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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1112. Levi32
"Somehow the convection of these thunderstorms within the hurricane seems to organize the hurricane better and improve its rotation," Price said.

Not sure why he said it as if we don't already know why that happens.
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I think we should already have been to Claudette.

90L should have been Ana, TD 1 should have been Bill, and 92L should have been Claudette.

While it's just my opinion, they all at one point were a TS...or a STS in 92L's case.
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1109. Makoto1
Same thing happened here when the extratropical Ike sent strong winds here in Ohio. No one realizes that it just takes something falling on you can kill you. That's the biggest reason I stayed inside for that whole thing.
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129 people died from cat. 1 Agnes
Member Since: May 27, 2009 Posts: 0 Comments: 4438
from the link you supplied st.simons

this is the forcast for texas the day a cat 4 hurricane was going to hit:

north to east winds, probably high on the coast.

the weather map also has no indictation of a hurricane. they do have a low pressure system sitting off the gulf coast, but NOT A SINGLE mention of cyclone, hurricane, or any other word the NWS deemed inappropiate at the time.
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I'm a little confused about something:
(the following is from the NHC's may 2009 outlook for this hurricane season)
"we estimate a 70% probability for each of the following seasonal ranges:

9-14 Named Storms,
4-7 Hurricanes
1-3 Major Hurricanes,
An ACE range of 65%-130% of the median ."
So if they dont issue a numerical "scientific best guess", what would this be considered? Just a little confused.
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Homestead Air Force Base peak wind gusts were likely near 200-mph.The lowest barometric pressure recorded on land in Andrew was 27.25 inches (923 mb) in Homestead. Only three other tropical cyclones have had a landfalling barometric pressure lower than hurricane Andrew in the United States - the Florida Keys Hurricane (1935), Hurricane Camille (1969), and Hurricane Katrina 05.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1104. Patrap
Lightning Warns of Hurricanes' Most Intense Moments

Convection Connection

The search for a connection between lightning and hurricane intensity stems from research done in the 1990s. Scientists found that storms intensify over warm waters due to greater vertical convection%u2014the upward movement of heat.

"Somehow the convection of these thunderstorms within the hurricane seems to organize the hurricane better and improve its rotation," Price said.


Related articles
Member Since: July 3, 2005 Posts: 428 Comments: 129902
Quoting gator23:


I agree I went through Andrew that is why I sometimes go crazy when I hear people who went through other storms say "Hurricanes arnt that bad."

What 9 ppl (?) died in Florida bc they thought Katrina was just a Cat 1 and blew it off...people don't realize all it takes is that falling tree....
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Some say Ike should have been a cat. 3 at landfall, but personally keeping it at a cat 2 should help the public realize the storm doesn't have to be a major hurricane to cause damage.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
1101. gator23
Quoting TampaFLUSA:

True, but we are talking about the anemometers that failed at 165mph 175mph and so on...


I agree I went through Andrew that is why I sometimes go crazy when I hear people who went through other storms say "Hurricanes arnt that bad."
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00z should be interesting.
Member Since: May 14, 2006 Posts: 8 Comments: 13841
Quoting TampaFLUSA:

True, but we are talking about the anemometers that failed at 165mph 175mph and so on...


The NHC itself recorded a gust to 164 mph before its equipment failed. Other areas had gusts over 175 mph.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Didnt realize someone else posted abour the change in the saffir simpson scale. :)
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Quoting gator23:
Hi all! I have been reading some of your comments about the whole Andrew debate. I think what is happening here is that while many people believe they have seen hurricane force winds most people havent seen anything past tropical storm force winds, so that when they actually get hurricane force winds they are "surprised"

True, but we are talking about the anemometers that failed at 165mph 175mph and so on...
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All this discussion about categories is an explicit example of why the NHC will be approaching the saffir - simpson scale differently this year. They will use the experimental Saffir Simpson Hurricane Wind Scale this year. This scale removes the mention of minimum central pressure, and storm surge ranges, so that public confusion is reduced.
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RE: Cat4 vs Cat5
With any hurricane that is devastating - where you live - it seems as if the storm should be recognized for it's full fury.
Folks effected by Andrew, saw the results of that fury first hand.
There are many along the SC coast, who feel that Hugo was under reported in terms of intensity

However, those of us who lived in Charleston when Hugo hit, know that if Hugo is what a Cat4 can do - we do not want to be anywhere within a hundred miles of a Cat5

Upgrading a borderline Cat4 to a Cat5, does not (IMHO), better prepare the public. (Goes for any borderline category storm)

EDITED: for clarity
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Quoting Stormchaser2007:
Interesting.

SAL has lessened quite a bit.





LOL try all most gone
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Well Considering Andrew was the 4th most Intense Atlantic Cane at landfall on record then it is no suprise it was bumped to Cat 5.
Member Since: May 27, 2009 Posts: 0 Comments: 4438
So Andrew had an hour before it hit land from the last "fix"...we remember how fast Charley strengthened bf landfall...
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Another 90L image
Member Since: June 9, 2007 Posts: 4 Comments: 15950
1090. Patrap
All Obs are relative ones.
One person dosent see the same effects from a System as another in a Different Locale.

Camille had a Official Wind Sustained at 212 from Keesler AFB in 69. But Butch Loper and others from Miss,emg mgrs and others know that at the Seabee Base in Long Beach,Miss a Sustained Wind of 231mph was recorded but not officially.


Einstein had it right a long time ago. EVERYTHING is relative to a single observer.
Always.
Member Since: July 3, 2005 Posts: 428 Comments: 129902
1089. gator23
Hi all! I have been reading some of your comments about the whole Andrew debate. I think what is happening here is that while many people believe they have seen hurricane force winds most people havent seen anything past tropical storm force winds, so that when they actually get hurricane force winds they are "surprised"
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1088. Levi32
Quoting Vortex95:
by the way wind speed is the ONLY thing the NHC counts now pressure ranges were phased out of the S-S scale. As long as it makes it to TS status than wind is the only thing that counts.


Well it makes sense because the central pressure of the storm in and of itself does not affect the people in its path. The wind, the rain, and the storm surge do. However I think it would be prudent if the NHC considered the central pressure when estimating the maximum winds, even when the recon can't find them.
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This was probably taken at about the time my parents house was losing its roof.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
Part of the final Andrew Report...
The final offshore "fix" by the reconnaissance aircraft came at 0804 UTC and placed the center of the hurricane only about 15 nautical miles, or roughly one hour of travel time, from the mainland. A dropsonde indicated a pressure of 932 mb at that time.
Based on the observations and an eastward extrapolation of the pressure pattern to the coastline, Andrew's minimum pressure at landfall is estimated to be 922 mb. This suggests that the trajectory of the dropsonde deployed from the aircraft did not intersect the lowest pressure within the eye.
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Quoting Stormchaser2007:


90L:






This was definetly a Tropical Storm with winds sustained at 50 mph, and gust at 65 mph.
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Quoting hurricane23:


Say that in the face of 150-165mph winds

I share THIS with you


Well I have no say in the upgrade of Andrew becuase at the time I was in West Palm enjoying cloudy sky's with 40 mph winds while you guys experienced 150+mph winds. I am neutral in the discussion.
Member Since: June 9, 2007 Posts: 4 Comments: 15950
1082. Patrap
2004 Regional Imagery Products Gulf Of Mexico
Member Since: July 3, 2005 Posts: 428 Comments: 129902
1026...

here is the official NWS report for galvaston texas sat sept 8th (from the weather headquarters in washington) rain saturday, with high northerly winds, sunday rain followed by clearing.

NO mention of a hurricane or even a cyclone at all. and yet, that very weekend, the city was nearly wiped off the earth from one. funny how the cuban meteorologist father gangoite of the belen observatory knew about the hurricane and even the direction it was headed in.

but this information was surpressed by the nws as the felt the cubans had no understanding of the mechanics of the weather (which we now know is false).
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Quoting MrstormX:


The pressure drop is the best evidence of all


90L:
Impressive winds for an invest



Member Since: June 9, 2007 Posts: 4 Comments: 15950
1079. Patrap


NOAA Wilma Info Page
Member Since: July 3, 2005 Posts: 428 Comments: 129902
Quoting StSimonsIslandGAGuy:
I disagree with making Andrew a cat 5. To be the ultimate, a Cat 5, a hurricane should meet ALL of the qualifications, including pressure. Not just wind.


Well if you don't think Andrew was a cat 5 at landfall. What would you say it was? A cat 4?
And if Andrew was only a cat 4 at landfall, and seeing the damage he did, how could you possibly say a cat 4 hitting anywhere wouldn't be that bad? I don't know how much damage you've seen first hand but a cat 4 would be devestating ANYWHERE!

But I guess we are lucky to have people at the NHC who know what theyre doing. So they can warn the public in times of danger. So the public wouldnt have to get their information from people who say a cat 4 wouldnt be that bad.

Just my humble opinion.
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1077. Patrap
IKE NOAA IMAGE Map

Impact counts,not anyone's Belief nor SS numbers
Member Since: July 3, 2005 Posts: 428 Comments: 129902
Quoting TampaFLUSA:

The is definitely worth looking into...


The pressure drop is the best evidence of all
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting Stormchaser2007:


I have to agree with you about Andrew not being a Category 5 at landfall. I know Adrian will slap me upside the head for saying that though...


Say that in the face of 150-165mph winds

I share THIS with you
Member Since: May 14, 2006 Posts: 8 Comments: 13841
1074. Patrap

The Damage Swath NOAA Map

This one is 3 Hours Driving time from East to west..and vice versa
Member Since: July 3, 2005 Posts: 428 Comments: 129902
The Caribbean storm may very well be the most intresting thing we will see for weeks, lets just hope its not the next Ana
Member Since: May 27, 2009 Posts: 0 Comments: 4438
Quoting MrstormX:
Here is what I am talking about:

Link

This is definitely worth looking into...
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Quoting StSimonsIslandGAGuy:
Actually from what I understand, the pressure was believed to be 932 mb at the homestead landfall, and the pressure was recorded as being lower when several readings in the 922-925 mb range were reported from home barometers in the eye and the barometers inspected


You are right, the 922 came from a home I believe.
Member Since: April 26, 2009 Posts: 3 Comments: 3667
GFS mean precip column shows a large increase over the Caribbean.

Member Since: June 9, 2007 Posts: 4 Comments: 15950
In case anyone is interested in reading the analysis behind the upgrade of Andrew to a Cat 5, here is the Link
Member Since: April 26, 2009 Posts: 3 Comments: 3667
1066. Makoto1
Quoting Patrap:
Impacts counts,not any Man Made scale of Numbers.

Especially the SS scale.
Its a People Buisness,not a FACT buisness.

The numbers come with the territory,but at the end of the day,and beginning. Its all about saving Lives and protecting property and economic interests.


I couldn't have said it better myself.

Look at Ike, it was absolutely devastating, and yet it was only a Category 2. The category doesn't always show the level of destruction, that's for sure.
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1065. Patrap
Gulf of Mexico Coastal Ocean Observing System
Member Since: July 3, 2005 Posts: 428 Comments: 129902
1064. Levi32
Quoting StSimonsIslandGAGuy:
I disagree with making Andrew a cat 5. To be the ultimate, a Cat 5, a hurricane should meet ALL of the qualifications, including pressure. Not just wind.


In a perfect world you would be right, but the Saffir-Simpson Hurricane Scale is only for wind, not pressure. Andrew was a very small hurricane, and therefore very compact. That made the isobars closer together than a typical hurricane of his central pressure, and therefore the wind was higher than it normally would be. The reverse is true with very large spread-out storms, the wind will be lower relative to the central pressure of the storm.
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Quoting StSimonsIslandGAGuy:
I disagree with making Andrew a cat 5. To be the ultimate, a Cat 5, a hurricane should meet ALL of the qualifications, including pressure. Not just wind.

The lowest I belive was 922 3mil off...and didn't the hurricanes Hunters stop flying into the hurricane just before landfall as it was still intensifying....nether the less it shows that the saffir simpson scale should be modified....
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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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