CSU and TSR continue to predict a near-average hurricane season

By: Dr. Jeff Masters , 3:18 PM GMT on August 04, 2009

Share this Blog
1
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 472 - 422

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30Blog Index

Quoting presslord:


There is no such place as "the Carolinas"...it's either North Carolina ...or South Carolina...


Really?
Member Since: Posts: Comments:
I think my last post got lost in cyberspace but just making the observation that I do not think that this wave is going to "rapidly" organize into a TD and it will take some time and effort (to lift out of the ITCZ and fight off shear/dry air). But, convection has been pretty consistent for the last 24 hours.....If it cannot organize and lift out in time, it will keep heading West into SA and Barbados IMHO as a strong wave.
Member Since: Posts: Comments:
Best to track any Low riding ITCZ system in August,
The NHC has a good bead on it,its not like its gonna blow up into a Hurricane the next 48-72.

That isnt in the progs today.
Member Since: July 3, 2005 Posts: 428 Comments: 129833
Quoting Patrap:
Well..one thing for sure,,this aint IVAN.

And usually once a system passes thru the windwards,we will be more alert to its potential


IF you live in the US, but there are people here that live in those winward islands that would like to know info about it before it gets there
Quoting Weather456:


I'm glad to provide any info I can, especially if it is someone from the Carib.


Hi Weather456. I have been on this blog for a couple of years now. I just find that the powers to be are always too cautious when things are in the Atlantic east of the islands as they are essentially at least a week from the US. As someone said last night if this system were in the Gulf then for sure more attention would be paid to it. I do pay close attention to your and a few other's posts as you have a genuine interest in weather no matter where located. Everyone has an opinion and many here wishcast. Keep up the great work.
Member Since: Posts: Comments:
Quoting Weather456:
Soemthing interesting, one has to ask, despite everything put up against it, SAL, dry air, shear, ITCZ, why has persisted?



'cause mother nature likes to screw with us?
Member Since: Posts: Comments:
Quoting LiveFromTheCarolinas:


Why? Does PressLord have something against T.C.?


Presslord, would you like to elaborate?
Member Since: Posts: Comments:
Quoting LiveFromTheCarolinas:


Why? Does PressLord have something against T.C.?


There is no such place as "the Carolinas"...it's either North Carolina ...or South Carolina...
Member Since: August 13, 2007 Posts: 0 Comments: 10492
30min ago GONI landing


http://oiswww.eumetsat.org/IPPS/html/latestImages/EUMETSAT_MTP_MPE-indonesia.png
Member Since: Posts: Comments:
Well..one thing for sure,,this aint IVAN.

And usually once a system passes thru the windwards,we will be more alert to its potential
Member Since: July 3, 2005 Posts: 428 Comments: 129833
Soemthing interesting, one has to ask, despite everything put up against it, SAL, dry air, shear, ITCZ, why has persisted?

Member Since: Posts: Comments:
Quoting hurricanejunky:

I wasn't contradicting anything. Did I say I think it's harsh to ignore him for a difference of opinion and then say you should ignore him for a difference of opinion? No. Read it again and maybe you can tell the difference between hypocracy and observation. I was just calling it like I see it. Settle down there terminator.
I was just calling like I see it. I am just throwing in my two cents just like you did. I would elaborate on the hypocracy but it really doesn't matter, so back to the tropics watch for me.
Member Since: Posts: Comments:
Quoting hurricanejunky:

Quick! Change your handle before PressLord sees...LOL


Why? Does PressLord have something against T.C.?
Member Since: Posts: Comments:
Quoting SavannahStorm:




"Just the facts, ma'am. All we want are the facts."


Facts?!?!?!?!?! We don't need no steenkin' facts!!!!!!!!!!!!
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting gwadaman:


Good afternoon 456, I have been following your post and agree with your views so far. Barbados is not far away and I certainly remember Ivans path. It will be interesting to see the next 48hrs. I look forward to you further post and updates.


I'm glad to provide any info I can, especially if it is someone from the Carib.
Member Since: Posts: Comments:
I'm just a good ol' boy with no trainin but i swear that thing looks like its spinnin like my head does after Friday night at the Honky Tonk.
Member Since: Posts: Comments:
Quoting largeeyes:
It's losing convection, that's for sure. Dry air?


D-min
Member Since: Posts: Comments:
Quoting presslord:


too late

DOH! Sorry for the comic relief but I couldn't resist...
Member Since: Posts: Comments:
Quoting TampaSpin:


Can't tonite......secondly my darn son is a Red Sox nation person......I AM NOT TAKING HIM TO THAT STADIUM ....LOL


Should be one hell of a series to watch..may the best team win!!
Member Since: Posts: Comments:
Quoting SavannahStorm:




"Just the facts, ma'am. All we want are the facts."


Has a very nice moisture shield with it, dont think dry air is going to impact it
It'll be interesting once it lifts out of the ITCZ.
Member Since: May 17, 2009 Posts: 0 Comments: 559
Quoting CypressJim08:
TampaSpin a little off the weather track but you sure must be looking forward to the two games at the Trop tonight and tomorrow...are you going?


Can't tonite......secondly my darn son is a Red Sox nation person......I AM NOT TAKING HIM TO THAT STADIUM ....LOL
Member Since: Posts: Comments:




"Just the facts, ma'am. All we want are the facts."
Member Since: Posts: Comments:

Meteosat-8 SAL Split-Window
Member Since: July 3, 2005 Posts: 428 Comments: 129833
Quoting hurricanejunky:

Quick! Change your handle before PressLord sees...LOL


too late
Member Since: August 13, 2007 Posts: 0 Comments: 10492
Quoting LiveFromTheCarolinas:
This is starting to look like one to take seriously.

Quick! Change your handle before PressLord sees...LOL
Member Since: Posts: Comments:
TampaSpin a little off the weather track but you sure must be looking forward to the two games at the Trop tonight and tomorrow...are you going?
Member Since: Posts: Comments:
Going for a nice long run before the RAYS kicks Red Sox nations A...S...S tonite......LOL...BBL tonite..NO FIGHTING KIDS!
Member Since: Posts: Comments:
Offtopic: THIS is a cool picture from this morning.
Discovery was rolling out to the pad.
Member Since: Posts: Comments:
Tropical Storm Position Page

Atlantic Ocean Basin: Imagery

DATE/TIME LAT LON CLASSIFICATION STORM
No Current Positions
Member Since: July 3, 2005 Posts: 428 Comments: 129833
442. Skyepony (Mod)
C Atl blob looks a little better. The shadow from the setting sun isn't hurting it none but still looks to have stacked & tightened back up a little.
Member Since: Posts: Comments:
Quoting Weather456:
It has a tropical storm structure...lol



Good afternoon 456, I have been following your post and agree with your views so far. Barbados is not far away and I certainly remember Ivans path. It will be interesting to see the next 48hrs. I look forward to you further post and updates.
Member Since: Posts: Comments:
Quoting Seflhurricane:
w456 whats up, looks like this disturbance has been able to maintain itself does it look like we may have a weekend depression ??????


Hey everything's good.

Not 100% sure on TD at this point but its certainly not out of the realm of reality.
Member Since: Posts: Comments:
Two things.

Even though I am a humble, and (compared to others here) weather-uneducated layman, I do have my opinions thus:

- I did underestimate this wave, has lasted longer than I thought.
- Unfortunately, that also indicates to me, that the progression of the season may be quite harsh, from mid-August on.

My reasoning? That even with mildly unfavourable conditions, we have this wave fighting on.

So what happens when things get more favourable in a week or two?

Not good. I am not a pessimist, just a pragmatist.
Member Since: Posts: Comments:
Quoting tigerfanintexas:
I don't quite understand how you can defend one person and slam another in the same sentence. Seems like you show the same bias as the people who put drak on ignore. Besides have you never seen draks posts where he keeps track of the number of people on his ignore list. His opinions don't bother me nor do anyone's, but don't be a hypocrite and contradict what you're saying with what you're saying.

I wasn't contradicting anything. Did I say I think it's harsh to ignore him for a difference of opinion and then say you should ignore him for a difference of opinion? No. Read it again and maybe you can tell the difference between hypocracy and observation. I was just calling it like I see it. Settle down there terminator.
Member Since: Posts: Comments:
Drak, Its not ITCZ convection the NHC ran it as a Tropical Wave since the 805 AM EDT. This could be in terms of Genesis if it develops a Felix scenario. Not strength, just Genesis if it develops.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting Weather456:
If it conntinues on the southerly track it is definitely a feature to watch, shear forecast show a southerly track would benefit the disturbance.
w456 whats up, looks like this disturbance has been able to maintain itself does it look like we may have a weekend depression ??????
Member Since: Posts: Comments:
This is starting to look like one to take seriously.
Member Since: Posts: Comments:
Shear map.Link
Member Since: Posts: Comments:
Plan of the Day

000
NOUS42 KNHC 041245
WEATHER RECONNAISSANCE FLIGHTS
NATIONAL HURRICANE CENTER, MIAMI, FL
0845 AM EDT TUE 04 AUG 2009
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 05/1100Z to 06/1100Z AUGUST 2009
TCPOD NUMBER.....09-068

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY.....NEGATIVE.

II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.
JWP

Member Since: July 3, 2005 Posts: 428 Comments: 129833


We report, you decide.
Member Since: Posts: Comments:
Quoting Drakoen:
It looks like the ITCZ.


Drak i agree with nearly everything you have said about this blob but, honestly there has to be an area of Low pressure within the mix of the ITCZ to create such a disturbance. YOu would have to say that i would think.
Member Since: Posts: Comments:
If it conntinues on the southerly track it is definitely a feature to watch, shear forecast show a southerly track would benefit the disturbance.
Member Since: Posts: Comments:
One thing is for sure... based on the 18Z VORT MAX images... it has definitely consolidated towards the surface specially between 850MB and 700MB... it has definitely lost its mid level energy due to the easterly shear it encountered ealier. It will have to know work hard to get that energy build back up to 500MB by increasing its convection tonight during DMAX... else say Hello to Brazil and the Winward Islands... hehe.
Member Since: Posts: Comments:
Monitoring Atlantic Hurricane Potential


NOAA's Climate Prediction Center (CPC) works in close collaboration with NOAA's National Hurricane Center and the Hurricane Research Division to produce seasonal Atlantic hurricane outlooks and climate summaries of recent past hurricane seasons. The current atmospheric and oceanic conditions over the tropical North Atlantic are summarized in the links below
Member Since: July 3, 2005 Posts: 428 Comments: 129833
Member Since: Posts: Comments:
Quoting CybrTeddy:


Just like Felix did, that wasn't a fun one for them.


I'm beginning to think as i posted on my update that this might have Felix written all over it.....Just not sure what Shear will be like tho if it heads that way....Shear is so hard to predict more than 36hrs out.
Member Since: Posts: Comments:
Quoting atmoaggie:


Agreed. The only less than friendly remarks I see by reading back were from others (unless, of course, big modifications were made).

What I am seeing is the occasional sarcastic remark, or something somewhat biting. I think the bluntness of the remarks is what's getting to people.
Member Since: Posts: Comments:
422. IKE
1800UTC vorticity @ 850mb's shows the vort up near 11 north and 30 west....

I see a spin(not as noticeable as yesterday), near 9N and 36W....

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

Viewing: 472 - 422

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
27 °F
Overcast

JeffMasters's Recent Photos

Lake Effort Snow Shower Over Windsor, Ontario
Sunset on Dunham Lake
Pictured Rocks Sunset
Sunset on Lake Huron