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 cg2916:
Is it me or is the wave falling apart?

Looks like it's in a higher shear area. Probably will wax and wane over the next few days as it encounters shear, dust, but nothing is really strong enough at this point, IMO, to wipe it out. Persistence appears to be the key word this week.
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Based on 15Z VORT Charts... vorticity is starting to increase at lower levels (850MB to 700MB) with a 500MB still present but elongated still.

SAT images are starting to show this cyclonic turning... although convection has wane for now... it will have the opportunity to recover during DMAX now that DMIN is going to be peaking soon.
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Hello Everyone,

I haven't been on this blog since the last hurricane season. There was nothing to report but I have a gut feeling that this area of disturbance in the Atlantic is something to watch for. The only concern for this system, like Jeff Master said, is the wind 20 knt wind shear that can inhibit in significant development.

Lets keep our eyes on it.
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Quoting cg2916:
Is it me or is the wave falling apart?


I think its holding its own, convection waning a bit, but overall it still looks decent to me.
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Quoting BurnedAfterPosting:


It happens, it looks to be cloud covered is why, that is why they have those microwave images, so you can see those kinds of features. They are pretty easy to miss otherwise


Remember Dean? The "Eye-Less" major hurricane. If I remember correctly it wasn't until it was a cat 2 that the eye cleared out.
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Quoting BurnedAfterPosting:


It happens, it looks to be cloud covered is why, that is why they have those microwave images, so you can see those kinds of features. They are pretty easy to miss otherwise


Probably some cirrus clouds in the eye. Since its probably doesnt have enough low pressure to clear the eye cavity.
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Is it me or is the wave falling apart?
Member Since: December 21, 2007 Posts: 13 Comments: 3046
The hurricane report on my Blackberry (sponsored by the Weather Channel)this morning said the EPac systems are "no threat to land."
Wondering where they got that when it appears the Hawaiian Chain is within range. Correct?
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Quoting StormChaser81:


From that view, ya its an eye-wall alright. sorry about that. I was looking at visible and water vapor, wasnt present so pronouned as that image.


It happens, it looks to be cloud covered is why, that is why they have those microwave images, so you can see those kinds of features. They are pretty easy to miss otherwise
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Cool run 7544. Haven't seen that one before.
Up for air.
Link

Back to work after the 2 p.m. update!
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Quoting nrtiwlnvragn:


From that view, ya its an eye-wall alright. sorry about that. I was looking at visible and water vapor, wasnt present so pronouned as that image.
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Quoting SouthDadeFish:
Felicia just strengthened 20 knots in two hours. Thats a little bit more impressive than the atlantic wave.....
the rain over kentucky is more impressive than the atlantic wave that wave is ajoke i give it a 0 percent chance to develop
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Quoting nrtiwlnvragn:

Now THAT'S an eye! Wow
Member Since: December 21, 2007 Posts: 13 Comments: 3046
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108. 7544
and soon there will be two to watch

Link
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Quoting Thundercloud01221991:


and that is right over the middle
Visible even is showing a clearing developing




It might be forming but its not present yet through all the layers.
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Quoting BurnedAfterPosting:


The special advisory says she is forming an eyewall


and that is right over the middle
Visible even is showing a clearing developing
Member Since: August 1, 2006 Posts: 28 Comments: 3716
At the end of the day, I think that the T-Wave @ 20W will play a role with our C-Atl AOI @ 35.
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Quoting StormChaser81:


Really dont think thats an eye, little bit early to be forming an eye-wall. Most of the time cloud patterns will resemble eyes early in the intensification periods.


The special advisory says she is forming an eyewall-like feature as now almost a hurricane
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Microwave imagery indicates and eye-like feature with Enrique as well.
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Quoting Thundercloud01221991:
Felicia has a pinhole eye



Really dont think thats an eye, little bit early to be forming an eye-wall. Most of the time cloud patterns will resemble eyes early in the intensification periods.
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TS Enrique
~735 miles SW of Cabo San Lucas
~14.7N
~117.1W
~60mph
~WNW@16mph
~1000mb

TS Felicia
~1275mi. WSW of Cabo San Lucas
~12.3N
~125.8W
~70mph
~W@15mph
~990mb
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E-Pac systems are facinating to watch....I've never seen, in real time, two storms traveling so close to one another in the same general motion/direction.........
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Quoting Thundercloud01221991:
Felicia has a pinhole eye


So does Eduardo, a little.
Member Since: December 21, 2007 Posts: 13 Comments: 3046
Felicia has a pinhole eye

Member Since: August 1, 2006 Posts: 28 Comments: 3716
Quoting Thundercloud01221991:


That looks like an eye is forming on that one

pinhole eye. j/k
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yeah extreme thats more likely the case. It will be interesting to see how the two cyclones react to another as they strengthen. The NHC mentioned that the models believe Felicia will become dominate although Enrique is larger.
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Didn't even think to check the NHC site for any special advisories.
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000
WTPZ43 KNHC 041647
TCDEP3
TROPICAL STORM FELICIA SPECIAL DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP082009
1000 AM PDT TUE AUG 04 2009

THIS SPECIAL ADVISORY IS BEING ISSUED TO REVISE THE TRACK AND
INTENSITY OF FELICIA. A 1327 UTC TRMM MICROWAVE PASS RECEIVED JUST
AFTER ISSUANCE OF THE PREVIOUS ADVISORY SHOWS THE DEVELOPMENT OF AN
EYEWALL-LIKE FEATURE. IN ADDITION...RECENT VISIBLE IMAGERY SHOWS A
WELL-ORGANIZED TROPICAL CYCLONE WITH HINTS OF AN EYE. SPECIAL
DVORAK CLASSIFICATIONS FROM TAFB AND SAB INDICATE THAT FELICIA IS
NEAR HURRICANE INTENSITY AND THE INITIAL INTENSITY IS RAISED TO 60
KT. THE INTENSITY FORECAST IS INCREASED AND IS BASICALLY A BLEND
OF THE SHIPS/LGEM MODELS.

THE MICROWAVE DATA ALSO INDICATE THAT FELICIA IS CENTERED FARTHER
SOUTH THAN PREVIOUSLY ESTIMATED. THE OFFICIAL FORECAST TRACK HAS
BEEN ADJUSTED SOUTHWARD TO ACCOUNT FOR THE RELOCATION.

FORECAST POSITIONS AND MAX WINDS

INITIAL 04/1700Z 12.3N 125.8W 60 KT
12HR VT 05/0000Z 12.8N 126.9W 70 KT
24HR VT 05/1200Z 13.8N 128.8W 75 KT
36HR VT 06/0000Z 14.6N 130.5W 80 KT
48HR VT 06/1200Z 15.3N 132.0W 80 KT
72HR VT 07/1200Z 16.5N 135.5W 75 KT
96HR VT 08/1200Z 17.5N 141.0W 65 KT
120HR VT 09/1200Z 17.5N 147.0W 55 KT

$$
FORECASTER BLAKE/PASCH



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DRAKOEN what is your take on Dr Masters' disturbance? development or no development?

make a prediction!!!!
Member Since: August 22, 2006 Posts: 0 Comments: 2720
Quoting SouthDadeFish:
Felicia just strengthened 20 knots in two hours. Thats a little bit more impressive than the atlantic wave.....


Or they have been underestimating the cyclone so far.
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Enrique has near 4.0 on the ADT it's winds should be increased as well.
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Felicia just strengthened 20 knots in two hours. Thats a little bit more impressive than the atlantic wave.....
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Ok. I gotta go get some work done. This blog is addicting. Later folks.
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Quoting presslord:


...but...that's the fun part...


You guys crack me up!
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Quoting Drakoen:


The system exhibits a broad mid level turning there is not evidence of a surface circulation. I still believe that SAL will limit the development of this system regardless of what Jeff Masters says.


Whoa, Doc I think he's calling you out. LOL ;)
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Quoting GainesvilleGator:
As stated by both the NHC & Dr. Masters, any development will be slow to occur with the tropical wave off the coast of Africa. You won't miss anything if you take a peek at the satellite images every 4 hours or so. No point in sctutinizing every frame 24-7.



LOL!
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Quoting GainesvilleGator:
As stated by both the NHC & Dr. Masters, any development will be slow to occur with the tropical wave off the coast of Africa. You won't miss anything if you take a peek at the satellite images every 4 hours or so. No point in sctutinizing every frame 24-7.



...but...that's the fun part...
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I didn't mean a surface circulation, but the mid level turning is very evident. The IR imagery shows how ragged the system is though. It needs to continue to fire convection to fight off the dry air if it wants a chance at surviving.
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61. mikatnight - Thanks!
68. Stormchaser2007 - Impressed, yes. Prepare to be awed.
I know HGW & Aussie among others have kept us up to date on far off systems, but they do get a lot bigger when getting "closer in the rear view mirror", and they are "HEADED STRAIGHT FOR US".
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Quoting Stormchaser2007:
Looks like its lost much of its significant moisture.



Convection is predominantly ITCZ induced.
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.
Quoting bjdsrq:


Don't tell me..... you live in Palm Beach county, right? lol

Naturally. Born and raised here. Cleo & Isbell were my first. But they were comparatively weak here (as were Frances & Jeanne). I now live near the Intracoastal and if one of the storms comes through here like the '28 or '47 hurricanes...could easily top the all-time list. I don't like hurricanes - I'm facinated by them - but I damn sure don't want to endure a storm where it sounds like a freight train and a B-52 are doin' the cha-cha on my roof
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Looks like its lost much of its significant moisture.

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77. 7544
local newss just said our wave has a good counter clockwise spin to it 99l soon ?
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Quoting SouthDadeFish:
So based on the latest RGB Loop whats up with the low level clouds on the west side of the system moving east into the wave. Even the north side has some low level clouds being pulled southward. Possibly some sort of circulation trying to develop, most likely at the midlevels. Is anyone else seeing this?


The system exhibits a broad mid level turning there is not evidence of a surface circulation. I still believe that SAL will limit the development of this system regardless of what Jeff Masters says.
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Ramsdis now has a floater over the CATL Twave

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So based on the latest RGB Loop whats up with the low level clouds on the west side of the system moving east into the wave. Even the north side has some low level clouds being pulled southward. Possibly some sort of circulation trying to develop, most likely at the midlevels. Is anyone else seeing this?
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Quoting Stormchaser2007:
Impressive...



That looks like an eye is forming on that one
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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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