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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CAROLINAS!!!!!!!!!!
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I agreed some people just won't give up hopes
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Quoting WINDSMURF:
HEY GUYS, HAS ANYBODY HEARD FROM JFV/WEATHERSTUDENT LATELY I HAVE BEEN ON AND OFF ON THE BLOG AND DON'T KNOW IF HE IS STILL AROUND?


He is still around, he was on yesterday afternoon.
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GECKO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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DISTURBANCE AT 7n 26w IS A MATTER OF CONCERN SOMETIME DOWN THE ROAD
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Quoting Hurricane009:
I see we may have our next tropical system in the Carabbean. Anybody else think this???
not convinced yet the convection is all to the east of the low.
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We are beating a dead horse. I have been reading some of these posts and some people just do this every single day. We want Fred to develop so much we ignoring facts here.

The negative factors outweigh the positive factors with Fred and the upper low in the Eastern Caribbean.

ULL transition to a tropical cyclone is an uncommon phenomenon and is not as easy as one think. Give the tropics time.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Floodman:


I wasn't aware that there was a 72 hour rule on ULL conversion


lol. I dunno. I read that above somewhere in a comment. Perhaps I should have quoted it.
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Quoting Hurricane009:
Then why are you talking about not talking about the Fight Club???? lol


haha moving on ;)
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Quoting ParanoidAndroid:
What's the process for a ULL to become a tropical cyclone? What is required and why does it typically take about three days? Obviously, I'm not a meteorologist. Just a long-time weather nerd. Anyone care to educate me a bit?


I wasn't aware that there was a 72 hour rule on ULL conversion
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Quoting seminolesfan:
I'm not speaking of any poster specifically. My point is the ignore feature should be like FIGHT CLUB. You know what the first two rules of FIGHT CLUB are right?


#1 - The first rule of Fight Club is, you do not talk about Fight Club.

#2 - The second rule of Fight Club is, you DO NOT talk about Fight Club.
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What's the process for a ULL to become a tropical cyclone? What is required and why does it typically take about three days? Obviously, I'm not a meteorologist. Just a long-time weather nerd. Anyone care to educate me a bit?
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Quoting btwntx08:
haha real funny just leave that alone lets get back to the tropics here


Actually, we were being very serious, as folks will do from time to time...
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336. jipmg
Quoting iceman55:
exxx- fred go to WSW


upper level winds pushing convection south, its moving west at the surface
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Quoting StormChaser81:


btwntx08


oh ic ic, well I think I'll stay out of this one.

I did have an awesome EAS class today, we covered hurricanes and how they develop, we looked at Katrina, NOLA, etc, and we went over why el nino and la nina play such important roles in our hurricane seasons. We also discussed the Galveston Hurricane of 1900, and how the Cubans said it was going into the Gulf, but the US forecasters called for it to go to the East Coast, it was a very interesting day in class, I enjoyed it very much
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Quoting cirrocumulus:
Does anyone notice the little hurricane spinning up in the Carribbean this afternoon?


yup...we have flash flooding in central and south of the island...we are expecting flood in the capital later this evening...right now kinda stranded in work
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331. skook
deleted.


said enough.
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Quoting seminolesfan:
Link? Sea level pressure generally falls during the afternoon hours. At what rate are they dropping?


Also, how do they compare to yesterday's pressures?
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Quoting tornadodude:


good afternoon all, who are you guys referring to?
I'm not speaking of any poster specifically. My point is the ignore feature should be like FIGHT CLUB. You know what the first two rules of FIGHT CLUB are right?
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Quoting StormChaser81:


Then theyll use it for packing material when it comes out from the shredder.=)


LOL...
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Quoting tornadodude:


good afternoon all, who are you guys referring to?


btwntx08
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Quoting skook:




Im a lurker.. but no lol.. All he does is think everything is gonna develop, he was on the gom bandwagon really big for 2 weeks there.. its actually made me laugh trying to decode what he was trying to say.



Just gotta ignore( just pay no attention) most people, not even talking about trolls, when they make these predictions.. There are alot of good people on here, that I do read their posts.


Well put, skook...
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Quoting synthvol:
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
Link? Sea level pressure generally falls during the afternoon hours. At what rate are they dropping?
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Quoting seminolesfan:
I am of the opinion that any post referencing the ignore feature of the blog comments section is pointless.

Including this one. :)


good afternoon all, who are you guys referring to?
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Quoting Floodman:

Maybe you should send your resume to the NHC


Then theyll use it for packing material when it comes out from the shredder.=)
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Quoting btwntx08:
oh one thing tropic experts WILL NOT be ingored then non ones will


Yeah, but then again YOU will
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Does anyone notice the little hurricane spinning up in the Carribbean this afternoon?
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Quoting SQUAWK:
Does anyone really care if that little twit puts them on ignore??
I am of the opinion that any post referencing the ignore feature of the blog comments section is pointless.

Including this one. :)
Edit:This one referring to mine not the quoted.
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315. skook
Quoting SQUAWK:
Does anyone really care if that little twit puts them on ignore??




Im a lurker.. but no lol.. All he does is think everything is gonna develop, he was on the gom bandwagon really big for 2 weeks there.. its actually made me laugh trying to decode what he was trying to say.



Just gotta ignore( just pay no attention) most people, not even talking about trolls, when they make these predictions.. There are alot of good people on here, that I do read their posts.
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Quoting btwntx08:
2 pm two is out still two yellow just like i expect it

Maybe you should send your resume to the NHC
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Quoting synthvol:
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
'


Sure has plenty of time to make the transition. It usually takes 3 days and is a rather vigorous circulation.
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Rosenstiel has an ad in EOS for a Post Doc position in MJO - ENSO interaction ... etc. You more mature(!) students can check it out at EOS Vol. 90, No. 36, p.319 (8 Sept. 2009).
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Quoting SQUAWK:
Does anyone really care if that little twit puts them on ignore??


No not really lol, just found it laughable that he would ignore someone just because they disagreed with him. Tells me that he should be asking more questions than he does lol
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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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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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