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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Quoting StormW:


Haven't changed since this morning:

This wave is moving just slightly north of west, and I expect this motion to continue, with th area moving into the northern Bahamas / South Florida area in about 36 hours.

Based on current and projected track, and the current wind shear forecast, models indicate this wave will enter an area near the Bahamas with improving upper level conditions, with wind shear forecast to relax to favorable levels with some slight ridging north of the wave in about the next 16-20 hours. Tomorrow will tell about any chance of regeneration. However, given the surrounding dry air, any regeneration would be slow, and would most likely occur at the point of over the northern Bahamas, in which a short window of opportunity would exist before interaction with the Florida Peninsula.


Appreciate it! :)
Quoting Autistic2:
Ok, If MMGW is so bad why is the middle of Hurricane season without so much as a TD anywhere in the Atlantic basin ?

I thought MMGW was going to make all these supercanes?
Actually no on the supercanes. While MMGW is supposed to enhance hurricane strength, it won't make a season busier if other TC-influencing factors are in effect, eg. el nino.

Now, it may make a season like 1992, w/ 1 cat 5 'cane and not much else, more likely, but that's it.
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Quoting AllStar17:
456....chances Ex-Fred gets in GOM, please? (percentage)



I cannot give you an exact % but with every latitude Fred inches northward, the chances become less. Remember the models take it westward so as Fred continues wnw, that westward track will shift more and more north. The current chance is about 50/50 but if Fred reaches 28N, that becomes 30/70 and 30N >20/<80
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Good evening, all! Storm, please, your brief thoughts on Ex-Fred this evening, sir, if you wouldn't mind, that is? Thank you!!! :)
Ok, If MMGW is so bad why is the middle of Hurricane season without so much as a TD anywhere in the Atlantic basin ?

I thought MMGW was going to make all these supercanes?
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1036. JRRP
Quoting Weather456:


Thats a damned define circulation there.

in comparison with this morning.. it is much better




see you later
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It looks like things may be slow for a while, so I'm likely to be in and out of the blog tonight. Maybe tomorrow 98L will be looking more interesting in a general sense....
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1015. I didn't say 'which' groupthink people get banned for! LOL
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Evening everybody.

Glad to see FredEx is staying ex and not doing much of anything threatening right now. I don't mind a rainy Sunday if it means I don't have to batten up and worry about ppl....
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Quoting Weather456:


I call that rapid development or organization. Rapid intensification is where the intensity (pressure) drops significantly over 24 hrs. If 07L became a 50 mph TS, that would not be rapid intensification since the pressure will not fall more than 10 millibars from its current state.


Well said! Never thought of it that way.
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i am probably late with this info but do u guys know wunderground has a page on facebook?
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456....chances Ex-Fred gets in GOM, please? (percentage)
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Quoting JRRP:



Thats a damned define circulation there.
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Quoting Weather456:


I call that rapid development or organization. Rapid intensification is where the intensity (pressure) droops significantly over 24 hrs. If 07L became a 50 mph, that would not be rapid intensification since the pressure will not fall more than 10 millibars from its current state.


thank you for clarifying, because that to me shows everyone what rapid intensification means

as you can see if you look back a few posts, someone took your no rapid intensification idea as that Ex Fred would be no more than a remnant low.

That's why I asked so you could clarify.
1025. beell
Quoting StormW:


Which system?


The thread was regarding exFred.
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Quoting Herbertsbox:


Question is 456, what can Fred accomplish after a short trip across Florida.


You mean if it enters the GOM, well the potential is great, but it does not mean Fred will take advantage of its full potential.

I'm not saying it won't development, but at the same time I'm being realistic.
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1022. JRRP

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Quoting BurnedAfterPosting:


97L was an oopsie that was made a few days ago, when they designated 97E in the EPAC (now Marty); the accidently put it as 97L

I think the way their calculations work is it does not allow for 97L to be used again


What are they running a Tandy computer? I agree with you but doesn't that seem kinda ridiculous.
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Quoting BurnedAfterPosting:


depends on your definition of rapid intensification

from its current state, rapid intensification could be to a 50mph storm, which to me is not out of the realm of possibility



I call that rapid development or organization. Rapid intensification is where the intensity (pressure) drops significantly over 24 hrs. If 07L became a 50 mph TS, that would not be rapid intensification since the pressure will not fall more than 10 millibars from its current state.
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Quoting Weather456:
SSTs are warm but I don't think the upper environment would allow for rapid intensification of Fred.


Question is 456, what can Fred accomplish after a short trip across Florida.
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Quoting Weather456:
SSTs are warm but I don't think the upper environment would allow for rapid intensification of Fred.
I have to agree...the
remnants of Fred are just that....remnants..not
much of a threat imho....
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Rapid intensification, LMAO!!!!

A puff of clouds heading towards Florida, what did you expect? Wow this is going to be an interesting weekend of wishcasting. Probably the most funny weekend of the 2009 Hurricane Season.

Rapid intensification, lol, I can't stop laughing.
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Quoting pearlandaggie:


well, certain people get banned for the same infractions that others don't. also, if you don't conform to a certain groupthink, you could also be banned.


Thats why I got banned one time. Wrong side of GW.
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Quoting Weather456:
SSTs are warm but I don't think the upper environment would allow for rapid intensification of Fred.


depends on your definition of rapid intensification

from its current state, rapid intensification could be to a 50mph storm, which to me is not out of the realm of possibility

SSTs are warm but I don't think the upper environment would allow for rapid intensification of Fred.
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Quoting beell:
Quoting BurnedAfterPosting:
oh well 456, shear maps are wrong

bye bye Fred? lol


Quite a few of your posts are a little on the sarcastic side. My bad...maybe it was the lol that threw me off.



I had just got hit in the head about a minute before, dont mind me lol
So the question of the day: Does anyone think ex Fred stands a chance at redeveloping before it hits land or FL??
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1010. beell
Quoting StormW:


You are correct. I researched what they use, and it's high density satellite data,


Thanks.
It may be a narrow band of shear, but do you "buy" 20 knots based on wv/vis?
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000
ABNT20 KNHC 182339
TWOAT
TROPICAL WEATHER OUTLOOK
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT FRI SEP 18 2009

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

A SMALL LOW PRESSURE AREA...ASSOCIATED WITH THE REMNANTS OF FRED...
IS CENTERED ABOUT 490 MILES SOUTH-SOUTHWEST OF BERMUDA AND IS
PRODUCING DISORGANIZED SHOWER AND THUNDERSTORM ACTIVITY. UPPER-
LEVEL WINDS COULD BECOME MORE FAVORABLE FOR SOME DEVELOPMENT DURING
THE NEXT DAY OR TWO AS THE SYSTEM MOVES WEST-NORTHWESTWARD AT 10 TO
15 MPH. THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS
SYSTEM BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS.

SHOWER ACTIVITY ASSOCIATED WITH A BROAD AREA OF LOW PRESSURE
CENTERED ABOUT MIDWAY BETWEEN AFRICA AND THE LESSER ANTILLES SHOWS
SOME SIGNS OF ORGANIZATION. SLOW DEVELOPMENT OF THIS SYSTEM IS
POSSIBLE OVER THE NEXT COUPLE OF DAYS AS IT MOVES WEST-
NORTHWESTWARD AT AROUND 10 MPH. THERE IS A MEDIUM CHANCE...30 TO
50 PERCENT...OF THIS SYSTEM BECOMING A TROPICAL CYCLONE DURING THE
NEXT 48 HOURS.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER BEVEN

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1008. JRRP
mmmmmm

and 98L
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1007. beell
Quoting BurnedAfterPosting:
oh well 456, shear maps are wrong

bye bye Fred? lol


Quite a few of your posts are a little on the sarcastic side. My bad...maybe it was the lol that threw me off.

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Quoting JLPR:
question...
am I going nuts or did we skip 97L? xD


I've been wondering the same thing since yesterday.
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Quoting Weather456:


I think the shear maps used at CIMSS is calculates using satellite winds which shows winds of 30 knots in the upper levels and 10 knots in the lower levels to get a shear magnitude of 20 knots. Some model data is also incorporated into the shear analysis.



I "think" they use what we call Ballistic wind in the Navy. Is the mean Average of the winds aloft from sea level to any given height. Its what we would set on our fire control computers. We would normally launch a Balloon, and then track it thru the different layers with a Fire Control Radar.


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GOES satellite is down.
She was sparking a bit yesterday too...
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Quoting JLPR:


I see
lol so 97L was a oopsie
thats interesting :P


lol
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1000. JLPR
Quoting BurnedAfterPosting:


97L was an oopsie that was made a few days ago, when they designated 97E in the EPAC (now Marty); the accidently put it as 97L

I think the way their calculations work is it does not allow for 97L to be used again


Quoting tornadodude:


ok, remember when they accidentally classified 97E as 97L? well in order to avoid confusion, they skipped 97L, I think :P

I see
lol so 97L was a oopsie
thats interesting :P
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Quoting beell:


I'm wearing my aluminum foil hat!

But anyway! 45 knots at 200mb from the north, at least 10-15 at 850mb from the SE/ESE on the 18Z GFS analysis (00Z) hr gotta yield more than 20 knots if you believe the model.


I'm thinking the shear maps used at CIMSS is calculates using satellite winds which shows winds of 30 knots in the upper levels and 10 knots in the lower levels to get a shear magnitude of 20 knots. Some model data is also incorporated into the shear analysis.

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Quoting beell:


Is it out of the realm of possibility for a shear map to be wrong?


Um no not at all, what gave you that idea that I didnt think it was possible?
Quoting JLPR:
question...
am I going nuts or did we skip 97L? xD


ok, remember when they accidentally classified 97E as 97L? well in order to avoid confusion, they skipped 97L, I think :P
Member Since: June 28, 2006 Posts: 25 Comments: 8360
Quoting JLPR:
question...
am I going nuts or did we skip 97L? xD


97L was an oopsie that was made a few days ago, when they designated 97E in the EPAC (now Marty); the accidently put it as 97L

I think the way their calculations work is it does not allow for 97L to be used again
995. beell
Quoting BurnedAfterPosting:
oh well 456, shear maps are wrong

bye bye Fred? lol


Is it out of the realm of possibility for a shear map to be wrong?
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Quoting BurnedAfterPosting:


We just finished stating how the shear maps are wrong lol and rapid intensification is not likely
I'm sorry, I just got on and didn't read any other posts.
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993. JLPR
question...
am I going nuts or did we skip 97L? xD
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Quoting tornadodude:


yeah, oh well, its no big, I'm unbanned :P


i got banned for posting pictures of unusual clouds...go figure!
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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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