Disturbance 98L probably no threat to land

By: Dr. Jeff Masters , 1:46 PM GMT on September 18, 2009

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A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has a well-defined surface circulation, and has developed a modest amount of heavy thunderstorm activity overnight. This morning's QuikSCAT pass (Figure 1) shows a complete, circular wind pattern around the low pressure center of 98L, but top winds were only 25 mph. Wind shear is moderate, about 15 knots, and Sea Surface Temperatures are 28°C, which is about 2°C above the 26°C threshold needed to support a tropical cyclone. There is a large amount of dry air to the north and west of 98L, and this dry air is interfering with development.

The global computer models predict differing amounts of wind shear in the path of 98L as it moves west-northwest at 10 mph over the next three days. The ECMWF, GFS, and UKMET models do not develop 98L, while the NOGAPS, GFDL, and HWRF do. The models that do develop 98L predict that a strong trough of low pressure will turn 98L to the northwest and then north beginning on Monday, with the result that 98L misses the Lesser Antilles Islands by at least 500 miles. Given the moderate or higher wind shear in 98L's path, and dry air to the northwest, the system should develop only slowly. NHC is giving 98L a medium (30 - 50%) chance of developing into a tropical depression by Sunday. At this time, it does not appear that 98L will ever threaten any land areas.

The remains of Hurricane Fred are still spinning away, near 25N 66W, about 900 miles east of Florida. Wind shear is 20 knots, which is marginal for development, and there is very dry air surrounding ex-Fred on all sides. None of the computer models develop ex-Fred, and it will have a tough time regenerating with so much dry air and wind shear. The remains of Fred should move over Florida Monday night or Tuesday morning.


Figure 1. Morning QuickSCAT image of the Atlantic, showing the well-defined surface circulation of disturbance 98L. Image credit: NOAA/NESDIS.

One year anniversary of Hurricane Ike
I've been focusing this week on the 20th anniversary of Hurricane Hugo, but we also passed the one year anniversary of Hurricane Ike. Many areas along the Texas and Louisiana coast affected by Ike have fully recovered, but recovery efforts will still take many more years in other areas. In Galveston, which suffered $3.2 billion in damage, 75% of the businesses have reopened, and 95% of the population has returned. Boston.com has posted a very nice series of clickable images that show before and after scenes of some of the areas that have recovered from Hurricane Ike.

Ike washed away huge sections of beach and dunes that helped protect the Texas coast from more serious damage, and this week the state legislature approved $135 million in funds to help replace these critical natural protection systems. The restored beaches will probably last ten years, barring another strike by a hurricane of Ike's stature. Texas considers two-thirds of its 367-mile shoreline to be critically eroding, which it defines as a historical rate of more than 2 feet a year. Much of this erosion can be blamed on sea level rise. Global sea level rose seven inches over the past century, and is expected to rise at least that much over the coming century.


Figure 2. Villagers in Haiti plant one of their "Million Tree Campaign" trees. Image credit: Lambi Fund of Haiti.

Hurricane relief donations
There hasn't been a need for new hurricane-related disaster relief efforts this year, in stark contrast to 2008. However, the charities we rely on to provide disaster relief still require funds to operate in quiet years, and I encourage you to consider a donation at this time to one of my two favorite disaster relief charities. Portlight.org, which was very effective at helping out isolated, under-served communities in the wake of Hurricane Ike, is committed to raising $12,000 to purchase and outfit a mobile kitchen. This kitchen will be capable of feeding up to 2,000 people two hot meals per day in post-disaster situations. The Lambi Fund of Haiti has launched its "Million Tree Campaign", which aims to use local labor to plant a million trees over the next three years along severely deforested slopes in Haiti. Both of these charities wrote to me several times last year about the stunning generosity readers of this blog showed with their donations. Thanks!

Twenty years ago today
As Hurricane Hugo approached the U.S. Virgin Islands in the early morning hours of September 18, 1989, the storm slowed down to 10 mph. The slower speed allowed Hugo to punish the island of St. Croix with the worst beating of any location along the hurricane's destructive path. At 2am local time on September 18, 1989, Hurricane Hugo's eyewall struck St. Croix, bringing incredibly ferocious Category 4 winds, sustained at 140 mph. The hurricane's gusts were remarkably violent, and many residents witnessed tornado-like vorticies barreling across the island as the hurricane raged about them. A storm surge of 2 - 3 feet, topped by battering waves 20 - 23 feet high, assaulted the coast, adding to the destruction. Wunderground member Mike Steers wrote me to describe his experience on St. Croix: "Hugo was incredible. Many vortexes came in that night. The roar and intensity of the winds that night were incredible. When the eyewall came over, we were forced to take refuge in the bathroom as the rest of the house came apart. The pressure was so low outside the house that all of the water was sucked out of the toilet and an air draft was created through the toilet. Just when I thought it was as bad as it would get, the intensity of it all dialed up even higher. Dozens and dozens of times, my ears would violently pop due to rapid pressure changes. The next morning, of course, the devastation was unbelievable. In my front yard was a 18-foot boat with an outboard on it, that had been picked up from a marina two miles away. I had lost my house, and job, the Seaplane company I was a pilot for. After a couple months, I had to leave everything behind. In some respects, after 20 years, there an many aspects of the society that have yet to recover". Two people were killed on St. Croix, 80 injured, and 90% of the buildings were damaged or destroyed. Damage estimates for St. Croix were astronomical, over $1 billion, and the island's entire infrastructure was virtually wiped out. Six weeks after the hurricane, only 25% of the public roads had been cleared, and only 25% of the island had power.


Figure 3. GOES visible satellite image of Hurricane Hugo taken on September 18, 1989. Note the lack of cloud cover on the hurricane's southwest side, indicating that strong upper-level winds from the southwest were likely creating wind shear, weakening the storm. Image credit: Google Earth rendition of the NOAA HURSAT data base.

As Hugo departed St. Croix, strong upper-level winds from the southwest created wind shear that weakened the storm to a Category 3 hurricane with 130 mph winds. The upper level winds also caused Hugo to accelerate to 15 mph and turn more northwest. The eye passed over Puerto Rico's Vieques Island at 8am and over Fajardo on the extreme northeastern tip of Puerto Rico at 9am. On Culebra Island, an island twelve miles east of Fajardo, a gust to 170 mph was recorded by the ship Night Cap in the main harbor. The south-facing harbor received sustained southerly winds in excess of 120 mph for several hours as Hugo roared by to the south. The resulting wave "set-up" created a storm surge in excess of 13 feet in the supposedly hurricane-proof harbor. A large portion of the Caribbean's charter boat fleet, some 200 boats, was sheltering in Culebra's harbor, and 136 of these boats were badly damaged or sunk. Over 80% of the wooden structures on both Culebra and Vieques were destroyed.


Figure 4. Damage on St. Croix (two top photos), Culebra Island (bottom right), and Puerto Rico's Roosevelt Roads Navy Base (bottom left), after Hurricane Hugo. Image credit: NOAA Photo Library.

Along the northeastern coast of Puerto Rico, waves up to ten feet high riding on top of a 3 - 4 foot storm surge caused severe coastal flooding of low-lying areas. Hugo's winds tore into Puerto Rico's El Yunque rainforest, downing thousands of trees. The agricultural sector was devastated, with nearly all of the island's banana and coffee crops wiped out. Twelve deaths in Puerto Rico were attributed to Hugo, six of which occurred in the southern city of Guayama where some residents were electrocuted by downed power lines. Nearly 28,000 people were left homeless by the storm, and damage to the island exceeded $1 billion.

Storm chaser Michael Laca was at Luquillo Beach on the northeast shore of Puerto Rico, and has posted a remarkable 28-minute video on YouTube of Hurricane Hugo footage.

Jeff Masters

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Member Since: Posts: Comments:
Quoting Fshhead:
Afternoon Everyone,
Am I missing something here??? The sat loop shows ex-Fred getting its cloudcover totally ripped off & shooting it towards the south?? It almost looks like it skipped south(but didnt) the shear is so strong..


the shear isnt SO strong as you put it lol, about 20 knots, will improve tonight
Quoting Hurricane009:
Hey Grothar!!!


Hey 009. If things keep up they may name an invest after you 009L! Catch up on what has been posted. They put up some good graphics today.
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Quoting Grothar:


Wow! No wonder you're failing math. When do you have time to do all that. Incredible stuff. What pictures. I did extended research on the New Madrid earthquakes a few years back. 1800 quakes in 2 mo. If I remember by data.
1811-1812..Right in my back yard.....
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ZOOMED IN 80 PERCENT

ZOOMED OUT 40 PERCENT


07L/LO/FRED
MARK
26.2N/67.3W
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Quoting Grothar:


Wow! No wonder you're failing math. When do you have time to do all that. Incredible stuff. What pictures. I did extended research on the New Madrid earthquakes a few years back. 1800 quakes in 2 mo. If I remember by data.


I found time when I was banned :P and yeah, that number seems right, so, point is, the midwest has bizarre weather too
Member Since: June 28, 2006 Posts: 24 Comments: 8185
Afternoon Everyone,
Am I missing something here??? The sat loop shows ex-Fred getting its cloudcover totally ripped off & shooting it towards the south?? It almost looks like it skipped south(but didnt) the shear is so strong..
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Quoting tornadodude:
Grothar-

Did you look at my blog that I was referring to? link


Wow! No wonder you're failing math. When do you have time to do all that. Incredible stuff. What pictures. I did extended research on the New Madrid earthquakes a few years back. 1800 quakes in 2 mo. If I remember by data.
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07L maybe be too small to be shown closed on the quickscat or the system's circulation is too small to penetrate the surface flow enough to closed it off directly at the surface but could easily be closed at a layer just above the surface hence lower level circulation.
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Quoting StormChaser81:
Dead head Fred isn't dead until hes ready to die. Hes been vacationing across the Atlantic, then making a stop in the bahamas for some warm water and sun shine. =)
He is alive, he is dead, he is open, he is closed......yyyaaaawwwwnnn!
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Quoting serialteg:


id edit that tdude, bans are common now


oh, I did already, I just got off a ban last night
Member Since: June 28, 2006 Posts: 24 Comments: 8185
Quoting watcher123:
638:

I gotta agree. I don't know what other people are looking at, but if that isn't a closed circulation I'm a balogna sandwich.


What's the latest QScat show? If it looks like this morning's image, you'll need some mustard
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Quoting Ameister12:

Bye, Fred!


Its not as intense as it was before so we'll see what happens.
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Quoting tornadodude:


is he?



id edit that tdude, bans are common now
Member Since: August 22, 2006 Posts: 2 Comments: 1975
Quoting Stormchaser2007:


The dry air isnt moving anywhere.

Its just sitting there waiting for Fred.

Bye, Fred!
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sure looks like fred-ex is starting to show banding all around like never before......wait check that.....in a long time :)!
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Quoting TheCaneWhisperer:


I don't have any weather balloons so I, like the rest of us, will have to go by the tools that are available and the NHC guidance which both show favorable shear ahead ;-)


Ok, well, that guidance has been wrong, dead wrong, quite few times this season. so i'm not sure why you'd put much stock in it.

what you could do is look at the indivdual layers of the atmosphere in the model runs...look closely at various sat images to see evidence of shear...look at soundings from nearby areas...it's more work than simply looking at a 1-parameter map, but likely to be more accurate.
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Quoting Ameister12:

Where's the SAL heading and how fast?


The dry air isnt moving anywhere.

Its just sitting there waiting for Fred.
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I see what the others have been discussing now. 007l does appear to be moving slightly to thw WSW. But should begin more of a wnw when it reaches that feature over the Bahamas. The animated version shows it much more clearly. I also see the "building" high.
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Quoting tornadodude:


is he?


Lol!
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.
Member Since: June 28, 2006 Posts: 24 Comments: 8185
Quoting reedzone:


Unless, it's just the clouds, the winds might not be wrapping all the way.. So maybe I'm wrong.


The circulation is not closed in the SW quadrant.

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661. DDR
Aye people,rain falling like crazy in trinidad
floods all over
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Fred is dead !!
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Quoting Stormchaser2007:


We'll see.



all that SAL in front of freddy is conspiring against...
Member Since: August 22, 2006 Posts: 2 Comments: 1975
Quoting Stormchaser2007:


We'll see.


Where's the SAL heading and how fast?
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Grothar-

Did you look at my blog that I was referring to? link
Member Since: June 28, 2006 Posts: 24 Comments: 8185
Quoting rwdobson:
"According to the 12ZGFS Shear will be pristine ahead in 18 hours and an Upper level anti-cyclone over the bahamas in 30."

This is a bulk shear predicition based on 200-850mb, a thick slice of the atmosphere.

So far this season, the bulk shear has not been a very reliable indicator of cyclone development. Several storms have had apparently favorable bulk shear but were still killed by strong shear in small layers.


You mean it is simply wind shear. Bulk shear involves the surface and a layer above the surface.
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Quoting watcher123:
638:

I gotta agree. I don't know what other people are looking at, but if that isn't a closed circulation I'm a balogna sandwich.


now that would be something
Member Since: August 22, 2006 Posts: 2 Comments: 1975
Quoting watcher123:
638:

I gotta agree. I don't know what other people are looking at, but if that isn't a closed circulation I'm a balogna sandwich.


Unless, it's just the clouds, the winds might not be wrapping all the way.. So maybe I'm wrong.
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Quoting reedzone:


Yes, he's "Double 07L" ;)

I like the James Bond concept.
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Quoting reedzone:


Just ahead is some favorable conditions, won't get there until tonight or tomorrow.


We'll see.

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Quoting Drakoen:


Visible imagery and microwave imagery. There are no surface observations close enough to the low pressure center to confirm a closed low using this tool.


Perhaps the best answer all day, Thanks Drak.
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Quoting Grothar:


Hey reed. Did see it but didn't want to mention it, because you-know-why? I guess it will be a wait and see, but I doubt it shall have enough time to get too strong, you think?


I think this will ramp up right before landfall into a TD or weak TS. Something similar to Claudette this year, just on the East Coast this time.
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Quoting Stormchaser2007:
07L.



Just ahead is some favorable conditions, won't get there until tonight or tomorrow.
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98L seems to be getting a little better looking.
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Quoting reedzone:


If you look at the visible, you'll see a well defined circulation, which is closed. :)


Hey reed. Did see it but didn't want to mention it, because you-know-why? I guess it will be a wait and see, but I doubt it shall have enough time to get too strong, you think?
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07L.

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Dead head Fred isn't dead until hes ready to die. Hes been vacationing across the Atlantic, then making a stop in the bahamas for some warm water and sun shine. =)
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About JeffMasters

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