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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invest 96L
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884. JRRP
Quoting Gearsts:

jajajjjjaajaajajajaja
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POST-TROPICAL CYCLONE JULIETTE DISCUSSION NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102013
800 PM PDT THU AUG 29 2013

ALL THAT REMAINS OF JULIETTE IS A WEAK LOW-LEVEL SWIRL WITH NO
ASSOCIATED THUNDERSTORM ACTIVITY. BASED ON THE LACK OF ORGANIZED
DEEP CONVECTION FOR A GOOD PORTION OF THE DAY...JULIETTE IS
DECLARED A REMNANT LOW AND THIS IS THE LAST ADVISORY. THE INITIAL
INTENSITY IS LOWERED TO 25 KT...AND THIS COULD BE GENEROUS BASED ON
A PARTIAL ASCAT PASS FROM EARLIER. THE CYCLONE SHOULD CONTINUE TO
WEAKEN OVER COLD WATERS WHILE IT MOVES TO THE WEST-NORTHWEST...AND
ALL OF THE GLOBAL MODELS LOSE THE LOW-LEVEL CIRCULATION WITHIN
24-36H.

FOR ADDITIONAL INFORMATION ON THE REMNANT LOW PLEASE SEE HIGH
SEAS FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER
AWIPS HEADER NFDHSFEPI AND WMO HEADER FZPN01 KWBC.


FORECAST POSITIONS AND MAX WINDS

INIT 30/0300Z 26.7N 114.8W 25 KT 30 MPH...POST-TROP/REMNT LOW
12H 30/1200Z 27.6N 116.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
24H 31/0000Z 28.5N 118.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
36H 31/1200Z...DISSIPATED

$$
FORECASTER BLAKE
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting 875. K8eCane:


yeah but now I realize Leo Farnsworth would not be proud of me


You made my night
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Quoting 874. PanhandleChuck:


Now that was funny girl!


I thought Funny Girl was with Barbra Streisand. I didn't know she played baseball.


I don't know. I still see that other low moving around the high.

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BULLETIN
POST-TROPICAL CYCLONE JULIETTE ADVISORY NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL EP102013
800 PM PDT THU AUG 29 2013

...JULIETTE BECOMES A REMNANT LOW...
...THIS IS THE LAST ADVISORY...


SUMMARY OF 800 PM PDT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...26.7N 114.8W
ABOUT 205 MI...330 KM NW OF CABO SAN LAZARO MEXICO
ABOUT 80 MI...125 KM SSE OF PUNTA EUGENIA MEXICO
MAXIMUM SUSTAINED WINDS...30 MPH...45 KM/H
PRESENT MOVEMENT...NW OR 310 DEGREES AT 14 MPH...22 KM/H
MINIMUM CENTRAL PRESSURE...1008 MB...29.77 INCHES
Member Since: July 21, 2011 Posts: 83 Comments: 7167
Quoting 876. Grothar:
There's always another wave.



And another batch of dry air.
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SSD Floater is up for 96L
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Quoting 870. K8eCane:


YAY! I didn't realize baseball had started


Silly head :-P Everyone know he's talking about Foosball...
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There's always another wave.

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Quoting 874. PanhandleChuck:


Now that was funny girl!


yeah but now I realize Leo Farnsworth would not be proud of me
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Quoting 870. K8eCane:


YAY! I didn't realize baseball had started


Now that was funny girl!
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873. yoboi
Quoting 860. Tazmanian:




why wast your time with him?



said right said fred....
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Member Since: August 2, 2010 Posts: 0 Comments: 1960
Quoting 861. BaltimoreBrian:
Today's selection of articles about science, climate change, energy and the environment.

Sea change: A gathering of Pacific leaders worries about climate change

Electricity in Vietnam: A heavy load

*** The parable of the Clyde

Fukushima Fishermen Ruined by Tepco Now Key in Radiation Fight


Cheap Corn Deters Buyers in U.S. Sugar-for-Ethanol Plan

* Fracking Fluids Killed Fish in Kentucky Stream

The Yosemite Inferno in the Context of Forest Policy, Ecology and Climate Change

Rising CO2 'could devastate seas'

*** NASA Data Reveals Mega-Canyon Under Greenland Ice Sheet


Little Difference Between Heavy Metal Pollutants in Fish at Oil Platforms and Natural Sites


*** On Warming Antarctic Peninsula, Moss and Microbes Reveal Unprecedented Ecological Change

* 'Safe' Levels of Environmental Pollution May Have Long-Term Health Consequences


Where Can Coral Reefs Relocate to Escape the Heat?


Ozone Depletion Linked to Extreme Precipitation in Austral Summer


Hidden Shell Middens Reveal Ancient Human Presence in Bolivian Amazon


French court rejects planned wind farm near Mont Saint Michel

China halts environmental approvals for oil giants

Sweden's indigenous Sami in fight against miners

Farewell to Gus, Whose Issues Made Him a Star

'Trojan asteroid' discovered forming triangle with sun, Uranus

Saturn moon Titan sports thick, icy shell -- and that's a surprise
Steve Detwieler has that covered and more. You can get his science report through Graham Hancock's website.
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Quoting 869. caneswatch:
Touchdown Dolphins!


YAY! I didn't realize baseball had started
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Touchdown Dolphins!
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Quoting 867. Bluestorm5:
Why you wasting your time telling others what not to do?




no comment
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Quoting 860. Tazmanian:




why wast your time with him?
Why you wasting your time telling others what not to do?
Member Since: August 1, 2011 Posts: 28 Comments: 8041
Quoting 855. Patrap:
92L Final Guidance


LMAO!!
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Quoting 858. Levi32:


The system is an open wave on the FIM9, and has been for 5-6 runs now.
Member Since: August 2, 2010 Posts: 0 Comments: 1960
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
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Quoting TropicalAnalystwx13:

"The most recent seasonal forecast called for an active season. However, given the dearth
of activity up to this point, we are hesitant to call for as much as activity during the next
two weeks as we would otherwise given the favorable MJO conditions that are being
predicted."

"The primary reason why the forecast during the two weeks was a bust was due to the fact
that the MJO took a much longer time to amplify into hurricane-conducive conditions
than was predicted by the global models in the middle part of August (Figure 3 and 5).
In addition, vertical shear has been much stronger over most of the tropical Atlantic than
expected with the seasonal forecast issued in early August.
"


Well, there it is, then.

See you guys another time.
Stay safe.
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Quoting 855. Patrap:
92L Final Guidance


Like that Pat!
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Quoting 848. Bluestorm5:
What SAL? It's pretty low from what I see.

SAL time loop




why wast your time with him?
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Disclaimer: Models are not reliable more than two hours out.


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Quoting 851. Gearsts:
Doesn't the FIM show a tropical storm with a similar track to Irene?


The system is an open wave on the FIM9, and has been for 5-6 runs now.
Member Since: November 24, 2005 Posts: 635 Comments: 26684
Quoting 855. Patrap:
92L Final Guidance
LOL
Member Since: August 2, 2010 Posts: 0 Comments: 1960
Quoting 847. Tropicsweatherpr:
CSU two week forecast from 30 of August thru September 12 calls for an average period

"The most recent seasonal forecast called for an active season. However, given the dearth
of activity up to this point, we are hesitant to call for as much as activity during the next
two weeks as we would otherwise given the favorable MJO conditions that are being
predicted."

"The primary reason why the forecast during the two weeks was a bust was due to the fact
that the MJO took a much longer time to amplify into hurricane-conducive conditions
than was predicted by the global models in the middle part of August (Figure 3 and 5).
In addition, vertical shear has been much stronger over most of the tropical Atlantic than
expected with the seasonal forecast issued in early August."
Member Since: Posts: Comments:
92L Final Guidance
Member Since: July 3, 2005 Posts: 426 Comments: 129093
Member Since: August 2, 2010 Posts: 0 Comments: 1960
Quoting 846. CaneHunter031472:
Then after all the excitement of a lanfalling Mayor hurricane and all the time spent tracking it and riding it reality sets.

You come to realize the loss and death around you.

This is why I am more than happy to see how this season is turning out, and I just hope it continues this way.


Realities of real life, not fantasy, video game crap
Member Since: July 30, 2012 Posts: 4 Comments: 614
Quoting 849. pottery:

I've heard of ridges being pumped.
But you are suggesting that the ridge will do the pumping, to the TUTT ?

This is all too much for me.
I better get to bed....


HaHa! heres hoping you did not watch the mtv awards. That woulda done you in. It did me. Night!
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Quoting 842. Levi32:
Shear is being mentioned as a big problem for our central Atlantic wave. A shear axis along 17-20N is present right now near the NE Caribbean, but it's associated with a flat TUTT. It's been my observation that zonal TUTTs are much easier to break through when tropical disturbances shove heat upwards. In other words, an upper ridge can more easily nudge through the TUTT, dividing it into two separate upper lows/troughs.

The FIM9 200mb wind environment doesn't look half-bad in 5 days as our wave moves through the eastern Caribbean islands.

Doesn't the FIM show a tropical storm with a similar track to Irene?
Member Since: August 2, 2010 Posts: 0 Comments: 1960
Quoting CaicosRetiredSailor:
Who Dat!


Just lost the ball :P
Member Since: Posts: Comments:
Quoting Levi32:
Shear is being mentioned as a big problem for our central Atlantic wave. A shear axis along 17-20N is present right now near the NE Caribbean, but it's associated with a flat TUTT. It's been my observation that zonal TUTTs are much easier to break through when tropical disturbances shove heat upwards. In other words, an upper ridge can more easily nudge through the TUTT, dividing it into two separate upper lows/troughs.

The FIM9 200mb wind environment doesn't look half-bad in 5 days as our wave moves through the eastern Caribbean islands.


I've heard of ridges being pumped.
But you are suggesting that the ridge will do the pumping, to the TUTT ?

This is all too much for me.
I better get to bed....
Member Since: Posts: Comments:
Quoting 845. eyewallblues:
SAL dominates our lives. No reason to change the prediction:

7-0-0
What SAL? It's pretty low from what I see.

SAL time loop
Member Since: August 1, 2011 Posts: 28 Comments: 8041
Then after all the excitement of a lanfalling Mayor hurricane and all the time spent tracking it and riding it reality sets.

You come to realize the loss and death around you.

This is why I am more than happy to see how this season is turning out, and I just hope it continues this way.
Member Since: Posts: Comments:
SAL dominates our lives. No reason to change the prediction:

7-0-0
Member Since: Posts: Comments:


30-40 kt shear and dry air. Does it do the overnight disappearing act again?
Member Since: July 30, 2012 Posts: 4 Comments: 614
Quoting 816. StormHype:
Live HAIL coring on mobile stream from N. MN:
Live video link


This link works
Member Since: August 24, 2010 Posts: 0 Comments: 4758
Shear is being mentioned as a big problem for our central Atlantic wave. A shear axis along 17-20N is present right now near the NE Caribbean, but it's associated with a flat TUTT. It's been my observation that zonal TUTTs are much easier to break through when tropical disturbances shove heat upwards. In other words, an upper ridge can more easily nudge through the TUTT, dividing it into two separate upper lows/troughs.

The FIM9 200mb wind environment doesn't look half-bad in 5 days as our wave moves through the eastern Caribbean islands.

Member Since: November 24, 2005 Posts: 635 Comments: 26684
where is invest 96L GOING!!
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Who Dat!
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I'm too tired,

You all have nice evening. Happy blogging!
Member Since: January 1, 2008 Posts: 0 Comments: 3785
Although,

The National Weather Service in Duluth MN has issued a

* Severe Thunderstorm Warning for...
southeastern Aitkin County in east central Minnesota...
southwestern Carlton County in northeast Minnesota...
northern Pine County in east central Minnesota...

* until 945 PM CDT

* at 858 PM CDT... a severe thunderstorm was located 6 miles west of
Ronald... and moving southeast at 45 mph.

Hazard... tennis Ball size hail and 70 mph wind gusts.

Source... radar indicated. Trees were reported blown down with this
storm 7 miles south of McGregor.

Impact... people and animals outdoors will be injured. Expect hail
damage to roofs... siding... windows and vehicles. Expect
considerable tree damage. Wind damage is also likely to
Mobile homes... roofs and outbuildings.

* Locations impacted include...
Banning State Park... Arthyde... Denham... Willow River... Rutledge...
Finlayson... Friesland... Sandstone... Askov... Bruno... Kerrick and
Sturgeon Lake.
State Highway 27 south and east of McGregor.
Interstate 35 between Moose Lake and Hinckley.

Precautionary/preparedness actions...

For your protection move to an interior room on the lowest floor of a
building.


Lat... Lon 4642 9340 4660 9317 4627 9242 4608 9255
4602 9291
time... Mot... loc 0158z 310deg 39kt 4640 9311

Hail... 2.25in
wind... 70mph

Miller
Member Since: January 1, 2008 Posts: 0 Comments: 3785
836. SLU
Quoting 815. TropicalAnalystwx13:
The recent 5-day GFS skill scores are the lowest I've ever seen. Maybe double check with another model before using the GFS for northern hemisphere weather? (probably should do that anyways)

GFS. What are you doing.



It has fabricated too many false alarms this month. It's behaving like that miserable little boy who cried wolf.

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Quoting beell:


There are transgressions committed against the poor down-trodden masses yearning to be free from oppression on this blog everyday. Please don't limit your considerable talents to the defense of one. Defend them all.


Yeah. Wot he said. Eloquent, too.
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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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