Average hurricane season foreseen by CSU, NOAA, and TSR

By: Dr. Jeff Masters , 4:45 PM GMT on June 02, 2009

Share this Blog
2
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 362 - 312

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27Blog Index


The New Fancy Smancy TDWR Radar from the Airport shows a Lil rotation.
Member Since: July 3, 2005 Posts: 419 Comments: 127371
Some Echo Tops to 53K out there in the red.

NEXRAD Radar
New Orleans, Echo Tops Range 124 NMI
Member Since: July 3, 2005 Posts: 419 Comments: 127371

NEXRAD Radar
New Orleans, Base Reflectivity 0.50 Degree Elevation Range 248 NMI
Member Since: July 3, 2005 Posts: 419 Comments: 127371
No kidding Pat, I am all for that!

Member Since: Posts: Comments:
We need better Buoy Data...SJ

Who's for Mo Buoys with better Data ?





Member Since: July 3, 2005 Posts: 419 Comments: 127371
lol wpb :~)
Member Since: Posts: Comments:
Looks pretty impressive..but..still I think not a lot of time to develop...If it stays intact, I agree the areas it will affect.

Member Since: Posts: Comments:
Also WPB, the shear seems to be taking the convection to the NE, but according to the 18z GFS, the vort field is moving towards the Big Bend/Panhandle area.
Member Since: Posts: Comments:
Some comedy relief..

Member Since: Posts: Comments:
Quoting Stormchaser2007:
There is an extremely low chance of that area of thunderstorms in the GOM becoming anything at all.


That pretty much sums it up. lol
Member Since: Posts: Comments:
Quoting StormJunkie:
Oh, I hear you WPB, I often like to play devils advocate with these iffy areas...

Will be interesting to see if this is a wind shift, or just thunderstorm induced...

I am guessing Quickscat misses it tonight...


There are some really Strong Thunder Storms in the area of the Station and there is Rotation on Radar.It is possible that a weak area of Low Pressure could develop but nothing significant atm.

Member Since: Posts: Comments:
There is an extremely low chance of that area of thunderstorms in the GOM becoming anything at all.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Oh, I hear you WPB, I often like to play devils advocate with these iffy areas...

Will be interesting to see if this is a wind shift, or just thunderstorm induced...

I am guessing Quickscat misses it tonight...
Member Since: Posts: Comments:
Quoting Acemmett90:

did you see the report on cbs so i would watch it



That video was total Media BS and a person like me who knows a thing or two about the Tropics would be in awe and discust.That guy on that video is the male version of the 'weather girl', you know the pretty woman in a bikini or skimpy outfit reading the weather. If you read the bio you can also see the "he is in the forefront of reporting environmental concerns and global warming" which means this little report is the next step in the 'climate change' (AKA global warming), that is due to man the pattern of hurricane formation is changing. However as those of us who follow and study the tropics know this is not a change in the pattern. They make it seem legitmate by either taking parts of interviews with experts that fit the view of the report or talk to sensationalists, like JB, who are trying to drum up business or viewership. It does not suprise me to see this kind of thing, but it does disgust me. What a joke...
Member Since: Posts: Comments:
I always respect your opinion StormJ...just don't think it has enough time.
Member Since: Posts: Comments:
Quoting GeoffreyWPB:
The Gulf area of convection will be on shore within the next 36 hours.


Maybe 42-48 hrs, but that is splitting hairs...If a llc were to develop it has a little time over water, and shear is on the drop...Has a outside chance of becoming a invest imvho...A lot depends on where a llc develops if it does...
Member Since: Posts: Comments:
Quoting Acemmett90:
Do you think the storm in the gulf could become somthing


Its not a Storm,
Its an area of Thunder Storms caused by Upper Level Divergence.
Member Since: Posts: Comments:
Quoting Acemmett90:

disgree on that becuase hurricne seasons are mostly unpredictible


Have my crow ready on June 16!
Member Since: Posts: Comments:
The Gulf area of convection will be on shore within the next 36 hours.
Member Since: Posts: Comments:
Ivest 92L Is still producing 50 mph winds but I think it is still may become a tropical system

It has winds at an excess of >35 mph, which is the necesarry amounts for a tropical storm

Although what the system lacks is Tropical Chareteristc's

If it is not named it still could become an unamed storm when the national hurricane center reviews the season in the spring of 2010.

Until then there still can be some forming of tropical charestics but it is unlikely becasue it is in very cold waters at the time
Member Since: Posts: Comments:
LOL,
I guess its not getting named...
Member Since: Posts: Comments:
imo...no ana within the next two weeks..
Member Since: Posts: Comments:
Not too bad for two days into hurricane season 3 invests one of which becoming a TD. I say we'll get our first system on the 12th
Member Since: Posts: Comments:
Quoting Patrap:
Station 42040 - MOBILE SOUTH 64 nm South of Dauphin Island, AL


That buoy has already gotten me couple of times this year Pat; stinks it does not have wind direction...
Member Since: Posts: Comments:
Quoting MrstormX:
Out of curiosity does anyone know where Invest 94W is in the Pacific?


Link
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Station operated by Shell International E&P
Fixed Drilling Platform
27.800 N 90.670 W (27°48'0" N 90°40'12" W)

Air temp height: 37 m above site elevation
Anemometer height: 122 m above site elevation
Barometer elevation: 37 m above mean sea level
Water depth: 910 m


Wind speed at this drilling platform now 27.2kts.

Link to wind speed graph below:

Link
Member Since: June 2, 2008 Posts: 0 Comments: 157
Out of curiosity does anyone know where Invest 94W is in the Pacific?
Member Since: May 27, 2009 Posts: 0 Comments: 4436
Quoting canesrule1:
what is up with this 92L i checked the quikscat and there is an LLC and there is convection, why is this not a STS or ETS???


NHC has chosen the option in NATIONAL WEATHER SERVICE INSTRUCTION 10-601:

NHC will issue subtropical cyclone advisories. However, due to the lack of well-defined criteria for distinguishing subtropical from non-tropical lows, marginally-subtropical systems may be handled as non-tropical gale or storm centers in High Seas forecast products.
Member Since: September 23, 2005 Posts: 14 Comments: 10838
Quoting canesrule1:
yea, i know


Those never get named.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Quoting Stormchaser2007:


ETS? You know that stands for Extra-tropical storm?
yea, i know
Member Since: Posts: Comments:
Quoting canesrule1:
what is up with this 92L i checked the quikscat and there is an LLC and there is convection, why is this not a STS or ETS???


ETS? You know that stands for Extra-tropical storm?
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Quoting Drakoen:


It's not going to get named.


Exactly.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Quoting Stormchaser2007:


Read the TWO.


THE NON-TROPICAL AREA OF LOW PRESSURE CENTERED ABOUT 400 MILES
NORTH-NORTHEAST OF THE AZORES ISLANDS HAS CHANGED LITTLE IN
STRUCTURE TODAY. THE LOW...WHICH IS OVER WATER TEMPERATURES OF
NEAR 60 DEGREES
...IS ACCOMPANIED BY WINDS OF 45-50 MPH CLOSE TO THE
CENTER BUT IS ASSOCIATED WITH ONLY LIMITED THUNDERSTORM ACTIVITY.
THE LOW HAS BEEN MEANDERING OVER THE PAST SEVERAL HOURS BUT IS
EXPECTED TO BEGIN AN EASTWARD MOTION TOMORROW AND GRADUALLY WEAKEN.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL OR SUBTROPICAL CYCLONE DURING THE NEXT 48
HOURS.


It's not going to get named.
Member Since: October 28, 2006 Posts: 57 Comments: 29864
Station 42040 - MOBILE SOUTH 64 nm South of Dauphin Island, AL
Member Since: July 3, 2005 Posts: 419 Comments: 127371
Quoting canesrule1:
what is up with this 92L i checked the quikscat and there is an LLC and there is convection, why is this not a TS???


Read the TWO.


THE NON-TROPICAL AREA OF LOW PRESSURE CENTERED ABOUT 400 MILES
NORTH-NORTHEAST OF THE AZORES ISLANDS HAS CHANGED LITTLE IN
STRUCTURE TODAY. THE LOW...WHICH IS OVER WATER TEMPERATURES OF
NEAR 60 DEGREES
...IS ACCOMPANIED BY WINDS OF 45-50 MPH CLOSE TO THE
CENTER BUT IS ASSOCIATED WITH ONLY LIMITED THUNDERSTORM ACTIVITY.
THE LOW HAS BEEN MEANDERING OVER THE PAST SEVERAL HOURS BUT IS
EXPECTED TO BEGIN AN EASTWARD MOTION TOMORROW AND GRADUALLY WEAKEN.
THERE IS A LOW CHANCE...LESS THAN 30 PERCENT...OF THIS SYSTEM
BECOMING A TROPICAL OR SUBTROPICAL CYCLONE DURING THE NEXT 48
HOURS.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Member Since: July 15, 2006 Posts: 168 Comments: 53285
what is up with this 92L i checked the quikscat and there is an LLC and there is convection, why is this not a STS or ETS???
Member Since: Posts: Comments:
NOLA Long Range Radar

Houston Long range Radar

18Z NAM/GFSO Multi-Model

Member Since: July 3, 2005 Posts: 419 Comments: 127371
NHC TWD:

CONSIDERABLE UPPER LEVEL MOISTURE COVERS THE
ENTIRE GULF. EXPECT...A WEAK LOW TO FORM OVER THE NORTH CENTRAL
GULF WITH CONVECTION OVER THE NEXT 24 HOURS
Member Since: Posts: Comments:
Quoting KEEPEROFTHEGATE:
AOI
MARK
28N/90W


That area of convection should be dead and gone by tomorrow.
Member Since: June 9, 2007 Posts: 4 Comments: 15776
Well if the "BLOB" becomes something then it has very little time to organize itself
Member Since: May 27, 2009 Posts: 0 Comments: 4436
AOI
MARK
28N/90W
Member Since: July 15, 2006 Posts: 168 Comments: 53285
Pretty quiet in the East Pacific:

Member Since: June 9, 2007 Posts: 4 Comments: 15776
Member Since: July 15, 2006 Posts: 168 Comments: 53285

Viewing: 362 - 312

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Mostly Cloudy
81 °F
Mostly Cloudy