Forecast continuity - or the lack thereof...

Anchored off Motuarohia, Bay of Islands

35° 13' 0" S, 174° 16' 0" E

Spending the South Pacific Cyclone Season in New Zealand

As an illustration why that weather window mentioned in the previous post has so far been elusive... The image on the left above shows a computer model forecast (NOAA GFS) from this morning, valid for next Monday. That forecast made a Saturday/Sunday departure look favorable with good conditions along the way. The image shows isobars, wind arrows (each full barb representing 10kn), and blue shading indicates rain intensity.

The image on the right is also valid for next Monday but shows the model forecast from this evening, 12 hours more recent. This one shows a related but very different picture. What has been a shallow undefined area of low pressure west of Fiji in this morning's forecast (and projected to move off to the east and dissipate) has turned into a well formed depression on it's way south in this evening's forecast (and projected to further intensify over the following 24 hours). No longer a favorable departure window...but of course things may all be changed by tomorrow morning again ;-)

What this probably shows is the difficulty of forecasting even a rough outline of weather developments beyond 72 hours in this part of the world as long as the South Pacific Convergence Zone is active. The only things that can probably be gleaned from the longer term model output is the lack of confidence/instability indicated by the significant differences in results from successive model runs.

So we may be in for a few more days in the Bay of Islands until things settle down a bit. Not a bad spot to be in in any case...

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