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:


Just the convection. What happens is, the mid an upper portions get blown in the direction the shear is going, so the system is "tilted", or what we call not vertically stacked.


BTW Storm you always have a patience and a way of explaining things that makes us novices feel important yet help us learn at the same time.
Thanks for your knowledge.
You definitely bring a levelheadedness to this blog.
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Quoting WaterWitch11:


i went back into the blog to see what this means, i can't figure out what you are talking about.


you know I have asked you questions in the past and never get a response, so I guess I get the message and will stop asking you - thanks!
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Good Evening guys,
Choiwan's eye is MASSIVE!!!
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Quoting StormW:


I'll have to see what the updated steering layers show. That's one possibility. It's a pain trying to figure out when they stall.


Ok thank you Storm. I know you are busy and this season is a trying one. Lol. :)
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Quoting homelesswanderer:


Oh ok. Thanks :)


You're welcome. That's the 2 main things that can influence steering but when something stalls anything can happen. Plus it's not even a storm.
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1086. JLPR


98L is watching you lol XD
Member Since: September 4, 2007 Posts: 36 Comments: 5223
1085. JLPR
Quoting StormW:


As it stands right now...yes.


I see
thanks for the answer :)
Member Since: September 4, 2007 Posts: 36 Comments: 5223
1083. docrod
Part of Key West's weather discussion today

.CLIMATE...
ON THIS DATE IN KEYS WEATHER HISTORY...IN 1926...THE GREAT MIAMI
HURRICANE OF 1926 MADE ITS UNITED STATES LANDFALL JUST SOUTH OF
MIAMI AT CATEGORY 4 INTENSITY. THIS HURRICANE SEVERELY DAMAGED THE
ROADWAY AND BRIDGES BEING BUILT IN THE UPPER KEYS. IN KEY WEST...
THE MINIMUM CENTRAL PRESSURE WAS 29.48 INCHES AND THE PEAK WIND WAS
52 MPH. THE GREAT MIAMI HURRICANE OF 1926 IS THE 10TH DEADLIEST
HURRICANE IN THE HISTORY OF THE UNITED STATES. IN ADDITION...THE
GREAT MIAMI HURRICANE OF 1926 IS THE 13TH MOST INTENSE HURRICANE TO
EVER STRIKE THE UNITED STATES.
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1082. hercj
Quoting StormW:


Just the convection. What happens is, the mid an upper portions get blown in the direction the shear is going, so the system is "tilted", or what we call not vertically stacked.
Ok I get it, thanks Storm, I really appreciate your help.
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Quoting HurricaneKing:


Either the high trying to build in (Which would push fredex west) or the trough trying to move in from the nw.(Which would push fredex north)


Oh ok. Thanks :)
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Quoting StormW:


A tour of stormno's weather office.


I think I'll pass. LOL
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Quoting homelesswanderer:


After that what will steer it? The building high?


Either the high trying to build in (Which would push fredex west) or the trough trying to move in from the nw.(Which would push fredex north)
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Quoting StormW:
Just a quick update concerning ex-Fred. Just looking at a few steering things, shallow layer steering has changed somewhat. ex-Fred should be allowed to move a little further north, as a weakness has become apparent NE of the Bahamas and the east of the SEUS coast



the steering looks weak in vicinity of Fred..we'll see how that goes.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting StormW:


We have a winner!


After that what will steer it? The building high?
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Quoting StormW:


We have a winner!


Gee so we could have the remnants of Fred in the Bahamas with that warm water and decent shear, not moving much

Yea I feel much better StormW lol
DISTURBANCE FRED (AL072009) 20090919 0000 UTC


...INITIAL CONDITIONS...
LATCUR = 26.2N LONCUR = 68.2W DIRCUR = 295DEG SPDCUR = 11KT
LATM12 = 25.3N LONM12 = 66.0W DIRM12 = 292DEG SPDM12 = 11KT
LATM24 = 24.9N LONM24 = 63.3W
WNDCUR = 30KT RMAXWD = 15NM WNDM12 = 25KT
CENPRS = 1011MB OUTPRS = 1015MB OUTRAD = 150NM SDEPTH = S
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM
Member Since: September 23, 2005 Posts: 14 Comments: 11209
Quoting StormW:


We have a winner!


What I win? Huh huh huh? LOL.
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1070. hercj
Quoting StormW:


Because it's under 15-20 kts of shear from the NNE.
So is the COC being moved as well or is it just the convection surrounding it? Sorry for the questions Storm, just trying to learn something about atmospherics.
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Quoting hercj:
Storm W, why does it look like on the atl sat that the convection to Ex-Fred is being pulled SSW?
Quoting StormW:


Could be...depends on a couple things. What do you notice about the weakness?

hands ups hands up...shear baby shear
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Quoting Weather456:


no, I was giving the probabilities of several outcomes


i went back into the blog to see what this means, i can't figure out what you are talking about.
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1065. JLPR
Quoting StormW:
Just a quick update concerning ex-Fred. Just looking at a few steering things, shallow layer steering has changed somewhat. ex-Fred should be allowed to move a little further north, as a weakness has become apparent NE of the Bahamas and the east of the SEUS coast



how about 98L?
to the west?
Member Since: September 4, 2007 Posts: 36 Comments: 5223
1062. JRRP
12 GMT 09/18/09 12.6N 39.2W 25 1008 Invest
18 GMT 09/18/09 12.8N 39.9W 25 1008 Invest
00 GMT 09/19/09 13.1N 40.4W 25 1008 Invest
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1061. beell
Tuesday's GFS
Valid Friday, 00Z

Photobucket
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Quoting StormW:


Could be...depends on a couple things. What do you notice about the weakness?


No steering in the weakness. All motion slows to a crawl.
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1059. hercj
Storm W, why does it look like on the atl sat that the convection to Ex-Fred is being pulled SSW?
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1058. jipmg
Quoting StormW:


Could be...depends on a couple things. What do you notice about the weakness?


the low that was fred is moving NW as we speak, thats what I notice
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Quoting StormW:
Just a quick update concerning ex-Fred. Just looking at a few steering things, shallow layer steering has changed somewhat. ex-Fred should be allowed to move a little further north, as a weakness has become apparent NE of the Bahamas and the east of the SEUS coast



I think somewhere b/w florida to NC for what's left of fredex. I wouldn't be surprised if he doesn't turn into a subtropical thingamabober when he starts to interact with the old front in the area.
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DISTURBANCE INVEST (AL982009) 20090919 0000 UTC


...INITIAL CONDITIONS...
LATCUR = 13.1N LONCUR = 40.4W DIRCUR = 280DEG SPDCUR = 6KT
LATM12 = 12.9N LONM12 = 39.2W DIRM12 = 266DEG SPDM12 = 6KT
LATM24 = 13.2N LONM24 = 37.9W
WNDCUR = 25KT RMAXWD = 45NM WNDM12 = 25KT
CENPRS = 1008MB OUTPRS = 1012MB OUTRAD = 210NM SDEPTH = M
RD34NE = 0NM RD34SE = 0NM RD34SW = 0NM RD34NW = 0NM

Member Since: September 23, 2005 Posts: 14 Comments: 11209
1052. jipmg
Fred looks like a TW to me.. and its under a pocket of heavy shear, if it doesn't regenerate tonight, florida is only getting a tropical wave.
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Quoting WeatherStudent:
So is the coast all clear then for SF, 456?


no, I was giving the probabilities of several outcomes
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Sorry if this has been posted. From Miami NWS...

.PREV DISCUSSION... /ISSUED 232 PM EDT FRI SEP 18 2009/

DISCUSSION...A WEAK TROF IS DRIFTING WEST ACROSS THE NORTHERN
BAHAMAS AND THE STRAIGHTS THIS AFTERNOON ALONG WITH A FEW WEAK
EMBEDDED VORTS (ONE IS LOCATED JUST SOUTH OF THE MIDDLE KEYS) WHILE
AN AREA OF HIGH PRESSURE CONTINUES TO RIDGE INTO THE GULF AND
ALONG THE WEST COAST OF FL. ALSO, A CUT-OFF LOW CONTINUES TO MILL
ABOUT LOUISIANA AND ANOTHER INVERTED TROF (THE WEAK REMNANTS OF
FRED) IS HEADING WEST AND IS LOCATED NORTH OF PUERTO RICO. THE
WEAK INVERTED TROF LOCATED JUST S AND EAST OF S FL WILL CONTINUE
TO SLOWLY HEAD WEST BOUND THIS EVENING AND EVENTUALLY INTO S FL
TONIGHT. SCT SHRA AND TSRA WILL INCREASE ALONG THE E COAST
OVERNIGHT AND EVENTUALLY SPREAD ACROSS THE REST OF THE CWA AS SAT
PROGRESSES WHILE BECOMING MORE NUMEROUS AS DAYTIME HEATING OCCURS.
BEHIND THIS TROF, AND ON MONDAY NIGHT AND SUNDAY, THE RIDGE IS
EXPECTED TO PUSH BACK INTO THE AREA FROM THE NORTH AS THE CUT-OFF
LOW FINALLY EJECTS OUT OF THE LOWER MS VALLEY SHOVING THE SURFACE
RIDGE ALONG THE ATLANTIC SEABOARD SOUTHWARD. AS THE RIDGE PUSHES
SOUTH THIS WILL KEEP THE REMNANTS OF FRED ON AN EASTWARD COURSE
AND EVENTUALLY TOWARD FL.
THIS IS EXPECTED TO INCREASE RAIN
CHANCES DURING THE FIRST PORTION OF THE WEEK AS THE WEAKENING SYSTEM
PUSHES THROUGH. BEHIND THE REMNANTS OF FRED AND DURING THE MIDDLE
AND END OF NEXT WEEK THE RIDGE OVER THE ATLANTIC IS EXPECTED TO
SLOWLY SAG SOUTHBOUND AND INCREASE THE DEPTH OF THE EASTERLY FLOW.
THIS WILL ALLOW NOCTURNAL AND MORNING SHRA AND A FEW TSRA ALONG
THE EAST COAST WITH AFTERNOON AND EVENING TSRA ALONG THE WEST
COAST AND OVER THE INTERIOR, HOWEVER GUIDANCE ALSO INDICATES A
FAIRLY STRONG MID LEVEL RIDGE SETTLING IN ACROSS THE REGION WHICH
MAY KEEP COVERAGE FAIRLY SPARSE AT BEST.

I'm sure they meant west.

Link
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1049. JLPR
Quoting JRRP:



according to that
98L is right under the convection on the west side
Member Since: September 4, 2007 Posts: 36 Comments: 5223
i'm out for the evening...have a good one!
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1046. beell
Oh well,back to the real world...
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1043. jipmg
so why isn't 98L a TD? It has a closed low
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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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