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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Anyone want to go to Hawaii?
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nrti where do you get the updates on the strength of current systems?

IF it is the same site you gave me last night, let me know where on the site to find it

thanks in advance
.
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Quoting Dakster:
Orca - What was the temp today for you? Another 100 + degree scorcher?


High today was only 28.8
A very nice day... :)
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1017. beell
Quoting tornadofan:


I second that...


3rd that
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Quoting AllStar17:


Oh......come on.


Too many times do people do this. They write a disturbance off, and then it flares back up. It is only diurnal cycles. If you look at a satellite, you can still clearly see a spin, just with limited convection. Wait another 24 hours before writing it off.


if it cant maintain convection during dmin than there is nothing there.it can spin all it wants but no surface low means no storm.it will gradually move into ca as a blob
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1014. BDAwx
Hurricane Felicia looks pretty good looks like by the time the new thunderstorms near the eye wrap all the way around it could be a major hurricane. It's sibling Enrique looks like its struggling...

IMO the AOI in the Atlantic doesn't look too good right now but we will see what happens... stranger things have happened than a storm forming from something that looks like that.
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Quoting Dakster:
Someone edumacate me. What superstorm of 1993? I was busy trying to get my life in order after Andrew wrecked everything I owned.
wasnt that the perfect storm? east coast of fl. had 20ft. waves, washing over a1a.
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Quoting Dakster:
Someone edumacate me. What superstorm of 1993? I was busy trying to get my life in order after Andrew wrecked everything I owned.

Link
One of the biggest non-tropical storm in the US in the 20th century...see above link.
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.
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1009. Dakster
Orca - What was the temp today for you? Another 100 + degree scorcher?
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My page on the 93 superstorm.
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Quoting CyberStorm:
RIP central atlantic wave.moving on


Oh......come on.


Too many times do people do this. They write a disturbance off, and then it flares back up. It is only diurnal cycles. If you look at a satellite, you can still clearly see a spin, just with limited convection. Wait another 24 hours before writing it off.
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Stormpetrol, just looked it up and seems like Gilbert passed about 120 miles off Grand Cayman. We had winds of 119 gusting to 136
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AOI

AOI

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1004. Dakster
Someone edumacate me. What superstorm of 1993? I was busy trying to get my life in order after Andrew wrecked everything I owned.
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RIP central atlantic wave.moving on
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1001. flsky
It's funny how you can always tell whose been drinking when they post....
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1000. Dakster
I just got back from taking a quick scat... What did I miss? I see our Yellow circle is still there...
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Lotsa good writing in Rescue Me,..but then again,..there is like 6 comedians in the cast.
Member Since: July 3, 2005 Posts: 427 Comments: 129439
Quoting tornadofan:


You mean like the SuperStorm of 93, after the relatively inactive 92 hurricane season? (Outside of Andrew.)

I guess we would need to find how above normal the GOM was in 93...though the parameters didn't necessarily depend soley on the GOM....
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Quoting stormpetrol:
Let me tell you all something about Gilbert, Gilbert passed basically nearly as close as Hurricane Ivan to Grand Cayman 2004, Gilbert was in 1988, Gilbert had wind gusts at 158mph in Grand Cayman if I remeber correctly and to me Gilbert was just a Summer squall compared to Ivan of 2004, electricity was out at the most 48 hours for most in Gilbert , for me in Ivan it was 5 weeks , some nearly 3 months. I personally think they need review the scale on which hurricanes are graded, some are way underrated and some are way overrated , just my personal opinion from experiencing 2 of the 10 most intense Atlantic Hurricanes on record.
I asm sorry on this one but Gilbert passed almost 200 miles from Grand Cayman and Ivan passed about 25 miles off. No
way did we have 158 mph winds with Gilbert.
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996. IKE
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Storm....

any new thoughts on our disturbance, even though convection has waned?
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O.o
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Quoting StSimonsIslandGAGuy:


There may actually be something to that. If the hurricane season does turn out to be very weak, with no storms of consequence in the Gulf of Mexico, the heat content may not be tapped and mixed out, and help intensify winter storms.
Quoting StSimonsIslandGAGuy:


There may actually be something to that. If the hurricane season does turn out to be very weak, with no storms of consequence in the Gulf of Mexico, the heat content may not be tapped and mixed out, and help intensify winter storms.


You mean like the SuperStorm of 93, after the relatively inactive 92 hurricane season? (Outside of Andrew.)
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Local students win science competition with new hurricane scale

Congratulations to Barbers Hill Middle School in Mont Belvieu for winning a regional award in the eCybermission science competition!

Sabrina Galloway, Jacob Marek, Lucas Coburn and Bailey Lee developed a new hurricane intensity scale that could be used to estimate the total threat from tropical systems. Among more than 2000 entries from schools across the country, the eighth graders won the "Innovation, Originality and Creativity" award for the Southwest Pacific region.
Member Since: July 3, 2005 Posts: 427 Comments: 129439
o.O
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Excellent timing Storm W. Or better yet nice opening statement.
Member Since: August 18, 2008 Posts: 0 Comments: 3113
Quoting conchygirl:
even though I don't post much, I do lurk....ditto.


Right on Conchy! Power to the Lurkers!
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986. IKE
Quoting conchygirl:
even though I don't post much, I do lurk....ditto.


conchygirl...I noticed women don't really post that much on here this year. Must be due to fear or we're just dumber....lol.
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Wave action were ever Morakot comes ashore will be ferocious.
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Evening Chief,..same ol same ol..seems.
Member Since: July 3, 2005 Posts: 427 Comments: 129439
Quoting tornadofan:


I second that...
even though I don't post much, I do lurk....ditto.
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Atlantic AOI..easily found here.
Member Since: July 3, 2005 Posts: 427 Comments: 129439
979. IKE
What a blog.
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yikes
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Quoting BurnedAfterPosting:
nrti its not worth it, you give very good information, dont want to lose you on the blog


I second that...
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nrti its not worth it, you give very good information, dont want to lose you on the blog
973. whitewabit (Mod)
HGW... thats what I thought too...
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Blog dead all of the sudden :(
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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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