Negative NAO for now

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EDR1222
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Negative NAO for now

#1 Postby EDR1222 » Mon Jul 25, 2005 8:05 am

I saw this excerpt in the NWS Melbourne Forecast discussion for early Monday morning. I am not sure how long the NAO stays in a given phase, or what effect it has on the tropics, but just thought I would throw this out there for discussion and see if anyone would like to comment on it:

WHILE FRONTAL TROFS TYPICALLY DO NOT PENETRATE THAT FAR SOUTH...
RECENT NCEP ANALYSIS SHOWS THE NORTH ATLANTIC OSCILLATION HAS SWUNG
BACK TO THE NEGATIVE PHASE...BECOMING QUITE STRONG IN RECENT DAYS.
SUCH A PATTERN USUALLY RESULTS IN WEAK RIDGING OVER THE WRN ATLC...
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#2 Postby boca » Mon Jul 25, 2005 8:39 am

You beat me to this post I saw the same thing out of Melbourne. I guess if a storm formed the Atlantic ridge is so weak the storm would most certainly recurve out to sea.
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#3 Postby WeatherEmperor » Mon Jul 25, 2005 8:48 am

is that normal for this time of year or did it just form for no apparant reason?

<RICKY>
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#4 Postby x-y-no » Mon Jul 25, 2005 8:51 am

The NAO index is a normalized difference between the pressure in the North Atlantic and the subtropical Atlantic.

A positve NAO indicates strong subtropical ridgeing, negative indicates a weak ridge, which means greater chance of storms recurving way out at sea.

We have very little skill at forecasting the NAO, so this doesn't tell us much about what's going to happen in the heart of the season.
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#5 Postby boca » Mon Jul 25, 2005 8:53 am

During the winter months I sometimes go on the winter forum and they talk about if the NAO goes neg that will bring Florida some good cold fronts.I guess this time of year it would just be troughs going down to the SE US weakening the Bermuda high and changing the steering patterns enough to recurve systems that do develop.
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#6 Postby EDR1222 » Mon Jul 25, 2005 9:00 am

x-y-no wrote:The NAO index is a normalized difference between the pressure in the North Atlantic and the subtropical Atlantic.

A positve NAO indicates strong subtropical ridgeing, negative indicates a weak ridge, which means greater chance of storms recurving way out at sea.

We have very little skill at forecasting the NAO, so this doesn't tell us much about what's going to happen in the heart of the season.


It will be interesting to see how long it persists.
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#7 Postby Steve » Mon Jul 25, 2005 9:46 am

I think Dennis had a lot to do with the turn to hard negative as some of its remnants merged up there off the Canadian East Coast with a polar low.

http://www.cpc.ncep.noaa.gov/products/p ... ensm.shtml

Steve
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