Jeff Callaghan

John
A question probably for Graham Mills. Its important for us forecasters to
understand predictability and  I think this is something we must try to
impart to users of forecasts.
Jeff
 

The attached PV sequence indicates that an upper trough reached peak amplitude on the 18th and then weakened as it approached Auckland at
0000UTC 20th (lower right panel). The 200hPa conventional charts showed a similar weakening pattern.
At this later time the Warm air advection was extremely strong in the Auckland area when the bomb began to deepen dramatically.
Ckeck these winds from Whenuapai. 2300UTC 19th 080/45 knots (950hPa) 075/59 knots (900hPa) 065/64 knots
(850hPa) 035/55 knots (800hPa) 005/29 knots (700hPa) 345/27 knots (600hPa) 340/56 knots (500hPa) 315/81 knots (250hPa). Note that the winds are
coherently backing with height throughout the troposphere.

The development of this warm air advection was partly associated with the large high (see EC MSL sequence attached) which developed east of NZ by the
20th. This helped to advect low level warm tropical air to the east of the PV anomally.