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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Quoting icmoore:


No he doesn't and I suspect his age is over rated :) unlike his status as Chief Blobologist here. I am probably ahead of him or not far behind, and alas next week another year bites the dust :)


Well Happy Birthday to you! Im 53 and loving every minute of it LOL
Member Since: April 26, 2006 Posts: 5 Comments: 3041
Quoting Tropicsweatherpr:
Latest microwave shows Leslie looking better.


Why is everyone surprised Leslie looks good on Microwave. She has always looked good via microwave as it's able to look through the convection down to the core. She has always had a solid core, just her convection has been sheared for a long time now.


They keep pushing it back....
120H 08/0600Z 30.8N 64.1W 80 KT 90 MPH
120H 08/1200Z 31.5N 64.5W 80 KT 90 MPH
120H 08/1800Z 30.5N 65.0W 85 KT 100 MPH
120H 09/0000Z 31.0N 65.0W 85 KT 100 MPH
120H 09/0600Z 32.0N 65.3W 90 KT 105 MPH
120H 09/1200Z 33.0N 65.5W 90 KT 105 MPH
120H 09/1800Z 34.0N 65.8W 90 KT 105 MPH(My 23:00 prediction)
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Quoting aislinnpaps:


Who's that guy on Warehouse 13, or is it Alpha's, who lives forever but doesn't age in appearance? That's Gro.

Eight at night and still 88 degrees with a heat index of 91 here in Louisiana.


75 degrees with a dewpoint of 70 here in Montgomery. A couple of days of non-tropical/semi-tropical rains really helped. Right back up into the mid-90's tomorrow though.
Member Since: October 2, 2004 Posts: 0 Comments: 9957
Quoting TomballTXPride:

It's not strange, Bud. I wouldn't put too much credence in it beyond 10 days. Even beyond 120 hours is pushing it.
I am glad we have the model police on duty.

I think if a model is consistently showing a feature over several runs then we should pay attention, even if it is a week out. Pretty sure the pros perk up if several runs of the GFS or the ECMWF show a storm forming in 5-7 days. Something to watch, y'know.
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Quoting K8eCane:


Check out his pic. He doesnt look 9,385.


No he doesn't and I suspect his age is over rated :) unlike his status as Chief Blobologist here. I am probably ahead of him or not far behind, and alas next week another year bites the dust :)
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the katrina and andrew debate has been going on since this morning..you would think someone would have conceded by now..
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Facebook message by NHC confirming the future GOM system will be Nadine instead of Issac.

Our view is that while this disturbance has some association with Isaac, the primary remnant of Isaac was a separate decaying circulation to the north of this one. Therefore, should this disturbance develop into a tropical cyclone it would get a new name.
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Quoting AussieStorm:

As I said, it was for a laugh. I was no way taking it serious.


Not criticizing you.
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Closest Bermuda Approach Pressures

Model raw / adjusted

18z GFDL 962mb / 960mb
18z HWRF 947mb / 953mb
18z GFS 974mb / 963mb
12z Euro 939mb / 942mb*

avg raw: 956mb
avg adj: 955mb


* adjustment is derived since initialization is offset 6 hours.

without Euro

avg raw: 961mb
avg adj: 959mb
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Quoting victoria780:
THE WEATHER MAY AFFECT PRESIDENT OBAMA SPEECH.MOVING TO A SMALLER VENUE TO SPEAK IN NORTH CAROLINA /.FROM A 70,000 AREA TO A 20,000 SEAT ARENA.Report: Democrats Scramble to Move Obama Speech to Smaller Venue

Report: Democrats Scramble to Move Obama Speech to Smaller Venue

DIDNT KNOW IT WAS GOING TO RAIN?



He's not going to speak until Thursday. There's a 30% chance of thunderstorms. There's always a 30% chance of thunderstorms in the South. He also won't speak until 10:00 pm. Any storms should be dissipating by then. Where did you come up with this melange of headlines? Here's a link to an actual story:
Link
Member Since: October 2, 2004 Posts: 0 Comments: 9957
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Quoting snowboy:


Leslie is making her move to join the big leagues..


Ahead of schedule, too, she's actually looked good for most of the day... which is odd for her. She usually only comes out at night. It might make for an interesting night.
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Quoting victoria780:
THE WEATHER MAY AFFECT PRESIDENT OBAMA SPEECH.MOVING TO A SMALLER VENUE TO SPEAK IN NORTH CAROLINA /.FROM A 70,000 AREA TO A 20,000 SEAT ARENA.Report: Democrats Scramble to Move Obama Speech to Smaller Venue

Report: Democrats Scramble to Move Obama Speech to Smaller Venue

DIDNT KNOW IT WAS GOING TO RAIN?



We've had very heavy rain the past few afternoons in Charlotte and the weather forcast is for a chance again tomorrow but not as heavy and for Thursday they are saying even less. They are planning for everything to be at the stadium unless there is "dangerous" weather and then they would move back to the Arena. We have what I call the "summer storms" all of the time here in Charlotte and when they planned to have the DNC here they knew that. They are just being prepared but I don't think based on what our weather people are saying that they will have to move it.
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Quoting K8eCane:


Check out his pic. He doesnt look 9,385.


Who's that guy on Warehouse 13, or is it Alpha's, who lives forever but doesn't age in appearance? That's Gro.

Eight at night and still 88 degrees with a heat index of 91 here in Louisiana.
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Quoting KoritheMan:


Sure.

Andrew

"HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 45 MILES FROM THE CENTER
...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140 MILES
FROM THE CENTER."

Katrina

"HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 125 MILES FROM THE
CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP
TO 230 MILES."

There's literally no comparison.


Wish I had the original measurements in nautical miles... but I was able to do a conversion anyway and calculate the "size and wind field power factor" for the two storms, plus Hurricane Isaac:



Have you calculated these numbers using the model you proposed? Fyi, I used the Isaac advisory numbers from here: Link

Under the modified Saffir Simpson scale, Andrew would remain "category 5" but Katrina would be bumped up to category 4 at landfall and Isaac would be bumped up to category 2.

Note: UPDATED to replace dated analysis of andrew wind speed that was provided by korintheman in post #668

Member Since: December 28, 2010 Posts: 0 Comments: 134
Quoting RTSplayer:


Wow. What a waste of code and computer processing power.

Until you get 5 day forecast skill to like 0.99 it's useless to really talk about anything at all beyond 15 days, and even that is laughable.

10 days is about the max that is somewhat believable, and once in a while accurate, at present time.

As I said, it was for a laugh. I was no way taking it serious.
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THE WEATHER MAY AFFECT PRESIDENT OBAMA SPEECH.MOVING TO A SMALLER VENUE TO SPEAK IN NORTH CAROLINA /.FROM A 70,000 AREA TO A 20,000 SEAT ARENA.Report: Democrats Scramble to Move Obama Speech to Smaller Venue

Report: Democrats Scramble to Move Obama Speech to Smaller Venue

DIDNT KNOW IT WAS GOING TO RAIN?

Member Since: July 20, 2008 Posts: 0 Comments: 326
Quoting Abacosurf:
This years Debby or debbie.
Elongated trough with strongest winds on the south and east side.



Ah, OK, that would be TS Debby then. She stalled off FL because the steering currents were almost non-existant. Flight level winds are pretty strongly ENE once the low rounds the big bend, so whatever this becomes shouldn't spend more than 24-36 hours over water before making landfall.
Member Since: October 2, 2004 Posts: 0 Comments: 9957
As per usual... Leslie looks much better at night.
Member Since: August 29, 2009 Posts: 12 Comments: 482
Quoting Tropicsweatherpr:
Latest microwave shows Leslie looking better.



Leslie is making her move to join the big leagues..
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Quoting icmoore:


Okay, you are such a tease I'm going to read your blog now :)


Check out his pic. He doesnt look 9,385.
Member Since: April 26, 2006 Posts: 5 Comments: 3041
Quoting Grothar:


So was my blog I wrote this morning. :) I see two systems developing.


Okay, you are such a tease I'm going to read your blog now :)
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Quoting Tropicsweatherpr:
Latest microwave shows Leslie looking better.



Developing eyewall, looks nice. Let us see if Leslie doesn't get sheared to death tonight again.
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Looks like we are getting left overs for supper tonight(ISSAC).Went to football game had a 60+MPH Wind gust out of north.There was some blowing and shakeing going on.
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Quoting Tropicsweatherpr:
Hi Grothar. Plenty of activity in West Africa right now. The models have been bullish on a CV development.



So was my blog I wrote this morning. :) I see two systems developing.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
Latest microwave shows Leslie looking better.

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Hi Grothar. Plenty of activity in West Africa right now. The models have been bullish on a CV development.

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Just looking over everything - the remnants (or whatever) of Isaac with a 10% chance. The low you can barely see in the mid GOM. The ULL that's been floating east of Fl for the past couple of days. Leslie getting stronger wvery night and then loosing some during the day and then there is Michael.

Any chance that these are possibly affecting each other - or could down the road????
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Quoting Charmeck:

Reminds us of Isaac - he did the same thing!


Yes, it did.
Member Since: July 17, 2009 Posts: 64 Comments: 23749
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Quoting MAweatherboy1:

That dry air isn't helping Leslie, but with shear supposed to relax to low levels dry air wouldn't be a problem.
Member Since: March 16, 2012 Posts: 123 Comments: 7890
Quoting sar2401:


Which Debbie/Debby are you talking about? There have been a lot of them. :)
This years Debby or debbie.
Elongated trough with strongest winds on the south and east side.

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Quoting GeoffreyWPB:


I remember we were talking about this. I thought I jumped the gun. But if you take the averages of what we both thought, it turns out correct.


Sure looks like it :)
Member Since: August 14, 2008 Posts: 4 Comments: 4881
Quoting Civicane49:
Large Leslie and midget Michael.


Leslie always seems to get bigger at this time and smaller in 12 hours.
Member Since: March 16, 2012 Posts: 123 Comments: 7890
Quoting hunkerdown:

If we are talking landfall...Andrew was far more powerful at landfall in SFla then Katrina was in LA/MS. Forget the size, the windspeed difference between the two is/was exponentially more devastating and destruction in favor of Andrew.


The reality is it is not.

Katrina's much larger size means that the water damage and the prolonged wind damage more than makes up for it.

Katrina's storm surge went 6 to 12 miles inland in Mississippi.


Seriusly, if Katrina took Andrew's track and hit at the same intensity as the LA/MS landfall, it would be way worse in Florida than it was for the real Andrew. It's massive size would crush areas that barely even had any effects from Andrew.


Meanwhile, if Andrew takes Katrina's path, and holds Andrew's Florida landfall intensity through Katrina's LA/MS landfall track, then NOLA doesn't flood, and I don't even get Tropical Storm force winds at my house, and probably don't even lose power, and the storm surge in Mississippi would be half as much, and Alabama and the Florida panhandle have minimal or zero impacts.

How do I know that?

Camille had almost identical track to Katrina, and it was way more intense than Andrew based on pressure and wind speed, and it was bigger than Andrew, and it didn't do the damage Katrina did. Camille had 190mph winds at landfall.
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Member Since: February 11, 2012 Posts: 79 Comments: 7303
Quoting TropicalAnalystwx13:
Nothing unexpected.

AL, 12, 2012090500, , BEST, 0, 252N, 628W, 55, 994, TS, 50, NEQ, 60, 0, 0, 0, 1014, 250, 50, 0, 0, L, 0, , 0, 0, LESLIE, D,

AL, 13, 2012090500, , BEST, 0, 274N, 437W, 45, 1006, TS, 34, NEQ, 30, 30, 20, 30,

I didn't think we would see much change and this confirms that.
Member Since: March 16, 2012 Posts: 123 Comments: 7890
Quoting MAweatherboy1:
The models are coming into better agreement on an eventual NE turn for Leslie... The official forecast will likely need to be tweaked some at 11 as it doesn't show that:



(4,000th comment!!)


Since February, no less. You need to spend more time away from the computer. :) I offered Keeper of the Gate a $50 bet for Portlight that Leslie would pass at least 50 miles east of Bermuda rather than reducing the island to bare rock. I don't think he wants to take that bet now.
Member Since: October 2, 2004 Posts: 0 Comments: 9957
Quoting Grothar:
4th night in a row at the same time, Leslie gets bigger.


Reminds us of Isaac - he did the same thing!
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Quoting WxLogic:
I see we have a 10% now and based on the wording it sure looks like it will get a new name if it does develop and not Isaac.

I was really expecting a 10% by 2AM.


I remember we were talking about this. I thought I jumped the gun. But if you take the averages of what we both thought, it turns out correct.
Member Since: September 10, 2007 Posts: 0 Comments: 10589
Quoting TomballTXPride:

It's not strange, Bud. I wouldn't put too much credence in it beyond 10 days. Even beyond 120 hours is pushing it.


Don't fret, "bud" most of us are aware of accuracy and models changing this far out but as was explained to you earlier there is more to learn from them about weather patterns, etc...
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Large Leslie and midget Michael.

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4th night in a row at the same time, Leslie gets bigger.

Member Since: July 17, 2009 Posts: 64 Comments: 23749
I see we have a 10% now and based on the wording it sure looks like it will get a new name if it does develop and not Isaac.

I was really expecting a 10% by 2AM.
Member Since: August 14, 2008 Posts: 4 Comments: 4881
No changes at the 0z ATCF updates- Leslie stays 65mph and 994mb, Michael stays 50mph and 1006mb.

Edit: Guess I was beaten to it, lol.
Member Since: February 11, 2012 Posts: 79 Comments: 7303
Nothing unexpected.

AL, 12, 2012090500, , BEST, 0, 252N, 628W, 55, 994, TS, 50, NEQ, 60, 0, 0, 0, 1014, 250, 50, 0, 0, L, 0, , 0, 0, LESLIE, D,

AL, 13, 2012090500, , BEST, 0, 274N, 437W, 45, 1006, TS, 34, NEQ, 30, 30, 20, 30,
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Quoting Abacosurf:
I don't think this will be a small system...look at the cloud structure already and the way the models have elongated it to the NE in 3-4 days.

I would expect to see something more like Debbie.

But Time will tell.



Which Debbie/Debby are you talking about? There have been a lot of them. :)
Member Since: October 2, 2004 Posts: 0 Comments: 9957
Quoting RTSplayer:


Wow. What a waste of code and computer processing power.

Until you get 5 day forecast skill to like 0.99 it's useless to really talk about anything at all beyond 15 days, and even that is laughable.

10 days is about the max that is somewhat believable, and once in a while accurate, at present time.


As we saw with Isaac, sometimes even five days isn't enough.
Member Since: March 7, 2007 Posts: 521 Comments: 19144
Quoting washingtonian115:
Anyone know when the next CSU forecast comes out?.

December 5-10.
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Quoting AussieStorm:


for a laugh...



















Wow. What a waste of code and computer processing power.

Until you get 5 day forecast skill to like 0.99 it's useless to really talk about anything at all beyond 15 days, and even that is laughable.

10 days is about the max that is somewhat believable, and once in a while accurate, at present time.
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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.