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:
It looks like the wave is losing convection.


yep its near D-Min over there
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221. HadesGodWyvern (Mod)
Here is the latest Tropical Cyclone Bulletin issued by the Hong Kong Observatory.

The No. 8 Southeast Gale or Storm Signal is in force.

This means that winds with mean speeds of 63 kilometres per hour or more are expected from the southeast quarter.

At 2 a.m., Severe Tropical Storm Goni was centred about 140 kilometres west-southwest of Hong Kong (near 21.7 degrees north 113.0 degrees east) and is forecast to move west or west-northwest at about 10 kilometres per hour skirting the coastal areas of western Guangdong.

According to the present forecast track, Goni will move away from Hong Kong gradually. When gale force winds of Goni no longer post a threat to Hong Kong, the Observatory will consider issuing a lower Tropical Cyclone warning signal.
Member Since: May 24, 2006 Posts: 52 Comments: 46911
Quoting IKE:
stormpetrol...everyone has a right to an opinion on any tropical system.




I didn't say there was no spin. I said I don't see much spin left with it. What spin I do see is near 9N and 36W.

Agreed 100%, but let's be reasonable, I'm not weather expert, but one know should certainly recognize when a pot is being stirred just to get the boiling going, enough said on my part, I'll just sit back and watch what happens.
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It looks like the wave is losing convection.
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218. CUBWF
Good afternoon everyone. The calm before the storm, and it's not in the Atlantic. Disagree is good, it bring better results, but respect each other, even if we don't care others opinions. In this stage, the center can be pinpoint until it really make it.
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Quoting Weather456:
Nice spin

LINK
Looks like TD 2 in the making. :S
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Quoting Elena85Vet:
East Atlantic Imagery for 18Z is available now.

Link


system is in the CATL now, updates much more frequently
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Nice spin

LINK
Member Since: July 24, 2005 Posts: 407 Comments: 19076
East Atlantic Imagery for 18Z is available now.

Link
Member Since: August 18, 2008 Posts: 0 Comments: 628
Quoting StormW:


That's true...100%...but when we put out information, let's try to be as accurate as possible. Saying there isn't much spin, when you can see rotation as plain as day, is not accurate.
you're right...even I could see the rotation...as a matter of fact...are there 2 areas of rotation?
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211. IKE
stormpetrol...everyone has a right to an opinion on any tropical system.


Quoting StormW:


That's true...100%...but when we put out information, let's try to be as accurate as possible. Saying there isn't much spin, when you can see rotation as plain as day, is not accurate.


I didn't say there was no spin. I said I don't see much spin left with it. What spin I do see is near 9N and 36W.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Looks like there's some spin around 9N 35.5W
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Quoting stormpetrol:
I see so much bull on this blog , the flies are even starting to gather on my monitor. :)


LOL, WU should supply free fly swatters
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Quoting stormpetrol:
I see so much bull on this blog , the flies are even starting to gather on my monitor. :)

hehe...rotfl
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I see so much bull on this blog , the flies are even starting to gather on my monitor. :)
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Disorganized mess it may be, but it's not going away.
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Quoting Drakoen:
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.
~shocked~
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I still say the Disturbance near 8-9N/35-36W WILL become the first named storm of the 2009 Atlantic Hurricane Season, looks much better this afternoon convection tightening and deepening near a potential COC. JMO
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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.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
200. HadesGodWyvern (Mod)
StormW

The Joint Typhoon Warning Center will mark anything an invest =P
Member Since: May 24, 2006 Posts: 52 Comments: 46911
Quoting Weather456:



Thank you


LOL! The better half speaks!
Member Since: October 28, 2006 Posts: 57 Comments: 30825
198. HadesGodWyvern (Mod)
Central Pacific Hurricane Center: Honolulu, Hawaii

Tropical Cyclone Outlook (4:00 AM HST)
========================================
Isolated thunderstorms associated with former Tropical Depression Lana are located 500 to 600 miles SW of Honolulu.

Any re-development of this system will be slow to occur as it drifts slowly west

Tropical Cyclone Formation Potential
=================================
There is a low chance of this disturbance to re-develop into a tropical cyclone within the next 48 hrs
Member Since: May 24, 2006 Posts: 52 Comments: 46911
Quoting StormW:


Maybe you should pull up a closeup RGB or Visble loop.


I stare at the loop for a few hours i'm sure I will see some spin.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting BurnedAfterPosting:


Agreed, seems to me he is just here contradicting everyone. If he thinks its such a mess then go do something else.



Thank you
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting CosmicEvents:

Hi Tennisgirl....I saw you talking about hurricane names the other day.
Check out my blog for my thoughts on the subject.


Cool. Thanks!
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Quoting IKE:
Accuweathers take on the Atlantic.

You listen to them?
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Quoting BurnedAfterPosting:


Agreed, seems to me he is just here contradicting everyone. If he thinks its such a mess then go do something else.


I can do whatever I want.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting IKE:


I'm not seeing much spin anymore.


Me either.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting StormW:
If it's so disorganized and a mess, explain to me what the difference is between this mess, or a naked swirl in the far NE Atlantic?



Agreed, seems to me he is just here contradicting everyone. If he thinks its such a mess then go do something else.
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That mess looks better to me lmao!
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Tropical Depression Eight-E developed out of a broad area of low pressure several hundred miles southwest of Baja California Sur shortly after Tropical Depression Seven-E formed directly to the east. It strengthed into a tropical storm and was named Felicia early on August 4. It rapidly strengthened that morning as an eyewall quickly developed.


Link
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Quoting tennisgirl08:
Good Afternoon, All!

Hi Tennisgirl....I saw you talking about hurricane names the other day.
Check out my blog for my thoughts on the subject.
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Eastern Pacific storms, monitoring Atlantic
Chris Dolce, Lead Meteorologist, The Weather Channel
Aug. 4, 2009 1:54 pm ET
There are two active systems in the eastern Pacific which are no threat to land.

Tropical storm Enrique with top sustained winds of 60 mph is located just over 730 miles southwest of Cabo San Lucas, Mexico. Enrique is forecast to strengthen some, but stay just below hurricane status as it moves to the west-northwest in the open Pacific.

Just to the west of Enrique, is Tropical Storm Felicia. Felicia is forecast to strengthen gradually and should become a hurricane over the next couple of days. The system is located around 1200 miles southwest of Cabo San Lucas, Mexico and is no threat to land...

Link

I guess those teensy weensy Hawaiian Islands are kinda hard to see...
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Quoting Drakoen:


It is being sheared... disorganized ugly ITCZ mess.


Drak, the shear is not expected to continue. At least not for the next 2-3 days.
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Ok...

1) Felicia looks like she's trying to gain a monster eye

2) This has to be Ana right because East. Pac. is up to the 'F' and we haven't even gotten the 'A'.
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182. IKE
Quoting Drakoen:


It is being sheared... disorganized ugly ITCZ mess.


I'm not seeing much spin anymore.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
181. HadesGodWyvern (Mod)
Morakot (kiko) sure is intensifying quickly now
Member Since: May 24, 2006 Posts: 52 Comments: 46911
180. IKE
Accuweathers take on the Atlantic.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting IKE:
Look at a visible loop of the blob in the EATL, you can see higher cloud tops being blown from east to west.

20 knots of shear.....



It is being sheared... disorganized ugly ITCZ mess.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
178. HadesGodWyvern (Mod)
706
TCNA21 RJTD 041800 CCA
CCAA 04180 47644 MORAKOT(0908) 10225 11336 13344 235// 92709=
GONI(0907) 09219 11127 13134 225// 93008=

18:00 PM UTC August 4 2009

STS Morakot (0908)
22.5N 133.6E
Dvorak Intensity: T3.5

TS Goni (0907)
21.9N 112.7E
Dvorak Intensity: T2.5
Member Since: May 24, 2006 Posts: 52 Comments: 46911
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Good Afternoon, All!

I will try to not be so wordy on my posts today:)

Glad to see a yellow circle, but will be curious to see when the NHC declares the AOI an invest. Hopefully by tonight or tomorrow morning.

Also, Dr. Master's reports on the CSU and British analysis seem to surprise me a bit and looks as they are still calling for a normal hurricane season. Not below average - so, this should hush all that crazy talk about a "dud" season.

One other point, I am surprised as to the amount of CV activity, as I thought this year would have more home-grown storms. Well, we will see what Sept brings.
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would mid level shear have an effect on this blob
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Alockwar21

Based on what scientific data?????
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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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