Bomb

We arrived in Great Barrier late Wednesday just before a forecast gale arrived with 35 knot winds and gusts over 40. All week, the Met Service has been calling for a Weather Bomb on Saturday. While the rain passed quickly, the winds at great Barrier blew from Wednesday night until around 2 AM Friday. A brief period of light winds was forecast for Friday with deteriorating conditions Friday evening.

We made the decision to head off at first light to take advantage of the brief window. I firmly expected ugly conditions after 36 hours of wind, but Joe told me that things settle quickly here. He was right – there was very little evidence of the prior blow and by the time we hit the Hen and Chicks, it was practically flat with light south westerlies. The old adage of the calm before the storm applied and you could see that something bad was afoot in the clouds.

Steve Dashew does a great job explaining a meteorological bomb in his Weather Handbook, but a short version follows. There was a very deep troff on the 500 mb charts moving in from the Tasman and a developing surface low over New Zealand. As the upper level troff approached the developing surface low, the surface low literally exploded as the upper level troff pulled air out of the low – hence the term weather bomb.

The following is a shot of the system from MetVu. You can see the central pressure is around 980 mb – pretty impressive.

Winds with this system over open water were reported to be over 65 knots. We had 40 knot gusts in the marina.

Anyway, the winds started coming up in the evening, torrential rains arrived around midnight and it really started howling at 2 AM. Why it always happens at 2 AM is still a mystery to me.

Best