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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What if California go hit with a hurricane, that would be one of the rarest events ever witnessed. If I recall Hurricane Linda nearly did that in 1997, and some tropical storms hit in the 1930's.
Member Since: Posts: Comments:
1996 longest track of Cape Verde storm developed as it entered Carribbean,

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Quoting NRAamy:
hey ...wait a minute....we're not all here yet...

where's STORMTOP?!

;)


He posted a week or two ago.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting Floodman:
Canewarning, I got into trouble for that last year; apparently some trolls took exception to my ignoring them...LOL

I'll simply poof them and not say anything about it this year (having learned my lesson)


Yeah I remember that. :)
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting Vortex95:
I have always wondered if it was possible for a strom to start off as a cape verde then head to central america or the yucatan cross into the pacific and than go all the way to Japan.


Dont know, but I've seen a few get close to Hawaii or at least half way there
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LOL, Strormtop is out there somewhere, Predictin'.
Quoting NRAamy:
hey ...wait a minute....we're not all here yet...

where's STORMTOP?!

;)


Probably in his mom's basement hope for a storm to hit him.
Member Since: Posts: Comments:
hey ...wait a minute....we're not all here yet...

where's STORMTOP?!

;)
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Good afternoon. good to see some old faces around ("old" is used in a relative sense). Although, come to think of it, ancient would apply to some.
Press, until you receive your further instructions, stand at ease. On one foot.
745. clwstmchasr 1:25 PM PDT on June 03, 2009
Now that we are all blob watching and model watching waiting for Ana, what would happen to everyone one on this blog if we had a repeat of 1914 in which we had only one tropical storm?


we'd all get fat eating up our emergency supplies of Spam and Poptarts before they expired....I mean, you can't let that stuff go to waste!!!


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I'm good flood how about you?
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...so...

Who's in charge here today?!

...and...

What are my orders?!
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There probably was more than one storm in 1914 but obviously their were no radar, satilites etc.
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Jerry...maybe you could poot instead....

;)
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My old friend Hahaguy...how are you?
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Canewarning, I got into trouble for that last year; apparently some trolls took exception to my ignoring them...LOL

I'll simply poof them and not say anything about it this year (having learned my lesson)
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719.

No, I run the field operations and IT for a medium Independent Property Adjusting firm; we do a lot of catastrophe work, so hurricanes cut into my free time LOL
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716.

Yep, darlin'...though things could pick up at any moment
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Quoting NRAamy:
any bets on who'll be the first to eat crow this year? Deep fried or BBQ'd?

;)


Sushi with plenty of wasabi, thanks
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Hey Floodman.
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As is usual, Pat: uneasy rests the head, you know...LOL
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I give the GOM Blob no chance to develop, the future Caribbean blob has caught my interest however.
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734. IKE
6-10 day precip outlook....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
Satellite Imagery from the University of Miami


Gulf of Mexico Sector


Member Since: July 3, 2005 Posts: 421 Comments: 127664
Link

Some of the latest stuff and more specifics on the plane crash. Out - L8R
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Quoting NRAamy:
any bets on who'll be the first to eat crow this year? Deep fried or BBQ'd?

;)


My money is on Tampa. He sticks to his guns alot to the end which is admirable.
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Quoting IKE:


Interesting...more model support.


It's only a model........



....LOL
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Great writeup as well Levi. Good read.
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Flood is the Poof-meister...

;)
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Three Crow Recipes
From Debbie, courtesy of her Mom's WW II cookbook
Member Since: July 3, 2005 Posts: 421 Comments: 127664
Floodman is the *Poof* guy...right?
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Quoting Floodman:
Howdy, Vike!


Howdy Flood!
Member Since: August 25, 2006 Posts: 1 Comments: 3016
Quoting Michfan:
92L go bye bye. Next serving of blobs please. Carribean is indeed looking to be an area of interest next week. Things are about to get ugly! Blob Watch 2009 is in full swing.


haha! no kidding
Member Since: August 30, 2007 Posts: 0 Comments: 1837
any bets on who'll be the first to eat crow this year? Deep fried or BBQ'd?

;)
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Quoting CaneWarning:


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.

I think it will do okay. SST are okay, shear is low, it has low level vorticity and is hanging onto it's convection. Now it's got a weak anti-cyclone setting up above it.
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Quoting Floodman:
I was in and out...once Ike made landfall it was all over though...lots of training and supervision, you know...


Do u do construction?
Member Since: August 30, 2007 Posts: 0 Comments: 1837
Jovial to Have ya Back Floodman,How goes the Populace?
Member Since: July 3, 2005 Posts: 421 Comments: 127664
92L go bye bye. Next serving of blobs please. Carribean is indeed looking to be an area of interest next week. Things are about to get ugly! Blob Watch 2009 is in full swing.
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Quoting Floodman:
I was in and out...once Ike made landfall it was all over though...lots of training and supervision, you know...

Good to see things are calming down for you Flood.
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I was in and out...once Ike made landfall it was all over though...lots of training and supervision, you know...
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Quoting Patrap:
The Great Red Spots seems to be trending,..er..west?



Howdy, Pat! Yep, and I mis-spoke myself before...it's JOVIAN warming...LOL
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713. IKE
Quoting SomeRandomTexan:
Levi---
nice... guess we will be waiting and watching..


I'll 2nd your opinion. Nice description Levi.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Flood--
have you been on since Dolly? that's the last I remember seeing you...lol
Member Since: August 30, 2007 Posts: 0 Comments: 1837

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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.