Persistent non-westerly systems

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shovelopikis
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Persistent non-westerly systems

Unread post by shovelopikis »

As most know, New Zealand sits on / above the roaring forties and most of all new zealands weather systems and fronts roll at us from the westward direction.

of course this fluctuates more depending on the season, but in general its mainly barrels towards us from the west.

My question, has there been any length or period of time that this altered or changed
any notable dates, weather, events to speak of?

Cheers (from a warm, sunny Hanmer Springs)
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TonyT
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Re: Persistent non-westerly systems

Unread post by TonyT »

I'm not sure I totally understand your question. This winter is an example of a season with lessened westerlies. The big storm and snow event of early June would be an example of an event which flowed directly from this regime change. So would the late summer drought in the North Island earlier in the year. Looking longer term, you could go back to the mid 1970s as an example of a reduced westerly time (frequent depressions moving over NZ with heavy rainfalls and floods). Conversely the mid to late 80s was an example of a time with enhanced westerly flow which brought droughts to eastern regions and flooding to western districts. If you want to find out why this happens, google and read up on the PDO (the Pacific Decadal Oscillation). We are currently in the midst of a negative PDO cycle, which will probably last for another 3-5 years at least, perhaps longer (this tends to suppress westerlies). You might also find some information about El Nino/Southern Oscillation (ENSO) and its relationship with the PDO (we tend to have more frequent and more severe El Nino events in positive PDO times, and fewer El Nino events in negative PDO times, such as at present).
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Re: Persistent non-westerly systems

Unread post by NZ Thunderstorm Soc »

I thought that the current anticyclone might back-track eastward or get some support from bubbles of high pressure to the west but it dosen't look likely now as a westerly regime may come into play, hindering that :-k
JohnGaul
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