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Atlantic Tropical Action 2011 - Part IV


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Cherry

"A NON-TROPICAL LOW PRESSURE SYSTEM LOCATED ABOUT 425 MILES

SOUTHWEST OF BERMUDA CONTINUES TO PRODUCE GALE FORCE WINDS

OVER AN AREA EXTENDING SEVERAL HUNDRED MILES TO THE NORTH OF

THE CENTER. THE ASSOCIATED SHOWERS AND THUNDERSTORMS

CONTINUE TO SHOW SIGNS OF ORGANIZATION...AND THE LOW COULD

ACQUIRE SUBTROPICAL CHARACTERISTICS TONIGHT OR ON TUESDAY.

THIS SYSTEM HAS A HIGH CHANCE...60 PERCENT...OF BECOMING A

SUBTROPICAL CYCLONE DURING THE NEXT 48 HOURS AS IT MOVES SLOWLY

WESTWARD TODAY AND NORTHWESTWARD ON TUESDAY.

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Looks like some more subtropical nonsense late next week

Yep, all ingredients will be there, including above normal SSTs in the midlatitudes in the Atlantic. Not my cup of tea, especially in November, but if it can transition to full warm core, I will be following it. And it may not be the last (tropical or subtropical), with the reemerging Niña, below normal shear, above normal SSTs, and favorable MJO we might see threats well into Dec... though disturbances this late in the season are very fragile and vulnerable to the westerly gods.

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Post analysis is moving along. We'll see what they do with that system.

I am curious about the post-analysis process. What do that they look at when they are doing the post analysis that they didn't see the first time? Is it additional data or just a fresh set of eyes on the old info?

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I am curious about the post-analysis process. What do that they look at when they are doing the post analysis that they didn't see the first time? Is it additional data or just a fresh set of eyes on the old info?

For Nate, for example, they received data from PEMEX oil rig platforms afterwards that confirmed 1min winds around hurricane force for a brief time. Recon data at the time was close to hurricane force, but they didn't upgrade because of the satellite appearance. Most of the time is the same data plus some additional data not available at operational time,. Probably there are times where it's mostly the same data available at operational time, but there's more time for analysis and consultation.

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I am curious about the post-analysis process. What do that they look at when they are doing the post analysis that they didn't see the first time? Is it additional data or just a fresh set of eyes on the old info?

They (The NHC) basically perform an intensive case study on the event. They pour over the observed and model data and make logical inferences, which may or may not have been made operationally. They then come up with a "best track" and evaluate the intensity errors from their official forecasts, model forecasts and long-term average errors to arrive at a maximum sustained surface wind speed curve associated with the "best track".

For example...flight level winds may or may not be considered representative of a cyclone's intensity operationally...but during post analysis they may see data only hrs apart that suggest those winds were in fact representative after all. Hence, the official time/location may be adjusted as to when the TC become a tropical storm.

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They (The NHC) basically perform an intensive case study on the event. They pour over the observed and model data and make logical inferences, which may or may not have been made operationally. They then come up with a "best track" and evaluate the intensity errors from their official forecasts, model forecasts and long-term average errors to arrive at a maximum sustained surface wind speed curve associated with the "best track".For example...flight level winds may or may not be considered representative of a cyclone's intensity operationally...but during post analysis they may see data only hrs apart that suggest those winds were in fact representative after all. Hence, the official time/location may be adjusted as to when the TC become a tropical storm.

Thanks for the information.

Does the NHC also reanalyze cherries (tropical disturbances which are deemed to have more than a 50% chance of tropical cyclone development on their Tropical Weather Outlooks) and tropical depressions which were only 4 MPH too shy of becoming tropical storms?

I know there was a cherry in September that had an 80% chance of developing into a tropical cyclone and its surface winds were over 40 MPH already; so if it had a closed circulation, it would have been deemed as a tropical storm. Tropical Depression #10 this season had 35 MPH winds but never seemed to gain 40 MPH winds. Both of these systems were way out in the Atlantic so I doubt there were recon missions in them. Thus, I would think there is a remote chance that at least one or both of these systems get designated as tropical storms in the post-season analysis as the NHC would be able to better sample more data from these two systems.

It's interesting to wonder the ramifications of this would be if those two systems and the hybrid system that affected Florida two months ago would get upgraded. That would bring up the named systems in the Atlantic this year from 18 to 21. Add to that the lemon out there in the Atlantic that may develop later on and that would be a possible 22 storms, which would place us on par for 2005's grand total of 27.

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Thanks for the information.

Does the NHC also reanalyze cherries (tropical disturbances which are deemed to have more than a 50% chance of tropical cyclone development on their Tropical Weather Outlooks) and tropical depressions which were only 4 MPH too shy of becoming tropical storms?

I'm not sure how much, if any, reanalysis and possible upgrades of outlooked storms are performed. I don't see why they wouldn't include the higher end storms in a reanalysis project tho. That'd be a good question to ask the NHC. They've been discussing a couple reanalysis projects lately on their FB page and I'm sure they wouldn't mind the question.

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@HurricaneJosh: Wow, thanks for that interesting case study on that unclassified and outlandish cyclone! It was only deemed as having a low chance of tropical cyclone development; so I'm sure that the cherry in September that I mentioned above has a good chance to being added into the database. It's also impressive to see that the 2006 cyclone developed into a 50-MPH tropical storm at 40N latitude; when in reality, it's hard-pressed for a cyclone to maintain its intensity above 35N overall. @Ed Lizard: If that lemon can consolidate a bit more, it has a better chance of becoming a cyclone. I wonder how much shear is over this system right now because it looks like its northern outflow is hitting a wall to the north.

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