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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Niether will the mass of to the East I say, assuming the two share the same humidity
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He is also embedded within a very dry airmass, and his surface circulation is gone. I highly doubt he will regenerate.
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Thanks KoritheMan,

That puts Fred in 25 knot wind shear, increasing. Things don't look too good!


He is on course for lighter wind shear, but size will be the main factor in Fred's potential death. If so, R.I.A. FRED 9/7/09 3p.m. GMT to 9/19/09.

He was such a good hurricane, his potential ruined by the evil wind shear *SNIFF* *SNIFF*

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Quoting F5Tornado:
Hi all!

Do any of you guys know the location of Poor Tropical Invest Fred? I would like to track his wind shear.

,Thanks
ZKN


I'd say around 22N 63W. That conclusion of course, is made only after taking a brief look at a stilled satellite image -- I can certainly do much better at pinpointing centers in tropical disturbances, but not when it's 3 in the morning. >_>
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Hi all!

Do any of you guys know the location of Poor Tropical Invest Fred? I would like to track his wind shear.

,Thanks
ZKN
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1255. HadesGodWyvern (Mod)
Tropical Cyclone Warning Center Perth
TROPICAL CYCLONE OUTLOOK
Forecast for area south of 10S between 90E-110E
12:15 PM WST September 17 2009
=====================================
A Tropical Low near 5.5S 94.7E is expected to move slowly southwest over the next few days, but not move into the area.

Tropical Cyclone Formation Potential
======================================
Friday: Low
Saturday: Low
Sunday: Low

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1253. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Advisory #41
TYPHOON CHOI-WAN (T0914)
15:00 PM JST September 17 2009
=========================================

SUBJECT: Category Four Typhoon near Ogasawara Shoto

At 6:00 AM UTC, Typhoon Choi-wan (935 hPa) located at 21.0N 140.3E has 10 minute sustained winds of 95 knots with gusts of 135 knots. The typhoon is reported as moving northwest at 9 knots

RSMC Dvorak Intensity: T6.0

Storm-Force Winds
=================
120 NM from the center

Gale-Force Winds
================
270 NM from the center

Forecast and Intensity
=======================
24 HRS: 24.1N 138.8E - 95 knots (CAT 4/Very Strong Typhoon)
48 HRS: 29.2N 141.4E - 95 knots (CAT 4/Very Strong Typhoon)
72 HRS: 36.0N 147.6E - 85 knots (CAT 4/Very Strong Typhoon)
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Yep, its quiet in the tropics this early morning. Got catch some sleep, I'll check back tomorrow.
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1251. JLPR
Not much left of either Ex-Fred or the wave





and now off to bed :)
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Iceman55, are there any models that forecast it to regenerate? I was looking at 200 mb level winds and see a lot of shearing upper westerlies from that upper trough offshore from the U.S., even near the Bahamas. I just wonder how the models show the upper atmosphere evolution over the next couple of days?
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Thanks for the info, iceman55. By the way, what do you think about ex-Fred? Do you think it has even a slight chance of redeveloping?
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Quoting iceman55:
Bobbyweather what pic

post 1229
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Good night all! Almost 2 am here in galveston got mom duty in 3 hrs check with ya'll later today to see if we have any development or re-development
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Quoting iceman55:

Hi iceman55. What does the blue circles it this picture mean?
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.
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just curious to other opinions
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In my opinion, I don't think that the eastern Caribbean blob could join with the remnants of Fred. The eastern Caribbean blob is thunderstorms produced by divergence from an upper level low, that upper low is tracking westward and so will the storms that are produced by it. Ex-Fred seems it will pass too far north to have any interaction with that upper low.
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My take on Ex-Fred:

Right now, the shear is low while located among deep-layered easterly winds north of the upper low its entangled with, but Fred has not been able to produce persistent organized convection (maybe from dry air around it), and thus has lost its closed circulation (was downgraded to a surface trough today in the TAFB analysis on the NHC website). It looks like its got no more than one day to regenerate into anything, after that there seem to be a lot of upper westerly winds that will tear it apart as it nears the Bahamas.

Unless the major upper trough just offshore from the United States does not lift out, Fred's done for. I wonder how the models that do forecast regeneration handle the trough (I don't see signs of it lifting out now).
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what is the possiblity of the remnants of Fred and the blob west of the antilles joining together before the bahamas
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Im kidding about the aggrevation part
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to confusing to keep up with all of the chat sites a little safer to stay here and aggrevate these guys
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
Sorry true to wunderground
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Quoting iceman55:




I can see Choi-Wan very clearly in that picture.
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Quoting texascoastres:
hmm that leaves no one but me! Ok i did it! I killed the blog!



no one in particular but was an observations I made that even when the tropics are quiet we get a constant reminder.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
thanks Bobbyweather
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Let's go to tropics chat, everyone
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Quoting texascoastres:
hmm that leaves no one but me! Ok i did it! I killed the blog!

No you didn;t
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hmm that leaves no one but me! Ok i did it! I killed the blog!
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From Dr. Masters blog:
"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."
Let's wait for at least 2~3 days.
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Quoting Bobbyweather:
umm.....did i kill the blog?



no
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting btwntx08:

oops thanks for the heads up but he's wrong on the conditions he's in 10 kts of shear thats favorable idk y avila thinks its not

Maybe because the conditions are not favorable. There's more than shear for cyclogenesis.
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I am a little concerned it will redevelop in the bahamas or carribean
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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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