Tropical Weather Briefing #2, Week of September 18  

GEORGE KASICA - 9/19/2006 11:12 AM

Tropical Weather Briefing #2, Week of September 18 

Forecaster: Kasica

Basin: Atlantic

Storm: Hurricane Gordon

I decided for the second briefing to switch from Hurricane Helene which is currently no threat to land or population in the next 24 hours to Hurricane Gordon which, although not as intense, is an immediate threat to the Azores Island Group ( within the next 24 hours.

At 15Z Hurricane Gordon is currently located at 38.0N, 35.4W or about 455 miles west of Lajes Air Force Base in the Azores. Winds were near 85mph and its motion was to the East at near 27kts (31mph) which is amazingly fast for a tropical system.

As stated in the discussion ( limited shelf life warning applies) the intensity is expected to decrease as the storm moves over the colder waters (20-22C see attached Global SST from the E-Wall) and also as it transitions to an extratropical system in the next 24 hours.

You can see in the latest Satellite image (attached) that Gordon no longer has a distinct eye and the circulation is also elongated likely due to its rapid progress and pending transition to an extra tropical system in the near future.

The last image I am including is the Hurricane Force Wind Probability Graphic from the NHC website that shows the percentage chance of hurricane force winds occurring at a given location within the next 36 hours (you can pick a view out to 120 hours at Limited shelf life warning applies again). As you can see the graphic doesn’t show a very high percentage chance for hurricane force winds to occur in the Azores, which is a contradiction to the public advisory that his been issued at so a possible topic for briefees would be why the contradiction in these products both issued from the NHC??

Another item to pursue again like Shanshan earlier in the weekend is the exact track and landfall time and intensity of Gordon at it reaches the Azores.

Have a great Tuesday, 



re: Tropical Weather Briefing #2, Week of September 18
WILLIAM BURNS - 9/19/2006 05:11 PM
George, I'll take a stab at this and say that the Wind field graphic shows it missing the Azores but is time-stamped 8AM AST 8/19/06, whereas the NHC advisory is 5PM AST so something must have changed quite a bit since that last graphic. Again, like Steve said, the model is only as good as the initialization.
re: Tropical Weather Briefing #2, Week of September 18
WILLIAM BURNS - 9/19/2006 05:23 PM
George, I attached the 12hr UKMET prog showing the track directly over the Azores by 0Z 9/20/06.  


re: Tropical Weather Briefing #2, Week of September 18
WILLIAM BURNS - 9/19/2006 05:33 PM
While I was posting this, I realized the contradiction is still there. This prog was initialized at 1200Z which is close to the time of that wind field graphic....and it shows the center of Gordon passing right over the where DID that wind field graphic come from...a much earlier initialization ?

re: Tropical Weather Briefing #2, Week of September 18
PHILIP LUTZAK - Edited 9/19/2006 07:04 PM
Hey George and William,
  I can't explain why they don't have the higher possibilities for hurricane winds going through the Azores either. The trop storm fcst map (attach 03) has 100% for the islands. In addition, I noticed this:
  This is from the last 5PM NHC public advisory: 
And here are the NHC forecast positions from the 5PM discussion:

INITIAL      19/2100Z 37.9N  31.6W    75 KT
12HR VT    20/0600Z 38.1N  26.0W    65 KT
24HR VT    20/1800Z 39.0N  18.0W    55 KT...EXTRATROPICAL
36HR VT    21/0600Z 42.1N  10.0W    45 KT...EXTRATROPICAL

  That is straight through the heart of the islands. 

  What’s interesting is that the NHC map from 5PM this evening (01) doesn’t jive with those forecast positions. Those center positions on the map are not going through the middle of the islands, but south of them. But the 18Z NAVY (02) map shows the positions perfectly. Don’t ask me why!  But it is bothersome.


re: Tropical Weather Briefing #2, Week of September 18
Steve Seman - 9/19/2006 07:10 PM
I don't know if I see what you guys are seeing on the NHC track graphic.  It looks to me that the initial position is around 38ºN, and by 2 pm Wednesday (less than 24 hours into the future) it's approaching 39ºN.
re: Tropical Weather Briefing #2, Week of September 18
PHILIP LUTZAK - Edited 9/19/2006 07:30 PM
OK, Steve. My apologies!
After looking ever more closely, I can see that they must be the same. It's just that the NHC map is on such a large scale, leaving the islands so tiny, that it's hard to make out detail. I missed the dot they have for Sao Miguel at 37.8N, 25.5W. Also, when I copied the NAVY map into here, it changed size and detail so that it doesn't look any much clearer. If you go to their sight and click on the map there, it gives very fine detail. I should have mentioned that. Sorry...   
But I'm still confused as to why they have such low probabilites for hurricane force winds at the islands. It doesn't jive with the 5PM discussion and forecast advisory.
re: Tropical Weather Briefing #2, Week of September 18
BRANDON JONES - 9/19/2006 10:36 PM
Earlier this afternoon Gordon's satellite presentation was still remarkable for it's location. At that time Gordon's eye was remaining visible. Here's is the latest satellite loop from the NHC: (
Gordon's is losing its organization and may not be a hurricane any more. In the loop, you can see that the deep convection has been pushed farther east than the center of the storm. Also note the low level clouds, especially in the western half of the storm. Perhaps the NHC kept the intensity forecast a little higher just for a precaution, in case the storm pulled any suprises.
re: Tropical Weather Briefing #2, Week of September 18
ROBERT SANDBERG - 9/19/2006 10:58 PM
Hey guys, 

I think I might be missing something on the original questions here.  The NHC graphics indicate the probability of sustained hurricane force or tropical storm force winds are based on 1 minute surface wind speed averages depending on track and intensity.  The tropical storm force conditions have a larger radii than the hurricane force winds as you can seen on the cumulative distribution. 

This brings me to a question. Are the hurricane probabilities lower due to the intensity and track or is it due to poor model initialization or combination of both?


re: Tropical Weather Briefing #2, Week of September 18
Steve Seman - 9/20/2006 12:11 AM
Robert is right.  Gordon is a storm that's barely a category 1 storm (and weakening) as it's moving through the Azores area, and the area of hurricane-force winds extends up to 40 miles from the center.  But, in reality, the areas experiencing hurricane-force sustained winds are pretty small within that larger framework.  That lends itself to lower probabilities.  The probability of tropical storm-force winds is much higher, because they extend out much farther from the center and while it's not entirely certain that Gordon will remain a hurricane for long, it surely will maintain the strength of a tropical storm.


re: Tropical Weather Briefing #2, Week of September 18
LEE GRENCI - 9/20/2006 07:22 AM
Here's the updated cumulative winds.  Looks like Gordo did not, technically, make landfall.  Close but no cigar.  Am I correct?


re: Tropical Weather Briefing #2, Week of September 18
WILLIAM BURNS - 9/20/2006 09:29 AM
Lee, you are right. It just missed. The eye passed between the islands of Sao Miguel and Santa Maria. 

From the Associated Press (2 hrs 36 mins ago)

"The eye of Gordon moved between the islands of Sao Miguel and Santa Maria, and was rapidly moving east, according to the National Hurricane Center in Miami."

“As it stands right now it will not make land fall,” said Dave Roberts, a hurricane forecaster for the National Hurricane Center. “There are still some winds there. They definitely felt some effect, but the eye didn’t pass on land.”

The full link:
re: Tropical Weather Briefing #2, Week of September 18
WILLIAM BURNS - 9/20/2006 09:37 AM
Here's a map of the Azores showing Sao Miguel and Santa Maria so you can see how close Gordon passed to the basically "threaded the needle" between the 2 islands !
re: Tropical Weather Briefing #2, Week of September 18
LEE GRENCI - 9/20/2006 09:53 AM
Thanks Bill!
re: Tropical Weather Briefing #2, Week of September 18
DANIEL DEPODWIN - 9/20/2006 11:07 AM
The NHC discussion mentions that Gordon is in the process of becoming extraptropical and merging with a cold front:


The 0z CMC (12 hr--see attached) run has a tough time finding a center of circulation for Gordon.  The Vorticity image (upper right) clearly shows the cold front just to the East of the Azores but no sign of the circulation of Gordon.  This shows that the core is basically imbedded in the front at this point.