CSU predicts a very active hurricane season: 16 storms, 9 hurricanes

By: Dr. Jeff Masters , 4:30 PM GMT on June 01, 2011

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A very active Atlantic hurricane season is on tap for 2011, according to the seasonal hurricane forecast issued June 1 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 16 named storms, 9 hurricanes, and 5 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 166% of average. Between 1950 - 2000, the average season had 10 named storms, 6 hurricanes, and 2 intense hurricanes. But since 1995, the beginning of an active hurricane period in the Atlantic, we've averaged 14 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is identical to their April forecast. The forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (48% chance, 31% chance is average) and the Gulf Coast (47% chance, 30% chance is average). The risk of a major hurricane in the Caribbean is also high, at 61% (42% is average.)

The forecasters cited four main reasons for an active season:

1) Neutral to weak La Niña conditions are expected during the most active portion of this year's hurricane season (August-October). This should lead to average to below average levels of vertical wind shear.

2) Above average May sea surface temperatures in the tropical Atlantic.

3) Below average surface pressures during May in the tropical Atlantic.

4) We are in the midst of a multi-decadal era of major hurricane activity, which began in 1995. Major hurricanes cause 80-85 percent of normalized hurricane damage.

Analogue years
The CSU team picked five previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: neutral to weak La Niña conditions in the equatorial Eastern Pacific, and above-average tropical Atlantic and far north Atlantic SSTs during April - May. Those five years were 2008, which featured Hurricane Ike and Hurricane Gustav; 1996, which had two hurricanes that hit North Carolina, Fran and Bertha; 1989, which featured Category 5 Hurricane Hugo; 1981, a very average year with 12 named storms, 7 hurricanes, and 3 intense hurricanes; and 1951, a year that featured 6 major hurricanes. The mean activity for these five years was 12 named storms, 8 hurricanes, and 4 intense hurricanes.

How accurate are the June forecasts?
The June forecasts by the CSU team between 1998 and 2009 had a skill 19% - 30% higher than a "no-skill" climatology forecast for number of named storms, number of hurricanes, and the ACE index (Figure 1). This is a decent amount of skill for a seasonal forecast, and these June forecasts can be useful to businesses such as the insurance industry and oil and gas industry that need to make bets on how active the coming hurricane season will be. Unfortunately, the CSU June 1 forecasts do poorly at forecasting the number of major hurricanes (only 3% skill), and major hurricanes cause 80% - 85% of all hurricane damage (normalized to current population and wealth levels.) This year's June forecast uses a brand new formula never tried before, so there is no way to evaluate its performance. An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.41 to 0.62 for their June forecasts made between 1984 and 2010, which is respectable.


Figure 1. Comparison of the percent improvement over climatology for May and August seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 1999-2009 (May) and 1998-2009 (August), using the Mean Squared Error. Image credit: Verification of 12 years of NOAA seasonal hurricane forecasts, National Hurricane Center.


Figure 2. Comparison of the percent improvement in mean square error over climatology for seasonal hurricane forecasts for the Atlantic from NOAA, CSU and TSR from 2001-2010, using the Mean Square Skill Score (MSSS). The figure shows the results using two different climatologies: a fixed 50-year (1950 - 1999) climatology, and a 2001 - 2010 climatology. Skill is poor for forecasts issued in December and April, moderate for June forecasts, and good for August forecasts. Image credit: Tropical Storm Risk, Inc.

TSR predicts 25% more activity than normal
Expect the Atlantic hurricane season to be about 25% more active than usual, the British private forecasting firm Tropical Storm Risk, Inc. (TSR) said in their pre-season forecast issued on May 24. TSR calls for 14.2 named storms, 7.6 hurricanes, 3.6 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 124, which is 22% above average. Their May 24 forecast numbers are very close to their previous forecast issued in April. TSR predicts a moderate 55% chance that activity will rank in the top 1/3 of years historically, and a 59% chance that U.S. landfalling activity will be above average. TSR rates their skill level as 16-25% higher than a "no-skill" forecast made using climatology, though an independent assessment by the National Hurricane Center (Figure 1) gives them somewhat lower skill numbers.

TSR projects that 4.4 named storms will hit the U.S., with 1.9 of these being hurricanes. The averages from the 1950-2010 climatology are 3.1 named storms and 1.5 hurricanes. They rate their skill at making these June forecasts for U.S. landfalls at 7 - 11% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.3 named storms, 0.6 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their forecast of an active season:

1) Their model predicts that sea surface temperatures will be 0.11°C warmer than average in August and September over the Main Development Region (MDR) for Atlantic hurricanes. They define this as the area between 10°N and 20°N, between the coast of Africa and Lesser Antilles Islands (20°W and 60°W). It is called the Main Development Region because virtually all African waves originate in this region. These African waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.)

2) Their model predicts slower than normal trade winds in August and September over the Main Development Region (MDR). Trade winds are forecast to be 0.19 meters per second (about 0.4 mph) slower than average. This would create more spin for developing storms, and allow the oceans to warm up, due to reduced mixing of cold water from the depths and lower evaporational cooling.

FSU predicts a very active hurricane season: 17 named storms
The Florida State University (FSU) Center for Ocean-Atmospheric Prediction Studies (COAPS) issued their third annual Atlantic hurricane season forecast today. This year's forecast calls for a 70% probability of 14-20 named storms and 8-10 hurricanes. The mean forecast is for 17 named storms, 9 hurricanes, and an accumulated cyclone energy (ACE) of 163. They cite warm tropical North Atlantic sea surface temperatures, a weakening of La Niña conditions, and the ongoing positive phase of the Atlantic Multi-decadal Oscillation as the major factors influencing their forecast.

Other seasonal forecasts
The UK Met Office's Glosea4 model is predicting a moderately more active season than normal, with 13 named storms and a ACE index of 151. The Cuba Institute of Meteorology is calling for 13 named storms and 7 hurricanes. NOAA predicts 15 named storms, 8 hurricanes, and 4.5 intense hurricanes. Pennsylvania State University predicts 16 named storms.

A surprise tropical disturbance for Florida
The Atlantic hurricane season is officially underway, and Mother Nature appears to be taking her cue from the calendar, as we have a surprise storm off the coast of Florida that is a threat to develop into a tropical depression later this week, after it crosses Florida into the Gulf of Mexico. An cluster of thunderstorms called a Mesoscale Convective System (MCS) pushed across southern New England early yesterday, emerged over the ocean, and rotated clockwise towards Florida, steered by a large high pressure system centered over Kentucky. The center of the disturbance stayed over the warm waters of the Gulf Stream, a region of low pressure developed, and intense thunderstorms began to build yesterday afternoon. Early this morning, the National Hurricane Center (NHC) designated the disturbance Invest 93L, and gave it a 10% chance of developing into a tropical depression. At 8am EDT, they upped those chances to 30%. Invest 93L is becoming increasingly organized, with Melbourne, Florida radar showing the beginnings of some rotation, with a solid band of heavy rain on the southwest side of the disturbance. The pressure and winds have leveled out at Buoy 41012, 40 nm ENE of St. Augustine, Florida. Winds peaked at 19 mph, gusting to 22 mph, at 10:50am EDT. Satellite imagery shows a small but intensifying region of thunderstorms. Sea surface temperatures (SSTs) are about 26°C (79°F) off the east coast of Florida, which is just warm enough to support formation of a tropical depression, and about 0.5°C above average. Wind shear is a low 5 - 10 knots, and it is likely that 93L will continue intensifying until it makes landfall over Central Florida this afternoon. A 50-mile wide swath of Florida from Daytona Beach to just north of Tampa can expect 1 - 3 inches of rain from 93L as it tracks over the state this afternoon and tonight. A Windsat pass this morning did not show a closed circulation, and I doubt 93L has enough time to develop into a tropical depression before landfall in Florida. The coast between Daytona Beach and Cocoa Beach could see wind gusts of 25 - 35 mph this afternoon, though.


Figure 3. Afternoon radar image of 93L from the Melbourne, Florida radar.

Fate of 93L once in the Gulf of Mexico
Since 93L is expected to continue its rapid west-southwest motion at 15 - 20 mph through Thursday, it will cross the Florida Peninsula in about 12 hours and emerge over the Gulf of Mexico early Thursday morning. It is possible that the passage over Florida will greatly disrupt 93L, since it is such a small system. I give a 40% chance that the storm will see its peak strength this afternoon, and not significantly regenerate over the Gulf of Mexico. However, the latest SHIPS model forecast predicts that wind shear will remain low to moderate, 5 - 15 knots, as 93L moves westwards over the Gulf of Mexico Thursday and Friday. SSTs in the Gulf are about 27°C (81°F), 0.5 - 1.0°C above average, and it is possible that 93L could gain enough strength to become Tropical Depression One as it crosses the Gulf. Since 93L will be moving parallel to the coast a short distance offshore, it is difficult to predict where the storm might make a second landfall, since a slight change in heading will make a large difference in landfall location. I don't expect widespread heavy rains from 93L along the Gulf Coast, since the storm is so small, but some locations close to the coast could receive 2 - 4 inches as 93L brushes by. Heavier rains are possible at the eventual landfall location. Since 93L is so small, the computer models are having trouble seeing the system, and are not very helpful forecasting the behavior of the storm over the Gulf of Mexico. The Hurricane Hunters are on call to fly into 93L Thursday afternoon at 2pm EDT, if necessary.

Central Caribbean disturbance
Moisture and heavy thunderstorm activity continues to slowly increase in the region between Central America and Jamaica, and wind shear is falling. With wind shear now 20 - 30 knots, we can expect this disturbance to show increased organization today, and recent satellite images show the beginnings of a surface circulation trying to get going about 100 miles off the coast of Northeast Nicaragua. All of the computer models predict that an area of low pressure will form in this region by Thursday, and this low will have the potential to develop into a tropical depression late this week or early next week. A surge of moisture accompanying a tropical wave currently south of Hispaniola may aid development when the wave arrives in the Western Caribbean on Thursday. Water temperatures in the Central Caribbean are about 1°C above average, 29°C, which is plenty warm enough to support development of a tropical storm. Residents of Jamaica, Cuba, the Cayman Islands, Haiti, Honduras, and Nicaragua should anticipate the possibility that heavy rains of 2 - 4 inches may affect them Thursday through Saturday this week.


Figure 4. Satellite image of the Central Caribbean disturbance.

Catch my intro to the 2011 hurricane season on Internet radio
I'll be discussing the coming hurricane season on our Internet radio show, the Daily Downpour, tomorrow (Thursday) at 4:30pm EDT. Fellow wunderground meteorologists Shaun Tanner and Tim Roche will be hosting the show. We'll talk about the latest model runs, hurricane research, modeling accuracy, and hurricane climatology, and answer any questions listeners email in or call in. The email address to ask questions is broadcast@wunderground.com. Welcome to the hurricane season of 2011!

Jeff Masters

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Quoting caneswatch:


I have some 650 miles away and some 1400 miles away. I'd rather go with the ones that are 1400 miles away LOL
When a hurricane usually makes landfall up here it's all gloomy.But I'd rather have that then the real thing.
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1243. aquak9
washingtonian- I knew it was a fake Keeper right away- the real Keeper would NEVER wear lavender.
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Quoting aquak9:
thanks, ya'll. We met thru WU, and the rest is weather history.

And it IS really nice to see some old members showing back up.


Still can't find that place on the member blogs where their age is! How do you do that? ;)

p.s. Happy anniversary. :)
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Congrats Aquak9! I've not been around since last season. Just started frequenting again this week.
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Quoting washingtonian115:
Better safe than sorry.If any reletive has to evacuate they can always come up to my house.It's a safe eh...700-900 miles from where they live.


I have some 650 miles away and some 1400 miles away. I'd rather go with the ones that are 1400 miles away LOL
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1239. trey33
Quoting Dakster:
Starting out rather early in the season I see... Thankfully this looks like a rainmaker more than anything else for Florida. Hopefully it is nothing more for the other side of the GOM, wherever it may go.


We so needed it though. It it the first day in months my a/c has been able to take a break. The rain in Tampa was certainly welcomed, but apparently everyone forgot how to drive in it.
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Quoting KEEPEROFTHEGATE:
replaced with empty space just like whats in his head
Oh I just love this say'in!.I think you should make a shirt of it!!.
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1237. bwi
Good evening, back for the start of the season. Was in Bonaire last week on vacation -- trade winds much lighter than when we visited last year, and water a nice warm 82 degrees F. As usual, I won't post much except the occasional surface observation or buoy reading, but looking forward to insights from all the great tropical weather watchers on here this season.
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Quoting KEEPEROFTHEGATE:
replaced with empty space just like whats in his head


Thank you to the real Keeper!
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Quoting caneswatch:


That's my plan if it stays a Category 3 or below LOL


I have the luxury of rarely having the opportunity of seeing a full-fledged Category 4 or 5 hurricane in my neck of the woods. I'm like 70 miles inland.
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1234. aquak9
thanks, ya'll. We met thru WU, and the rest is weather history.

And it IS really nice to see some old members showing back up.
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By the way -- hello everyone -- Happy Anniversary Aquak
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Quoting caneswatch:


That's my plan if it stays a Category 3 or below LOL


Similar to mine but I'm thinking Cat 2 or lower.
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1231. KEEPEROFTHEGATE (Mod)
Quoting galvestonhurricane:
What happened to the fake Keeper of the Gate?
replaced with empty space just like whats in his head
Member Since: July 15, 2006 Posts: 170 Comments: 53536
Quoting Thundercloud01221991:
Did anyone see this?


STORM 2... BINGER-EL RENO-PIEDMONT-GUTHRIE

PRELIMINARY DATA...
EVENT DATE: MAY 24, 2011
EVENT TYPE: TORNADO
EF RATING: EF-5
ESTIMATED PEAK WINDS (MPH): GREATER THAN 210 MPH
INJURIES/FATALITIES: UNKNOWN/9
EVENT START LOCATION AND TIME: 8 WNW BINGER 3:30 PM CDT
EVENT END LOCATION AND TIME: 4 NE GUTHRIE 5:35 PM CDT
DAMAGE PATH LENGTH (IN MILES): 75 MILES
DAMAGE WIDTH: UNKNOWN
NOTE: RATING BASED ON UNIVERSITY OF OKLAHOMA MOBILE DOPPLER RADAR
MEASUREMENTS.

from the Oklahoma outbreak last week


Aye, it's from the DOW truck
Member Since: May 27, 2009 Posts: 0 Comments: 4438
We appear to be stuck in the cloud free area between North Florida and Southern Cuba. Would certainly like a day full of rain here. Getting tired of filling up the swimming pool.

The breeze from the pressure between the systems is very nice though.
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Quoting Grothar:


You know my family Canes! I think I would be safer in a hurricane.


Oh boy LOL. I gotta stay if there's nothing else I can do LOL
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Quoting fatlady99:

Congrats to you both. Wasn't Mother Nature nice to give you a low for your anniversary!
I wish my hubby was a weather freak...instead he's into all that sports,car...stuff.
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Quoting fatlady99:

Congrats to you both. Wasn't Mother Nature nice to give you storm for your anniversary!


Edit: sorry,.... multitasking again..
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Quoting presslord:


Happy anniversary...


Seconded.
Member Since: July 23, 2010 Posts: 1 Comments: 12414
Did anyone see this?


STORM 2... BINGER-EL RENO-PIEDMONT-GUTHRIE

PRELIMINARY DATA...
EVENT DATE: MAY 24, 2011
EVENT TYPE: TORNADO
EF RATING: EF-5
ESTIMATED PEAK WINDS (MPH): GREATER THAN 210 MPH
INJURIES/FATALITIES: UNKNOWN/9
EVENT START LOCATION AND TIME: 8 WNW BINGER 3:30 PM CDT
EVENT END LOCATION AND TIME: 4 NE GUTHRIE 5:35 PM CDT
DAMAGE PATH LENGTH (IN MILES): 75 MILES
DAMAGE WIDTH: UNKNOWN
NOTE: RATING BASED ON UNIVERSITY OF OKLAHOMA MOBILE DOPPLER RADAR
MEASUREMENTS.

from the Oklahoma outbreak last week
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1223. Grothar
Quoting caneswatch:


I do have one. It's called "In case of major hurricane, drive north to your family 5 days before the storm arrives."


You know my family Canes! I think I would be safer in a hurricane.
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What happened to the fake Keeper of the Gate who always flooded the forum and the tropics/weather chat?
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Quoting aquak9:
Dakster!! a pleasure, my friend.

And I'd like to say "Happy Anniversary" to my hubby, Rainman32. Yes we got married on June 1st, appropriately. That'd be RainmanWeather to most of you folks.

I am SO LUCKY to be married to a weather freak.

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Quoting aquak9:
Dakster!! a pleasure, my friend.

And I'd like to say "Happy Anniversary" to my hubby, Rainman32. Yes we got married on June 1st, appropriately. That'd be RainmanWeather to most of you folks.

I am SO LUCKY to be married to a weather freak.



Awesome! Congrats!
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Quoting KoritheMan:


I have one also. It's called "stay here, film the storm, and later upload to YouTube". ;)


That's my plan if it stays a Category 3 or below LOL
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Quoting Grothar:


We have to keep the idle banter down during the busy season. All of that nonsense should be reserved for the WU mail.


Don't know any other kind. :(
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Quoting presslord:
Aqua...I'm feeling ignored....it hurts...


Pishaw, read back....:)
Member Since: July 23, 2010 Posts: 1 Comments: 12414
1216. aquak9
"Deep down inside, I gotta heart of steel..." -Galactic

hi press. Someone's gonna get whacked this year.

One weak Cat3 making full landfall. A skirt from a Cat5. A Cat3-4 raising a ruckus in the carib. Three TS's causing flooding, two in the gulf, one on the east coast.
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Well we will have to wait and see.
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Quoting Grothar:


I'll just let sleeping dogs lie.


LOL! get that lip down, mister. no bones for you!
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Quoting aquak9:
Dakster!! a pleasure, my friend.

And I'd like to say "Happy Anniversary" to my hubby, Rainman32. Yes we got married on June 1st, appropriately. That'd be RainmanWeather to most of you folks.

I am SO LUCKY to be married to a weather freak.



Congrats, Aqua! Many happy returns. :)
Member Since: July 23, 2010 Posts: 1 Comments: 12414
1212. Grothar
Quoting ElConando:
To the multiple people who posted a responce to me, thanks, I thought I was going insane for a second lol.



It is when you start talk to yourself that you are in trouble. At least that is what I tell myself.
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StormW now on the Show

wrbn on livestream.com. Broadcast Live Free
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To the multiple people who posted a responce to me, thanks, I thought I was going insane for a second lol.
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1205. Grothar
Quoting fatlady99:


Hey Grothar! My banter is never idle.. :)


I'll just let sleeping dogs lie.
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10-4-1
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Aqua...I'm feeling ignored....it hurts...
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1201. aquak9
Dakster!! a pleasure, my friend.

And I'd like to say "Happy Anniversary" to my hubby, Rainman32. Yes we got married on June 1st, appropriately. That'd be RainmanWeather to most of you folks.

I am SO LUCKY to be married to a weather freak.

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1200. Grothar
Quoting Bitmap7:


The new atmospheric analysis shows that there is some amount o stacking going on in the region as well.


Yes, you are right.

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Quoting caneswatch:


I do have one. It's called "In case of major hurricane, drive north to your family 5 days before the storm arrives."


I have one also. It's called "stay here, film the storm, and later upload to YouTube". ;)
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Quoting caneswatch:


I do have one. It's called "In case of major hurricane, drive north to your family 5 days before the storm arrives."
Better safe than sorry.If any reletive has to evacuate they can always come up to my house.It's a safe eh...700-900 miles from where they live.
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Did 93L develop into a big bow echo or something...
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting Grothar:


Just can't follow the rules, can you?? tsk tsk. How is the weather by you?


Good. Almost took a nap out on the patio earlier. How is it by you?
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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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