CSU and TSR continue to predict a near-average hurricane season

By: Dr. Jeff Masters , 3:18 PM GMT on August 04, 2009

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A tropical disturbance embedded in the Intertropical Convergence Zone (ITCZ), near 9N 35W, is moving west at about 15 mph. The heavy thunderstorm activity associated with this tropical wave has changed little over the past 24 hours, and remains disorganized. This morning's QuikSCAT pass showed a moderate wind shift, but nothing resembling an organized surface circulation. Top winds were in the 20 - 30 mph range. Strong easterly winds are creating about 20 knots of wind shear over the wave, which is marginally conducive for development. The disturbance is about 300 miles south of the Saharan Air Layer (SAL), so dust and dry air should not hinder development over the next few days.

Given the disturbance's current lack of organization, combined with the presence of 20 knots of wind shear, any development should be slow to occur. The forecast wind shear along the storm's path over the next five days is predicted to remain at or below 20 knots, which should allow some slow development. Sea surface temperatures (SSTs) will warm from about 28°C to 29°C as the storm progresses westward. The GFS model has been indicating some development is possible in several of its runs over the past few days, but has not been consistent with this prediction. None of the other models show any development of the system. NHC is giving the disturbance a low (less than 30% chance) of developing into a tropical depression over the next two days, which is a good forecast. The GFS and ECMWF models predict the system will be approaching the northern Lesser Antilles Islands by Sunday. Both models forecast the development of a band of very high wind shear just to the north of the islands at that time, so the long-range survival of anything that might manage to develop is in doubt.

CSU forecast team continues to predict an average hurricane season
A near-average Atlantic hurricane season is on tap for 2009, according to the seasonal hurricane forecast issued August 4 by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). The CSU team is calling for 10 named storms, 4 hurricanes, and 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 83% 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 June forecast, which called for 11 named storms, 5 hurricanes, and 2 intense hurricanes. Their April forecast 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 (27% chance, 31% chance is average) and the Gulf Coast (26% chance, 30% chance is average). The Caribbean is also forecast to have an average risk of a major hurricane (37%; 42% is average).

The forecasters noted that while sea surface temperature anomalies have increased in the tropical Atlantic and surface pressures have fallen in recent weeks, which normally would favor higher hurricane activity, the presence of El Niño conditions in the Eastern Pacific should counteract these influences. They forecast that the current weak El Niño event will strengthen to a moderate event by September:

El Niño events tend to be associated with increased levels of vertical wind shear and decreased levels of Atlantic hurricane activity. Tropical Atlantic sea surface temperatures anomalies have warmed somewhat since our early June prediction and surface pressures have fallen somewhat. But, the negative influences of El Niño-induced strong Caribbean Basin and Main Development Region vertical wind shear typically dominate over surface pressure and sea surface temperature in the tropical Atlantic.



Figure 1. Change in Sea Surface Temperature anomaly (in °C) between July 2009 and May 2009. Most of the tropical Atlantic has warmed, relative to normal, over the past 2 months. Image credit: NOAA/ESRL.

Analogue years
The CSU team picked four previous years when atmospheric and oceanic conditions were similar to what we are seeing this year: weak to moderate El Niño conditions, and average tropical Atlantic and far northern Atlantic SSTs. Those four years were 2002, which featured Hurricane Lili that hit Louisiana as a Category 1 storm; 1965, which had Category 3 Betsy that hit New Orleans; 1963, which had Category 4 Hurricane Flora that devastated Cuba; and 1957, which didn't have any hurricanes that hit hit land during the peak part of hurricane season. The mean activity for these four years was 9 named storms, 4 hurricanes, and 2 intense hurricanes--almost the same as the 2009 CSU forecast.

How accurate are the August forecasts?
The August forecasts by the CSU team have historically offered a skill of 45 -62% higher than a "no-skill" forecast using climatology (Figure 2). However, they are using a new forecast scheme this year, so it is difficult to judge how skillful this year's forecast might be.


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.

August 2009 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR) also issued a new forecast today, and have increased their numbers by 20% from their June and July forecasts. TSR is also calling for a near-average season, predicting 12.6 named storms, 6.5 hurricanes, 2.8 intense hurricanes, and an Accumulated Cyclone Energy (ACE) 103% of average. Their June forecast called 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 slightly above the 50-year average of 10 named storms, 6 hurricanes, and 2 intense hurricanes. TSR predicts a 40% chance of an above-average season, 44% chance of a near-average season, and a 19% chance of a below-average season, as defined by ACE index. TSR rates their skill level as 51% above chance at forecasting the number of named storms, 60% skill for hurricanes, and 44% skill for intense hurricanes. These are far higher skill numbers than the June ones: 26% above chance at forecasting the number of named storms, 15% skill for hurricanes, and 19% skill for intense hurricanes.

TSR projects that 3.8 named storms will hit the U.S., with 1.6 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 August forecasts for U.S. landfalls is 25% above chance. In the Lesser Antilles Islands of the Caribbean, TSR projects 1.1 named storms, 0.5 of these being hurricanes. Climatology is 1.1 named storms and 0.5 hurricanes.

TSR cites one main factor for their increased forecast: higher sea surface temperatures than expected over the tropical Atlantic, due to the fact that the trade winds over the Atlantic should be slower than originally anticipated. Faster than average trade winds 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.

The CSU and TSR groups are done making forecasts for the coming hurricane season, but NOAA is still due to put out an August update.

I'll have an update on Wednesday.
Jeff Masters

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yes! the buble in the Altlantic finally found momentum....
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Quoting atmoaggie:
I assume you guys saw the total lack of surface circ in this QuikScat plot. (Yeah, I know it is old)



Oh, and we are going to get to see the Dawg Tigah bait get mauled come October, Alaina. Worry not.

i dont see a total lack of circulation
i see a lack of total circulation
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Quoting cchsweatherman:
Right now, our Central Atlantic disturbance seems to be getting better organized. On the Tropical RAMSDIS Visible Satellite Loop, there seems to be an increasingly better defined low-level circulation center forming near 9N and 36W. As a few people have posted, the CIMSS 850mb Vorticity product also supports this conclusion as it shows increasing lower-level vorticity becoming more defined as well. These are all indications that we could be watching a developing system.

As for the future, its really difficult to determine since it will all depend upon the track and progression of the TUTT north of Puerto Rico. In taking a quick look at most models, they suggest that wind shear will remain quite hostile by the weekend in the Northern Caribbean when this disturbance is expected to move into the Leeward Islands. But, as we all know, the computer models can and will likely change many times before we get to that time frame, so for now, I'm just going to watch the disturbance and wait for it to get close to the Caribbean.

You can pick out a COC.
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Quoting atmoaggie:
I assume you guys saw the total lack of surface circ in this QuikScat plot. (Yeah, I know it is old)



Oh, and we are going to get to see the Dawg Tigah bait get mauled come October, Alaina. Worry not.


Yeah, I saw that. But, in the past few hours, satellite imagery would suggest that we could be seeing a developing low-level circulation.
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yes! the bubble in the Atlantic finally found momentum..
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Hurricane Felicia could potentially inflict serious problems to hawaii as a hurricane looks like they better get ready very very soon
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Alaina You have mail.
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Looks like we might have Ana before August 15th; most of the models agree on this system developing

I love this new simple-comprehensive graphic done by atmospheric modeling designer Allan Huffman. It shows the NAO levels forecasted by the ECMWF.

As I was saying since last week, we are currently in a weak positive phase, but a ride should start building near the east coast, and trigger a negative NAO. This means a greater chance for U.S east coast hits.



ECMWF-GFS long range troughing/ridging anomalies shows the trough weakening in the near future.

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Go Canes! Then Gators...FSU who??
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Quoting ssmate:
This is a hurricane geek forum.
Though I love college football. It bum's me out that the Big Ten is never included.

Its all pointless anyway the Gators are unstoppable!
oh yea and uh the Miami Hurricanes weather weather...
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WEATHER SUMMARY:
Fron the Barbados weather office:

Barbados Forecast valid for 04/2200z to 05/2200z, August , 2009.
Tuesday, August 04th, 2009

TROPICAL WAVES:

Three tropical waves are identified over the Atlantic at this time. Over the far Eastern Atlantic, one wave has just exited the African coast and is now near 20°W, south of 17°N, moving westward at about 10 knots. This wave should be in the vicinity of the island chain early next week. Another wave is approaching 35°W, south of 15°N, moving west at about 15 – 20 knots. Satellite imagery is showing a definite cyclonic turning associated with this feature, with a fairly organized area of deep convection centered near 10°N. Indications are that this system will continue to show signs of strengthening/development over the next few days. Model data is suggesting a gradual northwestward track for this wave, and takes it to the north of the island chain by Monday.
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I assume you guys saw the total lack of surface circ in this QuikScat plot. (Yeah, I know it is old)



Oh, and we are going to get to see the Dawg Tigah bait get mauled come October, Alaina. Worry not. At their house, no less.
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Quoting presslord:
besides...the only football that really matters comes out of Athens, GA...
Your're right press. We will come out of Athens this year with a W. Geaux Tigers!!!!
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Quoting BobinTampa:



okay, how bout this....does anyone think that USF's huge victory over FSU on Sept 26 will be affected by tropical activity??




nice
Member Since: August 13, 2007 Posts: 0 Comments: 10479
This is a hurricane geek forum.
Though I love college football. It bum's me out that the Big Ten is never included.
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Quoting alaina1085:


LMAO!


Hey how about them Miami Hurricanes. there weather AND sports
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Quoting Elena85Vet:
Here's a good water vapor look.

Give it a minute to download.

Link

awesome!
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Right now, our Central Atlantic disturbance seems to be getting better organized. On the Tropical RAMSDIS Visible Satellite Loop, there seems to be an increasingly better defined low-level circulation center forming near 9N and 36W. As a few people have posted, the CIMSS 850mb Vorticity product also supports this conclusion as it shows increasing lower-level vorticity becoming more defined as well. These are all indications that we could be watching a developing system.

As for the future, its really difficult to determine since it will all depend upon the track and progression of the TUTT north of Puerto Rico. In taking a quick look at most models, they suggest that wind shear will remain quite hostile by the weekend in the Northern Caribbean when this disturbance is expected to move into the Leeward Islands. But, as we all know, the computer models can and will likely change many times before we get to that time frame, so for now, I'm just going to watch the disturbance and wait for it to get close to the Caribbean.
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Quoting presslord:
besides...the only football that really matters comes out of Athens, GA...


I hear they do have some good HS teams in Athens ....
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Felicia track 5 days still huricane near Hawai.
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Quoting BobinTampa:



okay, how bout this....does anyone think that USF's huge victory over FSU on Sept 26 will be affected by tropical activity??



LMAO!
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Quoting presslord:
besides...the only football that really matters comes out of Athens, GA...


That's for sure.
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Quoting presslord:
alright y'all...let's behave...I know I started it but, as Pat would say, the sports blog is down the hall to the left...



okay, how bout this....does anyone think that USF's huge victory over FSU on Sept 26 will be affected by tropical activity??

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Quoting Stoopid1:


I agree!


Super Agree
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Quoting BenBIogger:
This is not a sports forum.

Right.
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This is not a sports forum.
Member Since: March 19, 2009 Posts: 0 Comments: 1421
Quoting BobinTampa:


Close, you got it backwards though. USF rules!!! We'll be handing you a loss this year. Sorry bout that.


I live in St. Petersburg now, but graduated from FSU. SO go USF and FSU. =)
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Quoting presslord:


There is no such place as "the Carolinas"...it's either North Carolina ...or South Carolina...

I wonder if the people living in North and South Dakota get just as upset over weather persons calling them "The Dakotas"? (I hear that all the time up here from our weather people.)
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http://www.nhc.noaa.gov/storm_graphics/EP08/refresh/EP0809T_sm2+gif/202458P_sm.gif

More than 50% probablity for FELICIA to be a MAJOR HURRICANE
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alright y'all...let's behave...I know I started it but, as Pat would say, the sports blog is down the hall to the left...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
Everybody with the Rebels on schedule better look out. We have them in early October before they really get their momentum going.
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Quoting StormChaser81:


FSU RULES!!!


Close, you got it backwards though. USF rules!!! We'll be handing you a loss this year. Sorry bout that.

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Quoting cg2916:

If you're talking about Clemson, then *cough* Go Furman! *cough*


Nah, LSU!
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Quoting Stoopid1:


I agree!



Watch it, pal!!! I know where you live...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
Last year yall wore all black to your own funeral.
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It's going to be funny when them "Pups" get spanked in Stillwater!
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Quoting presslord:
besides...the only football that really matters comes out of Gainesville, FL ...


I agree!
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Quoting weathermanwannabe:


I was in Athens three weekends ago for a wedding; made the mistake of wearing my FSU baseball cap for the drive and got dirty looks when I got into town....


FSU RULES!!!
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Quoting iluvjess:


Them dawgs is lucky the Tide ain't rollin in this year.



pppffff...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
*Coughs* GO TIGERS!!
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527. HadesGodWyvern (Mod)
Bobin

The NHC does TWO at 0:00AM UTC, 6:00 AM UTC, 12:00 PM UTC, and 18:00 PM UTC.
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Quoting weathermanwannabe:


I was in Athens three weekends ago for a wedding; made the mistake of wearing my FSU baseball cap for the drive and got dirty looks when I got into town....


bad move
Member Since: August 13, 2007 Posts: 0 Comments: 10479
Quoting presslord:


...damned straight...


Them dawgs is lucky the Tide ain't rollin in this year.
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FMDawg and mobilegirl...y'all are clearly good and righteous people...
Member Since: August 13, 2007 Posts: 0 Comments: 10479
Here's a good water vapor look.

Give it a minute to download.

Link
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Quoting JLPR:
Does anyone else think that the mid level low formed a low level low which has now separated from the mid level one and developing its own convection at 30W?

=P


I agree.
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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.