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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can you apply the same information to Southern Florida when it comes to the formation of major hurricanes or hurricanes for that matter? Would like to see the relation towards that
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Evening all.

I found this while searching for info on tropical systems affecting Georgia. Go figure.

A Historical Study of Tropical Storms and
Hurricanes that have affected Southwest
Louisiana and Southeast Texas


This work includes storms documented from 1886 through 1997 and is intended to add valuable knowledge about historical tropical cyclone activity in the County Warning Area (CWA) served by the Lake Charles National Weather Service Office. It should provide an excellent reference for those who live in Louisiana and Texas and those interested in the area's climatology.

Granted it is 12 years old but among other interesting tidbits this one really stuck out to me...

Years of moderate to strong warm ENSO events were checked for any possible relationship with tropical cyclones affecting Louisiana and southeast Texas. These warm events seemed to have no significant correlation to an increase or decrease in tropical storms and hurricanes entering the area; it has been recently discovered though that it does make a difference further down the Texas coast.

Unexpectedly, ENSO events seemed to have a strong correlation to major hurricanes in this area. Five of the eight major hurricanes struck the region during the middle of moderate to strong El Niño events. If one expands the criteria to within one year of a moderate ENSO seven of eight become included. Further study is needed to totally resolve this issue.

Oh Brother! Lol.
Anyway its pretty interesting.



Link
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905. plywoodstatenative 4:49 PM PDT on June 03, 2009
Keeper, usually when its this quiet in the Atlantic, is when mother nature wakes up and well the blog goes nuclear in ways


that's one way to put it!!!!

;)
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Quoting nrtiwlnvragn:


You can select the 850-200 mb shear in the field for the cmc, gfs and ngp at the FSU site.
Thank you, nrtiwlnvragn. Much appreciated.
Also found this:
Wind Shear - 4 Days Out

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Keeper, usually when its this quiet in the Atlantic, is when mother nature wakes up and well the blog goes nuclear in ways.
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Quoting KEHCharleston:
Afternoon all,

Does anyone have a model that goes beyond 72 hours for wind shear forecast?

Thanking you in advance


You can select the 850-200 mb shear in the field for the cmc, gfs and ngp at the FSU site.
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Drak, layman terms for those of us who are half awake plz.
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Quoting KEEPEROFTHEGATE:
Makoto1
Though I really was rooting for it to become Ana mostly for the laughs, the effects would have been the same either way.


ana may end up laughting at you


Only if it laughs at the NHC as well.
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Quoting WPBHurricane05:
Other than 92L (which will soon disappear), there is not one invest in the world. Link
a little too quiet
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700 mb curvature vorticity showing some kind of feature enhancing PV in the vicinity of the SW Caribbean, then advects it northward over the NW Caribbean. This is on time frame of 5-9 days.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Makoto1
Though I really was rooting for it to become Ana mostly for the laughs, the effects would have been the same either way.


ana may end up laughting at you
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Quoting plywoodstatenative:
Mrs, two things: One do not use caps in here as you will get ignored. Secondly, the only people that truly can declare a storm dead is the NWS and the blog owner.


Well the NWS kind of did, but besides the point thank you for the advice I am obviously new here so I will take any advice I recieve.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Other than 92L (which will soon disappear), there is not one invest in the world. Link
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Quoting plywoodstatenative:
Drak,

With this wave, lower shear values, and higher temperatures what is the forecast based on that? Also what is the forecast for troughs for the next few days?


The venting upper air circulation aloft with support a moisture surge in the Caribbean. Whether or not something forms is still questionable. The wave in the CATL may play a role in adding to the moisture once a decent low already forms in the SW Caribbean. The Southern branch of the jet stream looks to retreat northward to allow for the subtropical ridge to vent northward. The overall 500mb longwave pattern looks to features a series of shortwave troughs that will may act to erode the higher and allow for poleward movement. I would still like to see shear a little bit more conducive over a wider area.
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I could only imagine what the media would say if 92L became Ana.
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Quoting MrstormX:
92L IS KILLED


I knew it was looking weak.. So much for 92L.

Though I really was rooting for it to become Ana mostly for the laughs, the effects would have been the same either way.
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Mrs, two things: One do not use caps in here as you will get ignored. Secondly, the only people that truly can declare a storm dead is the NWS and the blog owner.
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Ike, its been out for a while. The question really becomes whether this season will follow to what Gray has said or whether we are looking at another neutral setup
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92L IS KILLED
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Drak,

With this wave, lower shear values, and higher temperatures what is the forecast based on that? Also what is the forecast for troughs for the next few days?
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889. IKE
Quoting nrtiwlnvragn:
FURTHERMORE...AS THE MID/UPPER TROUGH AMPLIFIES ACROSS THE GULF OF MEXICO...IT WILL INDUCE THE GRADUAL NORTHWARD AMPLIFICATION OF THE CLIMATOLOGICAL TROUGH OVER WESTERN COLOMBIA/PANAMA INTO THE SOUTHERN CARIBBEAN. IT IS TO ALSO FAVOR FORMATION OF A CLOSED LOW JUST SOUTH OF THE GULF OF PANAMA BY MID CYCLE...AND THE NORTHWARD MODULATION OF THE PACIFIC ITCZ INTO THE ISTHMUS/NORTHERN COLOMBIA. IN TANDEM WITH THIS EVOLUTION...DEEP TROPICAL MOISTURE WILL START TO SURGE ACROSS PANAMA/COSTA RICA INTO THE SOUTHERN CARIBBEAN BY 36 HRS...


TROPICAL DISCUSSION - INTERNATIONAL DESKS


Maybe I will stick my neck out. Get that crow out of the freezer.
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Quoting NRAamy:
hey ply!

you made need 2-ply by the time this blog is over....

;)


ROLF!
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lol, nice one. Amy how has MP been?
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Looking at the 700mb heights and 1000-500mb thickness the wave does not appear to be associated with the cyclogenesis in the southern Caribbean.
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hey ply!

you made need 2-ply by the time this blog is over....

;)
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Afternoon all,

Does anyone have a model that goes beyond 72 hours for wind shear forecast?

Thanking you in advance
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883. IKE
Quoting Weather456:
Wait, Ike, Sunday is 4 days away.

I said the marked moisture surge associated with the wave is expected to reach the W caribbean in 144 hrs or 6 days. Whether or not it contributes to the possible TC is yet to be seen.


Okay...you may be correct.
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882. IKE
Quoting plywoodstatenative:
its not about sticking your neck out, its about how much crow can one eat for a season this year?
LOL


Quoting NRAamy:
I just realized today is Wednesday. I've been thinking Tuesday. I need some sleep.:(

atleast you don't need Depends!

;)
LOL...hey a few years ago when my.....forget it.
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FURTHERMORE...AS THE MID/UPPER TROUGH AMPLIFIES ACROSS THE GULF OF MEXICO...IT WILL INDUCE THE GRADUAL NORTHWARD AMPLIFICATION OF THE CLIMATOLOGICAL TROUGH OVER WESTERN COLOMBIA/PANAMA INTO THE SOUTHERN CARIBBEAN. IT IS TO ALSO FAVOR FORMATION OF A CLOSED LOW JUST SOUTH OF THE GULF OF PANAMA BY MID CYCLE...AND THE NORTHWARD MODULATION OF THE PACIFIC ITCZ INTO THE ISTHMUS/NORTHERN COLOMBIA. IN TANDEM WITH THIS EVOLUTION...DEEP TROPICAL MOISTURE WILL START TO SURGE ACROSS PANAMA/COSTA RICA INTO THE SOUTHERN CARIBBEAN BY 36 HRS...


TROPICAL DISCUSSION - INTERNATIONAL DESKS
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lol Amy, thats one way to wake up a blog.
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I just realized today is Wednesday. I've been thinking Tuesday. I need some sleep.:(

atleast you don't need Depends!

;)
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456, South Florida might be underwater by then
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Wait, Ike, Sunday is 4 days away.

I said the marked moisture surge associated with the wave is expected to reach the W caribbean in 144 hrs or 6 days. Whether or not it contributes to the possible TC is yet to be seen.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
its not about sticking your neck out, its about how much crow can one eat for a season this year?
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875. IKE
Quoting sporteguy03:
Ike,
Are you ready to stick your neck out now or another day or so? lol:)


I was just sitting here thinking while watching the Braves on MLB.tv that I wouldn't be shocked if the GFS backed off on it's next run.

Then again, it does have some company. Think I'll wait until Thursday before sticking my 51 year-old neck out on a limb.

I just realized today is Wednesday. I've been thinking Tuesday. I need some sleep.:(
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Quoting plywoodstatenative:
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?


Does rain predict hurricanes?
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those SST's should have some sort of influence on either the wave or the blob in the Gulf. Its up to mother nature whether she wants to show her tricks yet or not.
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.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Ike,
Are you ready to stick your neck out now or another day or so? lol:)
Member Since: July 7, 2005 Posts: 0 Comments: 5306
Quoting WeatherStudent:


At least a possible TS, 456? Are you anticipating conditions down there to become that conducive for TC formation, bud?
as we progress into the season sooner or later the match is going to hit the striker then the game's begin lets finish the game
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I have my doubts but the GFS has been very acurate so far with Low pres. formation, also the posible system formation place is typical for this time of the year, a weak TS out of this is very posible due to clymatology data, but let the expert call it since I can't figure out the cyclogenesis.
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868. IKE
456....I don't think that wave is what will enhance the western Caribbean by Sunday/Monday....this from the afternoon Puerto Rico discussion....

"Highly amplified tropical wave along 37 per latest tpw and infrared
imagery will move west and enter the eastern Caribbean Sea on Tuesday based
on latest 12z GFS and using the climatological rate of 5 degrees
longitude per day. Vertical shear too strong for any tc development
and middle-upper level ridging expected to build over the area not all
that conducive to a lot of weather."
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Quoting antonio28:
Thanks 456, so it looks like at least a posible TS, do you have the cyclogenesis analysis for this one?


I did mentioned it this morning on my blog as we get a more clearer view, details will follow in subsequent entries. I can tell you it is quite possible given the available forecasts.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Just in case eveybodies eyes are on the tropics... a little heads up on what might be coming your way..
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LOL, I used to it, the heat of the summer finally arive to PR we hit the 90 for a couple of days in a row, finaly the tropical summer arive, to me later than normal.
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862. SomeRandomTexan 11:12 PM GMT on June 03, 2009
the blog is def coming alive...lol!

alot are running in stealth mode waitin
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the blog is def coming alive...lol!
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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.