It would appear at this stage that they got caught with a extremely active storm cell. All the exits North out of Wellington were closed just after they would have passed over. At Paekakariki the main trunk rail, and state highway 1 were both closed due flooding, and the water came up very rapidly. I am only 25 km north at Paraparaumu and the weather was shocking for a period of about 2hours, torrential rain, mostly falling horizontally the wind was so strong. The general weather was bad but this cell must have been exceedingly active, and it would have been well buried in the wx system.
Prospector