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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120 hour map for favorable development..

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Quoting 724. TropicalAnalystwx13:
Check out these waves:



Wow.
Member Since: July 17, 2009 Posts: 71 Comments: 26045
Quoting AussieStorm:
Morning all.
I'm back in Sydney after going down to spend time with my Dad after the 2 strokes he had on Wednesday. He's doing ok now. little steps is all it will be now.

Global Hawk HS3 tracking link: http://airbornescience.nasa.gov/tracker/

Sorry to hear this, Aussie.
Stay strong.
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Quoting 709. MiamiHurricanes09:
Or any year for that matter.
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48 hour still has a low near Florida..
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Quoting 717. Kyon5:
Can someone please give me the link to the Global Hawk mission? Thanks.



Mission Page


Flight Tracker
Member Since: September 23, 2005 Posts: 14 Comments: 11116
Quoting 722. hydrus:
The wave over Central Africa looks like a cat-1 already..


Until it hits the Atlantic. Then it falls apart. And if YOU are lucky it actually becomes something.
Member Since: March 10, 2006 Posts: 0 Comments: 10129
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Quoting 723. GatorWX:
nice pic gatorWX.
Member Since: June 11, 2013 Posts: 20 Comments: 2784
Check out these waves:

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Member Since: January 1, 2008 Posts: 0 Comments: 2874
The wave over Central Africa looks like a cat-1 already..
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Quoting 662. PalmBeachWeather:
I'm a model, you know what I mean
Your the XFS model aren't you?
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Quoting 707. yoboi:


for some reason I picture taz singing this song....what a season.....


Haha! He would be vary good ;)
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Whitewabit - Nice to see you around. Be careful though, Taz is hunting wabbits.... (earlier post).

Grothar - Blobcon 4? Could this one actually develope? Might we have something to track and 'cast to one area of the world or another? Inquiring minds want to know.
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717. Kyon5
Can someone please give me the link to the Global Hawk mission? Thanks.
Member Since: July 7, 2013 Posts: 0 Comments: 191
That low does look more like a tropical system this evening.
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715. yoboi
Quoting 712. hydrus:
Repotted



POOF offf tapic....:)
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Quoting 713. Grothar:
I may declare a blob before 11.




At night or before Sept 11th?
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I may declare a blob before 11.


Member Since: July 17, 2009 Posts: 71 Comments: 26045
Quoting 707. yoboi:


for some reason I picture taz singing this song....what a season.....
Repotted
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Looking MAH-velous...

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Quoting 699. hydrus:
Good evening 92. It is great, but wont last..." they " are comin, and it is my opinion that it is Florida,s year for a hit..I certainly hope I am way wrong..

I hope o
Quoting 699. hydrus:
Good evening 92. It is great, but wont last..." they " are comin, and it is my opinion that it is Florida,s year for a hit..I certainly hope I am way wrong..

I hope so Hydrus. After Andrew me and the family have been terrified of Hurricanes. I think I would still rather ride a cane than a tornado. At least a cane you have sometime to prepare.
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Quoting 698. nrtiwlnvragn:


Marlins were never expected to be that good this year.
Or any year for that matter.
Member Since: September 2, 2009 Posts: 130 Comments: 21166
708. whitewabit (Mod)
Isn't it unusual the NHC gives a wave just coming off Africa a 40% chance ..




TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 PM EDT THU AUG 29 2013

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

1. A BROAD AREA OF LOW PRESSURE ASSOCIATED WITH A TROPICAL WAVE IS
PRODUCING SHOWERS AND THUNDERSTORMS OVER WESTERN AFRICA. THIS
SYSTEM SHOULD MOVE WESTWARD OVER THE FAR EASTERN ATLANTIC OCEAN ON
FRIDAY...AND NEAR THE CAPE VERDE ISLANDS LATE SATURDAY.
ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR DEVELOPMENT...AND A
TROPICAL DEPRESSION COULD FORM OVER THE WEEKEND. AFTER THAT
TIME...THE ENVIRONMENT IS FORECAST TO BECOME LESS CONDUCIVE WHILE
THE SYSTEM MOVES TOWARD THE WEST-NORTHWEST OVER THE EASTERN
ATLANTIC. THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS...AND A MEDIUM
CHANCE...50 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE
NEXT 5 DAYS.

2. THERE HAS BEEN LITTLE CHANGE WITH A TROPICAL WAVE LOCATED ABOUT 900
MILES EAST OF THE LESSER ANTILLES. THIS WAVE IS FORECAST TO MOVE
WESTWARD TOWARD A REGION WHERE THE UPPER LEVEL WINDS ARE NOT
FAVORABLE FOR DEVELOPMENT. THIS SYSTEM HAS A LOW CHANCE...10
PERCENT...OF BECOMING A TROPICAL CYCLONE DURING THE NEXT 48
HOURS...AND A LOW CHANCE...20 PERCENT...OF BECOMING A TROPICAL
CYCLONE DURING THE NEXT 5 DAYS.

FIVE-DAY FORMATION PROBABILITIES ARE EXPERIMENTAL IN 2013. COMMENTS
ON THE EXPERIMENTAL FORECASTS CAN BE PROVIDED AT...

HTTP://WWW.NWS.NOAA.GOV/SURVEY/NWS-SURVEY.PHP?COD E=ETWO

FORECASTER BLAKE

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707. yoboi
Quoting 657. ihave27windows:


And you shake your little tush on the catwalk =P


for some reason I picture taz singing this song....what a season.....
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Quoting 698. nrtiwlnvragn:


Marlins were never expected to be that good this year.

Word!!!!! Lol and I as a resident that lives in Miami I will not support that team until Loria sells it. They have disappointed me in 97 and 03 when they sold a championship team.
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Quoting 701. Levi32:
Hopefully a good number of these dropsondes around our central Atlantic wave get into the 0z model cycle.



Eleven went into the 18Z, some of the later ones may go into the 06Z.
Member Since: September 23, 2005 Posts: 14 Comments: 11116
Quoting 701. Levi32:
Hopefully a good number of these dropsondes around our central Atlantic wave get into the 0z model cycle.



No kidding lol. They need everything they can get it seems.
Member Since: January 1, 2008 Posts: 0 Comments: 2874
From the Brainerd Dispatch in north central Minnesota:

Renee Richardson @Dispatchbizbuzz

#storm damage reports include trees and power lines down by Highway 6 by Remer and Highway 200

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Quoting 687. avthunder:
This looks bad. Classic hook echo. Unusual for this time of year. Hope folks are paying attention up there.


Definetly gotta watch out for the hookers up there.
Member Since: March 10, 2006 Posts: 0 Comments: 10129
Hopefully a good number of these dropsondes around our central Atlantic wave get into the 0z model cycle.

Member Since: November 24, 2005 Posts: 635 Comments: 26611
Quoting 696. MAweatherboy1:
Juliette is no more...

EP, 10, 2013083000, , BEST, 0, 265N, 1142W, 30, 1007, LO


Poor Romeo.

Member Since: March 10, 2006 Posts: 0 Comments: 10129
Quoting 694. Ilivedandrew92:
Good evening everyone. What are your takes on this years so far bust?
Good evening 92. It is great, but wont last..." they " are comin, and it is my opinion that it is Florida,s year for a hit..I certainly hope I am way wrong..
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Quoting 694. Ilivedandrew92:
Good evening everyone. What are your takes on this years so far bust?


Marlins were never expected to be that good this year.
Member Since: September 23, 2005 Posts: 14 Comments: 11116
Bye bye Juliette.

EP, 10, 2013083000, , BEST, 0, 265N, 1142W, 30, 1007, LO, 34, NEQ, 0, 0, 0, 0, 1009, 100, 25, 0, 0, E, 0, , 0, 0, JULIETTE, S,
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Juliette is no more...

EP, 10, 2013083000, , BEST, 0, 265N, 1142W, 30, 1007, LO
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Radar and storm spotters are indicating that the tornado in north central Minnesota likely dissipated just south of Hill City near the Quadna Mountain resort area. Very rough track would seem to put it from near Remer to near Hill City, or about 15 miles. Not enough information yet to determine how much of that was on the ground, or if it was on the ground before/after the radar signature.
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Good evening everyone. What are your takes on this years so far bust?
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Quoting 685. beell:


My contention is there is a baroclinic boundary trailing the wave to the SE. There is vertical motion along the boundary that is responsible for the convection in less than optimal background environmental conditions. There is also convergence along the boundary towards the wave.

Not an issue here just was not sure if your post was a disagree/agree/neither.
:)



I agree. It's a cool boundary. I just thought it was interesting that the northern hemisphere trade winds completely stop there, making it ITCZ-like in some respects. I agree that it's somewhat baroclinic in nature.
Member Since: November 24, 2005 Posts: 635 Comments: 26611


The wind shifted from ENE to ESE



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691. beell
Quoting 639. PalmBeachWeather:
I've always wondered what happened to the cow that was picked up in the tornado


ground beef
Member Since: September 11, 2007 Posts: 142 Comments: 16496
Quoting 643. stormpetrol:


Last night was quite stormy and from 11am today the rain has been nearly non stop, with bouts of lightning and thunder just getting a break now, but for how long?
No break in East End. Lightning was terrible last night plus no power up here from 11:30 p[m until 4:20 am. Still raining up here.
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Should have an invest by tonight I presume.
Member Since: September 2, 2009 Posts: 130 Comments: 21166
Lowerin my #...
14/4/2
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Quoting 641. Bluestorm5:
Got an cell in Minnesota west of Duluth that is under tornado warning. We'll see how this storm do.

This looks bad. Classic hook echo. Unusual for this time of year. Hope folks are paying attention up there.
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Quoting 653. Felix2007:
Jeez that's quite far out for an orange circle...


Just my impression, but it seems they have upped their percentages since that report about them under predicting development in the TWO's.
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685. beell
Quoting 661. Levi32:


Today, if you start at the equator and head northward at 40W, the first boundary you encounter is the one east of the wave at ~15N. This can't really be called the ITCZ, but it might as well be. Trade winds are non-existent south of it.


My contention is there is a baroclinic boundary trailing the wave to the SE. There is vertical motion along the boundary that is responsible for the convection in less than optimal background environmental conditions. There is also convergence along the boundary towards the wave.

Not an issue here just was not sure if your post was a disagree/agree/neither.
:)

Member Since: September 11, 2007 Posts: 142 Comments: 16496

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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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