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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Shear map is out, shear continues to decrease

Huge anticyclone to the systems SE
Yeah, you can see the spin better when you watch that burst of convection moving around the bottom in a circular motion. Granted, it is still in the ITCZ so it hasn't really proven anything but it maybe the most noteworthy wave we've seen so far this year, huh?
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Quoting StormW:
CATL JSL LOOP


Also notice how is starting to gain some latitude as it expands. Also the TPW agrees.
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Quoting cg2916:

So am I.



no....no....no....

You are a South Carolinian!!!!!!!!!!!!!!!!!!!!!
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Quoting cyclonekid:
Actually Yes...I should know...I am a Carolinian.

So am I.
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Quoting StormW:
CATL JSL LOOP

Looks like the wave is maintaining convection near the center.
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Quoting cyclonekid:
Can you give me the link to that website?

Cimss
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting TampaSpin:


Is thingamajiggy what they say in the Carolina's.........LMAO
Actually Yes...I should know...I am a Carolinian.
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Quoting IKE:


I don't see anything there that is going to cause any problem in the tropical Atlantic through August 14th.


True... nothing significant... yet!!! But at the very least it recognizing the existence of the disturbance.
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Just stick to the weather and move on....I placed "someone" on ignore last week because of the constant afternoon bikering and putdowns which take away from the reason most of us are here......To share and learn from each other in a respectfull maner....Need to be mindful of the general public out there that looks to the blog for some general info and guidance during h-season.
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201. Drakoen 6:30 PM GMT on August 04, 2009
I'm allowed to have my own forecast and philosophy regardless of whether it contradicts anyone in here. I really and truly don't care.

then you wont mind if i put you on ignore.
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309. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #11
TROPICAL STORM GONI (T0907)
3:00 AM JST August 5 2009
=========================================

Subject: Category One Typhoon In South China Sea

At 18:00 PM UTC, Tropical Storm Goni (990 hPa) located at 21.8N 112.8E has 10 minute sustained winds of 35 knots with gusts of 50 knots. The storm is reported as moving west-northwest at 7 knots

RMSC Dvorak Intensity: T2.5

Gale-force Winds
================
180 NM from the center in southern quadrant
120 NM from the center in northern quadrant

Forecast and Intensity
=========================
24 HRS: 22.2N 111.0E - Tropical Depression

---
I can not believe the big difference with intensity with this cyclone with the other weather centers in Asia..
Member Since: May 24, 2006 Posts: 50 Comments: 44896
Quoting weatherwatcher12:
New shear and vorticity maps in 32 minutes
Can you give me the link to that website?
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so 456 you think its going to go due north or is that another Low?
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Quoting presslord:



As opposed to a thingamajiggy?


Is thingamajiggy what they say in the Carolina's.........LMAO
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Jeffs713

I agree with you, and opposite view points are always healthy when there are open minds. What I have seen here are people who support their observations in spite of the obvious. Everyone here who posts must keep in mind that there are non-scientists on this site seeking information. I know for a fact that some of them take actions based off of the feeling of this board. Not so smart, but true.

People who have been affected...and I'll go ahead and say it...I am from St. Berard Louisiana, ground zero for Katrina, watch these boards because they wonder if they will be living in their homes by the end of summer. I am guilty of the same thing. Again, not necessarily so smart, but human nature is a powerfull thing. So all summer we lurk here and try to piece together what might be based on science and which posters just say anything. Sure we could just not come here, and personally I have taken leave of this blog for long periods because of the bickering etc., but our curiosity about the end of summer is overwhelming.

So those of you wishing for storms try to understand, we are hoping that there will never be an Anna.
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Gooder?
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303. IKE
Quoting WxLogic:
12Z ECMWF still has it... (850MB)


I don't see anything there that is going to cause any problem in the tropical Atlantic through August 14th.
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New shear and vorticity maps in 32 minutes
Member Since: May 16, 2009 Posts: 1 Comments: 1231
12Z ECMWF 72 hrs -

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One more thing: when there is disagreement and bloggers have to defend their positions, it helps the less-informed of us learn more gooder.

As long as it is respectful, we can all learn.

okay, NOW back to the tropics.
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Now, I know that we're nearing DMIN, but it looks like shear is what's causing the convection loss on the wave.
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Quoting Alockwr21:


Where in NC?
About 2 hours from Atlantic Beach...but that's not important.
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Whatever circulation there is, is removed from the convection.
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12Z ECMWF still has it... (850MB)
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Quoting tennisgirl08:


Drak, you are a very good forecaster, and have contributed to some very nice forecasts on the blog. However, with all due respect, your attitude lately is not very becoming of you. There are more tactful ways to disagree. You wouldn't want to lose your credibility on the blog - especially with some of the more experienced forecasters on here.


I dont post much here but what I am seeing is sad to say but I regarded him as a good member who made some good analysis of things in the tropics,but has lost credibility for me that I have him on ignore because of the mose recent actions that he has said against 456.
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Quoting cyclonekid:
Please anybody....make TWC stop going full coverage of Flooding in Louisville...I don't even live in KY. I live in a hurricane proned state...NC!!


Why? It is the biggest weather story in the US today, it makes sense that they are covering it.
Anyway, I will be back later. Have a good afternoon all.
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Quoting presslord:



Well! You're no fun ; )

Lol.
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Quoting cyclonekid:
Please anybody....make TWC stop going full coverage of Flooding in Louisville...I don't even live in KY. I live in a hurricane proned state...NC!!


Where in NC?
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Please anybody....make TWC stop going full coverage of Flooding in Louisville...I don't even live in KY. I live in a hurricane proned state...NC!!
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Quoting cg2916:
Why don't we forget about the whole disagreeing thing and focus on the tropics?



Well! You're no fun ; )
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Where is this thing going?
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Quoting StormW:


Oh.

I meant I wasn't afraid.

Ok.
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Quoting TampaSpin:
I think it may be trying to seperate from the ITCZ now looking at the loop.


could be
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284. IKE
12Z ECMWF shows all clear in the Atlantic.

I even checked the South America loop.
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Quoting kmanislander:
Hi there W456

For what it's worth I do see rotation out there but as most everyone on here knows that alone does not determine whether there is a potential cyclone in the making. In fact, we have all seen very strong waves that looked like tropical storms but did not have a closed low ( think Dolly ).

I am quite content to wait and see what it does. I don't care whether it looks good or bad or in between, it's just something to keep an eye on for now.



yea, and gives us something to watch in the meantime until Mid-August....
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Quoting Elena85Vet:


ThingamaBLOB?


Nice !
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Why don't we forget about the whole disagreeing thing and focus on the tropics?
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Give Me Just A Little More Time...



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278. CUBWF
No BAP, there is no way I said that. It was in reference to he is as respecfull people like Ike, even if he don't concurr with others opinion.
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Quoting cyclonekid:
Actually Enrique has 60mph winds :D

Link


Sorry I was looking at an older update.
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Quoting kmanislander:
Hi there W456

For what it's worth I do see rotation out there but as most everyone on here knows that alone does not determine whether there is a potential cyclone in the making. In fact, we have all seen very strong waves that looked like tropical storms but did not have a closed low ( think Dolly ).

I am quite content to wait and see what it does. I don't care whether it looks good or bad or in between, it's just something to keep an eye on for now.

Don't forget Fay.
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Quoting CUBWF:
Weather456, I'm with you. There is no way you and Drakoen have any interaction, without get involved in trouble. That is always the end. Just try not get into nothing with him, and viceversa. Is going to be the best for both, and even more, for all the bloggers. Just my opinion.


I don't quote his posts but he quotes mines. That says alot.

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Quoting Chicklit:
thingamabob: between a trough and a wave



As opposed to a thingamajiggy?
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Quoting conchygirl:
Thingamabob is the best description all day!


ThingamaBLOB?
Member Since: August 18, 2008 Posts: 0 Comments: 628
Quoting StormW:
250. cg2916 2:51 PM EDT on August 04, 2009
Quoting Weather456:


I'm all for the disagreeing. But I'm actually afraid of disagreeing with one person here. I don't want to get insulted.

Me too.


I'm not.

I meant I was for some disagreeing, so that we can see different viewpoints, and so the blog wouuldn't be boring.
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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.