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 515. Grothar:


Is that the same one you told us the other day, had a good sense of humor? :)
He's a wise man, that's for sure :) I met the remaining two professors at UNCA (we got 4) and I'm very glad I got this group of professors at UNCA. They are very committed to the success of undergraduates!
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634. beell
Quoting 422. Levi32:




Nothing about the MDR is drier than normal right now. You can see this on visible imagery too by the fact that there are puffy cumulus clouds on the ground, not strato-cumulus.



Some of those puffy clouds to the east of the central Atlantic wave may be forming along a baroclinic boundary between the tropical airmass and the marine inversion layer just to the north. The southern "Front" of the SAL may also be involved in some of the vertical motion.

Excuse the graffiti. Saved earlier for another reason. It looked like this yesterday. A boundary to the south of the black arrow?


09:15Z GOES RGB


Member Since: September 11, 2007 Posts: 143 Comments: 16729
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It looks like the Caymans are getting a lot of rain. Anyone from the islands on?

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Quoting 604. ncstorm:
I hear fiber works miracles..

18z currently running
Extremely
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Quoting 597. CybrTeddy:
FWIW - 18z GFS is back on the hurricane bandwagon for the wave emerging off Africa.
Yup. Has it stalling and intensifying nicely far out to sea.

Now it's a waiting game to see if it continues showing this...which based on how the GFS has been behaving the past few days, this may be the first and final run showing hurricane strength.
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Quoting 622. Llamaluvr:
Hi Andre! Hey, lets try to use the correct shear maps tonight. We don't want a repeat of that ugly incident two days ago, and we can't always rely on Taz being around to correct you. 8-D
here you go.
Member Since: June 11, 2013 Posts: 20 Comments: 3212
The best models only detected 9 to 23% of TC genesis in 2011. After reading Dr. masters blog, I dont see how any one can be suprised about how many times the models change? Hurricane season is far from over.
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Meanwhile...



Another dark and stormy night for Cayman?
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Quoting 622. Llamaluvr:
Hi Andre! Hey, lets try to use the correct shear maps tonight. We don't want a repeat of that ugly incident two days ago, and we can't always rely on Taz being around to correct you. 8-D
hi,okay,and right.
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Quoting 614. ncstorm:
18z Navgem..

dropped the TS..

I'm speechless as to whats really going on..


Good thing you didn't forecast a hyperactive season. You'd be eating crow right now.
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Quoting 619. HurricaneAndre:
Hi Andre! Hey, lets try to use the correct shear maps tonight. We don't want a repeat of that ugly incident two days ago, and we can't always rely on Taz being around to correct you. 8-D
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Quoting 614. ncstorm:
18z Navgem..

dropped the TS..

I'm speechless as to whats really going on..
Why speechless of the NAVGEM? just as it drops it the Gfs shows development.
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Quoting 613. hurricane23:


Hey Josh thanks for that.. Hope your doing well


Thanks, all is well here. Waiting for mid-September and a trip to Europe with a good friend. Should be magic I'm sure. Hope things are good on your end.

-Josh

This radioactive mahi is delicious. Not sure who caught it, found it in my mom's freezer. Dated 10/13/12.
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I still see lots of fish storms and going out to sea the next two weeks or more
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Quoting 614. ncstorm:
18z Navgem..

dropped the TS..

I'm speechless as to whats really going on..

Season a bust?
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18z Navgem..

dropped the TS..

I'm speechless as to whats really going on..
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Quoting GatorWX:
Adrian, finally remembered your other page. Still love it, useful. Thanks for keeping it going so long! My old computer took a dump and I took a break for awhile as I had a lot of other things going on. Now, having wifi finally, getting them all rounded up again.

-Josh


Hey Josh thanks for that.. Hope your doing well
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Quack'

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I think the blob south of Cuba is a pop-up MCC.

There is an elongated upper level anti-cyclone parked over it, so theoretically it should have ventilation.

The convection is actually somewhat west, by a few degrees, from the position of maximum low level convergence though, so maybe not that big of a deal after all.
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Quoting 606. allancalderini:
Major hurricane Gabrielle and hurricane Humberto I believe.
I just hope whatever it is that the models keep sending my way wimps out or skives off... REALLY not into the hurricane landfall thing this year.
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Quoting 605. hurricane23:


levi can you link to ur mjo maps? looked just about all over ur site and nothing.


If you mean 200mb velocity potential, the CFS, GFS, and NAVGEM have them for the global and north Atlantic regions only. E.g. go to GFS, pick global or North Atlantic, and then select "200mb Velocity Potential Anomaly & Anomalous Divergent Wind" at the bottom of the variable list.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Adrian, finally remembered your other page. Still love it, useful. Thanks for keeping it going so long! My old computer took a dump and I took a break for awhile as I had a lot of other things going on. Now, having wifi finally, getting them all rounded up again.

-Josh
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Quoting 602. Kyon5:

Pretty far out, but it has 2 systems in the Eastern Atlantic. Probably will drop it and then show it again, like always.


Major hurricane Gabrielle and hurricane Humberto I believe.
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Quoting Levi32:


Yeah, I'll figure something out. I'm also planning on adding equivalent potential temperature (Theta-E) anomaly at some point.


levi can you link to ur mjo maps? looked just about all over ur site and nothing.
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I hear fiber works miracles..

18z currently running
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Quoting 597. CybrTeddy:
FWIW - 18z GFS is back on the hurricane bandwagon for the wave emerging off Africa.
Might or might not,We are getting into the peak which is two weeks ahead and models are pretty uninterest in development.Btw hope you are having a nice birthday :)
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602. Kyon5

Quoting 599. Tropicsweatherpr:
Can anyone post the 18z GFS to see what it has if anything?
Pretty far out, but it has 2 systems in the Eastern Atlantic. Probably will drop it and then show it again, like always.


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Quoting 600. GatorWX:
How about whatever this argument is about, (really don't care and I'm sure everyone else feels the same) how about it stops now. Thanks. Pretty annoying.


Thank you...
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How about whatever this argument is about, (really don't care and I'm sure everyone else feels the same) how about it stops now. Thanks. Pretty annoying.
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Can anyone post the 18z GFS to see what it has if anything?
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Why is everyone at each other's throats here, complaining about no activity, when we may have a TS as early as the next 24-36 hours and possibly a brief weak hurricane sometime in the weekend? Come on, at least there's something to monitor, why is everyone ignoring that and only focusing on the negative factors? Not all, but some of you need to man up and pay more attention towards Africa than an insult war.
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FWIW - 18z GFS is back on the hurricane bandwagon for the wave emerging off Africa.
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So like um, where are all these storms the models keep predicting?

Its a head scratcher
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Just found out my friend got her visa for Spain, mahi is on the grill, rain is over and now it's "cool". Pressing post and getting my second glass, going with a Cote this time. Going to be a good night!!

Barcelona, less than three weeks away, hell yes! Never been to Europe. Going to be a long three weeks the way the tropics have been progressing. Oh well, I can deal with it.
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Quoting 542. TomTaylor:
Sigh.

Drak is a blog member just like the rest of us. Just because he is working towards a degree in meteorology doesn't mean he has the right to be a disrespectful brat. So, unfortunately for you, my "clucking" isn't going to any local hen house. As long as Drak keeps giving the 'tude to Levi (or any other blog members), I will be right here to call him out for it. Not sure why you and the rest of this community continue to turn a blind eye to his ridiculous behavior.
@ Tom... will you stop freaking out??? Levi and Drak have known each other a LOOONG while. They have a complicated relationship, IOW, can fight these things out between themselves.

Meanwhile, the rest of us would like to continue to discuss our desultory season and what's broken or not.

If you have a problem w/ Drak, ignore. Besides, Levi can handle himself.
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Look, let's take the topic of conversation away from me, please. I don't need it and neither does anybody else. Not everyone here knows what has gone on between myself and Drak over the last several weeks. He has treated me rather poorly of late, but that's between him and me. No need to drag the blog into the weeds over it.
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What's the UKMET forseeing?
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Quoting 152. CaneHunter031472:


I was 7 years old living in Puerto Rico at the time. We were supposed to get hit by it, but luckily we only got the torrential rains. Nevertheless David is what sparked my interest in weather forecasting and tracking.
Interesting... David's centre passed just to our east, and the storm was barely a cat 1 at the time... but it also sparked my interest...

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Quoting 582. wunderweatherman123:
18z GFS shows massive fish storms everywhere


Going to have ourselves a fish fry.Yummy
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Quoting 505. MiamiHurricanes09:
This is what we should be seeing. But...

12z CMC; 216 hours.



Biggen! lol
Member Since: January 1, 2008 Posts: 0 Comments: 3422
Quoting 578. KEEPEROFTHEGATE:
ya they will start to see flurries soon if not already sun is getting lower in the sky faster every day now
Cannot believe fall is a little over three weeks away. Man does time move fast.
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SEVERE WEATHER STATEMENT
NATIONAL WEATHER SERVICE DULUTH MN
529 PM CDT THU AUG 29 2013

MNC021-292245-
/O.CON.KDLH.TO.W.0009.000000T0000Z-130829T2245Z/
CASS MN-
529 PM CDT THU AUG 29 2013

...A TORNADO WARNING REMAINS IN EFFECT FOR NORTH CENTRAL CASS COUNTY
UNTIL 545 PM CDT...

AT 528 PM CDT...A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO
WAS LOCATED NEAR SCHLEY...AND MOVING EAST AT 15 MPH.

HAZARD...TORNADO AND TENNIS BALL SIZE HAIL.

SOURCE...RADAR INDICATED ROTATION.

IMPACT...MOBILE HOMES WILL BE DAMAGED OR DESTROYED. DAMAGE TO
ROOFS...WINDOWS AND VEHICLES WILL OCCUR. FLYING DEBRIS WILL
BE DEADLY TO PEOPLE AND ANIMALS. TREE DAMAGE IS LIKELY.

RADAR INDICATED A SECOND STRONG CIRCULATION WAS DEVELOPING BETWEEN
SUCKER BAY ON LEECH LAKE AND PORTAGE LAKE...ALSO MOVING EAST AT 15
MPH.

LOCATIONS IMPACTED INCLUDE...
SCHLEY...FEDERAL DAM AND PORTAGE LAKE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW. MOVE TO AN INTERIOR ROOM ON THE LOWEST FLOOR OF A
STURDY BUILDING. AVOID WINDOWS. IF IN A MOBILE HOME...A VEHICLE OR
OUTDOORS...MOVE TO THE CLOSEST SUBSTANTIAL SHELTER AND PROTECT
YOURSELF FROM FLYING DEBRIS.

&&

LAT...LON 4741 9426 4724 9420 4725 9460 4737 9461
TIME...MOT...LOC 2228Z 262DEG 11KT 4732 9446

TORNADO...RADAR INDICATED
HAIL...2.50IN

$$
MILLER


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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.