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


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....
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Quoting weatherwatcher12:

There is no 5 pm



crap! do I have to stay at work till 6:00 then?
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Quoting presslord:
besides...the only football that really matters comes out of Athens, GA...


YES!!!
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Quoting mobilegirl81:
hey presslord, how bout them dogs, lol


...damned straight...
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hey presslord, how bout them dogs, lol
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TS MORAKOT or must be called TYPHOON MORAKOT...
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513. 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
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oops 8pm I wish for the old days.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
God forbid anything making it in the gulf.
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besides...the only football that really matters comes out of Athens, GA...
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Quoting atmoaggie:

Take care, Grilled Cheese.


LOL
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Looking at the Cimms 850 Vort. Vort is on the increase. And as I mentioned earlier it is strongest at about 11N 29W, the T-wave behind may be the one to watch.
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The eye is starting to become cloud free.
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A Good GOM,is a quiet GOM




Member Since: July 3, 2005 Posts: 426 Comments: 128621
If anyone is interested the Criteria for a TCFA can be found here:
TCFA requirements
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Quoting SavannahStorm:


LOL- technically, they haven't ruled here in a while, either. Georgia was a part of the Province of Carolina until 1732.



; )
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503. IKE
SYNOPSIS VALID 1200 UTC TUE AUG 04.
24 HOUR FORECAST VALID 1200 UTC WED AUG 05.
48 HOUR FORECAST VALID 1200 UTC THU AUG 06.

.WARNINGS.

.NONE.

.SYNOPSIS AND FORECAST.

.ATLC FROM 19N TO 28N E OF 52W NE TO E WINDS 20 KT. SEAS TO 9
FT. FROM 15N TO 25N BETWEEN 52W AND 78W E WINDS TO 20 KT. SEAS
TO 8 FT.
.24 HOUR FORECAST FROM 16N TO 23N E OF 42W NE TO E WINDS TO 20
KT. SEAS TO 8 FT. FROM 20N TO 25N BETWEEN 60W AND 77W E TO SE
WINDS TO 20 KT. SEAS TO 8 FT.
.48 HOUR FORECAST FROM 12N TO 20N E OF 65W NE TO E WINDS 20 TO
25 KT. SEAS TO 10 FT IN E SWELL. S OF 27N W OF 65W E TO SE WINDS
TO 20 KT. SEAS TO 8 FT.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Quoting tigerfanintexas:
Well for the record I agree with you. It should be either north or south. One question, why do you suppose the call the panthers the Carolina Panthers? Why no North or South in front? just curious.


because they are marketing whores trying to appeal to Upstate South Carolina $$$
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Quoting presslord:
savannah....it's 2009...the Lords Proprietor have not ruled here in some time...


LOL- technically, they haven't ruled here in a while, either. Georgia was a part of the Province of Carolina until 1732.

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Alright guy's, there are 1000# steps that must happen in order and we are on number 8, you guys are talking about step 692.
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Quoting weatherwatcher12:

There is no 5 pm



It's five o'clock somewhere.
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Looks like the intensity models from this morning missed Felicia's hurricane status by about a day...but I will give them that it was probably poorly initialized, likely to improve with the next runs.


K. Emanuel's page
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Not much meat on the Waves Bones this afternoon.

Member Since: July 3, 2005 Posts: 426 Comments: 128621
savannah....it's 2009...the Lords Proprietor have not ruled here in some time...
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Quoting gordydunnot:
Code Orange foe 5pm prediction.

There is no 5 pm

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Member Since: July 3, 2005 Posts: 426 Comments: 128621
Quoting LiveFromTheCarolinas:
Off to work, BLT.

I want a sandwich.
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Quoting presslord:


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


for presslord: Foundation for the Carolinas

:)
(all in jest)
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Expansive

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Quoting Weather456:
Soemthing interesting, one has to ask, despite everything put up against it, SAL, dry air, shear, ITCZ, why has persisted?



As I said earlier, this is one of those waves that you pray conditions remain hostile, it WANTS to develop, and will, given the chance. Similar to 98L.
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Quoting LiveFromTheCarolinas:
Off to work, BLT.

Take care, Grilled Cheese.
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Code Orange for 5pm prediction.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
Not here press,..it would send some under the Bed,..LOL
Member Since: July 3, 2005 Posts: 426 Comments: 128621


Hurricane Felicia
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Off to work, BLT.
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Pat....do tell...
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Quoting presslord:



yes....really...


are you sure?
Member Since: March 19, 2009 Posts: 0 Comments: 1421
482. Gorty
The outflow is starting to look better.
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Quoting presslord:


I will concede you may have found a loophole...
Well for the record I agree with you. It should be either north or south. One question, why do you suppose the call the panthers the Carolina Panthers? Why no North or South in front? just curious.
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Quoting presslord:


I will concede you may have found a loophole...


Well.. maybe he's half in North Carolina, half in South. So his left half of him will be in South Carolina.
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Soemthing interesting, one has to ask, despite everything put up against it, SAL, dry air, shear, ITCZ, why has persisted?
Because it is the ITCZ. And one maxima of convergence along the ITCZ at that.

Even with all of those other detractors, convergence does youknowwhat, period.
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Quoting presslord:


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


The Province of Carolina from 1663 to 1712, was a colony of British America, controlled by the Lords Proprietary, a group of eight English noblemen led informally by member Anthony Ashley-Cooper, 1st Earl of Shaftesbury. Dissent over governance of the province led to the appointment of a deputy governor to administer the northern half of the colony in 1691.

The division between North and South became complete in 1712, but both colonies remained in the hands of the same group of proprietors. A rebellion against the proprietors broke out in 1719 which led to the appointment of a royal governor for South Carolina in 1720.
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I stayed in Middle Carolina once,but thats a "vary" long story.
Member Since: July 3, 2005 Posts: 426 Comments: 128621
Quoting tigerfanintexas:
What if you stood with one foot over North and one foot of South. Could you then say I am standing in the Carolinas?


I will concede you may have found a loophole...
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Question for the Experts

Is the Fujiwhara effect happening on Felicia and Enrique...If no, will it happen?
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Quoting BenBIogger:


Really?



yes....really...
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Quoting presslord:


There is no such place as "the Carolinas"...it's either North Carolina ...or South Carolina...
What if you stood with one foot over North and one foot of South. Could you then say I am standing in the Carolinas?
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Quoting presslord:


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


Really?
Member Since: March 19, 2009 Posts: 0 Comments: 1421

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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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