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 gator23:

why katrina

I don't get it. Everyone spends money with an impending landfall. Even Gustav-like cat2s with a fairly small windfield cause mass buying on the credit cards. Wouldn't that be great for the economy?
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701. kman
Sounds right, too

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Local winds are generally fresh

WTH does that mean? The Beaufort scale designation (no. 5)? Weird way to put it, if so.
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If something gets into the Gulf under the right conditions were in trouble.

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Quoting mobilegirl81:
The economy is pretty shakey right now , so forecasters are probably supposed to be alot more conservative than since before Katrina, I would suspect.

why katrina
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What about the stocks?
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716. HadesGodWyvern (Mod)
Here is the latest Tropical Cyclone Bulletin issued by the Hong Kong Observatory.

The Standby Signal, No. 1 was issued at 5:40 a.m.

At 6 a.m., Severe Tropical Storm Goni was estimated to be about 170 kilometres west-southwest of Hong Kong (near 21.7 degrees north 112.7 degrees east) and is forecast to move west at about 10 kilometres per hour skirting the coastal areas of western Guangdong.

Goni continued to move away from Hong Kong. Local winds are generally fresh, with occasionally strong winds over offshore waters and high grounds.
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If you tell people that there is a Potential development....GAS....INSURANCE....etc.. start to get tremored.
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714. HadesGodWyvern (Mod)
Meteo France
Eastern Atlantic
High Sea Forecast

Tropical wave along 20W south of 17N moving west 10 kts.

Tropical wave along 30/31W south of 15N with associated low by 11N 29W moving westward 10/15 kts.

ITCZ along 12N 16W 13N 23W 08N 34W 12N 46W 11N 52W 09N 60W.
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Quoting archer312:
Question-

since the area on the ITCZ under much discussion here apparently has some Spin,
when viewed on Sat Loops,
how come folks are saying it does not
seem to have any LLC (is that Low Level Circulation?), not upper circulation either?
What then am I seeing spinning on the Sat loops..???

That's the mid level circulation I believe.
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I can assure you,that economics nor politics is found in the Forecasting world.
If so,..Id like to see an example of it.
To say so is actually ludicrus.

Last time politics crept into anything Met wise was the former NHC director Bill Proenza debacle over quickscat,and that never affected one ioata of a forecast
Member Since: July 3, 2005 Posts: 428 Comments: 129841
Hurricane Iniki,Hawaii,,1992

Member Since: July 3, 2005 Posts: 428 Comments: 129841
Question-

since the area on the ITCZ under much discussion here apparently has some Spin,
when viewed on Sat Loops,
how come folks are saying it does not
seem to have any LLC (is that Low Level Circulation?), not upper circulation either?
What then am I seeing spinning on the Sat loops..???
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Back later
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The economy is pretty shakey right now , so forecasters are probably supposed to be alot more conservative than since before Katrina, I would suspect.
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Quoting archer312:
By the way,
SavannahStorm=

your town is Great,
a beautiful and dignified historic place.
I know some fine folks there, and I have had some good times there.

just fooling around with my Charlotte commentary, sorry if I did not
hit the Funny mark...
Not my intention, just kiddin' around.
I apoligize if I goofed.


No harm done, I'm thick-skinned. I've got cousins in Gastonia, that's a great part of the country.

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Hopefully we'll get a clear complete quikscat pass later.
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The 18 UTC surface analysis puts more eastward the axis of the surface trough,now at 30W.

Link
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704. amd
Without Dr. Lyons and Jim Cantore, TWC is worthless, IMO.

And, nothing is remotely imminent in the atlantic. The wave/blob is still trying to figure out what should be the dominant entity, the mid-level rotation at 9 N 36 W, or the lower level feature at 10 N 30 W.

Also in the Pacific, it will take at least 4 days or so before we know with any accuracy the effects of Felicia on the Hawaiian coastline.

Furthermore, I can't remember too many systems affecting the big island of Hawaii with any real intensity.

The big hurricanes of 1982 and 1992, Iwa and Iniki respectively, affected the western part of the Hawaiian island chain, where the waters are warmers and there is no stable air.
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What is up with this item? Just catchin up on today. ---- Nevermind, it has updated from 0600, oops

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Quoting archer312:
I did not know John Hope had died.
He was a fine man and a great messenger
and authority on severe weather.
Sad to hear he has gone,
he will be missed this season.


He died about 7 years ago.
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669. Dropsonde 4:40 PM EST on August 04, 2009

I just saw your post on this which is similar to my thinking except that you raise the possibility of the 850 vort having come off higher initially. My comment on that would be that over the last two days there was no 850 mb vort signature with this feature at all. The vorticity was at the 500 mb level, hence my hypothesis that what we see happening now at 10N 30W is convection responding to the 850 mb vort that only showed up there today for the first time as far as I can recall.
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Politics have NO influence on the Forecasters train of thought,ever.

If it does,than he or she wont have a Job very long.
Member Since: July 3, 2005 Posts: 428 Comments: 129841
Quoting archer312:
I did not know John Hope had died.
He was a fine man and a great messenger
and authority on severe weather.
Sad to hear he has gone,
he will be missed this season.


He died I think it was in 02.
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Quoting archer312:
I did not know John Hope had died.
He was a fine man and a great messenger
and authority on severe weather.
Sad to hear he has gone,
he will be missed this season.

He died in 2002

Member Since: June 21, 2007 Posts: 10 Comments: 1657
I think that forecasters are supposed to be very conservative because of a shaky economy right now.
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I did not know John Hope had died.
He was a fine man and a great messenger
and authority on severe weather.
Sad to hear he has gone,
he will be missed this season.
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695. IKE
Quoting tropicfreak:
Ever since John Hope died TWC coverage has hit rock bottom.


Just about unwatchable. I watch local on the 8's and not much more unless the Atlantic has something.

Miss hearing John Hope.
Member Since: June 9, 2005 Posts: 23 Comments: 37860
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By the way,
SavannahStorm=

your town is Great,
a beautiful and dignified historic place.
I know some fine folks there, and I have had some good times there.

just fooling around with my Charlotte commentary, sorry if I did not
hit the Funny mark...
Not my intention, just kiddin' around.
I apoligize if I goofed.
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Ever since John Hope died TWC coverage has hit rock bottom.
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Quoting Dropsonde:
I am fascinated by the two areas of interest around our disturbance. We have the area of high low-level vorticity at 10N30W and the area of high upper-level vorticity ("the" blob) at 9N36W. It may be the result of the easterly shearing that has taken place today, but I'm not sure that 20-25kts could account for such a distance between the two areas of circulation. I am more inclined to think it is an artifact of how the original African wave came off the coast, with the robust (then) mid-level circulation trailing and coming off farther north than the main convective area.

If you look back at the old runs of the GFS, this is exactly what it predicted for this time today. It furthermore predicts that the 10N 30W blob, the one that is gaining convection right now, will become dominant, pulling the blob we've been watching all day into it, and THAT is what will develop.

It's an interesting scenario, and it seems like it would make for a potent system, between the low-level vorticity of the 30W system and the vast moisture envelope of the 36W one. Development farther north than expected also would give the system an edge in lifting out of the ITCZ.

I think a lot hinges on how well the two areas do this evening. If either of them develops, it basically has to pull in the energy of the other one. This evening we will probably get a good idea as to which one will win.

Well stated.
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Quoting IKE:
TWC...The Hurricane Authority..Steve Lyons...downplaying Felicia's chances of affecting Hawaii...saying it'll be well SE of there in 5 days.

He said the Eastern Pacific...OOPS...Eastern Atlantic Dr. Lyons! and the GOM and Caribbean is "very quiet."

Didn't even make note of the blob or show it.

The Hurricane Authority.



Nothing imminent.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
GFS has change the sea-pressure for the next dyas in Atlantic, special mention to the anti-cyclone of Azores lossed power each day.

Member Since: July 21, 2009 Posts: 0 Comments: 552
Hello Experienced Wx Bloggers,
a Question-
Is the current thinking that the Blob in CATL we have been discussing, must move Off of the ITCZ in order to strengthen and become a storm?
Or does it strengthen, and Then Move away from the ITCZ, allowing it to get more organized?
Kind of Chicken and Egg question I guess?

Why is it that the NHC clearly is not impressed with this thing that looks pretty good to me on the sat images?
(I guess my novice stature is apparent here)
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Twc is becomming the tna = the nonsense authority.
Quoting kmanislander:
Compare to AVN image


Looks to be in the same place
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685. HadesGodWyvern (Mod)
Japan Meteorological Agency
Tropical Cyclone Warning #14
SEVERE TROPICAL STORM MORAKOT (T0908)
6:00 AM JST August 5 2009
=========================================

Subject: Category Two Typhoon In Sea South of Japan

At 21:00 PM UTC, Severe Tropical Storm Morakot (980 hPa) located at 22.5N 133.6E has 10 minute sustained winds of 50 knots with gusts of 70 knots. The storm is reported as west slowly

RSMC Dvorak Intensity:

Gale-force Winds
================
475 NM from the center in the southern quadrant
200 NM from the center in the northern quadrant

Forecast and Intensity
=========================
24 HRS: 23.5N 130.1E - 55 knots (CAT 2/Severe Tropical Storm)
45 HRS: 24.8N 126.9E - 60 knots (CAT 2/Severe Tropical Storm)
69 HRS: 26.5N 123.2E - 65 knots (CAT 3/Typhoon)
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684. IKE
TWC...The Hurricane Authority..Steve Lyons...downplaying Felicia's chances of affecting Hawaii...saying it'll be well SE of there in 5 days.

He said the Eastern Pacific...OOPS...Eastern Atlantic Dr. Lyons! and the GOM and Caribbean is "very quiet."

Didn't even make note of the blob or show it.

The Hurricane Authority.

Member Since: June 9, 2005 Posts: 23 Comments: 37860
Quoting weatherwatcher12:

Is this a sign of it lifting out of the ITCZ


Too early to say but this is certainly something new.
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Quoting kmanislander:
Compare to AVN image



Click -3 hours three times, and notice how this system has gotten better organized since then.
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Compare to AVN image

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Quoting kmanislander:
Here is something interesting. Convection firing up right where the 850 mb vorticity signature is on the vort map.

It may well be the the apparent circulation we are seeing further West has outrun the 850 mb circulation closer to the surface due to easterly shear and that the feature will now reorganize further East and North.

The next 6 hours should tell us whether that is happening or not.

It's what the past several GFS runs have said would happen, if you look at the 850mb vorticity run. If it verifies, my trust in the GFS will have been restored.
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18z GFS 24hrs
Member Since: July 21, 2009 Posts: 0 Comments: 552
Quoting kmanislander:
Here is something interesting. Convection firing up right where the 850 mb vorticity signature is on the vort map.

It may well be the the apparent circulation we are seeing further West has outrun the 850 mb circulation closer to the surface due to easterly shear and that the feature will now reorganize further East and North.

The next 6 hours should tell us whether that is happening or not.


Is this a sign of it lifting out of the ITCZ
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GFS barely shows develop lol. It thinks there is a closed surface low there which there is not. It is also overestimating the amount of convection in the region of highest vorticity.
Member Since: October 28, 2006 Posts: 57 Comments: 30825
Quoting kmanislander:
Here is something interesting. Convection firing up right where the 850 mb vorticity signature is on the vort map.

It may well be the the apparent circulation we are seeing further West has outrun the 850 mb circulation closer to the surface due to easterly shear and that the feature will now reorganize further East and North.

The next 6 hours should tell us whether that is happening or not.



Good observation kman
Here is something interesting. Convection firing up right where the 850 mb vorticity signature is on the vort map ( 10N 30W ).

It may well be that the apparent circulation we are seeing further West has outrun the 850 mb circulation closer to the surface due to easterly shear and that the feature will now reorganize further East and North.

The next 6 hours should tell us whether that is happening or not.

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674. IKE
18Z GFS @ 48 hours...

Member Since: June 9, 2005 Posts: 23 Comments: 37860
672. HadesGodWyvern (Mod)
oh no! rickrolling on a weather blog >.<
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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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