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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Flood--
have you been on since Dolly? that's the last I remember seeing you...lol
Member Since: Posts: Comments:
2005 Cyclones: phase evolution,Images and animation
Member Since: July 3, 2005 Posts: 426 Comments: 129090
Quoting CatastrophicDL:

I know... I think that the anticipated AOI in the Carribean next week will come from the tropical wave at 37W.


It's got a ways to go, but maybe it will give us a blob to watch. It is interesting that a couple of models now show something in that area.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Howdy, Vike!
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Quoting 69Viking:


I don't know about everyone but this blog sure has picked up the pace since this morning's crawl! Nice and wet here in the Panhandle along the coast too, as IKE would say currently raining with a temperature of 71!


lol! i don't even know if it was at a crawl.. more like it was stalled with slight variable movements
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Quoting CaneWarning:


Well it's just not all that tropical.

I know... I think that the anticipated AOI in the Carribean next week will come from the tropical wave at 37W.
Member Since: September 3, 2007 Posts: 3 Comments: 1519
Levi---
nice... guess we will be waiting and watching..
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IKE 2008 CMC animated Phase Diagram


GUSTAV 2008 CMC animated Phase Diagram
Member Since: July 3, 2005 Posts: 426 Comments: 129090
704. IKE
Quoting StormSurgeon:
Looks like NOGAPS is trying to drum up some late cycle activity in the W. Carribbean also.

Link


Interesting...more model support.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting NEwxguy:
Well,any of the ole gang missing now?Seems like everyone is back.


I don't know about everyone but this blog sure has picked up the pace since this morning's crawl! Nice and wet here in the Panhandle along the coast too, as IKE would say currently raining with a temperature of 71!
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Quoting CatastrophicDL:

I don't think it has interested you for a while :o) I bet you'll get a pretty good blob in 3-5 days.


Well it's just not all that tropical.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting cg2916:

That's NOT the surface forecast! That's another GFS forecast. The surface forecast is here.


It is surface......it just has 2m winds instead of 500-1000mb thickness like your's does, which makes no difference here.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Never NRAamy,..thats Bad form in the Social Scene..

Champagny?




Member Since: July 3, 2005 Posts: 426 Comments: 129090
Quoting Patrap:
The Great Red Spots seems to be trending,..er..west?



That's just a temporary jog.....LOL
Member Since: September 1, 2007 Posts: 0 Comments: 1793
697. IKE
Quoting cg2916:

That's NOT the surface forecast! That's another GFS forecast. The surface forecast is here.


?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
afternoon ECM has the weak low moving northeastward, looks like more rain for some parts of florida.
Member Since: May 14, 2006 Posts: 8 Comments: 13839
are you west-casting, Pat?


;)

Member Since: January 24, 2007 Posts: 317 Comments: 31946
Looks like NOGAPS is trying to drum up some late cycle activity in the W. Carribbean also.

Link
Member Since: September 1, 2007 Posts: 0 Comments: 1793
Quoting IKE:


I disagree...the 12Z GFS does show a low in the NW Caribbean....it drops it, unlike the 6Z, but it does still show it....now it's got the 12Z ECMWF to back it up....

12Z GFS @ 162 hours...


That's NOT the surface forecast! That's another GFS forecast. The surface forecast is here.
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Quoting CaneWarning:
I hope we have a Caribbean blob to watch. 92L doesn't interest me anymore.

I don't think it has interested you for a while :o) I bet you'll get a pretty good blob in 3-5 days.
Member Since: September 3, 2007 Posts: 3 Comments: 1519
Well,any of the ole gang missing now?Seems like everyone is back.
Member Since: September 6, 2007 Posts: 886 Comments: 15948
The Great Red Spots seems to be trending,..er..west?

Member Since: July 3, 2005 Posts: 426 Comments: 129090
Whoa whoa whoa whoooaaa this low is expected to move towards south Florida.Ha more rain for us and even worse if it develops into something more stronger.
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We will have almost an entire week to watch things evolve in the NW Caribbean. We've got the trough split beginning tomorrow night and drifting south for 4-7 days thereafter with wind shear eventually lowering as the EPAC high noses north and splits apart the subtropical jet.

Just something to keep an eye on. Trough Splits are one of the main causes of early-season tropical systems. See Tropical Tidbit from 12:30pm EST for more.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
StormSurgeon, after the arguments I've seen in this place over the virtues of 92L over 93L and where the declaration of 94L will be, I'll not be bringing up the great red spot...yikes! I can hear the fights now!

It's influenced by Mars!
No, you're an idiot, it's not!
Yes, it is!
No, it isn't!
It's all due to global warming!

LOL
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Just wanted to urge folks in southeast florida to make morning plans this upcoming weekend cause afternoon hrs look very wet with a good potential for some strong to severe storms.My local NWS office has put out some comments on what the GFS/ECMWF models have been showing which is some disturbed weather down in the western caribbean sometime next week.Im not looking for anything significant in terms of tropical cyclone development but a good slug of tropical moisture creeping northward of the caribbean seems like a good bet as of now.

Member Since: May 14, 2006 Posts: 8 Comments: 13839
685. IKE
Quoting K8eCane:
SOUTHEAST US/FL...
THE MODELS SHOW AN UPPER TROUGH AND WEAKENING FRONT ACROSS THE
REGION DAY THREE. THE FRONT WEAKENS WITH A REMAINING LOW LEVEL
BOUNDARY UNTIL THE SOUTHWEST ATLANTIC RIDGE BUILDS BACK INTO THE
REGION. THE 06Z GFS SHOWED A LOW DEVELOPING OFF THE SOUTHEAST FL
COAST WED 10 JUN...WITH A SMATTERING OF LOWS IN THE GULF OF
MEXICO...WITH NO SUPPORT FROM THE GEFS MEMBERS. ODDS FAVOR THE
06Z GFS DEVELOPMENT WILL BE A FALSE ALARM...SO THE
MEANS/OPERATIONAL ECMWF WERE PREFERRED HERE. THE 12Z GFS NO
LONGER HAS THIS DEVELOPMENT...WITH AN OCCASIONAL SPOT LOW IN THE
EASTERN


I disagree...the 12Z GFS does show a low in the NW Caribbean....it drops it, unlike the 6Z, but it does still show it....now it's got the 12Z ECMWF to back it up....

12Z GFS @ 162 hours...

Member Since: June 9, 2005 Posts: 23 Comments: 37858
I hope we have a Caribbean blob to watch. 92L doesn't interest me anymore.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting IKE:


See what you've missed.:)


Yes, and I'll tell you, after the winter I've had I needed this sort of thing!
Member Since: August 2, 2006 Posts: 10 Comments: 9922
Check my blog for today's tropical update.
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Here is the size of 92L off of portugal, via the IPP satilite data. convection has popped up somewhat but as seen probably not enough

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Quoting Weather456:
Our attentions may turn to the Caribbean next week. Just need the model to be conistent and more consensus.

Have you seen the GFS forecast for the surface? I don't think the Caribbean thing will do anything except maybe become 93L.
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679. IKE
Quoting Weather456:
Our attention may turn to the Caribbean next week. Just need the model to be conistent and more consensus.


I agree.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting Floodman:
Now we really have convered all the bases...gravity waves, subtropical and tropical systems and stalker astronauts and their choices in incontinence foundation garments...I love this place!


How's it going Flood? Why stop there when can move on to extraterrestrial cyclones?

Member Since: September 1, 2007 Posts: 0 Comments: 1793
I love this place!


damn skippy...

:)
Member Since: January 24, 2007 Posts: 317 Comments: 31946
SOUTHEAST US/FL...
THE MODELS SHOW AN UPPER TROUGH AND WEAKENING FRONT ACROSS THE
REGION DAY THREE. THE FRONT WEAKENS WITH A REMAINING LOW LEVEL
BOUNDARY UNTIL THE SOUTHWEST ATLANTIC RIDGE BUILDS BACK INTO THE
REGION. THE 06Z GFS SHOWED A LOW DEVELOPING OFF THE SOUTHEAST FL
COAST WED 10 JUN...WITH A SMATTERING OF LOWS IN THE GULF OF
MEXICO...WITH NO SUPPORT FROM THE GEFS MEMBERS. ODDS FAVOR THE
06Z GFS DEVELOPMENT WILL BE A FALSE ALARM...SO THE
MEANS/OPERATIONAL ECMWF WERE PREFERRED HERE. THE 12Z GFS NO
LONGER HAS THIS DEVELOPMENT...WITH AN OCCASIONAL SPOT LOW IN THE
EASTERN
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Our attentions may turn to the Caribbean next week. Just need the model to be conistent and more consensus.
Member Since: Posts: Comments:
Tropical Update
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673. IKE
Quoting Floodman:
Now we really have covered all the bases...gravity waves, subtropical and tropical systems and stalker astronauts and their choices in incontinence foundation garments...I love this place!


See what you've missed.:)
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Now we really have covered all the bases...gravity waves, subtropical and tropical systems and stalker astronauts and their choices in incontinence foundation garments...I love this place!
Member Since: August 2, 2006 Posts: 10 Comments: 9922
671. IKE
Quoting sporteguy03:


Ike have you ever thought of doing a youtube video of yourself watching the GFS and ECMWF models, I swear you'd be in the Guinness World Record Book lol!


LOL!

Speaking of that goofy EX-astronaut...from Wikipedia..."A pretrial status hearing has been scheduled for June 22, 2009. On April 1, 2009, the judge ordered Nowak to undergo two psychiatric evaluations before June 12, 2009.".....

If anyone cares.

Now...back to the weather, brought to you by Depends....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
SHORTWAVE MOVING THROUGH THE EAST FRIDAY/SATURDAY AND SURFACE LOW
MOVING FROM GEORGIA OFFSHORE THE EASTERN SEABOARD...
THE NAM HAS WAVERED WITH THIS SYSTEMS DEPTH OVER ITS PAST DAY OF
RUNS. THE GFS HAS TRENDED QUICKER/STRONGER WITH THIS LOW OVER ITS
PAST DAY OF RUNS. AS OF 00Z...THE ECMWF HAS TRENDED SLIGHTLY
QUICKER/STRONGER WITH THIS SYSTEM OVER ITS PAST COUPLE DAYS OF
RUNS BEFORE IT BECAME MORE STRUNG OUT ON ITS 12Z RUN. THE 12Z
NAM/00Z UKMET/06Z GFS ARE SLOWER/STRONGER THAN THE 00Z ECMWF AND
TO SOME DEGREE THE 00Z CANADIAN WITH THIS SYSTEM /WHICH FORMS A
SECOND SLOWER CYCLONE ON SATURDAY OFFSHORE THE MID-ATLANTIC
COAST/. THE 00Z GEFS MEMBERS SUPPORT THE QUICKER 00Z ECMWF/00Z
CANADIAN...WHILE THE 00Z ECMWF ENSEMBLE MEMBERS SUPPORT A SOLUTION
SLIGHTLY SLOWER THAN THE SLOWER GUIDANCE. WHEN THIS DISTRIBUTION
OF THE ENSEMBLE MEMBERS IS SEEN...COMPROMISING BETWEEN THE TWO
CAMPS WORKS BEST SINCE THE GEFS MEMBERS TEND TO BE QUICK WITH
RECURVING SYSTEMS AND THE ECMWF MEMBERS CAN BE TOO SLOW...SO WILL
PREFER A 06Z GFS/12Z NAM/00Z ECMWF COMPROMISE POSITION AND DEPTH
WITH THIS SURFACE LOW...WHICH IS SIMILAR TO THE 12Z GFS/12Z UKMET
SOLUTIONS


from the afternoon hpc model diagnostic discussion
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Looks like a rainy evening.......

Mobile Radar
Member Since: September 1, 2007 Posts: 0 Comments: 1793
Quoting IKE:
12Z ECMWF has picked back up on a Caribbean low.


Ike have you ever thought of doing a youtube video of yourself watching the GFS and ECMWF models, I swear you'd be in the Guinness World Record Book lol!
Member Since: July 7, 2005 Posts: 0 Comments: 5412
667. IKE
Quoting NRAamy:
the female astronaut? No, she used the Extra-absorbency Stalker Version...I just need the Glad-to-see-a-fellow-blogger-back mini version...

;)


She stopped here in metropolitan Defuniak Springs, on her way to confront her rival and spent a few hours at a motel my wife worked at. I guess to change diapers....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting NRAamy:
the female astronaut? No, she used the Extra-absorbency Stalker Version...I just need the Glad-to-see-a-fellow-blogger-back mini version...

;)


HaHaHaHa!!!
Member Since: September 1, 2007 Posts: 0 Comments: 1793
Quoting PensacolaDoug:



Ditto!

Remember the WALA tagline?

If you know Trainor, (sp?) you know the weather!


I remember now that you mention it. He was a fun weatherman......hated to see him go.
Member Since: September 1, 2007 Posts: 0 Comments: 1793
664. IKE
12Z ECMWF has picked back up on a Caribbean low.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
the female astronaut? No, she used the Extra-absorbency Stalker Version...I just need the Glad-to-see-a-fellow-blogger-back mini version...

;)
Member Since: January 24, 2007 Posts: 317 Comments: 31946
634.

Good to be seen...and I'm glad to see the Keeper is here...
Member Since: August 2, 2006 Posts: 10 Comments: 9922

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About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.