Disorganized Leslie headed towards Bermuda

By: Dr. Jeff Masters , 4:18 PM GMT on September 03, 2012

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Tropical Storm Leslie continues to struggle with moderately high wind shear of 15 - 20 knots, due to strong upper-level winds out of the northwest. The shear is keeping heavy thunderstorms confined to the southeast quadrant of the storm. These thunderstorms are as far removed from the center as we've so far with Leslie, as seen on satellite loops. According to the latest SHIPS model forecast, the shear is expected to stay moderately high through Tuesday night, then drop to the low category, 5 - 10 knots, by Wednesday night. At that time, Leslie will be over warm ocean waters of 29°C, and the reduction in shear and warm waters should allow Leslie to intensify into at least a Category 1 hurricane by Friday, as predicted by most of the intensity forecast models. Intensification to a stronger storm may be hampered by its slow motion, which will cause Leslie to churn up cool water from the depths that will slow intensification. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Saturday, as predicted by the HWRF and LGEM models. Steering currents for Leslie are expected to be weak on Tuesday - Friday, as Leslie gets stuck between two upper level lows. The latest guidance from our top computer continues to show Leslie making a very close pass by Bermuda on Saturday, and that island can expect a 3-day period of rough weather Friday through Sunday. Leslie will stay stuck in a weak steering current environment until a strong trough of low pressure approaches the U.S. East Coast on Saturday. This trough should be strong enough to pull Leslie quickly to the north on Saturday and Sunday, and Leslie may be close enough to the coast that the storm will make landfall in Canada on Monday, September 10. None of the reliable models have shown that a direct hit on New England will occur, but we can't rule that possibility out yet. The most likely long-term fate of Leslie will be for it to miss land entirely and brush by the coasts of Nova Scotia and Newfoundland, but any forecast of what a tropical cyclone might do a full seven days in advance is pretty speculative. Regardless, Leslie will bring an extended period of high waves to Bermuda, the U.S. East Coast, and Nova Scotia and Newfoundland this week. These waves will be capable of causing significant beach erosion and dangerous rip currents.


Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center is fully exposed to view, thanks to strong northwest winds creating 15 - 20 knots of wind shear.

Invest 99L in the Central Atlantic
A small extratropical low pressure system that got cut off from the jet stream and is now spinning away in the Central Atlantic, near 26°N 42°W, (Invest 99L), is headed west at 10 mph, and has developed a small amount of heavy thunderstorm activity. This storm is not a threat to any land areas, and in their 8 am EDT Tropical Weather Outlook on Monday, NHC gave 99L a 30% chance of developing into a tropical cyclone by Wednesday morning.

Jeff Masters

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We have eight more names between the most active month of the hurricane season that usually breeds 4-6 named storms, a slightly less active month that usually breeds 2-4 named storms, and a quiet month that usually breads 1-2 named storms.
Member Since: July 6, 2010 Posts: 113 Comments: 31508
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1320. Thrawst
Its amazing how the names go by... Could be at the greek by the end!
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At the moment, CIMSS puts both Leslie and Michael as tropical storms of T2.7, or 39kts. With this one, minor, inconsequential difference: the wind radii for Leslie are at 140km. For Michael? 30km.

Never been a better illustration as to why our current classification method stinks. Saffir-Simpson shows no difference, but these two storms couldn't be more dissimilar.
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Quoting PuntaGordaPete:


The HSI is close to useless for ordinary people. It is a measure of financial impact for the insurance industry and a measure of assistance needed for government and non-government agencies. Ordinary folks, those who need to prepare and evacuate, don't really care if someone else 200 miles away is also impacted. They care about maximum potential severity at their location.




How about a two number system classification. Isaac was a Cat 1 wind wise but a cat 3 surge wise, so that would make it a Cat 1.S3

Ike was a Cat 2 on landfall but had a surge of a Cat 4, so that would make it a Cat 2.S4

Irene on the other had was a Cat 1 on landfall and only brought minimal surge so that would make it a Cat 1.S1

Just a few more thoughts
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting RTSplayer:
I think that doesn't go far enough.

I think they should pick 2 or 3 analogs from each of 3 rating systems for expected landfall rating:

Predicted SS category to maintain continuity.
Predicted IKE value at landfall.
Predicted HSI value at landfall.

Pick 2 or 3 analogs from each ranking system, with a maximum of 1 overlapping storm across ranking systems.



The HSI is close to useless for ordinary people. It is a measure of financial impact for the insurance industry and a measure of assistance needed for government and non-government agencies. Ordinary folks, those who need to prepare and evacuate, don't really care if someone else 200 miles away is also impacted. They care about maximum potential severity at their location.
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Quoting jeffs713:

Yeah, but 13L is really close to an area of higher shear (to the SE, per CIMSS), and dry air (to the west). With its size, it will be highly sensitive to both shear and dry air - and the mid-level shear doesn't look very favorable either.

I think the NHC forecast is decent, so I wouldn't expect anything beyond a low-level TS, at best.

Kirk was close to high wind shear and dry air as well. Here is the first intensity forecast for Kirk by the NHC:

FORECAST POSITIONS AND MAX WINDS

INIT 28/2100Z 23.8N 43.9W 30 KT 35 MPH
12H 29/0600Z 24.1N 45.3W 35 KT 40 MPH
24H 29/1800Z 24.3N 47.4W 35 KT 40 MPH
36H 30/0600Z 24.6N 49.6W 35 KT 40 MPH
48H 30/1800Z 25.3N 51.7W 35 KT 40 MPH
72H 31/1800Z 27.5N 55.5W 35 KT 40 MPH
96H 01/1800Z 32.5N 55.0W 35 KT 40 MPH
120H 02/1800Z 40.0N 48.0W 35 KT 40 MPH
Member Since: July 6, 2010 Posts: 113 Comments: 31508
Quoting VR46L:
leslie looks rather top heavy yet part naked


I see the NHC have upped their 120hr forecast intensity from 100mph to 105mph. Up-welling anyone???

DUE TO THE LARGE SIZE OF
LESLIE AND ITS EXPECTED SLOW MOTION...LARGE SWELLS PROPAGATING AWAY
FROM THE TROPICAL CYCLONE WILL AFFECT BERMUDA AND NEARLY ALL OF
THE U.S. EAST COAST FOR MUCH OF THIS WEEK.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
1314. 7544
morning all its going to be fun to see if issaac could make a comeback once he hits the gulf and what size he will become will he get his name back if he did form again tia
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That ol' Euro had Isaac coming to central Gulf and we had to ignore it as it was an outlier. But in the end it was dead on the whole time. From east coast of Florida, to down the spine of Florida, to west coast of Florida, to East Gulf and panhandle of Florida, to Mobile, all the way west to NOLA impact and communities south taking the brunt in LA.
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Quoting CybrTeddy:


Who knows, Kirk was also a small system that was only predicted to be a moderate TS at best.

Yeah, but 13L is really close to an area of higher shear (to the SE, per CIMSS), and dry air (to the west). With its size, it will be highly sensitive to both shear and dry air - and the mid-level shear doesn't look very favorable either.

I think the NHC forecast is decent, so I wouldn't expect anything beyond a low-level TS, at best.
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From US National Weather Service Miami Florida on FB
Another round of heavy rainfall with some strong to even severe thunderstorms will be possible today...especially over the interior and east coast areas this afternoon/evening.
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Quoting AussieStorm:

The next one is going to bring very cold air behind it but it wont last long with a big as high setting in pretty quickly.


Has snow ever been reported at Perth?
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Quoting Progster:


The next cold front approaching SW Australia looks pretty nasty too. You've got some big snakes on the southern Jet Rossby wave.

The next one is going to bring very cold air behind it but it wont last long with a big as high setting in pretty quickly.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
1308. VR46L
leslie looks rather top heavy yet part naked

Member Since: March 1, 2012 Posts: 0 Comments: 6840
1307. WxLogic
Quoting GeoffreyWPB:
Will we see a yellow circle in the NE Gulf at the 11:00 a.m. update?


If it were to be the case (in the short term)... I would expect one at 2AM ET at the earliest. Since around this time is when I would expect most of the Mid/Low level energy from the remnants of Isaac to be in the N/NE GOM.
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Quoting AussieStorm:
Crikey, have a look at this......

first one of the new fire season.



The next cold front approaching SW Australia looks pretty nasty too. You've got some big snakes on the southern Jet Rossby wave.
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Quoting CybrTeddy:
Morning all, the ECMWF continues to want to bomb Leslie out into a very powerful major hurricane, the GFS is continuing to also show the development of Leslie into a major, same With the CMC and UKMET. The ECMWF/CMC duo also show that part of what appears energy associated with Isaac and a trough could develop into a system in the gulf. Active times continue.


Dont forget the possible CV development that the models also develop.
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Sorry for double posting, but I thought this was important enough for a new page, since I got screwed by the paging system.


So as you can see, I'm interested in alternative ranking systems for the severity of storms, which are easy enough to calculate so that meteorologists can communicate the destructive potential to the audience, so that they can make better decisions.


Current practices are to pick 2 or 3 analog SS scale rated storms and compare them to the expected landfall. With the occasional mentioning of "well this one is bigger in area, so it might be a little worse".

I think that doesn't go far enough.

I think they should pick 2 or 3 analogs from each of 3 rating systems for expected landfall rating:

Predicted SS category to maintain continuity.
Predicted IKE value at landfall.
Predicted HSI value at landfall.

Pick 2 or 3 analogs from each ranking system, with a maximum of 1 overlapping storm across ranking systems.

Example, since Katrina is a classic example of where no one ranking system is sufficient, you could use Katrina's landfall as an analog in all 3 ranking systems during a forecast, but you can't use any more overlaps. This would allow 2 additional analogs from each ranking system, which cannot overlap.


The benefits of this would be the ability to better select analog storms, the public does not necessarily need to know how they were selected, but it would help to go ahead and tell them.


For example, if you tell somebody Katrina landfall was a 36, Andrew landfall was no higher than 33, and "Storm X" is forecast to make landfall as approximately a 32, then everybody knows to evacuate, regardless of it's exact SS ranking.

Whereas if you say, "Well, it'll make landfall as a 115mph cat 3," lots of people will just ride it out, as was even the case with Rita and Katrina (ironically).
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1302. GetReal



T-storm activity coverage and intensity on the increase, in NW Florida and the adjacent coastal waters, as the remnants of Isaac make a run towards the GOM. There is still a hint of a cyclonic twist, and this maybe of some interest 36 hours from now.
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1301. yqt1001
Quoting CybrTeddy:


Who knows, Kirk was also a small system that was only predicted to be a moderate TS at best.


From the discussion:

THE FUTURE STRENGTH OF THE DEPRESSION IS NOT AN EASY PREDICTION AS
IT IS VERY CLOSE TO SOME STRONG NORTHWESTERLY SHEAR. HOWEVER...THE
BULK OF THE MODEL GUIDANCE IS NOW INDICATING THAT THIS SHEAR WILL
STAY AWAY FROM THE CYCLONE...WITH LITTLE CHANGE IN THE ENVIRONMENT
PROBABLE FOR THE NEXT COUPLE OF DAYS WHILE THE CYCLONE REMAINS OVER
WARM WATERS.
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Quoting unknowncomic:
Is that unusual?

Late winter/early spring strong fronts are common. Changing of the seasons can bring big changes.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting jeffs713:

I'm guessing I picked up about 2/3 of an inch. Both of the PWS nearest to me either were missed by the storm that hit my house (it was tiny, but rather intense), or weren't online Saturday. DW Hooks airport picked up 1.18", but it got one cell that just barely missed my house. In any case, it was enough that I don't have to water this week. :)


Was down in Galveston when storms rolled in Saturday on the seawall. Was at the Spot eating and watched that white draped curtain (rain shaft) come in over the water, was cool seeing it.
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So as you can see, I'm interested in alternative ranking systems for the severity of storms, which are easy enough to calculate so that meteorologists can communicate the destructive potential to the audience, so that they can make better decisions.


Current practices are to pick 2 or 3 analog SS scale rated storms and compare them to the expected landfall. With the occasional mentioning of "well this one is bigger in area, so it might be a little worse".

I think that doesn't go far enough.

I think they should pick 2 or 3 analogs from each of 3 rating systems for expected landfall rating:

Predicted SS category to maintain continuity.
Predicted IKE value at landfall.
Predicted HSI value at landfall.

Pick 2 or 3 analogs from each ranking system, with a maximum of 1 overlapping storm across ranking systems.

Example, since Katrina is a classic example of where no one ranking system is sufficient, you could use Katrina's landfall as an analog in all 3 ranking systems during a forecast, but you can't use any more overlaps. This would allow 2 additional analogs from each ranking system, which cannot overlap.


The benefits of this would be the ability to better select analog storms, the public does not necessarily need to know how they were selected, but it would help to go ahead and tell them.


For example, if you tell somebody Katrina landfall was a 36, Andrew landfall was no higher than 33, and "Storm X" is forecast to make landfall as approximately a 32, then everybody knows to evacuate, regardless of it's exact SS ranking.

Whereas if you say, "Well, it'll make landfall as a 115mph cat 3," lots of people will just ride it out, as was even the case with Rita and Katrina (ironically).
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Quoting jeffs713:

Yep. I will admit, I was kinda hoping to keep the routine of this year with all of the male storms being more intense (with the exception of Alberto).


Who knows, Kirk was also a small system that was only predicted to be a moderate TS at best.
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Quoting jeffs713:

But... what do I know?


Does my avatar apply to you as well?

Tropical Thunderstorm Michael


Hey, it did re-cover its COC and has a nice Thunderstorm... i mean CDO, over the center

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Quoting CybrTeddy:
SAB and TAFB as well as the ADT all show 13L at 2.5, or TS strength. Expect an upgrade to TS Michael at 11am.

What are Leslie's number.
T2.5/3.5 12L LESLIE
T2.5/2.5 13L NONAME
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting lobdelse81:
Any Cape Verde systems in the horizon that we need to worry about?
Another week there may be something to track.
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Quoting CybrTeddy:


Exposed COC is not usually a hindrance for an upgrade as long as the convection is somewhat close to the COC, and location is never a reason to not upgrade. Per ATCF, unless the NHC changes it's mind, we have Michael.

Yep. I will admit, I was kinda hoping to keep the routine of this year with all of the male storms being more intense (with the exception of Alberto).
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Quoting AussieStorm:
This is what the front that's going to hit Sydney dumped on Perth...







Is that unusual?
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Quoting jeffs713:

I don't agree with that, as TD13 is partially exposed, and WAAAAAAY out there. But... what do I know?


Exposed COC is not usually a hindrance for an upgrade as long as the convection is somewhat close to the COC, and location is never a reason to not upgrade. Per ATCF, unless the NHC changes it's mind, we have Michael.
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Quoting RitaEvac:
Jeff how much rain you get Saturday? I picked up an inch, wasn't expecting that either. Within the same city I live in got up to 3 inches only 1-3 miles from me, seems to be the norm with more rain always somewhere else even if it's a mile away literally.

I'm guessing I picked up about 2/3 of an inch. Both of the PWS nearest to me either were missed by the storm that hit my house (it was tiny, but rather intense), or weren't online Saturday. DW Hooks airport picked up 1.18", but it got one cell that just barely missed my house. In any case, it was enough that I don't have to water this week. :)
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WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0945 AM EDT TUE 04 SEPTEMBER 2012
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 05/1100Z TO 06/1100Z SEPTEMBER 2012
TCPOD NUMBER.....12-108


I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK: FIX OF TROPICAL STORM LESLIE
AT 06/1800Z NEAR 27.0N 62.8W.
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Quoting CybrTeddy:
SAB and TAFB as well as the ADT all show 13L at 2.5, or TS strength. Expect an upgrade to TS Michael at 11am.

I don't agree with that, as TD13 is partially exposed, and WAAAAAAY out there. But... what do I know?
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Jeff how much rain you get Saturday? I picked up an inch, wasn't expecting that either. Within the same city I live in got up to 3 inches only 1-3 miles from me, seems to be the norm with more rain always somewhere else even if it's a mile away literally.
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The consequences for what remains of Isaac re-entering the mix in the GOM could change things for what Leslie might feel and do, downstream.

Any speculation here, as to what, if say ... he redeveloped in any significant way?

My guess is that it would dissolve the ULL sitting off the East Coast, but that's as far as my mind takes it.
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The designation of TS Michael makes 2012 the third most active AHS so far.
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Quoting TomballTXPride:
September looks to remain active, while the overall steering pattern continues to favor recurves which is great news.



Actually from what we have seen the overall pattern favors landfalls, ie Isaac, Ernesto, ect. Suspect we will see another system like that before years out. This is due the abundance of dry air in the Atlantic, causing storms to go more westward.
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1283. VR46L
Is the Ghost of Isaac returning to the scene of the crime?

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1282. Patrap
Quoting jeffs713:

Nadine


Ahh, a Chuck Berry tune.
Member Since: July 3, 2005 Posts: 421 Comments: 127601
Quoting jeffs713:

That looks like sleet. (please send some to North America... I'm done with summer)

I'm very much looking forward to our upcoming summer. bring on the 100+ days. I love them. Not had them in since summer 2009.
Member Since: September 30, 2007 Posts: 9 Comments: 15932
Quoting TomballTXPride:
Who is next after Michael?

Nadine
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Quoting TomballTXPride:
So Michael already?



Yep
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Quoting Neapolitan:
13-5-0:

AL, 13, 2012090412, , BEST, 0, 268N, 435W, 35, 1006, TS, 34, NEQ, 30, 30, 0, 0, 1016, 120, 15, 0, 0, L, 0, , 0, 0, MICHAEL, M

Michael


Didnt see that, so yup, we have TS Michael.
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Quoting AussieStorm:
This is what the front that's going to hit Sydney dumped on Perth...








That looks like sleet. (please send some to North America... I'm done with summer)
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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.