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 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: 3046
811. IKE
Quoting Weather456:
I looked at the GFS precip and 500-1000 thickness and there is some truth to what CCH pointed out. The wave was early tracked westward by the kink in the thickness lines and moisture signature.

it approaches the islands in 90 hrs, and reaches the W Carib by 144 hrs, with a marked moisture surge




My gosh...how fast is it moving?
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting IKE:


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



Hey Ike; I just left Bonifay (back to Tally) about 2 hours ago;...... little bit of rain in your parts this afternoon?
Member Since: August 8, 2006 Posts: 0 Comments: 9024
I looked at the GFS precip and 500-1000 thickness and there is some truth to what CCH pointed out. The wave was easily tracked westward by the kink in the thickness lines and moisture signature.

it approaches the islands in 90 hrs, and reaches the W Carib by 144 hrs (though it maybe sooner since this is the 12Z runs), with a marked moisture surge. I don't know about cyclogensis as yet, but conditions are expected to be there for the potential.


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Quoting Weather456:
Neither Anrea nor Vince. The top image was taken by MODIS TERRA 1200 UTC 3 June 2009 and the bottom image was taken by MODIS AQUA at 1440 UTc 3 June 2009. That is Invest 92L, or I should rather say, that was Invest 92L.


This contest was fixed, ha ! Oh, wait, I guessed right, nevermind :)

Futuremet, can you boot up in safe mode at all?
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806. IKE
Quoting futuremet:
My computer crashed two days ago. I am trying to make a bootable CD recovery disk to fix the issue.

It looks like things will get interesting next week.


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

Member Since: June 9, 2005 Posts: 23 Comments: 37858
My computer crashed two days ago. I am trying to make a bootable CD recovery disk to fix the issue.

It looks like things will get interesting next week.
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Quoting Weather456:
Neither Anrea nor Vince. The top image was taken by MODIS TERRA 1200 UTC 3 June 2009 and the bottom image was taken by MODIS AQUA at 1440 UTc 3 June 2009. That is Invest 92L, or I should rather say, that was Invest 92L.

HOLY... not gonna say it.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
That darn 92L
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thanks cch none of the models agree on anything right now I think it was the GFS that showed the low the other day. current model shows same low hitting cuba then it goes out to the Atlantic
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Neither Anrea nor Vince. The top image was taken by MODIS TERRA 1200 UTC 3 June 2009 and the bottom image was taken by MODIS AQUA at 1440 UTc 3 June 2009. That is Invest 92L, or I should rather say, that was Invest 92L.
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LOL 799
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I'll take Tropical Storms for 500 ALex..

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Quoting StSimonsIslandGAGuy:
a tropical storm or Cat 1 hurricane can form easily on shallow warm water, for a major hurricane you need a deep warm surface layer to withstand mixing


Hey Folks...Been too busy at work today to get on but I would remind you that Andrew spun up, from TD status, (it fell apart crossing the Atlantic)around the relatively shallow Bahamas, hit the Gulf Stream, and we know what happened next.....Agree with your point about tropical storms and "shallow" (pun intended) Cat 1's, but we all worry about that rapid intensification issue for "local storms", which, under the right conditions, can "peak" shortly after formation which may be right before/at landfall.........
Member Since: August 8, 2006 Posts: 0 Comments: 9024
Quoting Weather456:
Andrea or Vince? Guess




Vince. Andrea had a clearer "eye".
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Ohh dear god, is that really 92L
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Anyone else? before i give the answer
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Been taking a closer look into the computer models and it does appear that when the tropical wave currently at around 38W moves into the Western Caribbean, it starts to undergo some tropical cyclogenesis, albeit very gradual, as it encounters sufficiently warm waters, deep tropical moisture due to an approaching strong MJO impulse into the Western Hemisphere, and a developing anticyclone over the Western Caribbean.

But, at this time, this remains to be seen and I would like to see much more model consensus and further consistency before I buy into this solution.
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92L LoL
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Ohh tough Looks like Andrea in nature, but don't see the SE coastline so Vince.
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Andrea or Vince? Guess



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are models still showing 1008mb low entwring GOM next week?
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Thanks all, I remember reading about the 150' level and can't for the life of me find it.

Pause--


Duh, it was from the last blog and not feet it was meters. I must be getting older everyday :)

Tropical Cyclone Heat Potential
It's not just the SSTs that are important for hurricanes, it's also the total amount of heat in the ocean to a depth of about 150 meters. Hurricanes stir up water from down deep due to their high winds, so a shallow layer of warm water isn't as beneficial to a hurricane as a deep one. The Tropical Cyclone Heat Potential (TCHP, Figure 3) is a measure of this total heat content. A high TCHP over 80 is very beneficial to rapid intensification. As we can see, the heat energy available in the tropical Atlantic has declined considerably since 2005, when the highest SSTs ever measured in the tropical Atlantic occurred. TCHP this year is similar to last year's levels, which were high enough to support five major hurricanes.


Interesting


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Current Maximum Potential Hurricane Intensity


The maps display potential minimum pressure and maximum winds, calculated according to a method developed by Dr. Kerry Emanuel. Dissipative heating is handled according to a method described in Bister and Emanuel (1998). The maps are based on data from the 00Z global operational analysis from NCEP for the date shown on the plot. The top panel shows the potential minimum central pressure for a hurricane at any given location (in millibars). Only values less than 1000mb are shaded. Cyan squares indicate grid points where the algorithm failed to converge. Also shown are the sea surface temperatures (°C). The bottom panel shows the potential maximum wind speed expressed in terms of the type and severity of storm they would represent (TD = Tropical Depression, TS = Tropical Storm, H1-H5 = Hurricanes of category 1-5 on the Saffir-Simpson scale).



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Quoting Ossqss:
They are marching N .

456, what is the relevance of the 150' 26%uFFFD temp depth on hurricanes? I seem to remember them needing or wanting that to propagate.





Heat capacity.

The deeper the the 26C waters the more potential enegery stored for the potential TC and less upwelling from surface winds. On of the requirements of TC formation and intensification is deep warm waters.

I'm not sure how they calculate the energy in kilojoules but it takes into account the dept of the 26C waters rather than just the surface temp.


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They are marching N .

456, what is the relevance of the 150' 26º temp depth on hurricanes? I seem to remember them needing or wanting that to propagate.



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Quoting Tropicsweatherpr:


Hi 456.Do you have the latest NAO projections in terms of when it will flip to negative? I know that StormW said in September,but that was 2 weeks ago.


StormW and I use the source I think, Accupro, the latest figures show a decline in the index from positive to negative but I expect it to continue to transition with negative through August-September.
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782. WAHA
92L is too high up in terms of water temperature to form anything at all. I give a 20 percent chance it does.
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Quoting Weather456:
SST really climbing. SST is one the factors to get an idea of the NAO also the trades



Hi 456.Do you have the latest NAO projections in terms of when it will flip to negative? I know that StormW said in September,but that was 2 weeks ago.
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SST really climbing. SST is one the factors to get an idea of the NAO also the trades. One think I could not resist notice is that we warmer temps near Bermuda this year.

2009



2008

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Quoting winter123:
For those that missed it, high quality loop proving 92L was subtropical:

Link


Yea 92L was subtropical with a ST # of 3.0
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Quoting Vortex95:
its june 3 yet Michigan still has to suffer with winter weather. Temps to dip in to the mid 30's for them tommorow morning.



Three Chineese cheers for global warming!



PHOOEY PHOOEY PHOOEY!
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Good evening
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A new book just came out on the 1935 Labor Day hurricane. I just purchased it but I was wondering if anyone had stumbled across it before me? It's called Cat 5: The 1935 Labor Day Hurricane by Thomas Knowles.



Link
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For those that missed it, high quality loop proving 92L was subtropical:

Link
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Afternoon all

Great to see ya back Jerry :~)
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Okay folks, I'll be back tomorrow; got to talk to some attorneys about "things" you know...be safe and be good to one another!
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Quoting Floodman:


Not too bad...keep getting called away to work...no rest for the wicked, as they say...



GASP!!! the season really has started.. your back from the 70's again :)
Member Since: October 1, 2007 Posts: 81 Comments: 26511

AOI #1

AOI #2
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Quoting hahaguy:
I'm good flood how about you?


Not too bad...keep getting called away to work...no rest for the wicked, as they say...
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Quoting Vortex95:
eddyeye may eat the most crow this season if he returns with his preditions of 6 majors hitting s florida so his school can be destroyed.


LOL, i remember him posting a lot last year. He was wishcasting Ike and Fay if I remember correctly.

On a weather-related note, we had about .48 inches of rain in about 15min here earlier. It was coming down at 3.92 inches per hour according to my PWS.
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Quoting NRAamy:
Jerry...maybe you could poot instead....

;)


I leave that to the trolls...they are quite adept
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HEY EVERYBODY
I was just remembering i got hooked on this place in 2004. I think i was k8e1 then. Anyway i was pretty obnoxious back then and for that i apologize. Stormtop was one of my favorite and i will never forget the 2005 hurricane season on here. I used to haggle with him just for the h### of it. I so hope he is ok
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Quoting NRAamy:
hey ...wait a minute....we're not all here yet...

where's STORMTOP?!

;)


SHHHH, Amy...
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Afternoon everyone. Really booming here. Crazy lightning. Back to the afternoon thunderstorms on a pretty regular basis. Unexpected move recently, so I'm back across the river now. Seems like that AB high wants to stay anchored where it is that. That concerns me to be honest. We'll see how that affects this season.
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Cesar-Douglas 1996 track

Member Since: July 14, 2008 Posts: 1 Comments: 9628
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.
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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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