Hurricane Hunters to check out remains of Fred; 98L more organized

By: Dr. Jeff Masters , 1:06 PM GMT on September 19, 2009

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A tropical disturbance (98L), is located midway between Africa and the Lesser Antilles Islands. This disturbance has shown a modest increase in heavy thunderstorm activity over the past day. This morning's QuikSCAT pass showed an elongated circulation, with top winds around 30 mph. Wind shear is low, 5 - 10 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.

Wind shear over 98L is expected to remain in the low range, 5 - 10 knots, through Sunday evening, according to the SHIPS model. This may allow the storm to organize into a tropical depression, assuming it can fight off the dry air that surrounds it. By Monday, the SHIPS model predicts shear will increase to the high range, 15 - 30 knots, so in is unlikely 98L will become anything stronger thatn a weak tropical storm over the coming 5-day period. The models 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. NHC is giving 98L a high (greater than 50%) chance of developing into a tropical depression by Monday. At this time, it does not appear that 98L will ever threaten any land areas.

Fred-ex
The remains of Hurricane Fred are still spinning away about 700 miles east of Florida. There has been a modest increase in heavy thunderstorm activity on the south side of Fred's circulation over the past day, but high wind shear and dry air have kept the thunderstorms from building over Fred's center. Wind shear is moderate, 15 - 20 knots, and there is substantial dry air surrounding ex-Fred on all sides. This morning's QuikSCAT pass showed top winds of 30 mph.

None of the computer models develop ex-Fred, and conditions for development are expected to remain marginal over the next three days, with wind shear of 15 - 20 knots and plenty of dry air around. Most of the models predict ex-Fred should move over Florida on Tuesday, but steering currents may weaken early next week, and ex-Fred could end up slowing down and turning northwest towards South Carolina. A hurricane hunter aircraft this afternoon was cancelled.


Figure 1. Morning visible satellite image of 98L and the remains of Hurricane Fred.

Twenty years ago today
On September 19, 1989, Hurricane Hugo moved away from Puerto Rico, and headed northwest at 15 mph. An upper-level low over Georgia, in combination with the steering currents imparted by the Azores-Bermuda High, were responsible for the northwesterly motion of the storm. Wind shear from strong upper-level winds continued to weaken the hurricane, and Hugo diminished to a Category 2 hurricane with 105 mph winds.


Figure 2. GOES visible satellite image of Hurricane Hugo taken on September 19, 1989. Wind shear had weakened Hugo to a Category 2 storm with 105 mph winds. Image credit: Google Earth rendition of the NOAA HURSAT data base.

I'll have an update this afternoon if there's any major developments to report.

Jeff Masters

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I've lost my link to ASCII hurricane hunter data. I'm looking for data in a format like this:
http://www.nhc.noaa.gov/text/URNT15-USAF.shtml?
but for historical data. If you have a link handy, can you kindly post it? Thanks.

EDIT:
Never mind. I found it: http://www.nhc.noaa.gov/archive/recon/2009/
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709. Relix
98L's convection is nearly non existant at the moment. It's also moving at WNW at a slow speed. Circulation and banding are pretty nice though, so I give this system high chances of becoming a TD soon, also thanks the good development environment. Still, something tells me this will be a fish
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Quoting hydrus:
I still believe we will have a couple more storms Keeper, that wave over Africa looks very strong, and the western Caribbean could easily produce something in October.
o for sure i agree with you but what we should be seeing and what we are seeing is two different things if anything may get a couple of east movers close to home in gom nw sw carb maybe sw atl. but after next week cv season will be as good as done imo
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Hi everybody!

98L is, truly, a medium risk. DMIN may be playing a role in its decrease in organization. I believe that 98L will probably fluctuate in organization, and simply just either be a wave or a TS.
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Quoting Weather456:


Some of the lowest sal I ever saw

funny huh 456 now that we are at the end of the cv season sal is next to nothing i notice ITCZ is startin to slowly move south from its maximum northern approach as well the newxt week or so should see even a bigger creep back
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Quoting KEEPEROFTHEGATE:
just like the tropics real quiet in here as well it will get even quieter as we get further along towards end of the season be lucky to get 100 posts in 24 hrs
I still believe we will have a couple more storms Keeper, that wave over Africa looks very strong, and the western Caribbean could easily produce something in October.
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699. JLPR
lets see if 98L will be one of those come back invests that end up a TD the other day
or if it will be one of the invests to poof even with favorable conditions xD
Member Since: September 4, 2007 Posts: 36 Comments: 5223
Link

Check this out...please forward, repost, etc...
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Quoting JLPR:
water vapor at the high levelsBR

water vapor at mid levels
a little dry but not enough to kill it


Don't have pics to show it, but my impression this season has been that the arcs thrown off by convection decaying due to dry air entrainment at the mid levels in these struggling TCs either aren't as apparent on vis or look different than what I was used to seeing in the past. Maybe due to more tilt/shear? Anyone else noticed this?
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Quoting JLPR:
water vapor at the high levels

not that dry


water vapor at mid levels


a little dry but not enough to kill it


Some of the lowest sal I ever saw

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Quoting markymark1973:
98L has taken a beating with all the dry air around it.


Nope, Serious case of Durinal Minimum.

Guys, this is about the 1000th time we've seem this happen. Weak systems like these always, ALWAYS, get beaten up at DMIN no matter how impressive it looked in the morning.
Member Since: August 10, 2009 Posts: 3 Comments: 672
just like the tropics real quiet in here as well it will get even quieter as we get further along towards end of the season be lucky to get 100 posts in 24 hrs in another 2 months
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692. JLPR
water vapor at the high levels

not that dry


water vapor at mid levels


a little dry but not enough to kill it
Member Since: September 4, 2007 Posts: 36 Comments: 5223
Quoting AllStar17:
Where'd the blog go?
maby with fred ...lol
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Where'd the blog go?
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686. CUBWF
Anybody at home?
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98L has taken a beating with all the dry air around it.
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683. CUBWF
Good afternoon. The vorticity of exfred has increased in the last 3 hours, as the lower convergence. 98L getting d-min no so well, but center is looking tightening at 13 and 42.6. Also the ULL in the west caribean might be trying to bring something in the coming days. Now it does appear to be moving more to wnw to nw.
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Quoting Weather456:


You are correct that more than 80% of hurricane season succeeding an El Nino is active however;

1)There is no guarantee that this El Nino will weaken in time for next hurricane season.

2)The 2005 Hurricane Season was an extreme anomaly of 28 storms and the last time that happen was 1933 with 21 storms. The chances of next year reaching 28 plus storms is very very slim regardless of the ENSO episode.
The only thing that can easily beat the number of storms we had in the Atlantic in 2005 is the Western Pacific. Which has that many storms regularly. I don,t believe we will witness a 28 storm season for decades. I hope I am correct, 2005 was a devastating year.
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Quoting stormpetrol:

lacking convection, but taking on the real look & structure of a tropical cyclone imo, its a large system and sometime they take a while to fire strong convection, but once they organize can usually maintain it, jmo.
Are you getting much rain in South Sound ? Very dark up here and lots of rain. Nice !
Member Since: October 9, 2008 Posts: 0 Comments: 8242
from what iam seeing i think cv season is done with num 3 AOI that came off the last of the last for the season if we remain at 6 named storms for the season we will tied 65 77 82 86 for that number
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98L is a very large system....and one burst of convection would propel this system to TD 8. I have to say I am very surprised NHC lowered chances to medium....yes, convection has waned, but structure remains excellent. It is still too early to say where 98L will eventually end up.
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Dont be confused with shear blowing the clouds south thinking it is moving south.
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Strong Northerly winds at 70W. This and interaction with the trough might be the reason for the lack of coalescence today

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Quoting JLPR:


yep I said that on the other page xD
convection has waned but it gotten better organized, its a wait and see situation =]

I thought the whole thing about developing TCs was in releasing energy through building and persistent convection and keeping a warm core intact, ventilated but not over ventilated or sheared. The subjective "look" or beauty of the swirl or even Dvorak type assessment doesn't mean much with the weakest upstart systems.
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Quoting watcher123:
Isn't fred drifting south and organising?

I realize the center elongated a few hours ago, but the convection keeps coming back, and it seems the strongest part of the circulation is drifting south.
If so, explains why models were calling for some SW movement of ex-Fred. Our local mets are suggesting wet and windy conditions in the SE Bahamas starting as early as tonight, with same spreading to the Central and NW by tomorrow evening. Just glad it didn't get any worse...
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Quoting reedzone:
As much as people don't want to read this (downcasters).. 07L is making another comeback attempt! The difference with this one is that it's in 10 knots of wind shear. We'll see what happens.


It is exactly at 70W, and there is still some northerly shear over the area. Wait until 10PM tonight, for it will move sufficiently away from the periphery of the weak upper ridge.

Nice Upper wind gradient at 70W

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Fred's got a well defined broad circulation now due to the trough axis. As it moves a little further west it just may tighten that circulation around the llc, which is currently producing strong convection. Could be a textbook example of cyclogenesis as he tightens, he'll start spinning faster. Fred could get the fever, Saturday Night Fever.
Member Since: August 3, 2005 Posts: 10 Comments: 5458
thanks 456 / JLPR
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664. JLPR
Quoting farhaonhebrew:


this year we have the leter G around the the same date...with la nina well established..maby the L..so sep 1998 was a neutral ENSO...


May June July were neutral months before that el niño was in control and after that a la niña took over
but the transition from one to another may have caused the late start to the season

dude check out the link I gave
the numbers are even in red and blue :)
Link
Member Since: September 4, 2007 Posts: 36 Comments: 5223
why is movin wsw?
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September 1998 was La Nina

1998 9 -1.44 -1.76 -2.15
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Quoting JLPR:
Well 98L is having a really bad d-min xD

Lets see how it does in d-max

lacking convection, but taking on the real look & structure of a tropical cyclone imo, its a large system and sometime they take a while to fire strong convection, but once they organize can usually maintain it, jmo.
Member Since: April 29, 2007 Posts: 0 Comments: 7506

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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.