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

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

Share this Blog
53
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 1124 - 1074

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

Michael is my kind of storm. Beautiful structure, with a well developed eye and out in the middle of nowhere!
Member Since: Posts: Comments:
Major Hurricane Michael the first major of the 2012 Atlantic Hurricane Season:



Member Since: Posts: Comments:
1122. GetReal



700-850mb Steering Layer:



IMO 90L is looking better this morning despite battling some shearing conditions... It appears that 90L will be sticking around the central GOM for at least the next 36 hours...
Member Since: July 4, 2005 Posts: 204 Comments: 8806
If Michael manages to become a Category 5 hurricane by this afternoon, it will be one of the fastest storms to strengthen from a tropical storm to a Category 5 hurricane.

WILMA : 60, 65, 75, 130, 150, 160 (peak)
FELIX : 60, 65, 85, 90, 115, 150 (peak)
Michael : 60, 65, 95, , ,
(wind speeds in kt)
Member Since: Posts: Comments:
1120. WxLogic
For now northerly shear affecting 90L and keeping it in check.
Member Since: August 14, 2008 Posts: 4 Comments: 4961
good job Michael haha :p
Member Since: Posts: Comments:
1118. WxLogic
Thankfully Mike is not hitting Bermuda.
Member Since: August 14, 2008 Posts: 4 Comments: 4961
What a waste of a name... Totally inflating the seasonal totals.

Member Since: February 11, 2012 Posts: 83 Comments: 7733
1116. WxLogic
Good Morning...
Member Since: August 14, 2008 Posts: 4 Comments: 4961
Congratulation to Michael for becoming the first major of the year, actually having something NHC likes since they kept refusing to give it to Gordon or Kirk.
Member Since: Posts: Comments:
13-7-1.


Defiantly wasn't expecting Michael to become a major hurricane.
Member Since: July 8, 2005 Posts: 259 Comments: 23880
records?...60s.first.photos.from.space..
Member Since: Posts: Comments:
Adding to my previous comment:
If this intensification continues, we will be looking at a Category 4 tomorrow. Michael strengthened from a 70 mph tropical storm to 115 mph major hurricane in just twelve hours, a 45 mph (40 kt) increase, so a minimal Category 5 is not out of the question, assuming it remains under favorable conditions.

But in my opinion, RI has to stop soon. If it doesn't, everybody will be saying CAT 5! CAT 5! by the end of the day.
Member Since: Posts: Comments:
1111. flcanes
Quoting Bobbyweather:
The recent rapid intensification is clearly shown here.


And according to NHC estimates,
the storm has strengthened from 45 kt to 100 kt, 1005 mb to 965 mb in 24 hours (55 kt increase in 24 hrs) proving the RI.

Nobody thought Michael would rapidly intensify, including the NHC:
24H 06/0600Z 29.4N 43.1W 50 KT 60 MPH

This shows how much more we have to do to understand the beauty of tropical cyclones.

By the way, rapid intensification means an increase in the maximum sustained winds of a tropical cyclone of at least 30 kt in a 24-h period.

wow
Member Since: Posts: Comments:
The recent rapid intensification is clearly shown here.


And according to NHC estimates,
the storm has strengthened from 45 kt to 100 kt, 1005 mb to 965 mb in 24 hours (55 kt increase in 24 hrs) proving the RI.

Nobody thought Michael would rapidly intensify, including the NHC:
24H 06/0600Z 29.4N 43.1W 50 KT 60 MPH

This shows how much more we have to do to understand the beauty of tropical cyclones.

By the way, rapid intensification means an increase in the maximum sustained winds of a tropical cyclone of at least 30 kt in a 24-h period.
Member Since: Posts: Comments:
A couple of nice-looking candidates, one emerging from Africa and the other moving across the continent:

Africa
Member Since: Posts: Comments:
WITH MICHAEL BECOMING THE SEVENTH HURRICANE OF THE SEASON EARLIER
TODAY...IT MARKS THE THIRD EARLIEST FORMATION OF THE SEVENTH
HURRICANE IN A YEAR...ONLY BEHIND 1886 AND 1893.
Member Since: Posts: Comments:
Quoting weathercat64:

Sunrise


Beautiful. It's funny because a lot us of thought Michael would amount to nothing, and I think the NHC was thinking the same when they started initiating advisories. Just goes to show...
Member Since: Posts: Comments:
Good morning, all. Another 94% humidity day, but the temps have gone from almost 90 degrees at 4:30 to ten degrees cooler. So Michael made it to a major, glad he is heading for land.
Member Since: Posts: Comments:
oh.no.no..evil.monkey
Member Since: Posts: Comments:
After the cold front goes across the CONUS, It is my belief hurricane season is over for the CONUS!
Member Since: Posts: Comments:
7 Hurricanes with no majors..that record didn't last long thanks to Michael.."The Little Engine That Could"
Member Since: Posts: Comments:

Sunrise
Member Since: Posts: Comments:
Good Morning MAJOR MIKE!
13-7-1 so far more to come!


Member Since: Posts: Comments:
Oh my, now I don't know whether to go to sleep finally. Michael is very interesting.
Member Since: Posts: Comments:
MICHAEL BECOMES THE FIRST CATEGORY THREE HURRICANE OF THE YEAR...
------------------------------------------------- -------------------------------

5:00 AM AST Thu Sep 6
Location: 29.6 N 41.7 W
Moving: NE at 7 mph
Min pressure: 965 mb
Max sustained: 115 mph


i got it right i knew it!
good morning major mike!

LESLIE CREEPING NORTHWARD WITH NO CHANGE IN STRENGTH...
------------------------------------------------- -------------------------------

5:00 AM AST Thu Sep 6
Location: 26.3 N 62.4 W
Moving: N at 1 mph
Min pressure: 985 mb
Max sustained: 75 mph

hey NHC might as well say stationary! SMH!
Member Since: Posts: Comments:
MAJOR HURRICANE OF THE SEASON MICHAEL
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Leslie still at 75 mph
Member Since: April 23, 2011 Posts: 104 Comments: 14873
Quoting smuldy:
Michael=major=outflow=trajectory change for Leslie/=Either storm being ripped to shreds by other+90L getting pulled NE in 3 days(probably)=most complicated synpotic setup I've ever seen for the Atlantic basin


I know right??

Got rain for a couple days when Isaac came through....Got rain day before yesterday when his remnant passed us going back south....and now it is back in the gulf??? Michael turning into a monster...I know that the Weather is a spectator sport....but crazy stuff like this is why we LOVE it!!
Member Since: Posts: Comments:
Michael the first major storm of the season?
Member Since: April 23, 2011 Posts: 104 Comments: 14873
1094. smuldy
Michael=major=outflow=trajectory change for Leslie/=Either storm being ripped to shreds by other+90L getting pulled NE in 3 days(probably)=most complicated synpotic setup I've ever seen for the Atlantic basin
Member Since: Posts: Comments:
wouldnt be surprised cat 3 115mph at 5am for mike
Member Since: Posts: Comments:
1092. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 37950
Wow, Michael is a Category 2 hurricane!
I can't believe it!
ADT is already thinking Michael is a major:
CI# /Pressure/ Vmax
5.5 / 959.6mb/102.0kt

Also ATCF is thinking 95 kt
...INITIAL CONDITIONS...
LATCUR = 29.4N LONCUR = 42.0W DIRCUR = 50DEG SPDCUR = 6KT
LATM12 = 28.7N LONM12 = 42.9W DIRM12 = 49DEG SPDM12 = 7KT
LATM24 = 27.8N LONM24 = 43.9W
WNDCUR = 95KT RMAXWD = 10NM WNDM12 = 60KT
CENPRS = 968MB OUTPRS = 1015MB OUTRAD = 150NM SDEPTH = D
RD34NE = 60NM RD34SE = 60NM RD34SW = 30NM RD34NW = 40NM
Member Since: Posts: Comments:
1090. LargoFl
Member Since: August 6, 2011 Posts: 4 Comments: 37950
Quoting bappit:

Get some sleep!


I wish...woke up and can't get back to sleep
Member Since: Posts: Comments:
What a season this is! :D
Member Since: Posts: Comments:
No track change either for 90L..... Coming right over northern central FL.

When is the shear supposed to drop to give this invest time to develop? What do you think are the chances and how strong?
Member Since: Posts: Comments:
1086. bappit
Quoting SpicyAngel1072:
It appears 90L strengthened since I look hours ago. Going to check the maps out now to see if track changed at all.

On a side note....I can't believe I'm up at this time ;-(

Get some sleep!
Member Since: Posts: Comments:
Intensity models are not showing more than 50mph winds for 90L
Member Since: Posts: Comments:
It appears 90L strengthened since I look hours ago. Going to check the maps out now to see if track changed at all.

On a side note....I can't believe I'm up at this time ;-(
Member Since: Posts: Comments:



Leslie
Member Since: Posts: Comments:
WOW!
Member Since: Posts: Comments:
Member Since: Posts: Comments:
well michael could be the first major this season. I think it can do it at 4am IMO
Member Since: Posts: Comments:
Member Since: Posts: Comments:
1078. sar2401
This has to be some kind of record. Middle of hurricane season, Michael just had a major upgrade, Leslie still out there, and 90L doing whatever it's going to do...and we had 12 posts in the last hour, including mine. Must be an early night for everyone. See you all in the morning, when I expect everything in the Gulf and Atlantic to be up to at least cat 4. :)
Member Since: October 2, 2004 Posts: 0 Comments: 14337
good morning everybody! just did a double today and gotta be back at 10am.I see we have two HURRICANES! invest 90L. It surely seems like september is the month to remember!

Member Since: Posts: Comments:
1076. sar2401
Quoting OracleDeAtlantis:
I see Isaac is back in the saddle again ...



Post 106. OracleDeAtlantis 7:23 PM GMT on April 05, 2012

No offense to the science of meteorology, but a butterfly in China can be observed to fly circles around Dr. Gray and his team; and I hear the butterflies in China are choking on U.S.

For upon her wings are the eyes of the earth, seeing the unfolding of every birth.

From above the trees and beyond sky, to the state of confusion what it denies.

Never before found such a plight that befell them that are without sight.

Now see before you the industry of sin, and return by fury the fallacy of men.



Well, that's 5:28 minutes of my life I'm never getting back. Oracle, you are officially nominated for Most Bizarre Post of the Year. :)
Member Since: October 2, 2004 Posts: 0 Comments: 14337
1075. VR46L
Quoting 954FtLCane:


awww..pretty green. It wants to be an Irish storm.


No thanks !!! LOL
Member Since: March 1, 2012 Posts: 0 Comments: 6877
1074. sar2401
Quoting popartpete:
Is 90L anyhow somehow from the remnants of Karen? LOL...couldn't resist. This is the oldest humor on the blog, but it gets old gracefully.

These are my real questions:

Now, the thought is that 90L will be Nadine if named, not Issac, correct?

Who thinks Leslie could go west? The models are spread. I go by the NHC line, but it could go west just as much as it could east. I heard that if a closed low formed off of Florida, Leslie would be pushed more northwest. Has that happened? It seemed like it has, with 90L. How I looked at climatology and half of the hurricanes went west and scraped the East Coast as strong systems.

Please let me know.


A hurricane went west and scraped the East Coast? Your understanding of geography is a little deficient. 90L does not have a single model that shows it going west of LA before turning back east towards FL. 90L is drifting SW now because the steering currents are weak. A strong trough should be out in the Gulf by Saturday, thus the abrupt turn to the east, as the trough pushes it in that directon. The chances that 90L could continue on westerly path are as close to zero as you can get.

Edit: Never mind, I was totally confused with your mention of 90L and didn't read carefully enough. I think the chances of Leslie bumping along the east coast are also very low but not zero.
Member Since: October 2, 2004 Posts: 0 Comments: 14337

Viewing: 1124 - 1074

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Scattered Clouds
63 °F
Scattered Clouds