Average hurricane season foreseen by CSU, NOAA, and TSR

By: Dr. Jeff Masters , 4:45 PM GMT on June 02, 2009

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A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued June 2 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 11 named storms, 5 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 88% 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 15 named storms, 8 hurricanes, and 4 intense hurricanes per year. The new forecast is a step down from their April forecast, which called for 12 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast calls for a near-average chance of a major hurricane hitting the U.S., both along the East Coast (28% chance, 31% chance is average) and the Gulf Coast (28% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane.

The forecasters cited several reasons for an average season:

1) Sea surface temperature (SST) anomalies in the tropical Atlantic are quite cool. In fact, these SST anomalies are at their coolest level since July 1994. Cooler-than-normal waters provide less heat energy for developing hurricanes. In addition, an anomalously cool tropical Atlantic is typically associated with higher sea level pressure values and stronger-than-normal trade winds, indicating a more stable atmosphere with increased levels of vertical wind shear detrimental for hurricanes. Substantial cooling began in November 2008 (Figure 1), primarily due to a stronger than average Bermuda-Azores High that drove strong trade winds. These strong winds increased the mixing of cool waters to the surface from below, and caused increased evaporational cooling.

2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. This occurs because El Niño conditions bring higher wind shear over the tropical Atlantic. The CSU team expects the current neutral conditions may transition to El Niño conditions (70% chance) by this year's hurricane season. I discussed the possibility of a El Niño conditions developing this year in a blog posted Friday.


Figure 1. Change in Sea Surface Temperature anomaly between November 2008 and 2009. Most of the Atlantic has cooled significantly, relative to normal, over the past 7 months. Image credit: NOAA/ESRL.

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 slightly warm ENSO conditions, slightly below-average tropical Atlantic SSTs, and above-average far North Atlantic SSTs during April-May. Those five years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 2001, featuring Category 4 storms Michelle, which hit Cuba, and Iris, which hit Belize; 1965, which had Category 3 Betsy that hit New Orleans; 1960, which had two Category 5 hurricanes, Ethyl and Donna; and 1959, which had Category 3 Hurricane Gracie, which hit South Carolina. The mean activity for these five years was 10 named storms, 6 hurricanes, and 2 intense hurricanes, almost the same as the 2009 CSU forecast.

How accurate are the June forecasts?
The June forecasts by the CSU team have historically offered a skill of 20 - 30% higher than a "no-skill" forecast using climatology (Figure 2). 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. This year's June forecast uses the same formula as last year's June forecast, which did quite well predicting the 2008 hurricane season (prediction: 15 named storms, 8 hurricanes, 4 intense hurricanes; observed: 16 named storms, 8 hurricanes, 5 intense hurricanes). An Excel spreadsheet of their forecast skill (expressed as a mathematical correlation coefficient) show values from 0.44 to 0.58 for their June forecasts, which is respectable.


Figure 2. Accuracy of long-range forecasts of Atlantic hurricane season activity performed at Colorado State University (CSU) by Dr. Bill Gray's team (colored squares) and Tropical Storm Risk, Inc. (TSR, colored lines). The skill is measured by the Mean Square Skill Score (MSSS), which looks at the error and squares it, then compares the percent improvement the forecast has over a climatological forecast of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TS=Tropical Storms, H=Hurricanes, IH=Intense Hurricanes, ACE=Accumulated Cyclone Energy, NTC=Net Tropical Cyclone Activity. Image credit: TSR.

NOAA's 2009 hurricane season forecast
The National Oceanic and Atmospheric Administration (NOAA), issued its 2009 Atlantic hurricane season forecast on May 21. NOAA anticipates that an average season it most likely, giving a 50% chance of a near-normal season, 25% chance of an above-normal season, and a 25% chance of a below-normal season. They give a 70% chance that there will be 9 - 14 named storms, 4 - 7 hurricanes, 1 - 3 major hurricanes, and an Accumulated Cyclone Energy (ACE) in the 65% - 130% of normal range. The forecasters cited the following main factors that will influence the coming season:

1) We are in an active period of hurricane activity that began in 1995, thanks to a natural decades-long cycle in hurricane activity called the Atlantic Multidecadal Oscillation (AMO).

2) There will either be an El Niño event or neutral conditions in the Equatorial Eastern Pacific. An El Niño event should act to reduce Atlantic hurricane activity. However, our skill at predicting an Niño in late May/early June is poor, so there is high uncertainty about how active the coming hurricane season will be.

3) Cooler-than-average SSTs are currently present in the eastern tropical Atlantic. These cool SSTs are forecast to persist through into August-September-October (ASO). ASO SSTs in the eastern tropical Atlantic have not been below average since 1997. Cooler SSTs in that region are typically associated with a reduction in Atlantic hurricane activity.

Thus, they expect that even though we are in an active hurricane period, the presence of an El Niño or cool SSTs in the eastern Atlantic could easily suppress activity, making a near-average season the most likely possibility. They note that two promising computer models, the NOAA CFS model and the European Center for Medium-Range Weather Forecasts (ECMWF) Global Climate Model System 3, both forecast the possibility of a below-average hurricane season.

2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) has joined the ranks of NOAA and Colorado State University in calling for near-average activity. The latest TSR forecast issued June 4 calls for 10.9 named storms, 5.2 hurricanes, 2.2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 72% of average. The storm numbers are close to the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes, and are sharp reduction from their April forecast of 15 named storms, 7.8 hurricanes, and 3.6 intense hurricanes. TSR predicts a 50% chance that this season will be in the bottom 1/3 of years historically, and a 40% chance that U.S. landfalling activity will be in the lowest 1/3 of years historically. TSR gives a 32% chance of a near-normal season, and a 17% chance of a below normal season. TSR rates their skill level as 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.2 named storms will hit the U.S., with 1.3 of these being hurricanes. The averages from the 1950-2008 climatology are 3.2 named storms and 1.5 hurricanes. Their skill in making these April forecasts for U.S. landfalls is 7 - 18% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 0.9 named storms, 0.4 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites two main factors for their reduced forecast: a large and unexpected cooling of sea surface temperatures in the tropical Atlantic, and warmer SSTs in the Equatorial Eastern Pacific (which might lead to an El Niño event that will bring high wind shear to the Atlantic). TSR expects faster than than normal trade winds from July - September over the Main Development Region (MDR) for hurricanes over the Atlantic (the region between 10° - 20° N from Central America to Africa, including all of the Caribbean). Trade winds are forecast to be 0.83 meters per second (about 1.7 mph) faster than average in this region, which would create less spin for developing storms, and allow the oceans to cool down, due to increased mixing of cold water from the depths and enhanced evaporational cooling. TSR forecasts that SSTs will cool an additional 0.3°C compared to average over the MDR during hurricane season.

Air France crash
The Air France Flight 447 A330 aircraft that disappeared over the mid-Atlantic Ocean yesterday definitely crossed through a thunderstorm complex near the Equator, according to a detailed meteorological analysis by Tim Vasquez. He concludes that "the A330 would have been flying through significant turbulence and thunderstorm activity for about 75 miles (125 km), lasting about 12 minutes of flight time" but that "complexes identical to this one have probably been crossed hundreds of times over the years by other flights without serious incident". See also the excellent CIMSS satellite blog for more images and analysis of the weather during the flight.

Invest 92
NHC is tracking a storm near the Azores Islands (Invest 92L) that is probably the remnants of the core of an extratropical cyclone that closed off some warm air at the center. The system has developed some heavy thunderstorm activity near its center, making this a hybrid storm. However, with ocean temperatures near 62°F (16°C), this storm has little chance of becoming a named subtropical storm.

Jeff Masters

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1061. Patrap
Impacts counts,not any Man Made scale of Numbers.

Especially the SS scale.
Its a People Buisness,not a FACT buisness.

The numbers come with the territory,but at the end of the day,and beginning. Its all about saving Lives and protecting property and economic interests.
Member Since: July 3, 2005 Posts: 426 Comments: 128621
Quoting StSimonsIslandGAGuy:
I disagree with making Andrew a cat 5. To be the ultimate, a Cat 5, a hurricane should meet ALL of the qualifications, including pressure. Not just wind.


My understanding is that the lowest pressure found was 922 mb. From what I have found they say a Cat 5 is 920 mb and under. That's not far off, and in reality, the pressure was probably lower and just not recorded due to instrument failure.
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Loop of the SAL backing off
Member Since: June 9, 2007 Posts: 4 Comments: 15920
1058. Patrap
Like I said Padawan,the NHC dosent issue a Numbered Seasonal Forecast.
Member Since: July 3, 2005 Posts: 426 Comments: 128621
NHC is just the NHC. They are just let us. People who love tracking tropical weather. When a blob pops up, it is labeled an Invest before you can even blink your eye.
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Quoting StSimonsIslandGAGuy:
I disagree with making Andrew a cat 5. To be the ultimate, a Cat 5, a hurricane should meet ALL of the qualifications, including pressure. Not just wind.


I have to agree with you about Andrew not being a Category 5 at landfall. I know Adrian will slap me upside the head for saying that though...
Member Since: June 9, 2007 Posts: 4 Comments: 15920
1054. Patrap
WAVCIS related Links
Member Since: July 3, 2005 Posts: 426 Comments: 128621
1053. aquak9
I read isaac's storm, the black cloud too....I think it's just the author's way of throwing a little conspiracy-spin into the story....certainly the NWS did not purposely want lives to be lost, but both books did tend to push that theory a little bit.
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1052. Levi32
Quoting Patrap:
Once again,,the NHC does not issue a Numbered Seasonal Tropical Forecast.

NHC Mission Statement

The NHC mission statement is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards. It is important for you to pay attention when you hear alerts, watches, and warnings provided by this official hurricane organization. By listening to information given and the official National Hurricane Center concern behind it, you will be able to make education decisions on preparing for a hurricane, preventative damage, and protecting your family.



Yeah....


NOAA: 2009 Atlantic Hurricane Season Outlook
Issued: 21 May 2009

"The 2009 Atlantic hurricane season outlook is an official product of the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center (CPC), and is produced in collaboration with scientists from the National Hurricane Center (NHC) and Hurricane Research Division (HRD). The Atlantic hurricane region includes the North Atlantic Ocean, Caribbean Sea, and Gulf of Mexico"
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Interesting.

SAL has lessened quite a bit.

Member Since: June 9, 2007 Posts: 4 Comments: 15920
Quoting TampaFLUSA:
It took the NHC years before they made Andrew a Cat 5...and it went right over them!!!!!


I always wonder why they did that. I lived Andrew, but what point is it changing it years after the storm?
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Here is what I am talking about:

Link
Member Since: May 27, 2009 Posts: 0 Comments: 4438
It took the NHC years before they made Andrew a Cat 5...and it went right over them!!!!!
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1046. Patrap
Once again,,the NHC does not issue a Numbered Seasonal Tropical Forecast.

NHC Mission Statement

The NHC mission statement is to save lives, mitigate property loss, and improve economic efficiency by issuing the best watches, warnings, forecasts and analyses of hazardous tropical weather, and by increasing understanding of these hazards. It is important for you to pay attention when you hear alerts, watches, and warnings provided by this official hurricane organization. By listening to information given and the official National Hurricane Center concern behind it, you will be able to make education decisions on preparing for a hurricane, preventative damage, and protecting your family.

Member Since: July 3, 2005 Posts: 426 Comments: 128621
Quoting aquak9:
I thought it was funny, reed.

Wonder if there's any correlation between liberal use of names vs. conservative use of names, depending on what's in the WhiteHouse.


I don't see one. 1995 was under Clinton, 2000 was under Clinton, 2006 was under Bush.
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Quoting Drakoen:


Very. But you have to keep in mind that the EWP is more of a statistical predictor of MJO rather than a dynamical predictor.


Yeah definitely gotta keep that in mind. The GFS and CFS have a much less impressive MJO phase coming through compared to the EWP.
Member Since: June 9, 2007 Posts: 4 Comments: 15920
Quoting CaneWarning:
I am still amazed that some people believe the NHC decides to name or not name something so they can "hit their numbers". The idea is laughable. Can you really see them sitting there doing that? Doing so would put their careers and the whole NHC at jeopardy.


lol they are the upmost Hurricane Authority, sorry weather channel your second. But I am curious why 90L was not at least a TD at landfall. And 92L was subtropical but obviously a better case on not naming it.
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1041. Makoto1
1040- Tropical Storm Ana.. Coultier?
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1040. aquak9
I thought it was funny, reed.

Wonder if there's any correlation between liberal use of names vs. conservative use of names, depending on what's in the WhiteHouse.
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1039. Levi32
Yup and the MJO pulse comes in also right around the time the low forms in the Caribbean. It may have a decent chance, but it's still a bit far away to start drawing conclusions.
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Quoting reedzone:
Sorry, thought I could add a bit of humor to the blog.. guess instead, I upset some people, I apologize.


No ones upset at all. Prediction just sounds like the NHC is some kind of fortune teller. lol
Member Since: June 9, 2007 Posts: 4 Comments: 15920
I am still amazed that some people believe the NHC decides to name or not name something so they can "hit their numbers". The idea is laughable. Can you really see them sitting there doing that? Doing so would put their careers and the whole NHC at jeopardy.
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Quoting Tazmanian:



that sould get things going vary fast


Yeah it'll be interesting to see if something forms while the pulse is occurring.
Member Since: June 9, 2007 Posts: 4 Comments: 15920
1034. Drakoen
Quoting Stormchaser2007:
Pretty impressive MJO pulse coming.


Very. But you have to keep in mind that the EWP is more of a statistical predictor of MJO rather than a dynamical predictor.
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1033. aquak9
You're in the electric wheelchair, Vort. I'm using your old walker now.
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Quoting reedzone:
I bet we'll here this from the NHC sometime this year.. They'll deff be naming less storms this year just to get the prediction right

WE HAVE FOUND WINDS OF 80 MPH WITH AN EYE LIKE FEATURE IN THE STORM. HOWEVER THE STORM IS NON-TROPICAL IN NATURE AND DEVELOPMENT IF ANY WILL BE SLOW TO OCCUR. THERE IS A LESS THEN 30% CHANCE.


that would be a valid reason to not declare..
Now if they said this.
RECON INDICATES THE TROPICAL WAVE IN THE CARIBBEAN HAS AQURIED A CLOSE CIRCULATION AND WITH 60 MPH WINDS, HOWEVER THIS SYSTEM IS CLOSE TO LANDFALL AND DEVELOPMENT..IF ANY.. WILL BE SLOW TO ACCOUR. THERE IS A LESS THEN 30% CHANCE OF THIS SYSTEM BECOMING A TROPICAL STORM OR A HURRICANE IN THE NEXT 48 HOURS.

Then I will be upset. But the NHC has every right to say a system isn't a system when, it isn't a system!
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Sorry, thought I could add a bit of humor to the blog.. guess instead, I upset some people, I apologize. It was a joke...
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Quoting Patrap:
The NHC dosent make Predictions ,er..sport.


Thats right. Its more of a somewhat educated guess.
Member Since: June 9, 2007 Posts: 4 Comments: 15920
Quoting Stormchaser2007:
Pretty impressive MJO pulse coming.



that sould get things going vary fast
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Quoting StSimonsIslandGAGuy:
A Cat 4 hitting Savannah would not be that bad. For one thing, Savannah is about 20 miles inland. For another, downtown and the old city are about 50 feet above sea level on a bluff. q.v.

Note the bluff and the sailing ships below the bluff:



Yes they said that about the old town surviving. I think they were talking about everyone else around there. How there is a long shallow shelf extending out and the water would pile up on it. And 20 miles inland, water or no water, a cat 4's winds would just about tear up all but the strongest homes. Not to mention all those beautiful old trees. I don't know looked pretty scary.
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1027. Patrap
1022. reedzone

The NHC dosent make Predictions ,er..sports fans.
Member Since: July 3, 2005 Posts: 426 Comments: 128621
Quoting reedzone:
I bet we'll here this from the NHC sometime this year.. They'll deff be naming less storms this year just to get the prediction right

WE HAVE FOUND WINDS OF 80 MPH WITH AN EYE LIKE FEATURE IN THE STORM. HOWEVER THE STORM IS NON-TROPICAL IN NATURE AND DEVELOPMENT IF ANY WILL BE SLOW TO OCCUR. THERE IS A LESS THEN 30% CHANCE.


lol, I second that. Obviously NOAA hasn't been the best in recent forecasts so why not help their cause a little bit and just declare things "non tropical"
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting Levi32:


I was even less of a thought than you were =P


LOL...
Member Since: June 9, 2007 Posts: 4 Comments: 15920
I bet we'll here this from the NHC sometime this year.. They'll deff be naming less storms this year just to get the prediction right

WE HAVE FOUND WINDS OF 80 MPH WITH AN EYE LIKE FEATURE IN THE STORM. HOWEVER THE STORM IS NON-TROPICAL IN NATURE AND DEVELOPMENT IF ANY WILL BE SLOW TO OCCUR. THERE IS A LESS THEN 30% CHANCE.
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Quoting StSimonsIslandGAGuy:
Levi I thought that too, but there are no reports of hurricane winds or winds close to hurricane force on the SC side of the track either.


I was 10 during David, and the west side of the eye went over us. Home barometer reached 28.66"

Winds were never above the 40-45 mph range, and were distinctly stronger after the eye passed.
Though David was not much of a wind event, my car was totaled because of water. It was as if the hospital where I worked was an island. People were paddling to the hospital in canoes to get in a dry building. Could not see anything but water from the door - would not have wanted to guess where the river edge began ;)

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1020. Levi32
Quoting Stormchaser2007:


During David I was -3. Wasnt even a thought yet.


I was even less of a thought than you were =P
Member Since: November 24, 2005 Posts: 635 Comments: 26652
Pretty impressive MJO pulse coming.
Member Since: June 9, 2007 Posts: 4 Comments: 15920
1018. Levi32
Quoting aquak9:
oh hush Levi! You're gonna make me hafta whop ya upside the head with my walker!


Lol believe me I need it ;)
Member Since: November 24, 2005 Posts: 635 Comments: 26652
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989. Patrap 12:50 AM GMT on June 04, 2009
Political Motives are a non issue in Forecasting.

To say they are is Ludicrous.

If you have issue with the NHC ,..they have a E-mail address. They are the Official Word here ALWAYS.

To demean the folks there without merit or fact does a Dis-service to the General Public at Large.
--------
i would have to disagree with you Pat. for many years, the NWS REFUSED to even use the word "tornado", as they thought it would cause unnessessary harm.

also, the NWS in the early part of the 1900s refused to use the word "hurricane" in official weather reports. read the book "isaac's storm" (a retelling of the great galvaston hurricane) and you will get a clear picture on how the NWS used to PURPOSELY surpress information.

with the advent of satelites and internet where anyone can check on the weather at any time, the NWS and the NHC cant pull this stunt as much. but they still do things based on political reasons many times.
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1015. aquak9
oh hush Levi! You're gonna make me hafta whop ya upside the head with my walker!
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1013. aquak9
yes...George Winterling. Earned his fame by being the only met to call Dora as a northern St.Augustine landfall, instead of a Daytona landfall, like everyone else.

He was my icon. I lived for his weather reports.
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1012. Levi32
During David I was....minus-12 years old lol.
Member Since: November 24, 2005 Posts: 635 Comments: 26652

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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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