NHC's Tropical Weather Outlook: How Accurate are its Predictions?

By: Dr. Jeff Masters , 2:46 PM GMT on July 20, 2013

Share this Blog
73
+

Every Internet-savvy tropical weather enthusiast is familiar with the National Hurricane Center's Tropical Weather Outlook (TWO), which details potential threat areas that might become a tropical cyclone. (Tropical depressions, tropical storms, and hurricanes are all tropical cyclones.) The Tropical Weather Outlook is issued four times per day during hurricane season, and beginning in 2010, NHC began issuing 48-hour forecasts of the probability that specific threat areas identified in the TWO could develop into a tropical cyclone. Their Graphical Tropical Weather Outlook now color-codes each threat area depending upon how likely development is expected to be. A yellow circle is drawn for 0%, 10%, and 20% chances; orange for 30%, 40% and 50% chances, and red for 60% and higher odds. For example, the Saturday morning, July 20 TWO gave a 0% chance of development for an area of disturbed weather near the Florida Panhandle (Figure 1.)


Figure 1. NHC's Tropical Weather Outlook for 8am EDT July 20, 2013, showed an area of disturbed weather over the Gulf of Mexico being given a 0% chance of development in 48 hours. In 2012, 8% of all disturbances being given a 0% chance of development actually did develop.

How accurate is NHC's Tropical Weather Outlook?
So the big question is, how good are these forecasts? When NHC gives a 30% chance that an "Invest" will become of tropical cyclone, does this happen 30% of the time? Well, according to the 2012 National Hurricane Center Forecast Verification Report, NHC should have drawn fewer yellow circles and more orange circles and red circles during 2012, as there was a tendency to under-predict when a threat area might develop. For example (Figure 2), for the 46 forecasts where a 30% chance of development was given, 50% of the threat areas actually developed. Every disturbance that was given a 70% and higher chance of development ended up developing. This under-prediction tendency in 2012 is in contrast to the results from 2011, when the genesis forecasts were closer to the mark. For example, the 59 forecasts for a 30% chance of development resulted in a 31% "hit" rate of the storm actually developing in 2011. So far in 2013, there seems to be a tendency to under-predict again. For example, 48 hours before Tropical Storm Barry developed, NHC was carrying just a 10% chance of development.




Figure 2. NHC did predictions on new formation of a tropical depression or tropical storm (cyclogenesis) beginning in 2010. The forecasts are expressed in the Tropical Weather Outlook in 10% probability increments, and in terms of categories (“low”, “medium”, or “high”) for a tropical cyclone forming within a 48-hour period. These genesis forecasts had a low (under-forecast) bias in the Atlantic basin during 2012 (top). For example, for cases where a 30% chance of formation was given, the actual percentage of storms that formed was 50%. However, there the 2011 forecasts showed no systematic bias, and were closer to the mark (bottom.)

Expansion of the Tropical Weather Outlook to 5 Days
By August of the 2013 hurricane season, NHC is planning to begin including information about a system’s potential for development during the following five-day period. This will supplement the 48-hour probabilistic formation potential already provided in the Tropical Weather Outlook. NHC is currently developing a corresponding five-day genesis potential graphic that might also be available in 2013.

Quiet in the Atlantic
There are no other tropical cyclone threat areas in the Atlantic to discuss today. Saturday morning's 06Z run of the GFS model predicted that a tropical wave expected to move off the coast of Africa on Monday will develop later in the week. None of the other reliable models develop this wave, though the unreliable Canadian (CMC) model also suggests that the wave could develop.

Have a great weekend, everyone, and I'll be back Monday with a new post.

Jeff Masters

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

Sign In or Register Sign In or Register

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 342 - 292

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54Blog Index

Member Since: Posts: Comments:
Not much on the CMC but a weak 850 mb. vorticity east of the Northern Leewards.

Member Since: June 30, 2013 Posts: 12 Comments: 9110
Member Since: Posts: Comments:
Quoting 336. Hurricanes305:
Nothing on the 12z CMC through 120 hours so I looks unlikely to develop on this run I more interested to see what our Euro has to say.


You need to look at 48 hrs and see the vort.Do me a favor and ignore the cmc,just look at the same vort,so this vort is not an imaginary vort.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
I really want something to track though..
Member Since: Posts: Comments:
Nothing on the 12z CMC through 120 hours so I looks unlikely to develop on this run I more interested to see what our Euro has to say.

Member Since: Posts: Comments:
Ggem model has the same vort,it struggles sustaining it due to the itcz...but that model is highly problematic when resolving even minor complexities.There is no question as to whether a system forms here,the track is still highly perplexing.
Member Since: Posts: Comments:
Quoting 326. Gearsts:
what are your thoughts on this system?


It has to first emerge Africa,develop a low pressure,deal with dry air,forward speed will be important,ridge of course to see where it will track. In other words,many variables to watch but for now model watching and how it does when it hits the water will be the first thing to watch.
Member Since: Posts: Comments:
12z models have sampled the vort exiting africa at a fairly low lat fairly honorably.Summary system is likely to form >95%. The track is uncertain,but initial intensification may be modest.Stronger intensifcation around 50w.Current thinking is it will pass close to the northern islands and then potentially head up the east coast in the 300+ hr range.
Member Since: Posts: Comments:
Quoting 320. wxchaser97:
Now it got up to 102hrs, not showing much at all.


Now that is a forecast we can love here in St Barths!
Member Since: Posts: Comments:
331. TXCWC
Quoting 311. Tropicsweatherpr:
GFS needs support from other models to have a good consensus.


GFS for past several runs in a row has been showing development - I will take the GFS within a 3 day forecast period over any other model (as long as it is consistently showing something over multiple runs)- even if no other model shows anything.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting 321. GeoffreyWPB:
Would that thar be "Dorian" about to come off the African coast?



Yep and it looks vigorous already. It should drop down a few latitudes into the ITCZ as what most tropical waves has been doing all year.
Member Since: Posts: Comments:
Quoting 319. MAweatherboy1:
12z CMC has no development through 102 hours so looks like the GFS is on its own still.



Edit: I beat you Isaac :)


Actually I was the first lol :-)
Member Since: Posts: Comments:
Quoting 323. washingtonian115:
GFS has been persistent though.
short term track yes long term not even close from bermuda to mexico
Member Since: Posts: Comments:
Quoting 322. Tropicsweatherpr:


Yes,that is it.
what are your thoughts on this system?
Member Since: Posts: Comments:
Quoting 322. Tropicsweatherpr:


Yes,that is it.

It looks to be coming off pretty far north, SSTs are still a little marginal up there.
Member Since: Posts: Comments:
Quoting 320. wxchaser97:
Now it got up to 102hrs, not showing much at all.


CMC is usually harder to get development from TW rather than system closer to the US where it constantly developing random ghost system. Its like a different model when it comes to waves.
Member Since: Posts: Comments:
GFS has been persistent though.
Member Since: Posts: Comments:
Quoting 321. GeoffreyWPB:
Would that thar be "Dorian" about to come off the African coast?



Yes,that is it.
Member Since: Posts: Comments:
Would that thar be "Dorian" about to come off the African coast?

Member Since: Posts: Comments:
Quoting 309. Gearsts:
Now the gem should show something similar.
Now it got up to 102hrs, not showing much at all. Edit: MA beat me to it :(
Member Since: March 16, 2012 Posts: 127 Comments: 7981
12z CMC has no development through 102 hours so looks like the GFS is on its own still.



Edit: I beat you Isaac :)
Member Since: Posts: Comments:
Quoting 316. moonlightcowboy:


Good morning, weathergeeks! :)

GT, this seems to be a favorite spot of the models this year. ;) Curious, do any of the models forecast outside of two weeks? I never pay too much attention to forecasts that far out.

Have a nice weekend, all! :)
Hey mlc, same to you, as far as models going out past 2 weeks the only one I know of is the CFS.
Member Since: June 30, 2013 Posts: 12 Comments: 9110
the last frame for africa

Member Since: Posts: Comments:
Quoting 293. GTstormChaserCaleb:
312 hrs.



Good morning, weathergeeks! :)

GT, this seems to be a favorite spot of the models this year. ;) Curious, do any of the models forecast outside of two weeks? I never pay too much attention to forecasts that far out.

Have a nice weekend, all! :)
Member Since: Posts: Comments:
Quoting 309. Gearsts:
Now the gem shold show something similar.

Whenever it gets going we'll see what it says as it's been stuck at 12hrs for a little while now.
Member Since: March 16, 2012 Posts: 127 Comments: 7981
Quoting 140. PalmBeachWeather:
Wash..Went to the movie last weekend and saw Despicable Me 2...A large drink and large popcorn was $12... What a rip
Absolutely disgusting. It use to be the one thing people could afford during bad economic times...Charging $12 for popcorn and a soft drink should be outlawed and punished accordingly. Anything that forms out there will be heading west for a long time. Shear will remain high in the Caribbean, but if a storm cruises over, or just north of the islands, shear will not be much of an issue.

Member Since: Posts: Comments:
so anywhere from mexico to out to sea. come on. as long as the GFS develops it that is good. future track is uncer and the steering pattern past 10 days is ridiculous.
Member Since: Posts: Comments:
Quoting 298. Stormchaser2007:
Land interaction and truncation does not bode well for the ghost system.

In the fantasy range, it does redevelop in the Gulf.


Without any other model support the storm itself is unlikely.


It has development of a wave in 78 hours that is about to hit water in 24-36 hours so I will watch this carefully.
Member Since: Posts: Comments:
GFS needs support from other models to have a good consensus.
Member Since: Posts: Comments:
Quoting 304. SLU:
Enters the Caribbean at 17 north and still makes landfall in NE Mexico. Amazing this ridge. Just amazing.




looks more like land fall in S TX
Member Since: Posts: Comments:
Now the gem should show something similar.
Member Since: Posts: Comments:
again..pay attention to the ensembles..
Member Since: Posts: Comments:
Quoting rod2635:
If the Canadian (CMC) model is unreliable,

1. Why even run it
2. Why continue to spend $ funding it

Or is there hope out there that it may someday attain 'reliable' status, by those who so confer it.

????????/


The CMC or GEM is generally unreliable in the tropics. It does pretty decent during winter over North America.
Member Since: Posts: Comments:
GFS is showing a forward speed well over 20mph again for this to move so far so fast. Does anyone else think this is a bit unusual historically (though not for this year)?
Member Since: Posts: Comments:
mexico it is on this run..

Member Since: Posts: Comments:
304. SLU
Enters the Caribbean at 17 north and still makes landfall in NE Mexico. Amazing this ridge. Just amazing.

Member Since: Posts: Comments:
Quoting 296. Hurricanes305:


Hold up it makes a come back at the end.



Please dont take the GFS run seriously after about 174 hours or so.


Right. Just know that we are getting a storm to follow very soon.
Member Since: Posts: Comments:
That was an interesting run, takes a strong TS into PR, dissipates it, and then reforms it in the Gulf with a Texas/Mexico border landfall.
Member Since: March 16, 2012 Posts: 127 Comments: 7981
Dorian:

Member Since: June 30, 2013 Posts: 12 Comments: 9110
300. TXCWC
Quoting 273. MAweatherboy1:
Hispaniola pretty much kills it this run.


That's a pretty long term track and is sure to change from run to run probably - beyond 3 or 4 days in track alot can change. One thing is pretty high in chance of happening right now is development in a few days (again would not bet against the GFS within a 3 day forecast)...we'll have to wait and see beyond that.
Member Since: Posts: Comments:
Now let's see how 12z CMC has it and if the Euro starts to show it.
Member Since: Posts: Comments:
Land interaction and truncation does not bode well for the ghost system.

In the fantasy range, it does redevelop in the Gulf.


Without any other model support the storm itself is unlikely.
Member Since: Posts: Comments:
Similar track of the Hurricane George?
Member Since: Posts: Comments:
Quoting 282. Hurricanes101:
The system basically falls apart at that point


Hold up it makes a come back at the end.



Please dont take the GFS run seriously after about 174 hours or so.
Member Since: Posts: Comments:






Member Since: Posts: Comments:
If the Canadian (CMC) model is unreliable,

1. Why even run it
2. Why continue to spend $ funding it

Or is there hope out there that it may someday attain 'reliable' status, by those who so confer it.

????????/
Member Since: Posts: Comments:
312 hrs.

Member Since: June 30, 2013 Posts: 12 Comments: 9110
Landfall near the TX/ Mexico border.
Member Since: Posts: Comments:

Viewing: 342 - 292

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54Blog Index

Top of Page

About

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

Local Weather

Overcast
52 °F
Overcast

JeffMasters's Recent Photos

Carrot Nose in Danger
Deep Snow in Brookline, MA
Sunset at Fort DeSoto
New Years Day Sunset in Death Valley