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 Sting13:
Not liking this latest GFS run..... landfall/very close pass to where I live in eastern Nova scotia


The only positive point I can see is that Leslie would have already transitioned to extratropical by that point, considering it would be entrained in the front, and looks baroclinic.
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Quoting sar2401:


Nah, the further he moves south, the better, at least in the short term. The high STT's in the Gulf are misleading. Once you get away from the contiental shelf, which ends about 75 miles off Mobile, the water depth rapidly drops to over 1500 meters. Water temperatures in this deep area are less than 60 degrees at 40 meters feet and go down to about 40 degrees in the deepest sections. It's not hard for a storm of any size to churn up enough water to cause upwelling.


Don't forget all of the cold rain water coming out of all the rivers cooling the near coastal waters too.
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122. JLPR2
Those two lows in the Central North Atl forming from a through look tropicalish.



+ 2 storms in the CATL/EATL
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121. HCW
Live streaming video of Portlight feeding people in Pearlington, MS

Link
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Quoting CloudGatherer:
I presume this means he's typing on a mobile device. On some older models, the period is on the main screen, while inserting a space requires clicking through several options, so people text with periods between the words.

Or maybe it's something else. Either way, no reason to be cruel.


See, the post you quoted he used the space bar, he/she's lying.
" samarra.c.rica..georgia.sorry..getting.a.kybd.for .t he.birthday "
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Quoting dogsgomoo:
http://bodyodd.nbcnews.com/_news/2012/08/29/13554 200-can-hurricanes-make-pregnant-women-go-into-lab or or dogs. :P
its the low pressure and they have said that for many many years..old news really
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Quoting stormchaser19:
168 Hr


Is that where it crosses or when it turns back into Florida?
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Quoting AussieStorm:
Hurricanes That Pass Over Fresh Water Can Be Stronger


There was a related article in our local paper the other day about this. It would explain why Hugo ramped up to Cat 4 just before landfall in '89.
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Quoting WXGulfBreeze:
I just got the cover back on my pool gazebo after taking it down for Isaac. Spent two days last week in the wind and rain on the western edge of Isaac. And now I wake up this morning, after more drenching rain yesterday, to find that Son of Isaac may be organizing and coming by for a return visit.

Can't seem to catch a break on the rainy weather this summer, but I guess it's better than the severe drought of the past two years.
yep your right there
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Quoting WarEagle8:

Churning bath water in upper 80 degree heat means more bath water. Seems it would take HIGH COLD cloud tops with LOTS of rain to semi-cool the bath temp water.


Nah, the further he moves south, the better, at least in the short term. The high STT's in the Gulf are misleading. Once you get away from the contiental shelf, which ends about 75 miles off Mobile, the water depth rapidly drops to over 1500 meters. Water temperatures in this deep area are less than 60 degrees at 40 meters feet and go down to about 40 degrees in the deepest sections. It's not hard for a storm of any size to churn up enough water to cause upwelling.
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Mapping Hurricane Vulnerability
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Quoting islander101010:
samarra.c.rica..georgia.sorry..getting.a.kybd.for .t he.birthday
I presume this means he's typing on a mobile device. On some older models, the period is on the main screen, while inserting a space requires clicking through several options, so people text with periods between the words.

Or maybe it's something else. Either way, no reason to be cruel.
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168 Hr
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Quoting Charmeck:


If you go to this link Link it's the US Geological Survey pages and they have all of the info on Earthquakes. You'd be surprise how many there are every day around the world. It's only the "big" ones that make the news or when they happen in unusual places. In some places, people are so use to the little ones that they don't pay no attention to them.


Yea, I realize there is all kinds of activity globally but what I'm curious about is the map you showed has many in a general area. Is that abnormal, are these just tremors or new quakes all together, and were they triggored by the intial CR quake? It just doesn't seem like you hear about that much activity in that area.
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Not liking this latest GFS run..... landfall/very close pass to where I live in eastern Nova scotia

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Quoting bappit:

The water temp drops off with depth. Strong winds mix the water.
Correct. Just parts off of the west coast of FL are not very deep for 100 miles from shore.
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I just got the cover back on my pool gazebo after taking it down for Isaac. Spent two days last week in the wind and rain on the western edge of Isaac. And now I wake up this morning, after more drenching rain yesterday, to find that Son of Isaac may be organizing and coming by for a return visit.

Can't seem to catch a break on the rainy weather this summer, but I guess it's better than the severe drought of the past two years.
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Quoting TropicalAnalystwx13:

You rant and complain too much.


i know.
Its what happens when i am under extreme torture/prison/school

anyway ill stop :P

Member Since: February 11, 2012 Posts: 0 Comments: 9760
Quoting sar2401:

Broken spacebar? Since 2010? I don't think that's the issue.


But so what? I mean if it bothers you for some reason maybe you could just ignore instead of sounding rude, maybe?
Member Since: July 18, 2005 Posts: 9 Comments: 4147
see, I think we all are falling for the old trap once again..concentrating on the WIND speeds..is it a tropical storm..is it a cat-1............with THIS storm..its the flooding,damaging rainfall totals that brings the destruction huh...i do hope the NHC is studying this and adding flood threat and all that when considering how destructive a tropical system can be..i know they are..talking about it..we'll see next year.
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156 Hr
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Quoting GeorgiaStormz:


o_0?

Keep thinking.

Anyway, you were not very nice.
Its obviously something of the sort.
And yes, its possible to have a broken spacebar for a long time, just ask my mom about her last laptop :)

Besides, its the internet, why should people get all worked up about things they cant control, and that dont really affect them, on the internet of all things?
Its absurd IMO, if you dont like it, skip over and move on, no reason to respond cruelly or call it his "meme" or whatever.

ok, sorry guys, rant over


Hey, I'll gladly send Islander a new keyboard if that's the problem. :) Anyway, point taken, back to weather...
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Quoting GetReal:



Partly cloudy skies here, the rain and dark skies are to the SE of NOLA over the coastal areas...

hope it stays that way
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Going to guess this is a bit stronger than 50mph.


Member Since: July 8, 2005 Posts: 259 Comments: 24580
Quoting WarEagle8:

Churning bath water in upper 80 degree heat means more bath water. Seems it would take HIGH COLD cloud tops with LOTS of rain to semi-cool the bath temp water.

The water temp drops off with depth. Strong winds mix the water.
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Quoting MrMixon:
Reports of shaking coming in from all across Costa Rica and even as far north as San Salvador:



Reports so far indicate only minimal damage and no casualties.

A photo proportedly showing minor damage to a hospital:



How appropriate.

A hospital has the hazardous, multi-storied brick facade.

As I've said before, this type of construction should be banned. It's a multiplier for injury and financial damage, especially on buildings along streets with adjacent parking, but this was apparently internal and could have hit doctors, patients, nurses, or visitors.

Great piece of modern engineering there; "form over function" BS that could get people killed unnecessarily.
Member Since: January 25, 2012 Posts: 33 Comments: 1520
Quoting GeorgiaStormz:


Be nice.
If your spacebar was broken im sure you would enjoy.me.talking.like.this.to.you.too.


Agreed, that was really unnecessary, next up Taz will get ripped for his orthography.

As the saying goes... if you don't have anything nice to say, don't say anything at all. :)
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Quoting GeorgiaStormz:


o_0?

Keep thinking.

Anyway, you were not very nice.
Its obviously something of the sort.
And yes, its possible to have a broken spacebar for a long time, just ask my mom about her last laptop :)

Besides, its the internet, why should people get all worked up about things they cant control, and that dont really affect them, on the internet of all things?
Its absurd IMO, if you dont like it, skip over and move on, no reason to respond cruelly or call it his "meme" or whatever.

ok, sorry guys, rant over

You rant and complain too much.
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Quoting Stoopid1:
Looks like Son of Isaac has more time over water than I thought. Conditions look generally favorable, and the system is pretty vigorous as is. Going with Doc on this one, depression by Friday.


Could be, although, having been through the son of Issac blob for the past three days, what struck me was the convection, torrential rain, but almost complete lack of wind, even in gusts. The low was never deep but seemed to have the ability to create lots of convection even from a relatively stable and rain cooled atmosphere. I don't know what this means now that it's over the Gulf but, wherever it goes, get prepared for a drenching.
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Quoting Msdrown:



You seem to be up on this. Is this a normal day for a global jolt or something different?



If you go to this link Link it's the US Geological Survey pages and they have all of the info on Earthquakes. You'd be surprise how many there are every day around the world. It's only the "big" ones that make the news or when they happen in unusual places. In some places, people are so use to the little ones that they don't pay no attention to them.
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Quoting sar2401:

Broken spacebar? Since 2010? I don't think that's the issue.


o_0?

Keep thinking.

Anyway, you were not very nice.
Its obviously something of the sort.
And yes, its possible to have a broken spacebar for a long time, just ask my mom about her last laptop :)

Besides, its the internet, why should people get all worked up about things they cant control, and that dont really affect them, on the internet of all things?
Its absurd IMO, if you dont like it, skip over and move on, no reason to respond cruelly or call it his "meme" or whatever.

ok, sorry guys, rant over
Member Since: February 11, 2012 Posts: 0 Comments: 9760
Quoting JasonRE:
So this thing will move Southwest and then turn to move Northeast and hit FL? Wow.....will LA see anything from this system?

They already are...rainfall.
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Quoting RussianWinter:


Sitting in the gulf is always good, that way the gulf will loose heat due to churned waters and the next storm will have a worse time getting organized.

Churning bath water in upper 80 degree heat means more bath water. Seems it would take HIGH COLD cloud tops with LOTS of rain to semi-cool the bath temp water.
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Quoting Neapolitan:
P24L/P25L
Looks pretty far south too..Eastern Africa has more coming across..
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So this thing will move Southwest and then turn to move Northeast and hit FL? Wow.....will LA see anything from this system?
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Quoting SherwoodSpirit:


The pictures they've been showing on St. Louis TV of the shelf cloud from that first line of storms are impressive. Got a good amount of rain and lightning off the weird back half coming from the southwest here in St. Peters.
Looks like it wants to rotate over me and follow the first one. Really deepening SE of Quincy on the northern edge - maybe that'll make it to you ILwthr.

Hard to believe that 100+ for StL, but I guess if the sun comes out behind it?
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Quoting Charmeck:

Yes, there are a lot of other places - BVI (3), Philippines, Indonesia, California (4), Taiwan, Hawaii, Solomon Islands, Mexico (2) Vanuatu and Costa Rica - have all had shakes today larger than 2.5 w target=_blank>Link



You seem to be up on this. Is this a normal day for a global jolt or something different?

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Quoting LargoFl:
This is NOT good..sitting in the gulf for 4 days? GFS 96hrs


Sitting in the gulf is always good, that way the gulf will loose heat due to churned waters and the next storm will have a worse time getting organized.
Member Since: August 21, 2011 Posts: 0 Comments: 666
A LOW PRESSURE SYSTEM LOCATED ALONG THE COAST OF THE WESTERN FLORIDA
PANHANDLE WILL MOVE SOUTHWARD INTO THE NORTH-CENTRAL GULF OF MEXICO
LATER TODAY. ENVIRONMENTAL CONDITIONS ARE MARGINALLY CONDUCIVE FOR
SOME GRADUAL DEVELOPMENT OF THIS DISTURBANCE AS IT MOVES SOUTHWARD
TO SOUTH-SOUTHWESTWARD AT 5 TO 10 MPH OVER THE NEXT FEW DAYS. THIS
SYSTEM HAS A LOW CHANCE...20 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 48 HOURS.
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Quoting GeorgiaStormz:


Be nice.
If your spacebar was broken im sure you would enjoy.me.talking.like.this.to.you.too.

Broken spacebar? Since 2010? I don't think that's the issue.
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Does anyone else here read this Blog?
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Looks like Son of Isaac has more time over water than I thought. Conditions look generally favorable, and the system is pretty vigorous as is. Going with Doc on this one, depression by Friday.
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Quoting HoraceDebussyJones:
Does anyone have links to any Bermuda webcams?
Link
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Quoting weatherman12345:
It is sitting right ontop of Isaac's upwelling though. So it shouldnt be terribly strong.
surface temps are mid 80's and shear is kinda low
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Does anyone have links to any Bermuda webcams?
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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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