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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the blog is def coming alive...lol!
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Thanks 456, so it looks like at least a posible TS, do you have the cyclogenesis analysis for this one?
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Good evening... lively crew today with the possible prospect in the NW Carib towards this weekend into early next week. Should be interesting what happens with 00Z ECMWF. NOGAPS have been hinting also towards this scenerio.
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859. Relix
Wait, that new wave... I wanted to hit the beach on Saturday here on Puerto Rico!! Don't wet my day please =D
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What I know is this, there are many people in south florida wondering is this amount of rain we are seeing a hindsight to something else later this year. Can anyone provide insight to that?
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851- rofl George gets a broken umbrella for Laura, thinking it's an odd form of black flower.
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h23 you have mail
Member Since: July 24, 2005 Posts: 407 Comments: 19076
23, when the shear decreases, is there any chance of development from the mess in the Gulf?
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Quoting antonio28:
Can anyone post a link of the GFS 18Z run?


LINK
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting antonio28:
Can anyone post a link of the GFS 18Z run?


HERE
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Can anyone post a link of the GFS 18Z run?
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Quoting hurricane23:


The way (ECM) is lowering shear i say theres a chance for possible development but never the less it looks like very deep tropcial moisture from the caribbean will begin to surge north in a few days.


Better have those umbrellas handy.

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Quoting Drakoen:
Looks like we have something to watch according to the aggressive GFS 18z. The GFS always likes to eject things out of the Caribbean like that this time of year. Decent MJO pulse and low wind shear may allow for some development.


The way (ECM) is lowering shear i say theres a chance for possible development but never the less it looks like very deep tropcial moisture from the caribbean will begin to surge north in a few days.
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Quoting IKE:


stormkat, is that you?


Nah...he didn't write it in stone.
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Look at the coast of South Carolina on the GFS Model Run 18z = 48 hrs


Then on this one, it develops a TS that will move up the Eastern Seaboard, about 50-80 miles away from Myrtle Beach, SC.


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846. IKE
Quoting Drakoen:


LOL. Where is kman at?


I was just thinking about him.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
845. IKE
Quoting Vortex95:
guess who: THIS IS A VERY SERIOUS SITUATION BUT NOT FOR FLORIDA,FLORIDA WILL GET RAIN FROM THIS BUT IT WILL BE A DEVASTAING FLOOD EVENT FO MISSISSIPPI, ALAMABA AND LA. IN AROUND 120 HOURS A 35 TD WILL BE FORMING BY 150 HOURS IT WILL BE A LEVEL WITH THE YUCATAN AS A 60 MPH TS. THEN WILL JET OVER TO THE GULF COAST AS A CAT 1 HURRICANE AT 198 HOURS AND HIT THE TOWN OF CHRISTIAN MISSISSIPI DIRECTLY AS A 90 MPH HURRICANE. HALFWAY UP THE STATE IT WILL STALL AND SINE IT WILL BE A BIG SYSTEM IT WILL DROP RECORD AMOUNTS OF RAIN IN THE GULF STATES. REPORTING FROM MY BASEMENT I AM IMPLORING ALL IN GULF COAST STATES TO PREPEARE NOW IN 6 DAYS I SHALL RETURN FOR MORE TO COMMENT IF I AM WRONG THEN I WILL NEVER FORCAST AGAIN!!!


stormkat, is that you?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
If this does develop, we should really give the GFS more credit. From May 26.
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Quoting IKE:
Now all of the Cayman Island bloggers will be posting.


LOL. Where is kman at?
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842. IKE
Now all of the Cayman Island bloggers will be posting.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:
GFS starts loading up the western Caribbean with abundant moisture by Sunday...that's only 4+ days away.

Pretty good bet that that is going to happen.


The solution does look more feasible and is within a reasonable time frame.
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839. IKE
GFS starts loading up the western Caribbean with abundant moisture by Sunday...that's only 4 days away.

Pretty good bet that that is going to happen.

EDIT>>> Should have said by Monday. My days are mixed up. I thought today was Tuesday.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Looks like we have something to watch according to the aggressive GFS 18z. The GFS always likes to eject things out of the Caribbean like that this time of year. Decent MJO pulse and low wind shear may allow for some development.
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Quoting MrstormX:
Predictions anyone on this upcoming Carribean storm


I think it will be named. If I'm wrong, I like my crow well done.
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835. IKE
Aims it for New England...Bastardi territory.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:
GFS seems to aim anything up the east side of Florida.


The GFS probably heard our complaints that it takes nearly all ghost storms into Florida and decided that it got sick of our complaints and now sends close call ghost storms. LOL
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Here's another,

Man strive to find the reason when the reason is beyond us - Climate Change
Member Since: July 24, 2005 Posts: 407 Comments: 19076
So, the GOM blob looks to be a little interesting. If it is to stay over GOM waters for another 36-48 hours, it wouldn't shock me to see a TD or TS form from this. Ana? probably so, but I don't think it will be in the Carribbean. My guess of the Lesser Antillies, and the GOM. or probably those low pressures with cold fronts that linger out the South & North Carolina coast line.
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831. IKE
GFS seems to aim anything up the east side of Florida.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
829. IKE
Quoting hurricane23:


Deep tropical moisture surge for florida.


I agree, whether anything ever forms or not.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
12Z ECMWF, this is one of the models I look for in determining potential cyclogenesis. Still, peristent is always important.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Weather456:
hurricane season sayings:

Where will it go comes after when it is formed.


Your wisdom is enlightening
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Quoting MrstormX:
Predictions anyone on this upcoming Carribean storm


Deep tropical moisture surge for florida.
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Wow how long has it been since I've been here?

Anyway, 92L overall looks impressive for how far north it is but I really can't see it being named.

GOM blob... I doubt it. We'll have to watch the Caribbean "just in case" but it's obviously way too far out to tell. Fun to watch it though.
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824. IKE
Quoting weathermanwannabe:


Yup....Going home now but saw a bad accident on I-10 near Marianna (someone slid off the road in the rain and into a power pole) on the way in to Tally.......Rain is good thing but best when you're sleeping and worst when your driving.....Time for everyone to check your tires and wipers for the summer rain season...Have a Good One Folks.


I10 is terrible when it's raining. I will usually take highway 90 instead.

I've hydroplaned on I10 before, in the rain, going up a hill and wound up in the fast lane. Fortunately there was no vehicle over in that lane or I would have likely been killed.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
hurricane season sayings:

Where will it go comes after when it is formed.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
822. IKE
18Z GFS deepens that potential system.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


Yes...had mostly light to moderate rain. According to a PWS about 6 miles from me... .40 inches of rain.

Sun is coming out now. I was over in Ponce DeLeon this morning on business....lol...you weren't too far away.


Yup....Going home now but saw a bad accident on I-10 near Marianna (someone slid off the road in the rain and into a power pole) on the way in to Tally.......Rain is good thing but best when you're sleeping and worst when your driving.....Time for everyone to check your tires and wipers for the summer rain season...Have a Good One Folks.
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Quoting MrstormX:
Predictions anyone on this upcoming Carribean storm


Can't give any predictions without an actual storm. This is all conjecture at this point based upon computer model runs. If we do get an actual system, then we can start to answer questions like that.
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819. IKE
cg2916....that's at 10 meters or about 30 feet.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Predictions anyone on this upcoming Carribean storm
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Quoting IKE:


My gosh...how fast is it moving?


15-20 knots

72 hrs

Member Since: July 24, 2005 Posts: 407 Comments: 19076
816. IKE
Quoting cg2916:

That's UPPER LEVEL, not surface. Only surface lows become tropical.


?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


My gosh...how fast is it moving?

Lol.
Member Since: December 21, 2007 Posts: 13 Comments: 3026
814. IKE
Quoting weathermanwannabe:


Hey Ike; I just left Bonifay (back to Tally) about 2 hours ago;...... little bit of rain in your parts this afternoon?


Yes...had mostly light to moderate rain. According to a PWS about 6 miles from me... .40 inches of rain.

Sun is coming out now. I was over in Ponce DeLeon this morning on business....lol...you weren't too far away.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE

According to the 18Z GFS it does. At only 120 hours....



That's why I said that lol


It is quite strange that the CMC is not jumping of all of this.
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Quoting IKE:


According to the 18Z GFS it does. At only 120 hours....


That's UPPER LEVEL, not surface. Only surface lows become tropical.
Member Since: December 21, 2007 Posts: 13 Comments: 3026

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About JeffMasters

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