Leslie headed towards Bermuda; Tropical Storm Michael forms

By: Dr. Jeff Masters , 3:01 PM GMT on September 04, 2012

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Tropical Storm Leslie continues to suffer from 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. Satellite loops show that Leslie has almost no heavy thunderstorm activity near its center, and the storm is crawling north at walking pace, 3 mph. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification. 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 Thursday afternoon. At that time, Leslie will be over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification. However, Leslie's motion will continue to be slow, keeping the storm over its cool water wake, and keeping any intensification slow. Once Leslie begins moving more quickly on Saturday, this effect will diminish, and Leslie could be at Category 2 strength on Sunday morning, as indicated in the official NHC forecast. Steering currents for Leslie are expected to be weak through Friday, as Leslie is stuck between two upper level lows. The latest guidance from our top computer models continues to show Leslie making a very close pass by Bermuda on Saturday. Leslie is a huge storm, and tropical storm-force winds are expected to extend outward from its center 250 miles by Friday. Bermuda is likely to see a 48-hour period of tropical storm-force winds beginning Friday night that lasts until Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, but the uncertainty in 4-day NHC forecasts is around 200 miles. Thus, the latest 11 am EDT NHC wind probability forecast calls for just a 12% chance of hurricane force winds on Bermuda on Saturday. Nevertheless, Leslie is capable of bringing an extended period of hurricane-force winds lasting six or more hours to Bermuda Saturday night through Sunday morning, should a direct hit materialize.


Figure 1. Morning satellite image of Tropical Storm Leslie. The low-level circulation center has very little in the way of heavy thunderstorms surrounding it, thanks to strong northwest winds creating 15 - 20 knots of wind shear.

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 Nova Scotia or Newfoundland, 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 storm may also miss land entirely, and brush by the coasts of Nova Scotia and Newfoundland. Large swells from Leslie reached Cape Hatteras, North Carolina last night, and will begin pounding the entire Eastern Seaboard today through Sunday. These waves will be capable of causing significant beach erosion and dangerous rip currents. The Hurricane Hunters are scheduled to make their first flight into Leslie on Wednesday afternoon.


Figure 2. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael forms in the Central Atlantic
Tropical Storm Michael has formed in the Central Atlantic on Monday, but is not destined for fame. Satellite loops show that this is a very small tropical cyclone, and the storm is well away from any land areas. Michael is under moderately high shear of 15 - 20 knots, and this shear is forecast to remain at 15 - 20 knots through Wednesday. Since Michael is such a small storm, just a modest increase in shear could destroy it. But if Michael survives until Thursday, when shear is expected to fall to the low range, it has the opportunity to strengthen.

Michaels's formation on September 4 puts 2012 in third place for earliest formation date of the season's thirteenth storm. The record is held jointly by 2005, which had Hurricane Maria form on September 2, and 2011, which had Tropical Storm Lee form on September 2 (there was an unnamed tropical storm that year before Lee.) None of the models show that Michael will threaten any land areas. Michael is a classic example of the type of storm that likely would have been missed before the advent of satellites, since the storm is small, far from land, and may be short-lived.

Jeff Masters

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Well, need to get dressed and head for my classroom. Hope everyone has a wonderful Wednesday.
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Good Morning...

Looks like we have Invest 90L:

AL, 90, 2012090506, , BEST, 0, 307N, 879W, 20, 1010, DB, 34, NEQ, 0, 0, 0, 0, 1011, 150, 0, 0, 0, L, 0, , 0, 0, INVEST, S,



Shouldn't amount to much... only if conditions become better than expected and the system stays small.
Member Since: August 14, 2008 Posts: 4 Comments: 4972
Quoting MahFL:
The GOM blob is getting bigger.


Let it get as big as it wants as long as it keeps heading south. It is a 'worry' to watch and see what it decides to do.
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Quoting MahFL:


It was Isaac's size and forward speed that did LA in. Also some people say the new levees sent extra water into places, and the forcast surge was for 4 to 8 feet, and they got 13.6 feet.


And the stall. Last spring when that storm stalled over us in west central Louisiana we were flooded unreal. There are stores in town that just closed up and aren't coming back. To stall over an area like Plaquemines Parish with the amount of rain coming down...
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982. MahFL
The GOM blob is getting bigger.
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Isaac dont wanna go away.
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980. MahFL
Quoting breeezee:
I am sure you have talked about this but the fact that isaac was getting stronger at land fall had something to do with the level of destruction that took place here in La


It was Isaac's size and forward speed that did LA in. Also some people say the new levees sent extra water into places, and the forcast surge was for 4 to 8 feet, and they got 13.6 feet.
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Quoting MahFL:


You must be female, you mean drift EAST.....


LOL, you mean the cute Phalene didn't give me away? Yeah, I meant east, but was thinking of the people in Plaquemines Parish when I was writing.
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978. MahFL
Quoting aislinnpaps:
So they think ex-Isaac will drift west towards Tampa? The people in south Louisiana do not need to see any form of Isaac again.


You must be female, you mean drift EAST.....
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Quoting breeezee:
I am sure you have talked about this but the fact that isaac was getting stronger at land fall had something to do with the level of destruction that took place here in La


That and the stall. The stall kept it from coming towards my part of Louisiana, but I would rather have had to deal with Isaac than for the people to have had to deal with all the flooding in Plaquemines.
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THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF SOUTH CENTRAL
ALABAMA...SOUTHWEST ALABAMA...NORTHWEST FLORIDA AND SOUTHEAST
MISSISSIPPI.

.DAY ONE...TODAY AND TONIGHT

NUMEROUS SHOWERS AND THUNDERSTORMS...MOSTLY OVER LOWER PORTIONS OF
FORECAST AREA...WILL MOVE SOUTH TOWARDS THE COAST AND OFFSHORE THROUGH
EARLY TONIGHT. PERIODS OF HEAVY RAIN COULD GIVE WAY TO MORE FLASH
FLOODING MOSTLY OVER COASTAL SECTIONS OF ALABAMA AND MOST AREAS OF
NORTHWEST FLORIDA THROUGH EARLY TONIGHT.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

A MODERATE TO STRONG COLD FRONT WILL MOVE ACROSS THE FORECAST AREA LATE
SATURDAY THROUGH EARLY SUNDAY. SHOWERS AND THUNDERSTORMS ARE EXPECTED
AHEAD AND ALONG THE FRONT. A FEW STRONG TO POSSIBLY SEVERE THUNDERSTORMS
WILL BE POSSIBLE AHEAD AND ALONG THE FRONT...MOSTLY SATURDAY AND
SATURDAY NIGHT.
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Quoting NovaScotia33:


Morning Largo. That track looks a bit better for a last minute recurve away from Nova Scotia?
so far so good up there, but remember its still far away and things can change
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Quoting CoopsWife:
Morning - jsut wanted to pop in and say thanks to Largo for keeping the updates going while our friends in AL/LA/MS are busy with cleanup. Your work is greatly appreciated!!
Good morning and thank you, so much trouble and misery there ,just want to say we are watching whats going on there and we care..stay safe out there
Member Since: August 6, 2011 Posts: 4 Comments: 38436
973. Sasha

Quoting LargoFl:
YELLOW CIRCLE HEADED TO THE GULF

AN AREA OF LOW PRESSURE LOCATED OVER SOUTHERN ALABAMA AND THE
WESTERN FLORIDA PANHANDLE IS EXPECTED TO MOVE SOUTHWARD INTO THE
NORTH-CENTRAL GULF OF MEXICO DURING THE NEXT DAY OR SO.
ENVIRONMENTAL CONDITIONS APPEAR MARGINALLY CONDUCIVE FOR SLOW
DEVELOPMENT OF THIS DISTURBANCE ONCE IT MOVES OVER WATER. THIS
SYSTEM HAS A LOW CHANCE...10 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.
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I am sure you have talked about this but the fact that isaac was getting stronger at land fall had something to do with the level of destruction that took place here in La
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971. VR46L
God love the Northern Gulf even if it don't become a storm ...

Member Since: March 1, 2012 Posts: 0 Comments: 6898

Quoting aislinnpaps:
So they think ex-Isaac will drift west towards Tampa? The people in south Louisiana do not need to see any form of Isaac again.
boy u just don;t know how true that is strongest cat 1 I ever seen
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Well, apparently this is the MLC remanants of Isaac so we get a new name if 90L forms.
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Good morning. 6z GFS 348 hours:

Member Since: February 11, 2012 Posts: 83 Comments: 7779
So they think ex-Isaac will drift west towards Tampa? The people in south Louisiana do not need to see any form of Isaac again.
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Morning - jsut wanted to pop in and say thanks to Largo for keeping the updates going while our friends in AL/LA/MS are busy with cleanup. Your work is greatly appreciated!!
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BEGIN
NHC_ATCF
invest_al902012.invest
FSTDA
R
U
040
010
0000
201209050953
NONE
NOTIFY=ATRP
END



We have Invest 90L, not sure if it's up yet elsewhere. It's for the associated energy from Isaac in the Gulf.
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Quoting LargoFl:


Morning Largo. That track looks a bit better for a last minute recurve away from Nova Scotia?
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Quoting sar2401:


Hey, I'm a ham radio operator, and I know Morse Code.
--. .-. --- - .... .- - .. ... --- .-.. -.. . .-. - .... .- -. -.. .. .-. -



And if you don't know morse, this link does.

Link
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You can watch it as a fan of weather, but it's a LONG ways away, and 15 days away from anything that GFS run shows. Feel free to ignore it until the GFS show that 3 days away, it's fantasy.

Quoting Gearsts:
Thats the big boy that we need to watch?
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Quoting NoloContendere:
Not to worry, it's been lower than that even in my lifetime. I can remember when the submarine Skate surfaced at the North Pole in 1958. If you want to worry about something, worry about global cooling and whether we're heading for a Dalton or Maunder type solar minimum. Think cold.

Born in the Eemian were you?
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Good morning, all, another day of 94% humidity with no rain, highs in the upper 90s. I think I'll save the gas and swim to work this morning...
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Member Since: August 6, 2011 Posts: 4 Comments: 38436
Member Since: August 6, 2011 Posts: 4 Comments: 38436
YELLOW CIRCLE HEADED TO THE GULF
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Good Morning folks....................
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Quoting Bobbyweather:

Nice picture!
Is there a possibility that this Medi-storm adds some convection to the center,then becomes a tropical-like storm?


Some days ago there had been a chance, but because of dry air from the south (Sahara) those chances dimished.
If you're interested, you may check the analyses of the last days in the archives of ESTOFEX (in English).
I have to go. Nice day to everyone.
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Member Since: August 6, 2011 Posts: 4 Comments: 38436
Member Since: August 6, 2011 Posts: 4 Comments: 38436
Quoting barbamz:
Good morning. System in the Mediterranean: Nothing really serious, but quite interesting to watch. COC as a naked swirl shows up this morning, right at the west coast of Italy.

Source Eumetsat/Lamma. Arrow by me :-)

Satloop

Nice picture!
Is there a possibility that this Medi-storm adds some convection to the center,then becomes a tropical-like storm?
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Good morning. System in the Mediterranean: Nothing really serious, but quite interesting to watch. COC as a naked swirl shows up this morning, right at the west coast of Italy.

Source Eumetsat/Lamma. Arrow by me :-)

Satloop
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I have a feeling the graphics for Leslie are an attemptnot to needlessly instill fear or panic in anyone. If it stays any where in the left part of the cone, it would be heading for New York City. That could happen, but no one seems to want to mention that. Even if it later turned out to sea, there would be a significant high water event for as long it heads northwest. As it gets closer, the water volume will increase, and the waves are increasing in height. They will only increase as the hurricane gets closer and intensifies. I fear a fringe effect most, and a direct strike or hit less. It is unusual and unlikely pattern, but no unprecedented for a storm in this area to hit the Northeast coast of the U.S. (Last Major 'Cane happened 191 years ago yesterday!)
I see this as an East Coast storm, not out to sea.
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Quoting trHUrrIXC5MMX:
LESLIE PRESSURE TO 992... THE SAME THING WITH THIS ONE...pressure down and same winds


yes... undergoing "Constant Wind Intensification"
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Quoting AegirsGal:
Some going there, some on the way to New England.


Isaac started affecting us in New England yesterday (tuesday)!
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Quoting trHUrrIXC5MMX:
LESLIE PRESSURE TO 992... THE SAME THING WITH THIS ONE...pressure down and same winds

Wind speed lags behind pressure drops. With a big storm I suspect the lag is greater, more air to accelerate.

From the forecast discussion on Leslie:

TRMM AND SSM/IS IMAGES...FROM 2223 AND 0013 UTC RESPECTIVELY...SUGGEST SOME RECENT INCREASE IN ORGANIZATION AS EVIDENCED BY THE FORMATION OF A CLOSED MID-LEVEL EYE...BUT THIS FEATURE CONTINUES TO BE DISPLACED 20-30 N MI EAST OF THE LOW-LEVEL CENTER. THE INITIAL INTENSITY IS HELD AT 55 KT IN AGREEMENT WITH A 0000 UTC SATELLITE CLASSIFICATION FROM TAFB. GLOBAL MODELS FORECAST A SUBSTANTIAL DECREASE IN SHEAR IN ABOUT 24 HOURS AS A LARGE-SCALE ANTICYCLONE FORMS OVER LESLIE. THE DEEP OCEANIC MIXED LAYER ALONG THE TRACK OF THE SLOW-MOVING STORM SHOULD ALSO MINIMIZE THE EFFECTS OF UPWELLING. STRENGTHENING IS FORECAST TO BEGIN AROUND THE TIME THE SHEAR RELAXES...BUT THE RATE OF INTENSIFICATION COULD INITIALLY BE SLOW DUE TO THE LARGE SIZE OF THE CIRCULATION.
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Quoting leftlink:



140mph, or 121.7 kts was the number provided by korintheman. You are right it was erronous, but unfortunately the NHC did not bother to update its archive material with any disclaimer: http://www.nhc.noaa.gov/archive/storm_wallets/atla ntic/atl1992/andrew/public/pal0492.033

If you are concerned about misinformation getting spread, then maybe it would be a good idea for some of your ire to be directed at the NHC so that we can convince them to put a big asterisk next to that 140mph number.

I updated my original post to use 165mph, or 143.4 kts. Which does not change my argument... that to provide ADVANCE WARNING about a storm prior to landfall, the system of only using wind speed to determine intensity level is broken.

What kind of change to the warning system would prevent the nhc from under-reporting the danger of a future Andrew?

When calculating intensities, the NHC first uses knots, then converts it into mph. Therefore, the official wind speed is 120 kt (140 mph; 138.1 mph to be exact) and 145 kt (165 mph; 166.9 mph to be exact).
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LESLIE PRESSURE TO 992... THE SAME THING WITH THIS ONE...pressure down and same winds
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Quoting sar2401:


I don't know for sure but I'll bet Andrew had to bear near the top of the list.


Andrew had a relatively small windfield to be such a monster....Labor Day Hurricane was even smaller when it hit the upper Keys.
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Quoting HurricaneHunterJoe:
Has the ever been a Cat5 Hurricane as small as Marcos/Michael?


I don't know for sure but I'll bet Andrew had to bear near the top of the list.
Member Since: October 2, 2004 Posts: 0 Comments: 15069
Quoting cheetaking:
I can't believe how huge the last advisory has Leslie being. Tropical storm force winds extend up to 230 miles from the center of the storm... that's a whopping 50 miles bigger than Isaac was at maximum intensity.

The Atlantic basin seems to have an unnatural propensity for producing really gigantic hurricanes these past few years. It seems like every single one has a gale diameter over 400 miles wide.


If Leslie were close to the coastline she would create a large surge for sure... which is exactly why the NHC scale should not call the storm just a "tropical storm". I think that Leslie, if she were to approach any coastline at this strength, should be called a hurricane, or a "strong tropical storm with hurricane-like storm surge."
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Quoting GTcooliebai:
Well have a goodnight all, you would have to seriously pay me to stay up and wait for the Euro to update.


GN, GT. Maybe Nadine will be a cat 3 when you wake up...or not. :)
Member Since: October 2, 2004 Posts: 0 Comments: 15069
Quoting hunkerdown:

what is your issue with the "." between each word???

Also, who is Issacc?? Come on, how hard is it to spell these names correctly...you aren't even close.


He does that all the time. I think it's his meme or something....or he just likes to be annoying. So far, he's batting about .100 with posts that make any sense.
Member Since: October 2, 2004 Posts: 0 Comments: 15069

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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.