has lost a tremendous amount of mass, so presumably it doesn't have to be moving as fast, but let's say it's moving at 30 miles an hour. So what ever the shear is in the hurricanes environment, the hurricane itself has developed a SHEAR OF 150 MILES PER HOUR. Right?

Not all shear is bad for hurricanes.

OK. Now lets say that at 30 thousand feet there is a north wind blowing. at ten miles per hour. Now there is a 20 mile per hour [environmental] shear on the whole storm. The outflow at high altitudes will be distorted to the south.

This is BAD shear. Right?

If this sort of sheer is great enough to diminish the storm's ability to maintain its "internal" shear, then teh storm will decrease in strength, because it will become much less efficient at converting potential energy to wind and moving water around.

But at that point the total sheer on the storm, internal and external will actually have diminished? NO?

Seems that way to me.

Calvin
2469. Smyrick145
2:58 PM GMT on September 29, 2007
IKE,
I don't know if it would be wise to jump the gun on Karen being dead. IMO
Member Since: September 30, 2006 Posts: 0 Comments: 14
2468. IKE
2:45 PM GMT on September 29, 2007
I guess the GFS was right after all.

And all the talk on here about her hitting the east coast. Not.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2467. mit5000
2:45 PM GMT on September 29, 2007
2466. BajaALemt
2:44 PM GMT on September 29, 2007
Link

Playing catchup this morning...this is the clearest pic I've been able to find of what looks like Karen's COC. Little sputter just south of the COC...so I'm not sure that Im ready to count this one out......YET *shrugs*
Member Since: September 25, 2007 Posts: 53 Comments: 8533
2465. IKE
2:44 PM GMT on September 29, 2007
Yup...they did...

"stronger than average shear near Karen is winning the battle.
Karen is becoming disorganized as the center is losing
definition and the convection remains well removed from the
area of minimum surface pressure. It looks like Karen is
becoming a trough of low pressure."....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
2464. hahaguy
2:43 PM GMT on September 29, 2007
they did shes at 30knts
Member Since: August 12, 2007 Posts: 2 Comments: 2838
2463. Drakoen
2:43 PM GMT on September 29, 2007
yes Ike they have...
Member Since: October 28, 2006 Posts: 57 Comments: 29942
2462. hurricane23
2:43 PM GMT on September 29, 2007
000
WTNT32 KNHC 291439
TCPAT2
BULLETIN
TROPICAL DEPRESSION KAREN ADVISORY NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007
1100 AM AST SAT SEP 29 2007

...KAREN NOT LIKELY TO SURVIVE THE HOSTILE ENVIRONMENT...

AT 1100 AM AST...1500Z...THE CENTER OF TROPICAL DEPRESSION KAREN WAS
ESTIMATED NEAR LATITUDE 16.8 NORTH...LONGITUDE 53.8 WEST OR ABOUT
530 MILES...850 KM...EAST OF THE LEEWARD ISLANDS.

THE DEPRESSION IS MOVING TOWARD THE NORTHWEST NEAR 9 MPH...15 KM/HR.
THIS GENERAL MOTION IS EXPECTED TO CONTINUE TODAY.

SATELLITE IMAGES INDICATE THAT KAREN HAS WEAKENED AND MAXIMUM
SUSTAINED WINDS HAVE DECREASED TO NEAR 35 MPH...55 KM/HR...WITH
HIGHER GUSTS TO THE EAST OF THE CENTER. KAREN COULD DEGENERATE INTO
AN AREA OF LOW PRESSURE LATER TODAY.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 1009 MB...29.80 INCHES.

REPEATING THE 1100 AM AST POSITION...16.8 N...53.8 W. MOVEMENT
TOWARD...NORTHWEST NEAR 9 MPH. MAXIMUM SUSTAINED WINDS...35 MPH.
MINIMUM CENTRAL PRESSURE...1009 MB.

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
500 PM AST.

$$
FORECASTER AVILA

Member Since: May 14, 2006 Posts: 8 Comments: 13640
2461. amd
2:43 PM GMT on September 29, 2007
Karen needs a burst of convection over the center of circulation in the next few hours or else it may finally be over for Karen.

Karen, as a storm, looks horrible right now.
Member Since: August 29, 2005 Posts: 0 Comments: 1024
2460. Drakoen
2:43 PM GMT on September 29, 2007
00
WTNT42 KNHC 291440
TCDAT2
TROPICAL DEPRESSION KAREN DISCUSSION NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007
1100 AM EDT SAT SEP 29 2007

STRONGER THAN AVERAGE SHEAR NEAR KAREN IS WINNING THE BATTLE.
KAREN IS BECOMING DISORGANIZED AS THE CENTER IS LOSING
DEFINITION AND THE CONVECTION REMAINS WELL REMOVED FROM THE
AREA OF MINIMUM SURFACE PRESSURE. IT LOOKS LIKE KAREN IS
BECOMING A TROUGH OF LOW PRESSURE. I WAS TEMPTED TO MAKE THIS THE
LAST ADVISORY BUT INSTEAD...AND A BETTER OPTION...IS TO DOWNGRADE
KAREN TO A TROPICAL DEPRESSION AND FORECAST IT TO BE A REMNANT LOW
WITHIN THE NEXT 12 HOURS. THIS WILL GIVE SOME TIME TO MONITOR IF A
NEW CENTER REFORMS NEAR THE CONVECTION. THIS IS BASED ON THE FACT
THAT GLOBAL MODELS INSIST ON KEEPING THE CYCLONE. MOREOVER...THE
GFDL AND HWRF MAKE KAREN A HURRICANE BY 3 TO 4 DAYS. THESE MODELS
ASSUME THAT KAREN WILL SURVIVE THE BAND OF STRONG SHEAR FOR ANOTHER
24 HOURS. ALTHOUGH THIS SOLUTION SEEMS UNLIKELY...I HIGHLY
VALUE THE NUMERICAL MODELS...SO KAREN OR ITS REMNANTS WILL CONTINUE
TO BE CLOSELY MONITORED FOR SIGNS OF REGENERATION DURING THE NEXT
FEW DAYS.

THE DEPRESSION...OR THE BROAD REMNANT CIRCULATION..IS EXPECTED TO
MOVE TOWARD THE NORTHWEST OR 315 DEGREES AT 8 KNOTS FOR THE NEXT
DAY OR SO UNTIL DISSIPATION. THERE IS NO REASON TO DISCUSS TRACK
GUIDANCE AT THIS TIME WHICH IN FACT HAS NOT CHANGED.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
2459. IKE
2:42 PM GMT on September 29, 2007
I haven't read the update on Karen, yet...but, looking at the visible, my guess is they downgraded her?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
2458. BajaALemt
2:39 PM GMT on September 29, 2007
Mornin' folks
Member Since: September 25, 2007 Posts: 53 Comments: 8533
2457. Cavin Rawlins
2:35 PM GMT on September 29, 2007
Navy has her as 30 knots....BBL

1345.goes12.x.vis1km_high.12LKAREN.30kts-1009mb-165N-535W.100pc.jpg

Tropical MetEd: Upper Level Low Transition to Tropical Cyclone
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2456. sporteguy03
2:35 PM GMT on September 29, 2007
eye,
Thank you for the analysis of Karen

Taz,
91W a cloud swirl?
Member Since: July 7, 2005 Posts: 0 Comments: 5202
2455. blueranch
2:34 PM GMT on September 29, 2007
anybody have a comment or analysis of western GOM?
2454. Cavin Rawlins
2:31 PM GMT on September 29, 2007
Looking at the big picture....an old frontal trough near the Bahamas...showers from yesterday moved into Central America....Karen fighting shear....Melissa in the far east.....except for Karen and Melissa u could say things have quiet down.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
2453. Drakoen
2:31 PM GMT on September 29, 2007
The only way Karen will survive is if she repeats what she did yesterday afternoon. We will know soon what her fate is.
Member Since: October 28, 2006 Posts: 57 Comments: 29942
2452. JAPWeather
2:30 PM GMT on September 29, 2007
DR. Masters has over slept.
2451. JAPWeather
2:28 PM GMT on September 29, 2007
Within the next 24 hours shear should start to lay off of our Karen.
2450. eye
2:21 PM GMT on September 29, 2007
I doubt Karen will regenerate, I think she will be an open wave by Sunday, real hard for them to regenerate when they degenerate to an open wave....

yeah yeah yeah Katrina Katrina Katrina....but how many didnt do that...ALOT more.(exception rather than the rule)
Member Since: August 21, 2006 Posts: 0 Comments: 147
2449. stormlvr
2:19 PM GMT on September 29, 2007
Good morning! Lurk on this blog much more often than I post reserving comments for times they may add value. There are so many variables involved in making a forecast. One can take a valid or invalid point and find supporting data for a logical argument sometimes intentionally I'm afraid. There are several posts that I watch for valued insight and analysis. Just wanted to say thanks. Without using names, I'm sure you will know who I'm referring to.
Member Since: August 12, 2007 Posts: 0 Comments: 323
2448. JAPWeather
2:14 PM GMT on September 29, 2007
With over 50 mph of shear im a trully amazed with this system.
2447. Sfloridacat5
2:12 PM GMT on September 29, 2007
In October action usually shifts South (Caribbean). S.W GOM.
Member Since: September 16, 2007 Posts: 0 Comments: 6227
2445. mit5000
2:10 PM GMT on September 29, 2007
this is like world war 6 for tropical cyclones

shear v ssts and a fighting convection patten

who will win?

(shear won last time!)
2444. bayoubug
2:08 PM GMT on September 29, 2007
do yall think the nw carib..could be the next hot spot..soon
Member Since: July 25, 2006 Posts: 0 Comments: 246
2443. Sfloridacat5
2:08 PM GMT on September 29, 2007
Local meteorologist (T.V.) mentioned something possibly spinning up in the Florida Straights in the next few days. I'm assuming that's the left overs from 97L.
I do see a very weak circulation moving towards that area.
Member Since: September 16, 2007 Posts: 0 Comments: 6227
2442. Tazmanian
2:07 PM GMT on September 29, 2007
i no and thats funny they put up 91W and there not sny thing there LOL
Member Since: May 21, 2006 Posts: 5091 Comments: 114783
2441. extreme236
2:07 PM GMT on September 29, 2007
karen could die, or she could survive...we dont know which of the two will happen...i will be back in a bit
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2440. Tazmanian
2:06 PM GMT on September 29, 2007
ok
Member Since: May 21, 2006 Posts: 5091 Comments: 114783
2438. JustSouthofEquator
2:06 PM GMT on September 29, 2007
Taz I don't see anything there
Member Since: June 3, 2006 Posts: 0 Comments: 190
2437. extreme236
2:05 PM GMT on September 29, 2007
Posted By: Tazmanian at 1:59 PM GMT on September 29, 2007.

By: extreme236 at 6:53 AM PDT on September 29, 2007.

already, as drak pointed out, the ULL north of karen is weakening, therefore shear is dropping



but it is too late the wind shear has done there job on here


Taz, there are several things that could happen with karen...she isnt dead yet, there is still some potential
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2436. mit5000
2:05 PM GMT on September 29, 2007
next 1 to watch: renmants of mellisa when it gets to the u.s.a
2435. Tazmanian
2:03 PM GMT on September 29, 2007
what you all think of 91W?

they this put this up not too long a go




Member Since: May 21, 2006 Posts: 5091 Comments: 114783
2434. vabeachhurricanes2
2:03 PM GMT on September 29, 2007
ty
2433. JustSouthofEquator
2:02 PM GMT on September 29, 2007
vabeachhurricanes2 go back to page 47. Terranova added circles on the satellite picture showing where the circulations are :)
Member Since: June 3, 2006 Posts: 0 Comments: 190
2432. TerraNova
2:02 PM GMT on September 29, 2007
If Karen dissipates, the remnant low may try to restrengthen.
Member Since: July 30, 2007 Posts: 76 Comments: 4063
2431. eye
2:01 PM GMT on September 29, 2007
Taz, are you ready to say.....

Poofed?
Member Since: August 21, 2006 Posts: 0 Comments: 147
2430. bayoubug
2:01 PM GMT on September 29, 2007
karen will be a open wave by afternoon..
Member Since: July 25, 2006 Posts: 0 Comments: 246
2429. eye
2:00 PM GMT on September 29, 2007
I agree with Taz, just like with Ingrid, the wind shear has so severely weakened Karen that she probably will not be able to take advantage of the favorable conditions(reminant low)
Member Since: August 21, 2006 Posts: 0 Comments: 147
2427. vabeachhurricanes2
1:59 PM GMT on September 29, 2007
can someone show me the COC on a satilite image?
2426. Tazmanian
1:59 PM GMT on September 29, 2007
By: extreme236 at 6:53 AM PDT on September 29, 2007.

already, as drak pointed out, the ULL north of karen is weakening, therefore shear is dropping



but it is too late the wind shear has done there job on here
Member Since: May 21, 2006 Posts: 5091 Comments: 114783
2425. eye
1:58 PM GMT on September 29, 2007
extreme. she still has a day and a half at least to deal with 30-40 kts(according to the wind shear chart), at least it is not 60kts, but i dont see how she will survive facing those winds much longer...and she looks terrible, worst she has looked since the shear started.
Member Since: August 21, 2006 Posts: 0 Comments: 147
2424. extreme236
1:57 PM GMT on September 29, 2007
but if she survives thru today into tomorrow, those chances for her survival spike upward
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2423. Drakoen
1:57 PM GMT on September 29, 2007
yes shear is starting to drop. Still has a long way to go.
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2422. bayoubug
1:57 PM GMT on September 29, 2007
the next hot spot could be the nw carib..
Member Since: July 25, 2006 Posts: 0 Comments: 246
2421. extreme236
1:56 PM GMT on September 29, 2007
She might not survive eye, that is why I gave her a 70/30 chance in favor of dying...lol
Member Since: August 2, 2007 Posts: 19 Comments: 19234
2420. Tazmanian
1:56 PM GMT on September 29, 2007
its all most time for GW season
Member Since: May 21, 2006 Posts: 5091 Comments: 114783

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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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