Bob Mc Davitt
Salsa af Stavsnas
Ellinor Ristoff Staffan Ehde
Sun 20 Jul 2014 22:53
Departing from NZ to the tropics
A compact and intense Low has been travelling east past northern NZ over
the weekend causing damage with heavy rain and strong onshore- easterly
winds for a while. This low has now gone off to the east of NZ and has
opened the way for a trough to form along 170W to east of the whole of NZ.
Lows from the southern ocean are likely to be drawn into this trough and
one should deepen there on Wednesday, and another on Friday..
It looks to me that the coldest week of the year for NZ is very likely to
be this week. I say this because the coldest time of the year is usually
late July/early August, and during the coming week air from the southern
ocean is likely to be shovelled onto New Zealand thanks to the southerly
flow that is being directed by the High to the west and the Lows to the
east˜ what is sometimes called an eggbeater southerly.
Negative storm surge
In this blog last week we looked at the storm surge at Marsden Point (off
Whangarei) in the storm that bothered Northland earlier this month. With
vigorous on-shore easterlies in the past few days a similar storm surge
of around .5m has been measured at Whitianga (off Coromandel).
One of my blog followers pointed out a corresponding drop in sea level at
the south end of NZ at Green Island (off Dunedin). During last week this
was as much as 0.6m and now it is still .4 of a metre. Imagine the
embarrassment of boats taking shortcuts across a mudflat when the real
tide is .6m below the computed tide!
Can anyone offer an explanation for these strong „sea sucks‰ ˆ I don‚t
think the winds at Dunedin have been strong off-shore for all of last
week, so what‚s the cause? It seems to mirror the shape and trend of the
storm surge on the NE coast- is this a clue to its cause, or a
coincidence?