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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Quoting Stormchaser2007:


If the NHC doesnt increase it potential to at least moderate by 2am tomorrow then I think chances will be slim for this to get named at all. The GFS has the wind field becoming elongated and messy at around 30hours so it better organize quick.


Agreed
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WPB, the last time someone said the blog was going to be quiet. Mother nature chose to disagree, so lets not just say that yet.
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Quoting extreme236:


I have doubts whether it will get named or not, but I'm interested in what the TWO says. If its a repeat of the 2pm TWO I'd say chances are slim.


If the NHC doesnt increase it potential to at least moderate by 2am tomorrow then I think chances will be slim for this to get named at all. The GFDL has the wind field becoming elongated and messy at around 30hours so it better organize quickly.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
JL, nice to see ya back in here
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Going to be a quiet two weeks at least...can the blog survive?
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with water temps this high in the Gulf, is that conducive to developing storms now or is shear still to high?
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Quoting plywoodstatenative:
Any activity in the ITCZ or is too early to be looking that way?

There is nice surface vorticity with the tropical wave at abt 5N 34W. Other than that I didn't see much, but I'm not an expert.
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255. JLPR
Quoting plywoodstatenative:
Any activity in the ITCZ or is too early to be looking that way?


yep too early but if anything formed there it wouldnt surprise me xD this season looks like its going to be a weird one =P
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Interesting, I just ran this loop and it looks like it has some new convection developing of about -50c south of the "eye".

IR LOOP
Member Since: June 9, 2007 Posts: 4 Comments: 15947
253. amd
Quoting plywoodstatenative:
23: My concern is the temps rising so fast after having the near tropical storm in the GOM, the fact that water is heating up as such gives cause for concern.


that is definitely true. In fact the water temperature 22 miles off the coast of Galveston has increased by 2 degrees in just one day.

Link
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Quoting Stormchaser2007:


Ill have to agree with that. For where it is and how cold the waters under it are, its a decent looking system.


I have doubts whether it will get named or not, but I'm interested in what the TWO says. If its a repeat of the 2pm TWO I'd say chances are slim.
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Compare it to STS Andrea although they are on oppisite sides of the Atlantic the features are simliar.

Member Since: May 27, 2009 Posts: 0 Comments: 4438
Any activity in the ITCZ or is too early to be looking that way?
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Quoting extreme236:


You make good points, although its convective activity I'd say is decently impressive considering where its at and what time of year it is.


Ill have to agree with that. For where it is and how cold the waters under it are, its a decent looking system.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
248. JLPR
interesting
92L doesn't look awesome right now convection wise

but in structure it is nice
maybe if it develops some more convection we could have STD 2 or STS Ana
xD its really strange to see this kind of storm this early in the season
the water up there is waaay cold

Hello everyone =]
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Atlantis and the 747 on the Ground at KSC

Member Since: July 3, 2005 Posts: 427 Comments: 129323
Quoting Stormchaser2007:


I know that, but 91L gained some impressive convection over it and looked pretty good suddenly. It would have been foolish for them not to declare it. Although with 92L we have a different story, 92L is a large sub tropical system thats not looking too good as of now(convection wise). The only impressive parts of it are the pressure, 50mph winds, and the developing warm core. We'll see what happens with the TWO at 8pm.


You make good points, although its convective activity I'd say is decently impressive considering where its at and what time of year it is.
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If 92L meets the criteria..it will be named. If not..nada, nada, nunca, nunca. All this nonsense about systems not being named due to political or internal issues is silly. The best one though...the Memorial Day weekend invest was not given a name because...it was a holiday and no one at the NHC wanted to ruin their holiday by having a named storm. Geez!
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With 92, you have to wonder if the NHC is going to leave the consideration up to whether or not that storm will make a major impact on lives or whether its for the fish.
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Quoting plywoodstatenative:
Is this season we have on tap going to be much like 92 when we had a bunch of Tropical disturbances and such but no real formations? All that until Andrew, could this be a repeat season of that?


Maybe but it is still early, we should know by early August
Member Since: May 27, 2009 Posts: 0 Comments: 4438
23: My concern is the temps rising so fast after having the near tropical storm in the GOM, the fact that water is heating up as such gives cause for concern.
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This was 92L yesterday:

Member Since: June 9, 2007 Posts: 4 Comments: 15947
Is this season we have on tap going to be much like 92 when we had a bunch of Tropical disturbances and such but no real formations? All that until Andrew, could this be a repeat season of that?
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Quoting hurricane23:
Quoting CatastrophicDL:
Can someone post a link to sea surface temps? Preferably one for dummies with nice easy to read colors and big numbers?


Adrian, thanks! I knew I had seen it on your website but I couldn't find it again. I finally found it at TWC. It is perfect for me since I suck at converting celsius to farenheit.
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Quoting CybrTeddy:


91L was declared to TD 1 when it was at Yellow.


I know that, but 91L gained some impressive convection over it and looked pretty good suddenly. It would have been foolish for them not to declare it. Although with 92L we have a different story, 92L is a large sub tropical system thats not looking too good as of now(convection wise). The only impressive parts of it are the pressure, 50mph winds, and the developing warm core. We'll see what happens with the TWO at 8pm.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
The sea temps around florida are warming up fast.
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Quoting Rainwalker:
Wow, the season might be "less-active"!!



As far as long range forecasts are concerned, in my mind the biggest factor by far is the presence of an El Nino or not. The next most important factor is plain luck which can be just as important when a strong EL Nino is in effect: which it isn't yet for this year as the recent warming indicates might be coming.

The way I look at it every season is that one has to just be patient. Some years you have a lot of storms and they all recurve. Some years few storms and two or more hit land. 1 1/2 hurricanes hit land per year on the average. It's like fishing for big fish; if you get one good game fish on a full trip it is a successful trip,. If you get 15 bites, but land no fish, the trip was poor. Or its like a defensive football matchup. You might get one touchdown all game: sometimes in the first quarter, sometimes you don't score until the fourth quarter. It's mostly just plain chance.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
Quoting Stormchaser2007:


There is no way that the NHC will declare it a Sub tropical storm if they only have it in a slight chance of development area. It needs to at least get up to a moderate. Personally I dont think the NHC will declare this a storm at all.


91L was declared to TD 1 when it was at Yellow.
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Quoting CatastrophicDL:
Zoo, are you laughing at me :o) How are you?



laughing, and agreeing.

Good how about you?
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Quoting amd:
I think 92L should be subtropical storm ana at 11 p.m. According to the 2 p.m. dvorak classifications, this storm is subtropical. Also, Quikscat shows winds greater than the minimum for tropical storm force close to the center, which shows some tropical characteristics. Besides, I just want to win the first storm contest. :)


There is no way that the NHC will declare it a Sub tropical storm if they only have it in a slight chance of development area. It needs to at least get up to a moderate. Personally I dont think the NHC will declare this a storm at all.
Member Since: June 9, 2007 Posts: 4 Comments: 15947
Quoting amd:
I think 92L should be subtropical storm ana at 11 p.m. According to the 2 p.m. dvorak classifications, this storm is subtropical. Also, Quikscat shows winds greater than the minimum for tropical storm force close to the center, which shows some tropical characteristics. Besides, I just want to win the first storm contest. :)


But will it be? Seems the nhc is cautious this year we will have to find out.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
231. amd
I think 92L should be subtropical storm ana at 11 p.m. According to the 2 p.m. dvorak classifications, this storm is subtropical.

Also, Quikscat shows winds greater than the minimum for tropical storm force close to the center, which shows some tropical characteristics.

Besides, I just want to win the first storm contest. :)
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Quoting WhipplePupley:
I THINK THE sPANISH COAST BETTER START BOARDING UP!


stormtop??
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Quoting CatastrophicDL:
Can someone post a link to sea surface temps? Preferably one for dummies with nice easy to read colors and big numbers?

Member Since: May 14, 2006 Posts: 8 Comments: 13841
Quoting WhipplePupley:
I THINK THE sPANISH COAST BETTER START BOARDING UP!


LOL
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AMSU B 89GHZ Microwave shows that 92L has been organizing.



Member Since: June 9, 2007 Posts: 4 Comments: 15947
Zoo, are you laughing at me :o) How are you?
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panama:it already landed,looks like they did a flyby down the beach near daytona!!!
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jeffs713, if your still out there, the graphs came out fine in the spread sheet. Good Job !

If possible, could you input this set of pics on it, Wxgirl,17,7,3,1,7-01 .

It was not in the original set of data points and was added later. My cut and paste mistake. Thanks ED
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I THINK THE sPANISH COAST BETTER START BOARDING UP!
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Quoting CatastrophicDL:
Can someone post a link to sea surface temps? Preferably one for dummies with nice easy to read colors and big numbers?


lol
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Quoting MrstormX:
Does anyone know what the Minimum central pressure of it is? (it being 92L not the blob)


MrsstormX

There is no accurate measurement of 92L's min. pressure, only estimates, and the estimates are covering a fairly wide range today.

A ship report from early this morning that was not in its center (which would suggest that the minimum central pressure was probably even a good bit less than this at the time) recorded a pressure of around 993hPa.

Earlier today, AMSU was estimating its central pressure at about 984 hPa, which is not at all outside of reasonable, given the corroborating ship report, nearby.

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That pressure makes me think its slightly strengthening considering our TD 1 was 1006 mbar at lowest
Member Since: May 27, 2009 Posts: 0 Comments: 4438
ESL by LSU
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Quoting MrstormX:
Does anyone know what the Minimum central pressure of it is? (it being 92L not the blob)


In post 198 the lowest reported pressure is 996 mb,

The navy has it as 995 mb

92LINVEST.45kts-995mb-440N-238W

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Quoting MrstormX:
Does anyone know what the Minimum central pressure of it is? (it being 92L not the blob)

998mb
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What is that blob in the GOM? And which direction is it heading?
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Does anyone know what the Minimum central pressure of it is? (it being 92L not the blob)
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting Weather456:
I don't know why some still say its entirely non tropical. A non tropical low does not have its highest winds near its center, nor is it warm-core and still non frontal at low levels (then it would be a warm seclusion) nor does it it have organize convection near its center. I'm not saying it deserves a name (because I won't be surprise if it does not) but at the same time I'm not calling it entirely non tropical based on the obvious evidence.


Even the NHC admits it has "tropical characteristics" but I doubt they will upgrade it, but maybe with a nudge from the UK MET office this might get a name.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Looks like it has its eye on Portugal/Spain eh, pun intended. Weekend weather is in jeopardy.


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I don't know why some still say its entirely non tropical. A non tropical low does not have its highest winds near its center, nor is it warm-core and still non frontal at low levels (then it would be a warm seclusion) nor does it it have organize convection near its center. I'm not saying it deserves a name (because I won't be surprise if it does not) but at the same time we cannot refer to it as entirely non tropical based on the obvious evidence.
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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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