Active 2009 hurricane season predicted by Colorado State scientists

By: Dr. Jeff Masters , 4:20 PM GMT on December 10, 2008

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It's going to be a moderately more active than average Atlantic hurricane season in 2009, according to the latest seasonal forecast issued by Dr. Bill Gray and Phil Klotzbach of Colorado State University (CSU) today. The CSU team is calling for 14 named storms, 7 hurricanes, 3 intense hurricanes, and an ACE index 30% above average (Accumulated Cyclone Energy (ACE) is a measure of the total destructive power of a hurricane season, based on the number of days strong winds are observed). An average season has 10 named storms, 6 hurricanes, and 2 intense hurricanes. The CSU forecast calls for a 63% chance of a major hurricane hitting the U.S., which is 11% above average. The odds for a major East Coast hurricane are put at 39% (a 31% chance is average), and odds for the Gulf Coast are put at 38% (30% chance is average). The CSU team's prediction of an above average hurricane season hinges on two main factors:

1) An El Niño event is not expected in 2009. The current pressure pattern in the Northeast Pacific is one frequently associated with the development of a La Niña event. A number of the computer models used to forecast El Niño are now calling for development of a La Niña event in 2009. Lack of an El Niño event in 2009 will lead to average to below average values of wind shear over the Atlantic, enhancing hurricane activity.

2) Sea Surface Temperatures (SSTs) in the North Atlantic have been anomalously warm in October and November. This implies we are still in the active phase of the Atlantic Multidecadal Oscillation (AMO), the active period of hurricane activity that began in 1995.


Figure 1. Accuracy of long-range forecasts of Atlantic hurricane season activity performed by Bill Gray and Phil Klotzbach of Colorado State University (colored squares) and 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.

How good are these December hurricane season forecasts?
Keep in mind that these December forecasts are a research project, and as yet have shown no skill in predicting the activity of upcoming hurricane seasons. They make this clear in the introduction to the December forecast, stating, "our real-time forecasts issued in early December from 1992-2007 did not show skill in real time". The CSU team talks extensively about their "hindcast" skill with these December forecasts, which means they can successfully predict the behavior of past hurricane seasons using their methodology. In their words, "It is only through hindcast skill that one can demonstrate that seasonal forecast skill is possible. This is a valid methodology provided that the atmosphere continues to behave in the future as it has in the past." The problem is that the atmosphere often does not continue to behave in the future as it has in the past, and a technique that is successful in a hindcast will often fail in a forecast. In their 2007 December forecast, they showed that the correlation coefficient (r squared), a standard mathematical measure of skill, was near zero for their real-time December forecasts between 1992-2007. They made a successful December 2007 forecast which was not included in that analysis, and their December skill is probably slightly positive now.

Another way to measure skill is using the Mean Square Skill Score (MSSS), which looks at the forecast 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 (Figure 1). The skill of the December forecasts issued by both CSU and Tropical Storm Risk, Inc. (TSR) have averaged near zero since 1992. Not surprisingly, the forecasts get better the closer they get to hurricane season. The TSR forecasts show more skill than the CSU forecasts, but it is unclear how much of this superiority is due to the fact that TSR issues forecasts of fractional storms (for example, TSR may forecast 14.7 named storms, while CSU uses only whole numbers like 14 or 15). TSR does an excellent job communicating their seasonal forecast skill. Each forecast is accompanied by a "Forecast Skill at this Lead" number, and they clearly define this quantity as "Percentage Improvement in Mean Square Error over Running 10-year Prior Climate Norm from Replicated Real Time Forecasts 1987-2006."

The June and August forecasts from CSU, TSR, and NOAA show some modest skill, and are valuable tools for insurance companies and emergency planners to help estimate their risks. The key problem with forecasts done in April or earlier is that the El Niño/La Niña atmospheric cycle that can dominate the activity of an Atlantic hurricane season is generally not predictable more than 3-6 months in advance. For example, none of the El Niño forecast models foresaw the September 2006 El Niño event until May of 2006. Until we can forecast the evolution of El Niño more than six months in advance, December forecasts of Atlantic hurricane activity are merely interesting mental exercises that don't deserve the media attention they get. There is hope for the December forecasts, since Klotzbach and Gray (2004) showed that their statistical scheme could make a skillful forecast in December, when applied to 50 years of historical data. However, these "hindcasts" are much easier to make than a real-time forecast. For example, before 1995, it was observed that high rainfall in the Sahel region of Africa was correlated with increased Atlantic hurricane activity. This correlation was used as part of the CSU forecast scheme. However, when the current active hurricane period began in 1995, the correlation stopped working. Drought conditions occurred in the Sahel, but Atlantic hurricane activity showed a major increase. The CSU team was forced to drop African rainfall as a predictor of Atlantic hurricane activity.

References
Klotzbach, P.J., and W.M. Gray, "Updated 6-11 Month Prediction of Atlantic Basin Seasonal Hurricane Activity," Weather and Forecasting 19, Issue 5, October 2004, pp. 917-934.

Jeff Masters

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421. IKE
3:19 PM GMT on December 12, 2008
NEW BLOG!
Member Since: June 9, 2005 Posts: 23 Comments: 37858
420. NEwxguy
3:08 PM GMT on December 12, 2008
Bone,flooded streets I can deal with,the ice you are getting can be a nightmare
Member Since: September 6, 2007 Posts: 862 Comments: 15043
419. HIEXPRESS
2:59 PM GMT on December 12, 2008
Ears are popping
Member Since: October 13, 2005 Posts: 4 Comments: 2155
418. Hurricane4Lex
2:45 PM GMT on December 12, 2008
okay now I know theres a problem when it snows here in Houston and a "blizzard" happens in New Orleans (looked like it on the videos I saw) and everyone else in the "snowing" parts of the US gets... rain?!

PS thanks IKE
Member Since: August 14, 2008 Posts: 0 Comments: 658
417. Bonedog
2:30 PM GMT on December 12, 2008
Sorry to hear about the flooding. Sounds like Worcester got nailed liek we did. ooking for news articles or reports from the areas nothing really. Guess they are all still in Oh F@#$ mode at droping the ball
Member Since: July 14, 2005 Posts: 14 Comments: 7418
416. IKE
2:29 PM GMT on December 12, 2008
Quoting Hurricane4Lex:
When can we expect the warm up to come over the GOM and the atlantic states?

I heard Dec 13-17

looks like we might not see a white xmas after all calls for a warm period to continue

someone verify this and correct me if im wrong


Should start Sunday.

Looks like it's limited to the southern and SE USA in the 6-10 day outlook....

Member Since: June 9, 2005 Posts: 23 Comments: 37858
415. GBlet
2:29 PM GMT on December 12, 2008
Bone, we get the same thing here! I'm kinda like you, I just try to stay prepared, to the amusement of my spouse and friends.
Member Since: September 13, 2007 Posts: 0 Comments: 435
414. Hurricane4Lex
2:26 PM GMT on December 12, 2008
When can we expect the warm up to come over the GOM and the atlantic states?

I heard Dec 13-17

looks like we might not see a white xmas after all calls for a warm period to continue

someone verify this and correct me if im wrong
Member Since: August 14, 2008 Posts: 0 Comments: 658
413. NEwxguy
2:25 PM GMT on December 12, 2008
Bone,streets are flooded,but stayed right around 33 so no icing,west of us about 30 miles,its bad,power lines down tree branches falling all over the place,around Worcester.
Member Since: September 6, 2007 Posts: 862 Comments: 15043
412. GBlet
2:23 PM GMT on December 12, 2008
Could someome please bring the blog an ecspresso, make that a double!
Member Since: September 13, 2007 Posts: 0 Comments: 435
411. Bonedog
2:21 PM GMT on December 12, 2008
GB there were no warnings for this ice storm unfortunatly. The had a winter weather advisory for light freezing rain with change over to snow ice accumulation less then 1/4 inch snow 1 to 2 inches

Instead we had 1/2 by 10pm lost power at 11:30 woke up at 4am to the tree in our yard snaping like a twig and walking outside and staring at 3/4 inches of ice on everything and sounds of cracking and snapping all over the place.

It caught everyone by surprise in my neighborhood. The 2 week supply is just what I
normally do anyways.
Member Since: July 14, 2005 Posts: 14 Comments: 7418
410. TheDawnAwakening
2:16 PM GMT on December 12, 2008
Heavy constant rain right now with some strong winds in gusts.
Member Since: October 21, 2008 Posts: 243 Comments: 3564
409. GBlet
2:14 PM GMT on December 12, 2008
Good morning everyone! Bone, at least you were prepared! Were the people prepared or do they ignore warnings like so many seem to do. I wish more people would pay attention and try harder to take care of themselves.
Member Since: September 13, 2007 Posts: 0 Comments: 435
408. Cotillion
2:06 PM GMT on December 12, 2008
Hmm... Met Office withdraws the snow warnings.

But GFS is adamant on blizzards tomorrow.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
407. Bonedog
2:05 PM GMT on December 12, 2008
Yea IKE I LOVE winter weather just not the ICE why couldnt it get a few degrees colder and give me snow instead or hell a few degrees warmer and just keep it all rain
Member Since: July 14, 2005 Posts: 14 Comments: 7418
406. IKE
2:01 PM GMT on December 12, 2008
Quoting Bonedog:
Hey NE hows things up your way?

I got hammered

3/4" of ICE
no power
multiple trees down on my property
multiple limbs down on the house
power supposedly out till midnight tomorrow and the minimum

so much for a rain storm =(


Sorry to read that.

And that ends my desire for winter weather...
Member Since: June 9, 2005 Posts: 23 Comments: 37858
405. Bonedog
1:59 PM GMT on December 12, 2008
Hey NE hows things up your way?

I got hammered

3/4" of ICE
no power
multiple trees down on my property
multiple limbs down on the house
power supposedly out till midnight tomorrow and the minimum

so much for a rain storm =(
Member Since: July 14, 2005 Posts: 14 Comments: 7418
404. melwerle
1:57 PM GMT on December 12, 2008
Couldn't resist Skypony...after hearing JFV ask a zillion times this year, I just couldn't keep from typing it.

I would LOVE to head north and play in the snow though - was praying for some of it here...if it can happen in NOLA, hey, it could happen in Savannah. What I don't get is every time it rains, it's in the high sixties/seventies here...then it's totally clear and it's in the 30s overnight. Need it all to come together to get some white stuff. My kids have never seen snow since they were born in CA and then we moved here. How far north do we have to go to go play?

Member Since: June 28, 2006 Posts: 12 Comments: 1837
403. IKE
1:56 PM GMT on December 12, 2008
Quoting melwerle:
ok...i just can't resist...

DO YOU THINK IT MIGHT HIT SOUTHERN FLORIDA? OMG...SHOULD I START PACKING????

ok...I'm done...just couldn't resist it since we heard it SOOOO many times this year...

oh, btw, GOOD MORNING.


LOL.....all of those type bloggers are nowhere to be found....I guess....:)))
Member Since: June 9, 2005 Posts: 23 Comments: 37858
402. hurristat
1:55 PM GMT on December 12, 2008
LOL TS DOLPHIN!!!! (sorry couldn't resist)
Member Since: October 15, 2008 Posts: 11 Comments: 2305
401. NEwxguy
1:47 PM GMT on December 12, 2008
GM all,from stormy new england,depending on where you live determines what type of weather.
Member Since: September 6, 2007 Posts: 862 Comments: 15043
400. Skyepony (Mod)
1:47 PM GMT on December 12, 2008
Morning Mel~ LOL, Oh defeniately, what ever excuse you need to head north to play in a little snow.
Member Since: August 10, 2005 Posts: 156 Comments: 36034
399. Skyepony (Mod)
1:44 PM GMT on December 12, 2008
Gfs & CMC are calling for straight up~ warm core. Have to take a look at how much energy that wave has.


NOAA's Nov US wrap up is out.

Member Since: August 10, 2005 Posts: 156 Comments: 36034
398. melwerle
1:35 PM GMT on December 12, 2008
ok...i just can't resist...

DO YOU THINK IT MIGHT HIT SOUTHERN FLORIDA? OMG...SHOULD I START PACKING????

ok...I'm done...just couldn't resist it since we heard it SOOOO many times this year...

oh, btw, GOOD MORNING.
Member Since: June 28, 2006 Posts: 12 Comments: 1837
397. Cotillion
1:34 PM GMT on December 12, 2008
Considering the trends of December storms over the last 15 years, definitely not impossible.
Member Since: August 23, 2008 Posts: 7 Comments: 5300
396. IKE
1:33 PM GMT on December 12, 2008
I had 3.58 inches of rain from Wednesday through yesterday afternoon.

Crestview,FL. had nearly 6 inches of rain.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
395. IKE
1:30 PM GMT on December 12, 2008
From the Jackson,MS. extended discussion....

Overall...no
strong/severe thunderstorm or heavy rain events are anticipated next week given
the dominance of the upper ridge over the Gulf and Gulf Coast
region.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
394. IKE
1:22 PM GMT on December 12, 2008
Quoting Skyepony:
Not impossible.. Looks like a wave + the tail of that front, which still has alot of energy to it. Ways out, have to see if we get some persistance


Could start out as a ST system and then transition to purely tropical. I can see it happening...low shear...high pressure strengthening....may take a couple of days to get going.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
393. Skyepony (Mod)
1:13 PM GMT on December 12, 2008
Not impossible.. Looks like a wave + the tail of that front, which still has alot of energy to it. Ways out, have to see if we get some persistance
Member Since: August 10, 2005 Posts: 156 Comments: 36034
392. IKE
1:06 PM GMT on December 12, 2008
Shear is low out there.....




Think I see the area....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
391. IKE
12:34 PM GMT on December 12, 2008
Looking ahead from the latest San Juan,PR discussion...

Looking ahead...strong low pressure system currently affecting
the eastern United States will move steadily northeast during the
next 48+ hours and is expected to push its associated cold front
across the southwest Atlantic and near the local area Monday
through Wednesday. At the same time...models still suggesting the
development of deep layered low pressure northeast of the local
islands Monday through at least Thursday of next week...and with
surface low pressure possibly dumb-belling back toward the local
area. Thus...there is the potential for increasingly active
weather next week but the details remain to be clarified.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
390. IKE
12:31 PM GMT on December 12, 2008
Quoting vortfix:
This is why I love the weather....the change in it...it doesn't stay the same.....

Absolutely Ike...I love it too...never a boring subject for too long.



Agree...there's always something going on.

Call me a wishcaster...I'm rooting for Rene to form and harm no one.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
389. vortfix
12:26 PM GMT on December 12, 2008
This is why I love the weather....the change in it...it doesn't stay the same.....

Absolutely Ike...I love it too...never a boring subject for too long.

388. IKE
12:23 PM GMT on December 12, 2008
Well.....


It snows in New Orleans one day and the next day several computer models show a significant system in the Atlantic....heading north of PR.

WTF?????????

This is why I love the weather....the change in it...it doesn't stay the same.....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
387. IKE
12:18 PM GMT on December 12, 2008
Uh-oh....what's the next name? LOL
Member Since: June 9, 2005 Posts: 23 Comments: 37858
386. JRRP
12:18 PM GMT on December 12, 2008
Link
Link
Link
TS near PR
Member Since: August 16, 2007 Posts: 0 Comments: 5073
385. IKE
12:17 PM GMT on December 12, 2008
6Z GFS shows it too....Link
Member Since: June 9, 2005 Posts: 23 Comments: 37858
384. IKE
12:09 PM GMT on December 12, 2008
Check out the 00Z ECMWF....out in the Atlantic....NE of Puerto Rico....a December system? Link
Member Since: June 9, 2005 Posts: 23 Comments: 37858
383. aspectre
11:58 AM GMT on December 12, 2008
369. pottery "Will rising temps cause more SAL ? I think so too. And that could possibly snuff out Atl. storms."

Dr.Masters "The Saharan Air Layer (SAL) is a layer of dry, dusty Saharan air that rides up over the low-level moist air over the tropical Atlantic...
...The level of drought experienced in the northwestern Sahel...is the key factor...in determining how much dust gets transported over the Atlantic..."
From today's blog
"...before 1995, it was observed that high rainfall in the Sahel region of Africa was correlated with increased Atlantic hurricane activity.
However, when the current active hurricane period began in 1995, the correlation stopped working. Drought conditions occurred in the Sahel, but Atlantic hurricane activity showed a major increase..."
Member Since: August 21, 2007 Posts: 0 Comments: 4860
382. MissNadia
11:34 AM GMT on December 12, 2008
Morning from Wilmington
52F with light SW winds
Partly cloudy and forecast to remain that way
Temp will rise to 56 during the day
Member Since: July 27, 2008 Posts: 0 Comments: 2865
381. all4hurricanes
11:01 AM GMT on December 12, 2008
well no snow last night not really surprising considering the temp never went below 37. So no two hour delay but I was expecting that but what really irks me it that after 2 days of rain and the temperature never allowed it to snow it will finally drop below 32 when it stops raining.
TS27 is strengthening, new trend. I think 60-80mph is the range of max intensity but I have been wrong on Wpac storms before.
Member Since: March 29, 2008 Posts: 0 Comments: 2338
380. HadesGodWyvern (Mod)
7:39 AM GMT on December 12, 2008
Japan Meteorological Agency
Tropical Cyclone Advisories #3
T2008-22 DOLPHIN
15:00 PM JST December 12 2008
===============================================

At 15:00 PM JST, Tropical Storm Dolphin (1000 hPa) located near 13.6N 140.4E has 10 minute sustained winds of 35 knots with gusts up to 50 knots. The cyclone is reported as moving west-northwest at 9 knots.

Gale-force Winds
================
150 NM from the center in north quadrant
120 NM from the center in south quadrant

Dvorak Intensity: T2.5

Forecast and Intensity
=====================
24 HRS: 13.7N 136.2E - 50 knots (CAT 2)
48 HRS: 13.2N 132.5E - 65 knots (CAT 3)
72 HRS: 13.3N 130.7E - 75 knots (CAT 3)
Member Since: May 24, 2006 Posts: 48 Comments: 43639
379. BahaHurican
7:24 AM GMT on December 12, 2008


Wow! The most intense rain is now happening over New Providence, when there's barely a wisp of heavy cloud in the area!
Member Since: October 25, 2005 Posts: 19 Comments: 20686
378. BahaHurican
4:49 AM GMT on December 12, 2008
Quoting pottery:
DDR, there are lots of theories. But really, no one knows for sure, what the weather will do, with rising temps. More severe storms would be my guess, but will rising temps create more shear? I think it might. Will rising temps cause more SAL ? I think so too. And that could possibly snuff out Atl. storms.
Its all going to be very interesting.
What I've heard that makes the most sense to me so far re. GW and TC activity is fewer storms, but increased intensity. This suggests we'll still cycle through the smaller patterns (ENSO, NAO, PAO, etc.) with the natural variation they bring, but will be likely to see the average number of cat. 3 - 5 storms increase over the long term. It's hard to tell, though, since the limited data we have doesn't provide much insight into the worldwide incidence of TCs. . .
Member Since: October 25, 2005 Posts: 19 Comments: 20686
376. BahaHurican
4:41 AM GMT on December 12, 2008
Quoting pottery:
Helloo all
Its 75 f, and its forecast to get down to 73 !!
Winter is here, big time.
LOL
Hear hear!

LOL
Member Since: October 25, 2005 Posts: 19 Comments: 20686
375. KoritheMan
4:41 AM GMT on December 12, 2008
Quoting pottery:
DDR, there are lots of theories. But really, no one knows for sure, what the weather will do, with rising temps. More severe storms would be my guess, but will rising temps create more shear? I think it might. Will rising temps cause more SAL ? I think so too. And that could possibly snuff out Atl. storms.
Its all going to be very interesting.


I find the theory that global warming will result in increased hurricane activity faulty at best. Rising air temperatures will lead to warmer SSTs, which will in turn lead to the development of convection, which will in turn cause shear. I also agree with you on the SAL thing.

What I think global warming will do, however, is cause an increase in the number of intense hurricanes that develop. In spite of the possibility of vertical shear increasing with warmer SSTs, and SAL increasing with warmer air temperatures, there will always be brief periods where shear and SAL will relax enough to allow a significant hurricane to develop. With more heat energy, the hurricanes that do develop will have a much greater chance to be as strong as the most notorious storms we know of (Andrew, Camille, Allen, Rita, Katrina, Wilma, Gilbert, etc.)
Member Since: March 7, 2007 Posts: 521 Comments: 19109
374. HadesGodWyvern (Mod)
4:31 AM GMT on December 12, 2008
Japan Meteorological Agency
Tropical Cyclone Advisory #2
12:00 PM JST December 12 2008
===============================================

At 12:00 PM JST, Tropical Depression (1002 hPa) located near 13.6N 141.0E has 10 minute sustained winds of 30 knots with gusts up to 45 knots. The depression is reported as moving northwest at 12 knots.

Dvorak Intensity:

Forecast and Intensity
=====================
24 HRS: 13.6N 136.7E - 35 knots (CAT 1)
Member Since: May 24, 2006 Posts: 48 Comments: 43639
372. DDR
3:50 AM GMT on December 12, 2008
Quoting pottery:
DDR, there are lots of theories. But really, no one knows for sure, what the weather will do, with rising temps. More severe storms would be my guess, but will rising temps create more shear? I think it might. Will rising temps cause more SAL ? I think so too. And that could possibly snuff out Atl. storms.
Its all going to be very interesting.
Indeed,its going to get interesting in years to come,That flood that crippled western Trinidad,i dont think that was a normal late November precipitation event,the local met office seemed to agree.
Member Since: April 27, 2007 Posts: 14 Comments: 1625

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About JeffMasters

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