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 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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Quoting btwntx08:
btw cv wave ain't gonna develop and if u give me reasons i'll ingore u not kidding


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?
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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!
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If anyone is interested

http://www.jma.go.jp/en/typh/typh5.html
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Quoting BurnedAfterPosting:


There is NO LLC with Ex Fred anymore, you can ask anyone, NO LLC



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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Quoting ElConando:
kinda concerned about the ULL luckily there is a small area of high wind shear in its way before it enters the sauna of the W carrbiean.
The NAM still keeps exFred around.
Member Since: September 27, 2007 Posts: 1 Comments: 20520
Quoting Patrap:


I think the other models were scared off.



That eye is just so... eyemasing.
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Quoting WaterWitch11:
Hey guys,

StormW, Patrap, Weather456 or anyone else. Why is the computer models for Choi Wan gone. GFS is only one there, but its null.


I think the other models were scared off.

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kinda concerned about the ULL luckily there is a small area of high wind shear in its way before it enters the sauna of the W carrbiean.
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Quoting btwntx08:
tampaspin i agree and bap i don't agree and u don't know what ur talking about my posts make sense i see what i see and idk about u though


There is NO LLC with Ex Fred anymore, you can ask anyone, NO LLC
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Quoting TampaTom:


Let's just hope October isn't the September we never had!


Lol.......Actually I think a lot of folks were spoiled by the 2005 season (a complete anomoly in terms of numbers but devastating in terms of Katrina) and numbers have been "dropping" so to speak since then.........But, we have been very lucky this season with two major canes (typical for even a low number year) which stayed away from land.......Had Bill gone west and made landfall, we would be praying for no more storms right now.
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229. TampaSpin 1:19 PM
So everyone knows to help others! I have showed in the graphic below what is the ULL and what is xFred!


THANK YOU!!!!
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Quoting Hurricane009:
good afternoon. home from school, got early release today...yes lol


Aren't you lucky? LOL Anyways, do you mind getting on Tropics Chat?
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Quoting btwntx08:
fred is letting go of the ull imo


Probably a WSW track will also be coming with xFred
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231. you need to give up, you are making comments that make no sense just to try and justify that Fred hasnt fallen apart

the circulation is gone, bye bye, see you later, it is now an open wave and nothing more and the chances of development are very very slim at this time and diminishing
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202: Next time you post somehting like tha note it as a ULL...I almost fell out of my chair...LOL
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Quoting RitaEvac:
Curious as to what the ULL does once it gets past Jamaica,
My sentiments exactly.
Member Since: September 27, 2007 Posts: 1 Comments: 20520
So everyone knows to help others! I have showed in the graphic below what is the ULL and what is xFred!



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Even though its not over, it has been a dud, Having nothing in the Carribbean all season is something I've never seen especially this late into the season
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227. JLPR
Quoting leftovers:
i know some of you all have an attachment to fred but have you looked on the visiable? fred is dead have a nice day


yep



LLC is mostly gone
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Quoting weathermanwannabe:


Yup; swirl city out there right now and plenty of blobs to keep an eye on......Reminds me of the August we never had :)


Let's just hope October isn't the September we never had!
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Curious as to what the ULL does once it gets past Jamaica,
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Evening everyone! Can anybody put in lamens terms what effect TUTT has on tropical systems? I just need a little help understanding the actual definition. Thanks!!
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Hey guys,

StormW, Patrap, Weather456 or anyone else. Why is the computer models for Choi Wan gone. GFS is only one there, but its null.
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King Tutt..
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Quoting Patrap:
Morning all..Sept is the Active Time.

Lots of potential,no threats yet though.

Swirls from Africa to the ArkLaTex..


Yup; swirl city out there right now and plenty of blobs to keep an eye on......Reminds me of the August we never had :)
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Looking at the IR on Choi-wan, it looks like it is going to the left of the forecast track anyone else have any thoughts on that?
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Perfect conceptual model of the Tropical Upper Tropospheric Trough (TUTT) and Fred is right in the middle.

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Quoting Floodman:


I would have to agree; the other thing is that when a system decides to drop to the surface it does it fairly quickly
And the BOC has some convection brewing.
Member Since: September 27, 2007 Posts: 1 Comments: 20520
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Quoting hydrus:
Ya know what Floodman, when that upper low (or whatever it is) gets in to the Western Caribbean Sea, that water is so warm, it could hit the surface and we could have a rapid forming storm..JMO...If the shear stays low.


I would have to agree; the other thing is that when a system decides to drop to the surface it does it fairly quickly
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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.