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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from accuweather/inaccuweather.com
Disturbed weather in the central Atlantic
Last Update: 4-AUG-2009 6:13pm EDT

An area of disturbed weather 1600 miles east of the Lesser Antilles is being monitored for possible tropical development later this week.

An area of showers and thunderstorms near 9 north, 36 west has been growing and dying during the past 12 hours. Satellite images show some cyclonic turning in the cloud motion. However, thunderstorms are not organizing enough to be too concerned for development during the next day or two. However, if if a more coherent lower level feature becomes established then development will have to be considered. Satellite derived products show sufficient warm water and low shear as positive factors for development. Other satellite derived data shows a considerable amount of dry air to the north of this feature preventing thunderstorm growth north of 10 north. Surface pressures over this area have fallen over the past 24 hours. So, given all these factors there is some potential for development.
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It has been fun all. This is why I love weather. The discussions and disecting the crud out of these storms is a blast. Have a good night. I work to early to stay up any longer. See ya all tomorrow and watch the excitment after it does refire a bt during dmax and then fade away again during dmin haha.
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Quoting HaboobsRsweet:

Right my bad...poor choice of words. I dont think it will reach TS again.


Neither do I. But, I have never seen the NHC forecast it to become a remnant low, only to then forecast it to become a depression once again.
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Good Evening All,

With all due respect – I don’t want to ruffle any feathers – but I was wondering, is there some sort of list of credentials or qualifications for the various blog members, so that one might be better able to discern to some degree the weight of a writer’s opinion? I assume not everyone is an actual meteorologist, and I do know that some – like StormW – may not have the paper, but their opinions are never-the-less regarded with respect by other members, and even in some cases – like StormW – by other meteorologists. I’ve clicked on a few icons, but I don’t think I’ve ever seen anyone “put their shingle out” as it were. So I was thinking there ought to be a list; sort of a brief summary of the main “clique” members, you know, kind of a “here we are – love us or leave us” deal. Yesno?
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Quoting AllStar17:


The E storm has not achieved hurricane status, nor do I think it will.

Right my bad...poor choice of words. I dont think it will reach TS again.
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Quoting HaboobsRsweet:

The E storm is forecasted to dip farther south. It will hit "warmer" waters but it wont make it all the way back to hurricane status.


The E storm has not achieved hurricane status, nor do I think it will.
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Quoting AllStar17:


You are right. The forecast discussion should be interesting.

The E storm is forecasted to dip farther south. It will hit "warmer" waters but it wont make it all the way back to hurricane status.
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Quoting HaboobsRsweet:


I dont see anything wrong either. Are you talking about it going from a weak depression to a low back to a depression? I think that is because it gets out from behind the other storm to undistrubed waters (warmer water) and has a chance to refire just a bit.


You are right. The forecast discussion should be interesting.
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Quoting AllStar17:
Tell me what is wrong with this map. (maybe it is not wrong....it is just weird)


I dont see anything wrong either. Are you talking about it going from a weak depression to a low back to a depression? I think that is because it gets out from behind the other storm to undistrubed waters (warmer water) and has a chance to refire just a bit.
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Tops approaching -84 degrees Celsius!

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http://oiswww.eumetsat.org/IPPS/html/MSG/RGB/AIRMASS/AMERICA/index.htm

The Meteosat view of the easterly wave.

For the E pac: looks like a Fujiwhara effect in the making
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Quoting extreme236:


I see nothing wrong.


potteryX is right. Maybe it is not wrong....it is just weird.
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148 km/h / 41.2 m/s from the East

http://www.wunderground.com/cgi-bin/findweather/getForecast?query=gnd&wuSelect=WEATHER&MR=0&extende dsun=sunon&theprefset=SUNRISEEXTEND&theprefvalue=1

???
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.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
D 24 hrs after L ??
Weird.
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Tell me what is wrong with this map. (maybe it is not wrong....it is just weird)

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Quoting BiloxiIsle:
I, for one, am glad that those two are not in the Atlantic.

No doubt about that and esspecially in the Gulf. Let them grow and not hit any land...send the warnings out to the ships to avoid the area for a few days and sit back and enjoy the beautiful Metsat shots we are getting.
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1105. JRRP
Impressive comments
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I, for one, am glad that those two are not in the Atlantic.
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Quoting StormW:


Nothing to be sorry for. If I'm wrong...I'm wrong. Hell, I've been wrong before...I am allowed one boo boo per season. I appreciate that you repsect my opinion. As HaboobsRsweet can tell you...meteorology is not an exact science...in fact, my meteorology professor told me she considers it more of an art.

Totally agree however I am put in a position often to give an exact answer haha. I have been wrong and will be the first to admit it if I am. I will be the first to tell you when I think a storm as a decent shot to form as well. As a met I wish we would get one but as a human I am glad we havent because I have been in 5 and now live in the land of Katrina.
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ZCZC MIATCPEP3 ALL
TTAA00 KNHC DDHHMM
BULLETIN
HURRICANE FELICIA ADVISORY NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP082009
800 PM PDT TUE AUG 04 2009

...FELICIA CONTINUING TO INTENSIFY RAPIDLY...

AT 800 PM PDT...0300 UTC...THE CENTER OF HURRICANE FELICIA WAS
LOCATED NEAR LATITUDE 12.8 NORTH...LONGITUDE 127.2 WEST OR ABOUT
1335 MILES...2145 KM...WEST-SOUTHWEST OF THE SOUTHERN TIP OF BAJA
CALIFORNIA.

FELICIA IS MOVING TOWARD THE WEST-NORTHWEST NEAR 12 MPH...19
KM/HR...AND THIS GENERAL MOTION IS EXPECTED TO CONTINUE FOR THE
NEXT COUPLE OF DAYS.

SATELLITE IMAGERY INDICATES THAT MAXIMUM SUSTAINED WINDS HAVE
INCREASED TO NEAR 100 MPH
...160 KM/HR...WITH HIGHER GUSTS. FELICIA
IS NOW A CATEGORY TWO HURRICANE ON THE SAFFIR-SIMPSON HURRICANE
SCALE. CONTINUED STRENGTHENING IS FORECAST AND FELICIA COULD BECOME
A MAJOR HURRICANE DURING THE NEXT DAY OR SO.

HURRICANE FORCE WINDS EXTEND OUTWARD UP TO 35 MILES...55 KM...FROM
THE CENTER...AND TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 85
MILES...140 KM.

ESTIMATED MINIMUM CENTRAL PRESSURE IS 975 MB...28.79 INCHES.

...SUMMARY OF 800 PM PDT INFORMATION...
LOCATION...12.8N 127.2W
MAXIMUM SUSTAINED WINDS...100 MPH
PRESENT MOVEMENT...WEST-NORTHWEST OR 285 DEGREES AT 12 MPH
MINIMUM CENTRAL PRESSURE...975 MB

THE NEXT ADVISORY WILL BE ISSUED BY THE NATIONAL HURRICANE CENTER AT
200 AM PDT.

$$
FORECASTER BRENNAN

NNNN

Still continuing to RI. BAP you were 15 mph too low! I thought you would be right.
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nevermind the source I was using is way off lol

8:00 PM PDT Tue Aug 4
Location: 12.8°N 127.2°W
Max sustained: 100 mph
Moving: WNW at 12 mph
Min pressure: 975 mb
Whats keeping it from developing a surface low?
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Quoting HaboobsRsweet:

That is incredible on how close they are and how they both are growing together. The models are all over the place with the first one and one would think that the first one would steal all the energy and drop water temps hurting the chances of the second one. Going to be interesting to see how the models are verifing tomorrow with the forecasted track. It does look like both will miss Hawaii just to the south. That is a great METSAT shot though.


Shoot I made a major mistake on this post hahaha. I got the names of the storms backwards. I havent look to hard at the Pac yet haha. I assumed the E storm was ahead of the F storm haha. So my reasoning makes sense since the E storm will fall apart behind the lead storm. I cracked myself up with that one. Must be getting late.
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Quoting StormW:


Nothing to be sorry for. If I'm wrong...I'm wrong. Hell, I've been wrong before...I am allowed one boo boo per season. I appreciate that you repsect my opinion. As HaboobsRsweet can tell you...meteorology is not an exact science...in fact, my meteorology professor told me she considers it more of an art.


OK. Thank you. The bold faced sentence is VERY true. Now that I think about it, the NHC has gotten track and intensity very wrong before.
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based on what I am seeing, winds will be increased on Felicia to 85mph
Quoting stormsurge39:
So, it needs a surface low to develope into a TD?


Yes.
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Quoting Stormchaser2007:
Wow...



On the other hand....Enrique looking very ill at the moment.
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So, it needs a surface low to develope into a TD?
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1091. Skyepony (Mod)
Felicia seemed destine to be the stronger, so much smaller. Small storms, like Andrew & Charley, have an advantage for strength. They have less drag, an easier time spinning.
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Quoting Stormchaser2007:
Wow...


That is incredible on how close they are and how they both are growing together. The models are all over the place with the first one and one would think that the first one would steal all the energy and drop water temps hurting the chances of the second one. Going to be interesting to see how the models are verifing tomorrow with the forecasted track. It does look like both will miss Hawaii just to the south. That is a great METSAT shot though.
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Quoting stormsurge39:
To whomever, Im not a met so i need help! Is there a low with

Not a surface low. New advisories for Enrique and Felicia due in a few minutes. Felicia adv. should be interesting.
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To whomever, Im not a met so i need help! Is there a low with the wave we are talking about?
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Let me clairfy what I think is going to happen. I do think convection will refire during Dmax tonight, that is a given and everyone will be excited in the morning. I am cool with that. I am concerned a few days down the road where all the other storms have been getting sheared apart ( you know that region where all the airplanes are getting rocked by turbulance). I think the models are a little aggressive on reducing shear that much in that region without the overall pattern really changing. If someone can point to me what is going to change in the longwave pattern to help aid the reduction in shear throughout that region then I may be swayed to change my opinion. This blob will survive for another 3 or 4 days maybe 5 or 6 haha most likely before we all will probably agree it is dead.
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Quoting Stormchaser2007:
Wow...



Looking good....and it will look even better if it can wrap all of that cold convection around the eye.
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Wow...

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Quoting StormW:


And I, yours. Agreed...plenty of days that no 2 mets agree. I too could be wrong on this...but that's part of the learning process...if it doesn't pan out...ya go back and look to see what you missed, or what else occured. I know I learn something new each season...and I've been dealing with tropical weather since 1996.


Storm, I did not mean to throw you under the bus. I am sorry. I respect yours and everybody else's opinions...and that is why we are all here for...discussing the tropics.
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1082. Skyepony (Mod)
Seems to me the blob got sheared, spread out & is dealing with the small bit of energy that was to the ENE, now drawing that in, slowly. Like the models have many times shown. Seems to me like it's going to be one of those many day struggles, like LANA was. Never real strong, up against a hard negative every other day sort of storms. A bad seed with no MJO.
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Quoting AllStar17:


Settle down just a bit....I did not mean to get you fired up as much as it seems you are.

I am cool man no worries. I am a very mellow person. Not too much bothers me to be honest. Of course I can see how tone is hard to gauge in here.
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Quoting HaboobsRsweet:

You are right I did not. Did it ever make it past a yellow circle? I do not think it did. Good comeback


Settle down just a bit....I did not mean to get you fired up as much as it seems you are. I do respect your opinion, also.
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Quoting 7544:


3am est hope this helps

Quoting AllStar17:


D-Max starts around 3 am

thanks very much
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Quoting wunderkidcayman:

when does D-max start


D-Max starts around 3 am
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...'sup?...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
1075. 7544
Quoting wunderkidcayman:

when does D-max start


3am est hope this helps
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Quoting wunderkidcayman:
hey guys when does D-max start

when does D-max start
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Quoting StormW:


Nice post.

TY and I know he referenced you and I truly do respect your opinion with the sound reasoning you give. There are plenty of days that no 2 mets agree on the weather. That is why I love this career field.
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