One storm down, another on its way
One storm down, another on its way
The intense low pressure system that developed in the Tasman sea late yesterday had become as strong as a category 2 tropical cyclone by 8am today, says NIWA meteorologist Ben Noll.
At that time the
pressure at the centre of the storm was estimated at 967
millibars. Mr Boll said overall it was an unusual, but not
unheard of, pattern of weather for
mid-summer.
Why such a strong
storm?
1. A very strong
jet stream (for the time of year) stretched from the
southern Indian Ocean to the Tasman Sea.
1. This
contributed to a strong south to north temperature gradient
across the Tasman Sea where rapid intensification took
place.
2. Warmer than average sea surface temperatures
in the western Tasman Sea.
3. A pulse
in the Madden-Julian Oscillation (MJO). The MJO is
characterised as an eastward moving area of enhanced cloud
and rainfall near the equator that usually recurs every 30
to 60 days.
As a result, very heavy rain occurred
across the South Island. The heaviest rainfall was across
the Southern Alps.
Top three rain amounts
(from 12:00 am Tuesday to 10:00 am today):
1.
Ivory Glacier, 343 mm
2. Arthur’s Pass, 310.2 mm,
including 44.8 mm in one hour late Wednesday evening. This
was the wettest hour at the location on record since the
climate station was erected in July 2005.
3. Mueller
Hut, 309.5 mm
http://imgur.com/a/R0H96
Other
heavy rain amounts (12:00 am Tuesday to 10:00 am
today)
1. Greymouth, 128.2 mm
2. Hokitika,
115.4 mm
3. Reefton, 104.0 mm
Strong wind
gusts were also observed across parts of the South Island
and lower North Island.
Top wind
gusts:
1. Baring Head, 138.6 km/hr
2.
Akitio, 131.8 km/hr
3. Wellington (Greta Point), 113.4
km/hr
4. Mahanga, 113.0 km/hr
5. Westport, 93.2
km/hr
http://imgur.com/a/Oiqtz
In
the storm’s wake, very chilly southwest winds are expected
to spread up the country and be in place by tomorrow
morning. Some snow is even possible across the Southern Alps
tonight. Spotty showers are forecast across the country
tomorrow as an autumn-like day unfolds.
After that,
another potent storm is on the cards for late Saturday into
Sunday, Mr Noll says.
“Some very heavy falls of
rain are possible in similar locations that received heavy
rain from the first storm.
“Some beneficial rain
is possible across the North Island, particularly in those
locations that are experiencing very to extremely drier than
normal soils. This relief will be short-lived, as mostly dry
conditions are expected to return to the driest locations
next week (Auckland, Northland, Hawke’s Bay, and
Gisborne).
In fact, Kerikeri received just 1 mm of
rain this month or less than 1% of normal. The normal
January rainfall is 112 mm.
Will proper
summer weather return soon?
Through the
end of January, patterns of southwest winds are expected to
alternate with northwest winds. Temperatures, for the most
part, will be cooler than average for the time of year,
although the east of both islands will experience a few
warmer than average days.
As we head into early
February, there is some indication for settled weather
patterns across New Zealand with a warming trend toward
mid-month. As such, soils across the north and east of the
North Island may continue to dry due to below normal
rainfall.
For now, we will have to tough it out
through an autumn-like chill in the heart of
summer!