First Category 5 storm of the year is Choi-Wan

By: Dr. Jeff Masters , 1:38 PM GMT on September 16, 2009

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The remains of Hurricane Fred continue to generate sporadic bursts of heavy thunderstorm activity over the middle Atlantic Ocean. These thunderstorms were generating winds up to 30 mph, according to this morning's QuikSCAT pass. However, QuikSCAT also showed that the remains no longer have a surface circulation. Water vapor satellite loops show that ex-Fred has moved beneath an upper-level low pressure system. This low features dry air on all sides, and this dry air will interfere with any redevelopment of Fred. While wind shear is now moderate, 10 - 15 knots, and is expected to remain in the moderate range for the next five days, the presence of so much dry air will require at least three days for the remains of Fred to overcome and regenerate a surface circulation. Only the HWRF model redevelops Fred, predicting it will develop on Sunday as it approaches the Bahama Islands. NHC is giving ex-Fred a low (less than 30% chance) of developing into a tropical depression by Friday. Fred's remains will be near the Bahamas on Sunday, and near Florida on Monday night. It is possible that a strong trough of low pressure expected to develop over the eastern U.S. early next week will turn Fred's remains northwards into South Carolina/North Carolina on Monday/Tuesday.

This morning's QuikSCAT pass shows a surface circulation near 13N 32, with a small region of heavy thunderstorms to the north. This region is about 450 miles west of the Cape Verdes Islands, and is headed west at about 10 mph. Satellite imagery shows a decrease in the amount of heavy thunderstorm activity this morning, and high wind shear of 20 knots is interfering with development. A band of high wind shear lies just to the north of the disturbance, and will continue to interfere with the system's development over the next three days. NHC is giving the system a low (less than 30% chance) of developing into a tropical depression by Friday.

The GFS model is predicting development of a new tropical wave coming off the coast of Africa early next week.


Figure 1. The remains of Hurricane Fred (left) keep on chugging across the Atlantic. A tropical wave is 450 miles west of the Cape Verdes Islands (right). The thunderstorms of the Inter-Tropical Convergence Zone (ITCZ) are far to the south, off the coast of Africa.

Super Typhoon Choi-Wan hits Category 5 strength
This year's first Category 5 tropical cyclone is Super Typhoon Choi-Wan, which intensified into a Category 5 storm with 160 mph sustained winds yesterday afternoon. Choi-Wan is over the open ocean south of Japan, and is not expected to impact any land areas. It is unusual to have to the globe's first Category 5 storm form this late in the year. Indeed, global tropical cyclone activity as measured by the ACE index, which measures destructive potential, has been near historic lows over the past two years. Only one Category 5 storm was recorded in 2008--Super Typhoon Jangmi, which attained winds of 165 mph at 06 GMT on September 27, as it approached the north coast of Taiwan. The last time so few Category 5 storms were recorded globally was in 1974, when there were none.

We got a rare treat yesterday when the Cloudsat satellite caught a perfect cross section through Choi-Wan when it was a Category 4 super-typhoon with 150 mph winds (Figure 2). The CloudSat satellite, launched in 2006, carries the first satellite-based millimeter wavelength cloud radar. It is the world's most sensitive cloud-profiling radar, more than 1000 times more sensitive than current weather radars. It collects data about the vertical structure of clouds, including the quantities of liquid water and ice, and how clouds affect the amount of sunlight and terrestrial radiation that passes through the atmosphere. The satellite has a narrow field of view, so can image only a small portion of the planet each day. About once per year, CloudSat happens to slice through the eye of an Atlantic hurricane. This happened last month, when Cloudsat caught a remarkable view of Hurricane Bill.


Figure 2. Top: conventional visible satellite image of Super Typhoon Choi-Wan at 3:57 UTC Tuesday, 9/15/09 from Japan's MTSAT. Bottom: cross section through Choi-Wan's eye taken at the same time, from the CloudSat cloud radar instrument. The CloudSat pass occurs along the red line in the top image. The CloudSat pass runs from south (left side of CloudSat image) to north (right side of CloudSat image). At the time of the image, Choi-Wan was strengthening into a Category 4 Super Typhoon (150 mph winds, 928 mb pressure), and reached Category 5 strength fourteen hours after this image was taken. In the CloudSat image, one can see 6+ isolated towers, marking the positions of spiral bands on the south side of the center. The eye is remarkably well-defined, with symmetric "hot towers" extending up to 55,000 feet, sloping outward with height. The thin solid grey line at 5 km marks the 0°C temperature line. Ice particles falling inside the hurricane melt at an altitude just below the 0°C line, creating a "bright band" of orange echoes throughout most of the hurricane. This is one a few inner eye images CloudSat has captured of an Category 4/5 tropical cyclone. Image credit: NASA/Colorado State University/Navy Research Lab, Monterey.

Twenty years ago today
On September 16, 1989, Hurricane Hugo weakened slightly as it underwent an eyewall replacement cycle. The tight inner eyewall that we had flown through the previous day had contracted to the point where it became unstable and collapsed. A new eyewall formed out of an outer spiral band, and Hugo's highest winds dropped to 140 mph--Category 4 strength. As this was occurring, the storm began a more northwesterly path and slowed down, in response to a region of low pressure north of Puerto Rico. By midnight, Hugo was only an hour away from its first encounter with land--the Lesser Antilles island of Guadeloupe.

Back on Barbados, our one undamaged P-3 Orion Hurricane Hunter aircraft flew a mission into Hugo, while the crew of the damaged aircraft remained on the ground. Our plane was grounded until a team of experts from the mainland could fly out and perform a detailed x-ray analysis of the wings to determine if the high g-forces we endured had caused structural damage. This might take a week, so the plan was to fly us back to Miami on a commercial jet. However, Hugo had forced the cancellation of virtually every commercial flight in the eastern Caribbean that day, so we were stuck on the island. Most of us spent a frustrated day touring the island on rented mopeds, getting a look at Hugo from the ground. We got thoroughly drenched by one of Hugo's outermost spiral bands, but the hurricane was too far away to bring any winds more than 20 mph to the island.

That night, our already jangled nerves got a new jolt--a tropical depression had formed due east of Barbados, and was headed right for us. In two days time, it seemed likely that Tropical Storm Iris would be paying us a visit.


Figure 3. AVHRR visible satellite image of Hurricane Hugo taken on September 16, 1989. Image credit: Google Earth rendition of the NOAA HURSAT data base.

Jeff Masters

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Quoting OracleDeAtlantis:
Also, since when do ULL's develop outflow, as the one in the Caribbean is currently doing on the northeast side?



i asked a question something like that yesterday and didn't get a response sooo i can't help u but i am wondering as well.
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I'm no expert at ANY of this, just multi-storm survivor. But all the buoys near the "ULL" in Carib (~P.R.) are dropping. I think it bears watching. JMHO
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Does anyone really care if that little twit puts them on ignore??
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Quoting Patrap:
Choi-Won Floater AVN Color Imagery Loop


thanks!
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Quoting Seastep:


As of right now, it would still be Fred. Per NHC 2pm discussion. Still a L that is the remnants of Fred. No closed circulation, but still a L. If the L is removed, then would be Grace if regeneration occurred.



right
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Quoting BurnedAfterPosting:


based on the NHC definition, if the LLC is no longer intact then it would be a different name; especially if it interacts with something else in order to develop



As of right now, it would still be Fred. Per NHC 2pm discussion. Still a L that is the remnants of Fred. No closed circulation, but still a L. If the L is removed, then would be Grace if regeneration occurred.

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303. MahFL
You can make self updating loops.

Check this one I made. The instructions are on the main page.

Loop

Build your own images
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this has been a very comfprtable september due to all the clouds and rain up here in walton county, florida
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Quoting mossyhead:
i would think it would be fred, now if there was no clouds or rain that would be different. but, i am not the nhc.


based on the NHC definition, if the LLC is no longer intact then it would be a different name; especially if it interacts with something else in order to develop

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So what's the story on the spinning blob in the Caribbean near 69W 16N? Is that a ULL? If so, does it have a chance to extend down to the surface?
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Quoting TheCaneWhisperer:



Very correct but, we all remember this one.

THE NWS RULES GOVERNING THE NAMING OF TROPICAL CYCLONES SPECIFY
THAT...WITHIN A BASIN...WHEN A CYCLONE FORMS FROM THE REMNANT OF A
PREVIOUSLY EXISTING CYCLONE...THE OLD NAME/NUMBER IS RETAINED.
TROPICAL DEPRESSION TWELVE HAS A COMPLEX GENESIS THAT LIKELY
INCLUDES A MID-LEVEL REMNANT OF FORMER TROPICAL DEPRESSION TEN. A
REVIEW OF SATELLITE AND RAWINSONDE DATA OVER THE PAST WEEK OR SO
SUGGESTS THAT A SECOND DISTURBANCE APPROACHED AND COMBINED WITH THE
MID-LEVEL REMNANT OF TROPICAL DEPRESSION TEN ON 20 AUGUST. BECAUSE
IT IS IMPOSSIBLE TO DETERMINE WHICH OF THESE TWO SYSTEMS IS
ASSOCIATED WITH TODAY'S GENESIS...WE HAVE ELECTED TO USE THE
DESIGNATION TWELVE RATHER THAN TEN FOR THE NEW DEPRESSION. THIS
SITUATION DIFFERS FROM LAST YEAR'S REGENERATION OF IVAN...IN WHICH
THE LOW-LEVEL REMNANT OF THAT SYSTEM REMAINED A DISTINCT FEATURE
THAT COULD BE FOLLOWED CONTINUOUSLY UNTIL IT REGENERATED.

FORECASTER STEWART
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Is it just my imagination, or is Freddy beginning to separate his dance with the ULL? It looks like he is moving a little faster, sliding under to the northwest now.

Also, since when do ULL's develop outflow, as the one in the Caribbean is currently doing on the northeast side?

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Quoting BurnedAfterPosting:


only if the circulation itself stayed intact, which isnt happening

at this point I think if whatever is left with Fred mixes with something near the Bahamas it would be Grace, not Fred
i would think it would be fred, now if there was no clouds or rain that would be different. but, i am not the nhc.
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295. MahFL
Ex Fred is blowing up again. Someone call Mayor Nagan !
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Good afternoon all, just popped in for a quick check. Some areas of interest to follow. Tampaspin thank you for your analysis. I can count on you to catch me up quick. Always good to see you on the blog. BBL
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Quoting TampaSpin:
I'm off for now......NO fighting KIDS!
no fighting...in this site? that will be the day!
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Quoting BurnedAfterPosting:
wave that just came off around 7N is really interesting too

yes interesting yet it needs to lift out of the itcz
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I'm off for now......NO fighting KIDS!
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Quoting DocBen:
Wouldn't Fred stay Fred it is is re-born? Then Grace could be either that wave out east or maybe that blob in the eastern Carib?


only if the circulation itself stayed intact, which isnt happening

at this point I think if whatever is left with Fred mixes with something near the Bahamas it would be Grace, not Fred
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wave that just came off around 7N is really interesting too
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Wouldn't Fred stay Fred it is is re-born? Then Grace could be either that wave out east or maybe that blob in the eastern Carib?
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Quoting Hurricane009:
how come everytime i try to go to your blog, it freezes????


Don't know! It does not happen to me. It does take a while to load because of the graphics...i use DSL..
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Quoting iceman55:



African wave starting to get some spin with it
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Quoting CybrTeddy:
It appears StormW was right, if Fred regenerates its not going to do it by itself. Fred's combined with that ULL and lost its SFC circulation, so I think it COULD later on become sub-Tropical Storm Grace.

true but lets see if it happens
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Quoting CybrTeddy:
It appears StormW was right, if Fred regenerates its not going to do it by itself. Fred's combined with that ULL and lost its SFC circulation, so I think it COULD later on become sub-Tropical Storm Grace.


thats possible
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Quoting TampaSpin:


Dang i wish they did, but no they don't!
how come everytime i try to go to your blog, it freezes????
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Quoting BurnedAfterPosting:
TS is very good at this yes, but it seems to me you are only going to listen to people that agree with you most of the time lol

If anyone God forbid disagrees with you, you put them on ignore.

not true i only ingore trolls and maybe sometimes ppl that disagree but not everyone lol
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It appears StormW was right, if Fred regenerates its not going to do it by itself. Fred's combined with that ULL and lost its SFC circulation, so I think it COULD later on become sub-Tropical Storm Grace.
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aoi in boc has some weak 850 vorticity and it has convergence and divergence as well
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TS is very good at this yes, but it seems to me you are only going to listen to people that agree with you most of the time lol

If anyone God forbid disagrees with you, you put them on ignore.
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Quoting TampaSpin:


I guess you need to put me on your ignor list then!

no not u tampaspin ur an expert i trust experts then the non experts in here
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Quoting btwntx08:
aoi in boc looks interesting gonna watch as it heads ne imo


nothing there either, looks just like normal daytime convection flaring up over Mexico that moved over the BOC, its already falling apart
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Quoting Weather456:
does Nasa satellite image loop self update?



Dang i wish they did, but no they don't!
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aoi in boc looks interesting gonna watch as it heads ne imo
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Atlantic Polar Image Composites


Gulf Of Mexico Coverage Area
Imagery From: DMSP SSM/I Microwave Instrument
Surface Winds

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Quoting btwntx08:
oh one thing tropic experts WILL NOT be ingored then non ones will



???????? Scratching my head ????????????????????
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does Nasa satellite image loop self update?

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i see shear to the wnw of the cv wave so am telling u it won't develop in time before it hits it
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Choi-Won Floater AVN Color Imagery Loop
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Today AOI and Tropical Update
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oh one thing tropic experts WILL NOT be ingored then non ones will
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257. TampaSpin 1:47 PM EDT on September 16, 2009
Here is my best thoughts on xFred of redevelpment or not!


Nicely put with some well thought out analysis, and charts to back it up, on probabilities........Thank You.

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Quoting BurnedAfterPosting:


Every single person in here can see how ridiculous that statement is

So let me get this straight, you feel the CV wave has ZERO chance of developing (which is fine), but if anyone disagrees with you or gives you reasons as to why it could develop you are going to ignore them?

Do you realize how childish that sounds?


I think the CV wave might or might not develop depending on the conditions it encounters. If anyone disagrees with me, I'll put them on ignizzle fo shizzle.
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Looks like the BOC convection will be pushed NE ..could affect C-S Fl.
Member Since: September 8, 2008 Posts: 1 Comments: 1083
Quoting TampaSpin:
Here is my best thoughts on xFred of redevelpment or not!

X-Fred is currently on the NW side of an ULL.

It has good Vorticity at 850mb


It has good Divergence caused by the ULL


It lacks much in Convergence which is needed for a developing system. So this must change before xFred will develop futher!


Shear is about to drop to about 10kts to its West but, the ULL could still be a Shear Problem.


Steering should continue to the West with some WSW eventually....as the Bermuda high builds to the West and the trough lifts out.


Summary--xFred is in an area of Dry air also. Until we see some Convergence in the Lower Levels Fred will continue as a open wave. I think xFred has about a 30% chance of redeveloping as it moves toward the West. For those that say xFred is dead may end up eating Crow. I'm not willing to rule out xFred developing or not developing! But, the way things have been this season, something unexpected would be more likely than not!

agreed fred is not DEAD and for the ones say it is u may be eating crow for being wrong
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Quoting btwntx08:
btw cv wave ain't gonna develop and if u give me reasons i'll ingore u not kidding


I guess you need to put me on your ignor list then!
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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.