Genesis of New Atlantic Tropical Cyclones: Which Model Should You Trust?

By: Dr. Jeff Masters , 3:29 PM GMT on August 29, 2013

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It's been a remarkably quiet late August in the Atlantic for hurricanes, with nary an "Invest", and precious few yellow 10% probability circles on NHC's Tropical Weather Outlook. When will this remarkable hurricane drought come to an end? The computer models we use to track hurricanes have conflicting ideas about this. Which model should we believe, and how far into the future can these models successfully predict genesis events of new tropical depressions in the Atlantic? Some answers come in a 2013 paper by a group of scientists led by Florida State's Daniel Halperin, just accepted for publication in the journal Weather and Forecasting, "An evaluation of tropical cyclone genesis forecasts from global numerical models." It turns out that two of the three most reliable models for predicting the genesis of tropical cyclones up to four days in advance are also the our top-performing models for predicting hurricane tracks: the American GFS model and the European ECMWF model. The UKMET model is also quite good at predicting tropical cyclone genesis events. The Canadian GEM model and the Navy NOGAPS model (now succeeded by the Navy NAVGEM model) do less well. When two or more models make the same genesis forecast, the odds of the event actually occurring are increased considerably. The models have improved greatly in making genesis forecasts in recent years; back in 2007, when our top three models made a 4-day genesis forecast, these verified only 17 - 28% of the time. By 2011, the hit rate had increased to 45 - 50%. However, the models still miss most genesis events. In 2011, the probability of detection of a tropical cyclone genesis event was only 8% - 23%, meaning that 77 - 92% of time, a tropical depression or tropical storm formed without the model predicting that it would form. The best model to use for looking at Atlantic tropical cyclone genesis in 2011 was the UKMET model, which combined a relatively high probability of detection rate with a low false alarm rate.


Figure 1. The probability of making a correct tropical cyclone genesis forecast for all forecast hours (06 to 96) by model, for the period 2004 - 2011. In 2011, three models--the GFS, UKMET, and European--made genesis forecasts that were correct 45 - 50% of the time. The Canadian GEM model and the Navy NOGAPS model did less well. Data taken from Halperin et al., 2013, "An evaluation of tropical cyclone genesis forecasts from global numerical models." Weather and Forecasting, doi: http://dx.doi.org/10.1175/WAF-D-13-00008.1

The paper looked at 135 Atlantic genesis events over the period 2004 - 2011, as predicted by five global computer weather forecast models: the GFS, ECMWF, UKMET, NOGAPS, and Canadian GEM. The regional GFDL and HWRF hurricane models were not considered, as they use output from the GFS model to drive them, and are not good at making genesis forecasts. The study only looked at forecasts made up to four days in advance. While there have been cases where I've seen genesis predictions made 7 - 10 days in advance come true, these are rare, and the "hit" rate of successful genesis forecasts even four days in advance is low. In the paper, a "hit" was defined as a forecast that successfully predicted genesis within 24 hours and 345 miles of the observed time and location. A "false alarm" occurred when the model predicted a storm that never developed. The other categories considered were "late genesis" events where a storm formed more than 24 hours before it was predicted to, and "early genesis", where a storm formed more than 24 hours after it was predicted to. Here are some details on each model's ability to make Atlantic tropical cyclone genesis forecasts:

European ECMWF model: The model is reluctant to predict genesis, and misses many genesis events (it had only an 8% probability of detection in 2011.) However, when it does predict genesis, it usually happens, with only a 16% false alarm percentage in 2011. The European model exhibits preferred regions of genesis, with over 60% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W. Although the ECMWF misses many tropical cyclone genesis events in the Gulf of Mexico (as do the other models), when it does forecast genesis there, it almost always occurs. The model was highly prone to making late genesis forecasts.

American GFS model: The GFS model improved substantially in its genesis forecasts beginning in 2010, most likely due to a major model upgrade in 2010. The GFS is more aggressive at predicting genesis than the European model, and is less likely to miss a genesis event (22% probability of detection in 2011.) However, the incidence of false alarms was 32% in 2011, double what the European model had. Like the European model, the GFS exhibits preferred regions of genesis, with nearly 60% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W.

UKMET model: The UKMET is more aggressive at predicting genesis than the European model, and is less likely to miss a genesis event (20% probability of detection in 2011.) The incidence of false alarms was 18% in 2011, similar to what the European model had. Like the European and GFS models, the UKMET exhibits preferred regions of genesis, with more than 67% of its genesis forecasts occurring in the MDR: 10-20°N, 60-20°W. The model was prone to making late genesis forecasts.

Canadian GEM model: The Canadian model was the least likely to miss a formation event, with a 23% probability of detection in 2011. False alarms have been a major issue, though, and the Canadian model generated the second highest number of bogus genesis events of any of the five models evaluated (42% of all its genesis forecasts in 2011 were false alarms.) The Canadian model does not seem to have a preferred region of genesis—all types of genesis events occur across the entire basin. The model performs best over the main development region (MDR; 10-20°N, 60-20°W), Caribbean Sea, and Gulf of Mexico (GOM).

Navy NOGAPS model: This model was retired in 2012, but we may be able to assume that its successor, the NAVGEM model, will have some of the same characteristics. False Alarms have been a major issue, and the NOGAPS model generated the highest number of bogus genesis events of any of the five models evaluated (60% of all its genesis forecasts in 2011 were false alarms.) The model also had a low probability of detection, just 9%. NOGAPS model does not seem to have a preferred region of genesis—all types of genesis events occur across the entire basin. Despite the high levels of hurricane activity in 2004 and 2005, the NOGAPS model failed to successfully forecast any genesis events those years.

Sources of Model Data
You can view 7-day ECMWF and 16-day GFS forecasts on wunderground's wundermap with the model layer turned on.
Longer ten-day ECMWF forecasts are available from the ECMWF web site.
FSU's experimental hurricane forecast page (CMC, ECMWF, GFDL, GFS, HWRF, and NAVGEM models)
NOAA's HFIP model comparison page (GFS, ECMWF, FIM, FIM9, UKMET, and CMC models.)
Experimental HFIP models

Very Quiet in the Atlantic
A tropical wave that came off the coast of Africa on Sunday is midway between Africa and the Lesser Antilles Islands. This disturbance is moving westward at 15 mph, has a modest amount of spin, but only a limited amount of heavy thunderstorm activity. In their 8 am EDT Thursday Tropical Weather Outlook, NHC left the 5-day odds of formation of this disturbance at 20%, but increased the 2-day odds of formation to 10%. Wind shear is a moderate 10 - 20 knots over the system, but there is an area of dry air and dust from the Saharan Air Layer (SAL) to the north and west that is interfering with development. With the exception of the NAVGEM model, there is little support from the models for developing the disturbance during the next five days. The wave could spread heavy rains and gusty winds to the Lesser Antilles Islands on Sunday and Monday.

A tropical wave expected to emerge from the coast of Africa on Friday and track over the Cape Verde Islands is also showing little support for development from the models. This wave is expected to take a northwesterly track, and would likely not be able to make the long trek across the Atlantic to threaten North America or the Caribbean Islands. In their 8 am EDT Thursday Tropical Weather Outlook, NHC put the 5-day odds of development at 20%.

Wunderblogger Lee Grenci has an excellent new post, "Atlantic Hurricane Season: The Saharan Air Layer and Vertical Wind Shear".

California's Rim Fire Now 6th Largest in State History, and is 30% Controlled
California's massive Rim Fire in Yosemite National Park continues to grow, but an army of over 4,000 firefighters are making headway against the blaze, and had attained 30% containment of the fire as of 9:20 am EDT on Thursday. According to Inciweb, fire has burned over 192,700 acres. This moves the fire into 6th place for largest fire in state history, according to statistics tabulated by wunderground's weather historian, Christopher C. Burt in his latest post, "The Worst Wild Fires in U.S. History". The Rim Fire will have difficultly surpassing California's largest fire on record--the Cedar Fire in San Diego County of October 2003. That fire burned 273,246 acres (430 square miles). California has had its driest year-to-date period, so it is no surprise that the state is experiencing an unusually large fire this summer.


Video 1. Time-lapse photography shows various perspectives of the 2013 Rim Fire, as viewed from Yosemite National Park. The first part of this video is from the Crane Flat Helibase. The fire is currently burning in wilderness and is not immediately threatening visitors or employees. The second half of the video is from Glacier Point, showing Yosemite Valley, and how little the smoke from the fire has impacted the Valley.

Jeff Masters

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Quoting 886. Grothar:


Wow... we may have our first 'loopdeloo'er in a few years. With this agreement, it's a near certainty.

I was checking out Kyle in detail the other day... now there was a storm that was dropped on his head.
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Quoting 917. Hhunter:

GFS HAS BIG STORM IN GULF MID SEPTEMBER...lol

EUROPEAN HAS STORM DEVELOPING IN BAHAMAS.
WE SHALL SEE


For giggles, can you post the link?
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Quoting 931. CybrTeddy:


Actually, they've all been utterly useless this year.
1) ECMWF failed to pick up Andrea, Barry, Chantal, Dorian, Utor, etc.
2) GFS developed for too many ghost storms.
3) CMC and NOGAPS.. well, lol.
4) UKMET has done pretty good this year so far.


The CMC has done surprisingly well in the WPAC for what it's worth. Not intensity-wise, but in terms of picking up on systems forming and their tracks.
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Quoting Patrap:
92L Final Guidance


It's all there. you just need to watch.
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Quoting 927. TampaSpin:



Not sure what you are talking about....the Models have performed incredibly well....What do you want them to do produce GHOST STORMS.....


Actually, they've all been utterly useless this year.
1) ECMWF failed to pick up Andrea, Barry, Chantal, Dorian, Utor, etc.
2) GFS developed for too many ghost storms.
3) CMC and NOGAPS.. well, lol.
4) UKMET has done pretty good this year so far.
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Member Since: August 2, 2010 Posts: 0 Comments: 1598
Aaaaand TA13 beat me to it :(
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Quoting 898. hurricanes2018:
Tebow for the win
Tim Tebow ended the preseason on a high note, tossing a touchdown pass to Quentin Sims in the final seconds of a win over the Giants!! wow!! we have invest 96L ITS starting to move wnw now! maybe going up to 50% at 2am!


high note? 54% accuracy with 1 INT against a third string defense isnt a good thing...
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Quoting 922. RyanSperrey:
Wonder why every model is horrific this year?  Sure every year they call a dozen false storms, but this year seems particularly bad...it's weird.

Funding cuts taking their toll I suppose.



Not sure what you are talking about....the Models have performed incredibly well....What do you want them to do produce GHOST STORMS.....
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@RyanMaue
5-day GFS forecast complete bust just verified at 00z 30 August. #tragic AC = 0.57 one of its worst forecasts ever.

Member Since: July 6, 2010 Posts: 113 Comments: 31608
I mean it's almost September. Hurricanes will form. They have to, it's a guarantee every year, it's a process the Earth must carry out. It's just where these storms go and how strong they get at this point that is significant.
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RE 855

Patrap:

Okay! You've succeeded in reducing this whole household into fits of giggles!!

Thanks

Lindy
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Member Since: August 2, 2010 Posts: 0 Comments: 1598
Wonder why every model is horrific this year?  Sure every year they call a dozen false storms, but this year seems particularly bad...it's weird.

Funding cuts taking their toll I suppose.
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Quoting 917. Hhunter:

GFS HAS BIG STORM IN GULF MID SEPTEMBER...lol

EUROPEAN HAS STORM DEVELOPING IN BAHAMAS.
WE SHALL SEE


Something is bound to form eventually.
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Member Since: August 2, 2010 Posts: 0 Comments: 1598
Quoting 896. K8eCane:
I just hope someone can come up with a definitive reason for such a lull. it will be interesting.

answered prayers :)
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Quoting 917. Hhunter:

GFS HAS BIG STORM IN GULF MID SEPTEMBER...lol

EUROPEAN HAS STORM DEVELOPING IN BAHAMAS.
WE SHALL SEE
lol it showed that like twice on the GFS and has since dropped it, and it showed it at hour 384 lol.

relax man no need to shout
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GFS HAS BIG STORM IN GULF MID SEPTEMBER...lol

EUROPEAN HAS STORM DEVELOPING IN BAHAMAS.
WE SHALL SEE
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Quoting 890. hurricanes2018:
WOW INVEST 96L is up!


Yup, this one's got PERSONALITY!

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Look what's on it's way....




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Quoting 910. TropicalAnalystwx13:
Well, that escalated quickly.

Member Since: August 2, 2010 Posts: 0 Comments: 1598
We are still ahead

Progress of the average Atlantic season (1966-2009). Date upon which the following number of events would normally have occurred.

We are only behind on Hurricanes.



So to say the season is over is just plain wrong.
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Quoting 902. will40:
i think homegrown systems will be the ones to watch this year


Sure seems like it.
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Even if in the increasingly likely event that 2013 fails to meet seasonal expectations in both ACE and seasonal totals, it'll really only take one or two this season to make it memorable. Think 2012, if we hadn't had Sandy the only thing that would have been noteworthy was Isaac, which paled in comparison in terms of the scope of damage that Sandy brought to the NE (Isaac though, was still a bad storm).

If you don't find that a valid comparison, then think to the Moore and El Reno EF-5s we've had this year. Little do many know the 2013 tornado season has been at record low levels. Does it matter? Not in the slightest, not after those two monsters ruined everyone's day.

Less storms this year, but we may get a true monster or two in the next two months.
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Well, that escalated quickly.

Member Since: July 6, 2010 Posts: 113 Comments: 31608
909. beell
Quoting 903. Levi32:
29 dropsondes, most in the vicinity of the central Atlantic wave from the Global Hawk mission, made it into the 0z run of the GFS.



Global Hawk and its descendants will put us all out of business one day, lol.
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Quoting 903. Levi32:
29 dropsondes, most in the vicinity of the central Atlantic wave from the Global Hawk mission, made it into the 0z run of the GFS.

thank levi you are the best
Member Since: March 12, 2013 Posts: 8 Comments: 13921
Quoting 855. Patrap:
92L Final Guidance



That's too funny. (Borrowing).
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Quoting 904. Camille33:

Pray to jesus!!
Hurricanes or football? Now I see the blog is really boring.
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Quoting 903. Levi32:
29 dropsondes, most in the vicinity of the central Atlantic wave from the Global Hawk mission, made it into the 0z run of the GFS.

Didn't the 18z run had data from them?
Member Since: August 2, 2010 Posts: 0 Comments: 1598
Quoting 901. j108764:
Tim Tebow the man!!

Pray to jesus!!
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29 dropsondes, most in the vicinity of the central Atlantic wave from the Global Hawk mission, made it into the 0z run of the GFS.

Member Since: November 24, 2005 Posts: 635 Comments: 26569
i think homegrown systems will be the ones to watch this year
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Quoting 898. hurricanes2018:
Tebow for the win
Tim Tebow ended the preseason on a high note, tossing a touchdown pass to Quentin Sims in the final seconds of a win over the Giants!! wow!! we have invest 96L ITS starting to move wnw now! maybe going up to 50% at 2am!
Tim Tebow the man!!
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Wow. Any chances of ANY action by the end of the season? Remember Ida of '09, that wasn't a favorable year at all--but that comes to tell that not ALL hurricanes form before the peak. We have a lot of time, stop saying nothing will happen.
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Quoting 896. K8eCane:
I just hope someone can come up with a definitive reason for such a lull. it will be interesting.
Really no major reason I can find now... even some experts are saying if the season doesn't get started, they got no idea why.
Member Since: August 1, 2011 Posts: 28 Comments: 7913
Tebow for the win
Tim Tebow ended the preseason on a high note, tossing a touchdown pass to Quentin Sims in the final seconds of a win over the Giants!! wow!! we have invest 96L ITS starting to move wnw now! maybe going up to 50% at 2am!
Member Since: March 12, 2013 Posts: 8 Comments: 13921
im interested in most everything about the ocean
Member Since: April 26, 2006 Posts: 5 Comments: 3076
I just hope someone can come up with a definitive reason for such a lull. it will be interesting.
Member Since: April 26, 2006 Posts: 5 Comments: 3076
Quoting 864. eyewallblues:
At least our friends at the NHC are catching up on their sleep. Lets hope for a different 2014. My PAVE THE SAHARA initiative is catching on like wildfire!!!
Many NHC workers are naming their children SAL.

See you all next year!!!

7-0-0
Why is everyone putting 7-0-0 the season has been 6-0-0 unless there has been another ts that I didn`t saw.
Member Since: October 15, 2011 Posts: 0 Comments: 4106
894. JRRP
Quoting Gearsts:
lol is just that that the season has been so depressing, 2012 was much better with all the little tc forming everyday and lasting for 2 hr.

is true
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Aye fish storm!

Pretty obvious this season will be a bust in a way.

Sucks to those who thought we would have a big season.
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Quoting 884. JRRP:

jajajjjjaajaajajajaja
lol is just that that the season has been so depressing, 2012 was much better with all the little tc forming everyday and lasting for 2 hr.
Member Since: August 2, 2010 Posts: 0 Comments: 1598
Quoting 887. K8eCane:


I saw that in the movie theatre in Myrtle Beach back in the 70s. Hilarious


Never saw that one
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WOW INVEST 96L is up!
Member Since: March 12, 2013 Posts: 8 Comments: 13921
Quoting 886. Grothar:

Heading right for the dry air and shear.It won't last long either.
Member Since: July 30, 2012 Posts: 4 Comments: 614
Quoting 871. Pallis:
Steve Detwieler has that covered and more. You can get his science report through Graham Hancock's website.
Good to know. In that case I'll stop posting my daily list of articles, leave wunderground forever, and let you direct people to that site.
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Quoting 882. PanhandleChuck:


You made my night


I saw that in the movie theatre in Myrtle Beach back in the 70s. Hilarious
Member Since: April 26, 2006 Posts: 5 Comments: 3076
Member Since: July 17, 2009 Posts: 69 Comments: 25575
invest 96L
Member Since: March 12, 2013 Posts: 8 Comments: 13921

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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.