Leslie near hurricane strength; Son of Isaac (90L) emerges in the Gulf

By: Dr. Jeff Masters , 3:05 PM GMT on September 05, 2012

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Tropical Storm Leslie is growing more organized and is approaching hurricane strength on its slow voyage northwards at 2 mph towards the island of Bermuda. Moderately high wind shear of 15 - 20 knots due to strong upper-level winds out of the northwest continues to keep most of Leslie's heavy thunderstorms pushed to the east side of the storm, but satellite loops show that Leslie now has an impressive blow-up of heavy thunderstorms with cold cloud tops near its center. Leslie's slow forward speed means that the storm is staying over the cold water stirred up by the storm's winds, inhibiting intensification, but the waters underneath Leslie are warm to great depth, making this less of a factor than usual. According to the latest SHIPS model forecast, the shear is expected to fall steadily today, reaching the low category, 5 - 10 knots, by Thursday afternoon. Leslie is over warm ocean waters of 29 - 30°C, and the reduction in shear and warm waters should aid intensification, and potentially allow Leslie to be at Category 2 strength at its closest pass by Bermuda Saturday night and early Sunday morning, as indicated by the official NHC forecast. The latest 11 am EDT NHC wind probability forecast calls for a 48% chance that Leslie will be a Category 2 or stronger hurricane Sunday morning at 8 am EDT. 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 42-hour period of tropical storm-force winds beginning Saturday morning near 2 am AST, and lasting until 8 pm AST Sunday night. The official NHC forecast shows Leslie nearly making a direct hit on Bermuda, and Leslie will be 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. NHC is predicting that hurricane-force winds will extend outwards from the center of Leslie by 35 miles on Thursday night, and I expect this will increase to at least 60 miles by early Sunday morning, when Leslie will be making its closest pass by Bermuda.


Figure 1. Morning satellite image of Tropical Storm Leslie. Heavy thunderstorms have built near the center of the storm, and Leslie is near hurricane strength.

Leslie's impact on Canada
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. The timing of this trough is such that Leslie will be pulled northwards and then north-northeastwards over the weekend. There are still significant differences among the models in the timing and speed of Leslie's track over the weekend, but we can now dismiss the threat of Leslie making a direct hit on New England. The storm is likely to make landfall in Nova Scotia or Newfoundland, though there are significant differences in the models' predictions of the timing of Leslie's arrival in Canada. The GFS model predicts an early Tuesday landfall in Newfoundland, but the ECMWF model is much faster and farther west, predicting a Monday afternoon landfall in Nova Scotia. Large swells from Leslie are pounding the entire Eastern Seaboard, and these waves will increase in size as Leslie grows in strength this week. The Hurricane Hunters are scheduled to make their first flight into Leslie on Thursday afternoon.


Figure 2. Morning radar image of Invest 90L off the coast of the Florida Panhandle.

Son of Isaac: Invest 90L emerges in the Gulf of Mexico
During Tropical Depression Isaac's trek across the center of the U.S. during the Labor Day weekend, the storm was ripped in half. One portion of the storm moved over the Northeast U.S., bringing heavy rains there, and another portion sank southwards over Alabama. You can see this split by studying an animation of the vorticity at 850 mb (the amount of spin at low levels of the atmosphere, near 5,000 feet above sea level) from the University of Wisconsin. This remnant of Isaac, which still maintained some of Isaac's spin, brought heavy rains of 5 - 10 inches that caused flooding problems over portions of Alabama on Tuesday. The storm has now emerged over the Gulf of Mexico near the Florida Panhandle, and was designated Invest 90L this morning by NHC. In their 8 am Tropical Weather Outlook, NHC gave 90L a 20% chance of developing into a tropical depression by Friday morning. According to NHC naming rules, "if the remnant of a tropical cyclone redevelops into a tropical cyclone, it is assigned its original number or name". Since "the remnant" refers to the primary remnant, and 90L does not fit the definition of a "primary remnant", the storm will be given a new name should it develop into a tropical storm, according to information posted on the NHC Facebook page. Esau or Jacob--the names of the sons of the biblical Isaac--would be fitting names for 90L, but the next storm on the list of Atlantic storms is Nadine.

Long-range radar out of Mobile, Alabama shows a large area of heavy rainfall along the coast due to 90L. The echoes do show some spiral banding behavior, but there is only a slight evidence of rotation to the storm. Infrared satellite loops show that the thunderstorms associated with 90L are not that vigorous and do not have particularly cold cloud tops, and the area covered by the thunderstorms is relatively small. Wind shear is a high 20 - 30 knots over the northern Gulf of Mexico, but is predicted to fall to the moderate range, 10 - 20 knots, by Thursday afternoon. Ocean temperatures in the Gulf have been cooled down considerably by the passage of Hurricane Isaac last week, and are 28 - 28.5°C. This is still plenty warm enough to support formation of a tropical storm, and I expect 90L will increase in organization on Thursday and Friday as it moves slowly south or south-southwest. 90L could become a tropical depression as early as Thursday, though Friday is more likely. A hurricane hunter aircraft is scheduled to investigate 90L on Thursday afternoon. A trough of low pressure and an associated surface cold front will move southeastwards over the northern Gulf of Mexico on Sunday, and this trough should be capable of pulling 90L to the northeast to a landfall along the Florida Panhandle or west coast of Florida on Sunday.


Figure 3. Morning satellite image of Tropical Storm Michael.

Tropical Storm Michael in the Central Atlantic
Tropical Storm Michael has strengthened to 50 mph winds, and appears to have a favorable enough environment to become a hurricane later this week. Satellite loops show that this is a small tropical cyclone, far out over the open Atlantic, and none of the models show that Michael will threaten any land areas.

Elsewhere in the Atlantic
The GFS and ECMWF models are predicting that a new tropical wave due to move off the coast of Africa on Friday will develop into a tropical depression by the middle of next week. It's too early to tell if this system might threaten the Lesser Antilles Islands.

Jeff Masters

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Quoting KingofNewOrleans:


Any pictures of all the nutria washing up over there?


Not by me, but the news crews over here have quite a few.
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Hello everyone, just got back from school and other stuff. I see Leslie has became a hurricane and that Michael is very close to being one.

Member Since: March 16, 2012 Posts: 127 Comments: 7972
Quoting sar2401:

Thse are nice pictures, but my old eyes are way too bad to make out anything. Can you dumb it down for me?
You will see it better here, scroll mouse over the day you want to see and right click and open image in new tab where you will be able to zoom in.

Link
Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting CloudGatherer:


Really?

The data from the closest NDBC observation point seem to correspond rather nicely with the NHC satellite estimates - it's hovering just above 1010MB. But the wind speed is now up to 4.1 knots. Batten down the hatches, boys!


Station 42040
NDBC
Location: 29.212N 88.207W
Date: Wed, 05 Sep 2012 15:50:00 UTC
Winds: W (270°) at 19.4 kt gusting to 23.3 kt
Atmospheric Pressure: 29.92 in and rising
Air Temperature: 74.3 F
Water Temperature: 82.4 F


Station KVKY
Federal Aviation Administration
Location: 29.248N 88.441W
Date: Wed, 05 Sep 2012 19:35:00 UTC
Winds: W (280°) at 25.1 kt
Air Temperature: 73.4 F
Dew Point: 71.6 F
Visibility: 8.7 nmi



Station KMIS
Federal Aviation Administration
Location: 29.296N 88.842W
Date: Wed, 05 Sep 2012 19:35:00 UTC
Winds: NW (320°) at 25.1 kt
Air Temperature: 77.0 F
Dew Point: 73.4 F
Visibility: 2.6 nmi


Station PACF1
NOS
Location: 30.152N 85.667W
Date: Wed, 05 Sep 2012 19:30:00 UTC
Winds: S (190°) at 8.9 kt gusting to 12.0 kt
Atmospheric Pressure: 29.90 in
Air Temperature: 76.5 F
Water Temperature: 82.6 F
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Quoting Grothar:


It is a little funny though. By the way, I saw it first.


You always see things first. For a guy from the Stone Age, you're pretty fast. :)
Member Since: October 2, 2004 Posts: 0 Comments: 17349
Quoting LargoFl:
..GRO..you ever seen a storm like this?


Yes, it has happened before. Odd, but it does happen. Probably no one noticed before.
Member Since: July 17, 2009 Posts: 71 Comments: 27208
Quoting yonzabam:
Quite incredible how much the record low Arctic ocean ice cover of 2007 is going to be beaten by this year. And there's still about two weeks of melting to go. Can't be long before it disappears completely in summer.

Odd that the northwest passage is still not open though, as it's been navigable for the past few years at the height of the melt. There's just a few miles of ice keeping it closed, so it could yet open up.

Click on the graph/map to enlarge:



Link


And I believe one of the models now has another major polar cyclone hitting hard up there later this week, though I can't recall now where I found the model.

The melt has been amazing this year. It's like standing witness to the death of a very old monarch.

And it is going to have serious effects much farther south, probably already is. The year of no summer ice is probably going to be a very strange one, and it's probably coming very soon. I can only hope that the strangeness kicks people enough to start _taking it seriously_.
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Quoting dabirds:
Ah, the birthday show @ the Fox, wish I could have been there, but have heard it was better to just see the film, so... Couldn't quite duck walk as well at 85 as he did at 70, but could still do it!

Looks like the last of the rain is moving out, but don't think StL will make 101, even if sun comes out - only 75 now. Your shields appear to have held up ILwthr, unfortunately. We were 6 from Issac btw.


St. Louis will be lucky to reach 90 today. They goofed a bit on the forecast for today, but thats what happens when overnight storms decide to do things of their own nature. Weekend should bring another good shot of half inch to inch rains area wide so here's to hoping.

Saturday & Sunday Total QPF Forecast...
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Quoting GTcooliebai:
12z GFS Ensembles (long range)


Thse are nice pictures, but my old eyes are way too bad to make out anything. Can you dumb it down for me?
Member Since: October 2, 2004 Posts: 0 Comments: 17349
Quoting sar2401:


I swear, if that thing gets to the Atlantic, recurves and hits Miami, then gets back out into the Gulf again, I'm going to go out and shoot some tires or something. This thing just doesn't want to die.


It is a little funny though. By the way, I saw it first.
Member Since: July 17, 2009 Posts: 71 Comments: 27208
kind of weird not o have any aftershocks in the USGS map from that 7.6 although I know many already have occurred
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Quoting Grothar:


I swear, if that thing gets to the Atlantic, recurves and hits Miami, then gets back out into the Gulf again, I'm going to go out and shoot some tires or something. This thing just doesn't want to die.
Member Since: October 2, 2004 Posts: 0 Comments: 17349
12z GFS Ensembles (long range)

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting CybrTeddy:


No, it's probably just a gap between the eyewall and the rest of the convection. That's what satellite shows me at least.

I agree, there's some drier air in there. Rapid strengthening is unlikely until it fixes that.

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Quoting RitaEvac:
It's begun...Local met in Houston is spreading the word.

It's time to change how we use the Saffir-Simpson Scale



Well, why not use BOTH ratings, and hyphenate it?

Isaac: 1-3

Katrina: 4-5

Andrew: 5-4

Charley: 4-2

Wow. So simple, and still accurate.
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Quoting TropicalAnalystwx13:

Leslie is going through an Eyewall Replacement Cycle already?


No, it's probably just a gap between the eyewall and the rest of the convection. That's what satellite shows me at least.
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Quoting sar2401:


I've been there - beautiful area but not without risks. The latest is two people have died, although it seems that only one was from the direct results of the quake. I'm glad to hear your family is OK.
Link


it's a big city...I only know from the section they live in.. Other damages are unknown to them around the other sides of the city
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Quoting trHUrrIXC5MMX:
Many nearby houses collapsed, my sister's the neighbor's and some others are cracked but standing...

look at this map... this map shows (south) western Costa Rica


click here for bigger pic


I've been there - beautiful area but not without risks. The latest is two people have died, although it seems that only one was from the direct results of the quake. I'm glad to hear your family is OK.
Link
Member Since: October 2, 2004 Posts: 0 Comments: 17349
Quoting GTcooliebai:
12z GFDL inner nest:



12Z HWRF inner nest:



12z ECMWF 96 hrs. 850. mb wind speeds and MSLP:



12z GFS 102 hrs. 900 mb. wind speeds and MSLP:



12z CMC 96 hrs. 10 meter wind speeds and MSLP:



12z NOGAPS 6-hourly Precip. MSLP & 850 hPa Temp.

..guess i'd better get up and clean out the gutters again, at the very least..alot of rain is coming later this weekend
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12z Euro tracks the CV development in a recurve way into Central Atlantic like GFS. I wonder if we are not going to get anymore threats in the Eastern Caribbean as the CV season winds down.


Member Since: April 29, 2009 Posts: 75 Comments: 14892
Ah, the birthday show @ the Fox, wish I could have been there, but have heard it was better to just see the film, so... Couldn't quite duck walk as well at 85 as he did at 70, but could still do it!

Looks like the last of the rain is moving out, but don't think StL will make 101, even if sun comes out - only 75 now. Your shields appear to have held up ILwthr, unfortunately. We were 6+ from Issac btw.
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Quoting 1900hurricane:



Leslie is going through an Eyewall Replacement Cycle already?
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Quoting Grothar:
..GRO..you ever seen a storm like this?
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NAM Composite Radar Reflectivity:

Member Since: August 31, 2009 Posts: 0 Comments: 5628
Quoting RitaEvac:
Gonna have to dumb it down such as "Cat 1 winds with cat 4 surge". That'll get coastal people out and make inland folks stay.

Flawed:
...see..cat-1...Min damage?...ask isaac survivors if it was Min damage there......ask miss and alabama residnets if the aftermath of isaac was really not that bad..flooding everywhere
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Many nearby houses collapsed, my sister's the neighbor's and some others are cracked but standing...

look at this map... this map shows (south) western Costa Rica


click here for bigger pic
Member Since: Posts: Comments:
Member Since: July 17, 2009 Posts: 71 Comments: 27208
12z GFDL inner nest:



12Z HWRF inner nest:



12z ECMWF 96 hrs. 850. mb wind speeds and MSLP:



12z GFS 102 hrs. 900 mb. wind speeds and MSLP:



12z CMC 96 hrs. 10 meter wind speeds and MSLP:



12z NOGAPS 6-hourly Precip. MSLP & 850 hPa Temp.

Member Since: August 31, 2009 Posts: 0 Comments: 5628


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Quoting RitaEvac:
Gonna have to dumb it down such as "Cat 1 winds with cat 4 surge". That'll get coastal people out and make inland folks stay.
yes that sure would, something needs to be changed..maybe actual damage it can cause..something..cant put my finger on what it should say so people really take notice....i remember one old guy in the NOLA area just before isaac hit..oh i was thru katrina and came out ok...then isaac hit..and his tone changed..maybe even scared because he stayed....every storm is different, even a tropical storm..can..take your house..and we forget..how many tornados are thrown off these storms..that too..only takes one to change your life or even take it.
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Quoting Hurricanes305:


B. 50%
but a TS once recon flies in tomorrow afternoon.


Really?

The data from the closest NDBC observation point seem to correspond rather nicely with the NHC satellite estimates - it's hovering just above 1010MB. But the wind speed is now up to 4.1 knots. Batten down the hatches, boys!
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Am I to assume that the further East Leslie is when she passes Bermuda the greater the chance of getting hit in Nova Scotia? Or is it much more dependant on the TROFF and steering currents after it passes the islands?
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Can anyone think of any notable storms with comparable tracks to the projected path of 90L?
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Quoting CaribBoy:


Thanks for your kindness, I also like the rain but I definitely don't want a dangerous storm here and elsewhere :-) Regarding Leslie's track, hopefully it won't be much than a category 1 near Bermuda. Every years they seem to be threatened.


I also like rain and bad weather. I don't understand why this season is so boring, no major hurricanes in the caribbean area like in 90's, only little funny storms with nothing special, or fish storms... we have hot temperatures...hot SST...and nothing comes...
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Quoting zicoille:
Bermuda residents, lucky men, have fun for us...


Say what? They have a potential cat 2 headed straight at them, and they're supposed to be lucky and have fun? You lost me there.
Member Since: October 2, 2004 Posts: 0 Comments: 17349
Gonna have to dumb it down such as "Cat 1 winds with cat 4 surge". That'll get coastal people out and make inland folks stay.

Flawed:
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The only thing for certain about the gulf blob is it won't go to Texas.
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Quoting icmoore:


Sorry I may not have worded that right what I meant was I am happy for you all that they were alive not happy about all the terrible damage, etc..


Yes I knew what you were trying to say..no worries
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Quoting SFLWeatherman:
What will 90L be at 8PM
A. 40%
B. 50%
C. 60%
D. 70%


B. 50%
but a TS once recon flies in tomorrow afternoon.
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Quoting trHUrrIXC5MMX:


Thanks...


Sorry I may not have worded that right what I meant was I am happy for you all that they were alive not happy about all the terrible damage, etc..
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Quoting LargoFl:
gee im so glad..someone is thinking along the same lines..some changes really do need to be made..thanks for posting that rita


He is appealing to NOAA Administrator Dr. Jane Lubchenco as well as Dr. Richard Knabb, Director of the National Hurricane Center to take another look at how the Saffir-Simpson Scale is used. We tell people to evacuate because of the storm surge, but we're sending them a mixed message if the category strength only ranks the force of the wind.
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Quoting RitaEvac:
It's begun...Local met in Houston is spreading the word.

It's time to change how we use the Saffir-Simpson Scale
gee im so glad..someone is thinking along the same lines..some changes really do need to be made..thanks for posting that rita
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Quoting SFLWeatherman:
S FL!!! GFS!
..this storm is going to drive us nuts lol..i just hope..in the long term..its a fast mover, i would be amazed if it again..reenters the gulf after visiting miami etc...would make the record books?
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It's begun...Local met in Houston is spreading the word.

It's time to change how we use the Saffir-Simpson Scale
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What will 90L be at 8PM
A. 40%
B. 50%
C. 60%
D. 70%
Member Since: Posts: Comments:
325. VR46L
Quoting LargoFl:
thanks for answering, my guess is,many have differing views on what exactly IS..a tropical storm..the word and meaning of tropical needs to changed maybe...only means its in the tropics, thus has alot of moisture etc..but somehow..the NHC saying..its a low end tropical storm..or whatever..somehow does NOT reach the peoples minds...somehow, someway..they need to come up with a different naming system..something that conveys the REAL threat a storm has...im at a loss to really explain what i mean but..anyways..thanks for replying



Quoting LurkyMcLurkerson:


Eh, people will think whatever they think. My preference would be that they look at the potential problems from any given system that looks like it could be sorta nasty, not just base their predictions on whether it's a "tropical storm" or a "tropical depression" or a "hurricane."

Hype -- under or over -- IMO comes from having poor information in general. You're never going to capture all of the information people need to assess risks in a single label.


I will agree that there is some tropical weather being lined up on that chart, rain and lightning event possible ... I just would really be concerned that people , in general, would take a NHC designated storm more lightly by calling something that is nowhere near their criteria a storm , but the NWS will issue warnings appropriate for those events . JMO
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Quoting icmoore:


Glad you got through to some family sounds like they're okay now keep us up to date when you hear more. Very happy for you all.


Thanks...
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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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