Dr. Jeff Masters' WunderBlog

Grading NHC's Tropical Weather Outlook
Posted by: Dr. Jeff Masters, 4:33 PM GMT on June 06, 2007 +4
The National Hurricane Center's Tropical Weather Outlook (TWO) is a text-only product that rates the potential of disturbed areas of weather to turn into tropical depressions or tropical storms. The outlooks are issued four times daily, at 5am, 11am, 5pm, and 11pm EDT. I've found them to be an excellent guide to what to watch out for. But how accurate are these outlooks? To find out, Jamie Rhome and Dan Brown, who are two of the hurricane specialists that write the Tropical Weather Outlook, verified the accuracy of all the outlooks issued in 2005 and 2006. They used a three-tiered classification of threat based on the following language appearing in the TWO:

High: "A tropical depression could form tonight or the next day."

Medium: "Some slow development is possible."

Low: "Tropical storm formation is not expected."


These forecasts were then graded by looking at the "best track" database of Atlantic hurricanes and seeing if a tropical depression formed within 48 hours of each TWO issued. The results, shown below, reveal that for the Atlantic in the years 2005 and 2006:

-When the TWO said, "A tropical depression could form tonight of the next day," a depression formed within 48 hours 53% of the time.

-When the TWO said, "Some slow development is possible," a tropical depression formed within 48 hours about 20% of the time.

-When the TWO said, "Tropical storm formation is not expected," a tropical depression formed within 48 hours only 3% of the time.




Figure 1. Verification of the Atlantic and Eastern Pacific Tropical Weather Outlooks issued in 2005 and 2006. Image credit: Jamie Rhome and Dan Brown, National Hurricane Center.

Jeff Masters
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1151. Patrap 10:06 PM GMT on June 09, 2007    
Observed at: New Orleans, Louisiana
Elevation: 3 ft / 1 m
[Mostly Cloudy]
92 °F / 33 °C
Mostly Cloudy
Member Since: July 3, 2005 Posts: 371 Comments: 111457
1152. WPBHurricane05 10:07 PM GMT on June 09, 2007    
The NHC says nothing is going to develop on there TWO.
Member Since: July 31, 2006 Posts: 56 Comments: 7928
1153. ClearH2OFla 10:07 PM GMT on June 09, 2007    
grr lol can someone tell me where the link is for the carribean blob please
1154. Thundercloud01221991 10:07 PM GMT on June 09, 2007    
The only thing I am looking at is there was an increase in convection noted on the inferred since the sun has gone down over there showing that it is tropical.
Member Since: August 1, 2006 Posts: 28 Comments: 3670
1155. Drakoen 10:08 PM GMT on June 09, 2007    
lol WPB. They will say something don't worry. 40 min to go.
Member Since: October 28, 2006 Posts: 57 Comments: 29010
1156. chessrascal 10:08 PM GMT on June 09, 2007    
Hi all I have updated my blog! How many think that NHC will upgrade it to a depression or atleast an Invest?
1157. ClearH2OFla 10:09 PM GMT on June 09, 2007    
Link

Here is the link
1158. WPBHurricane05 10:09 PM GMT on June 09, 2007    
NA
Wind shear rising in the W. Caribbean. I don't see any development in the near future.
Member Since: July 31, 2006 Posts: 56 Comments: 7928
1159. weatherbro 10:11 PM GMT on June 09, 2007    
I havnt been here in a while. I know the southern atlantic has seen activity. But has the southeastern atlantic ever saw eny tropical activity in history?
Member Since: May 26, 2007 Posts: 47 Comments: 1155
1160. WPBHurricane05 10:12 PM GMT on June 09, 2007    
chessrascal-I think there is a very low chance for the Caribbean disturbance to become an invest at this point. As for the wave off Africa I give it a 5% chance for invest.
Member Since: July 31, 2006 Posts: 56 Comments: 7928
1161. chessrascal 10:12 PM GMT on June 09, 2007    
The Carribean is really active what is that blob off of southern central America?

1162. WPBHurricane05 10:14 PM GMT on June 09, 2007    
There first needs to be a low pressure for it to be classified as an invest.
Member Since: July 31, 2006 Posts: 56 Comments: 7928
1163. Drakoen 10:15 PM GMT on June 09, 2007    
i give that blob in the SW Carrib a 15% chaance of develop. It looks very good on the IR image. Possible organized group of thunderstorm. I don't see the shear affecting it at this point. other wise there would be more outflow on the east side of the system.
Member Since: October 28, 2006 Posts: 57 Comments: 29010
1164. Drakoen 10:16 PM GMT on June 09, 2007    
I won't be able to tell if it has a spin. not on my computer :(.Java doesn't work.
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1165. chessrascal 10:16 PM GMT on June 09, 2007    
WPB i think u are being to pesimistic or however u spell it. lol
1166. StoryOfTheCane 10:17 PM GMT on June 09, 2007    
convection is lookin decent

1167. miamihurricane12 10:17 PM GMT on June 09, 2007    
WPB where did you find that graphic?
1168. StoryOfTheCane 10:18 PM GMT on June 09, 2007    
Wind Direction (WDIR): E ( 80 deg true )
Wind Speed (WSPD): 7.8 kts
Wind Gust (GST): 7.8 kts
Atmospheric Pressure (PRES): 29.84 in
Pressure Tendency (PTDY): -0.04 in ( Falling )
Air Temperature (ATMP): 83.7 °F
Water Temperature (WTMP): 84.7 °F
1169. WPBHurricane05 10:18 PM GMT on June 09, 2007    
I will start talking about development when I see this page say possible development. Link
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1170. Drakoen 10:19 PM GMT on June 09, 2007    
yes Storyofthecane lets see if there is a spin at the lower levels.
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1171. WPBHurricane05 10:20 PM GMT on June 09, 2007    
WPB where did you find that graphic?
Link

Also, EPAC has a yellow Link
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1172. WPBHurricane05 10:21 PM GMT on June 09, 2007    
There area in the Caribbean also has to watch out for that ULL.
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1173. Drakoen 10:21 PM GMT on June 09, 2007    
WPB sometimes you have to think outside of the box. Looks very organized to me and the pressure continues to fall.
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1175. WPBHurricane05 10:26 PM GMT on June 09, 2007    
If it is still around tomorrow at this time there might be a chance for it to develop. Wind shear isn't that big of a problem and SST are warm enough.
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1176. Drakoen 10:27 PM GMT on June 09, 2007    
i think it will still be around lets wait and see. TWC tropical update in 20 min.
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1177. SWFLdrob 10:29 PM GMT on June 09, 2007    
props to WPB for being more conservative than many here. Enjoy reading everything, but guys like WPB balance things out...as there tends to be a higher number of people here rooting/hoping for everything to develop.
1179. StormJunkie 10:38 PM GMT on June 09, 2007    
Afternoon all ☺

Interesting radar out of Wilmington. Strange echo, huge bow?

Has anyone seen the 12z 144hr CMC? It is a long way out, but that is the first I have seen of that. Also looks as if it would head to sea. Will be watching to see if CMC persists.

As for the SW Carib blob, there is a chance it will develop, but it will only be for a moment if it does. Looks as if it will run out of water in the next day or two.

Out at the beach with the family this week and weekend, so I hope to pop in when I can, but am going to mostly be enjoying my vacation☺ Will be keeping an eye on those wacky Canadians and their model.

Models and much more.

Member Since: August 17, 2005 Posts: 26 Comments: 15218
1180. Hellsniper223 10:39 PM GMT on June 09, 2007    
Already more activity than 2006.
Member Since: March 28, 2006 Posts: 0 Comments: 16
1181. RL3AO 10:39 PM GMT on June 09, 2007    
6% chance in the EPac. No invest?
1182. stormpetrol 10:45 PM GMT on June 09, 2007    
That SW Caribbean Blob north of Panama is sure looking impressive, I think there might me a low level spin though I'm not sure, looks like its making a more northward movement. I think this has to persist for at least another 12-24 hours before the NHC becomes interested in it, Pressures here in Grand Cayman are falling also according to the various reporting stations.
Member Since: April 29, 2007 Posts: 0 Comments: 6396
1183. Drakoen 10:46 PM GMT on June 09, 2007    
saying SWFL that we are not necessarily huyping for development. We are currently analyzing the current Sea- Surface Temperatures as well as the upper level winds. Also we are taking into consideration the current organization of the system as well as if there may be a low somewhere in or around the system. I say marginal development as of now only because i cannot verify that there is a low level spin. However if there was we would be talking about a Tropical Depression forming.
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1185. WPBHurricane05 10:52 PM GMT on June 09, 2007    
On this day in 1966 Hurricane Alma made landfall.
NA
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1186. louisianaboy444 10:53 PM GMT on June 09, 2007    
i hate the weather channel they dont go into any detail they dont say nothing
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1187. Patrap 10:55 PM GMT on June 09, 2007    
TWC,,candy for the masses.
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1188. kmanislander 10:57 PM GMT on June 09, 2007    
The SW Caribbean blob has held its convection quite well throughout the daytime hrs. Although there has been some warming of the cloud tops there has not been the typical significant daytime decline that one would expect to see. Once the cooler conditions set in tonight we should see much colder cloud tops and more intense convection
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1189. SWFLdrob 10:57 PM GMT on June 09, 2007    
was not saying anything about specific posters, or even talking about this current situation. Just saying that the conversation here, in general, tends to center around all the things a blob has going for it in terms of development - as opposed to what is working against it both in the short and long term.

Not attacking anyone...just saying it is good to see a little balance - which is what makes the conversation valuable. Often times, it is one-sided IMO.
1190. RL3AO 10:57 PM GMT on June 09, 2007    
Did you really expect the TWC to give analysis on a blob near Africa?
1191. kmanislander 10:58 PM GMT on June 09, 2007    
Stormpetrol

Wassup ?
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1192. stormpetrol 11:00 PM GMT on June 09, 2007    
well TWC or the NHC doesn't same to be mentioning the blob in the SW Caribbean, now I know for certain you have to watch it. :-)(just kidding) At the end of the day they both day do a good job once something has formed.
Member Since: April 29, 2007 Posts: 0 Comments: 6396
1193. sporteguy03 11:01 PM GMT on June 09, 2007    
Climatology favors that area but WPB has great points, I rather wait and see what the models and quikskat show overnight
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1195. WPBHurricane05 11:02 PM GMT on June 09, 2007    
just saying it is good to see a little balance

NA
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1196. sporteguy03 11:02 PM GMT on June 09, 2007    
Hopefully the system moves closer to the buoy South of the Cayman Islands
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1197. louisianaboy444 11:03 PM GMT on June 09, 2007    
i aint talking about an african blob i know that isnt going to form...its way too early i was laughing earlier when people were saying it would form.... i was talking about the more interesting flare up in the sw carbbiean twc didnt even mention it
Member Since: August 29, 2006 Posts: 17 Comments: 1219
1198. kmanislander 11:03 PM GMT on June 09, 2007    
Well I am watching it ( a bit lol )
These June blow ups take 24 to 36 hrs to do anything if they do get going. If it is still there tomorrow morning then it has a chance.
For now, it is just a typical SW Caribbean blow up. Hey thunder starting outside !

Must be from that W Cuba ULL causing a build up over us
Member Since: August 19, 2006 Posts: 0 Comments: 14939
1199. stormpetrol 11:04 PM GMT on June 09, 2007    
Hey Kman having a cold one on a Saturday afternoon, enjoying some music and browsing, just heard some thunder, wonder what that means. It sure has calmed down( the Sea) on the south side of South Sound today, was choppy ever since Barry formed Northwest of us.
Member Since: April 29, 2007 Posts: 0 Comments: 6396
1201. Drakoen 11:07 PM GMT on June 09, 2007    
i guess i gave TWC too much credit oh well. That Blob was right near that ladys belly and nothing mentioned. I guess she didn't have Steve Lyons write a script for her oh well. Lets see if the the system will gain some more convection overngiht.
SWFL we can't be talking about long term conditions when the system hasn't even developed yet. As of now we are talking about the short term which at this point is the main focus. That upper level low if a few hundred miles north of the "Blob". The shear charts showing moderate trend of marginal to favorable upper level winds. And the SST remain warm enough to support tropcal cyclone development.
Member Since: October 28, 2006 Posts: 57 Comments: 29010

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About JeffMasters
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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