NIWA Outlook: January – March 2017
NIWA Outlook: January – March 2017
Overview
The
tropical Pacific continues to exhibit mainly ENSO-neutral
conditions. Sea surface temperatures (SSTs) in the central
Equatorial Pacific Ocean remain marginally below average. In
the sub-surface ocean, the pockets of cooler than average
temperatures that were present in November 2016 have
contracted and warmed. Thus, it appears that any La
Niña-like oceanic signal has peaked and is subsiding back
toward neutral. The atmospheric setup is mixed as stronger
easterly trade winds in the central Pacific along with
enhanced convection over parts of the Maritime Continent are
consistent with La Niña conditions. The Southern
Oscillation Index (SOI) is weakly positive and is consistent
with ENSO-neutral conditions.
International guidance now strongly favours ENSO-neutral conditions (77% chance) over the next three month period (January - March 2017). By March-May 2017, the chance for neutral conditions rises to 87% with a meagre 8% chance for El Niño conditions and 5% chance for La Niña conditions. In summary, ENSO-neutral conditions are likely over the next 3-month period and should continue into autumn.
Consequently, the combination
of ENSO-neutral conditions, along with the absence of other
large-scale climate drivers for the remainder of summer into
early autumn, may result in only weak air flow anomalies.
Mostly typical summer conditions are expected with high
pressure systems crossing the North Island and prevailing
westerly winds over the South Island.
Outlook
Summary
January – March 2017 temperatures are about
equally likely to be near average (40% chance) or above
average (35-45% chance) for the north and east of the North
Island and for the east of the South Island. Near average
temperatures are most likely (40% chance) for the remainder
of the country. Sea surface temperatures around New Zealand
are expected to be near average or above average over the
next three months.
January – March 2017 rainfall totals
are about equally likely to be near normal (40% chance) or
below normal (40-45% chance) for all North Island regions.
Rainfall totals are about equally likely to be near normal
(40% chance) or below normal (35% chance) for the north of
the South Island. Near normal rainfall is most likely (40%
chance) for the east and west of the South
Island.
January – March 2017 soil moisture levels and
river flows are most likely (50% chance) to be below normal
for the north of the North Island and about equally likely
to be normal (40% chance) or below normal (45% chance) for
the east and west of the North Island and east of the South
Island. Near normal soil moisture levels and river flows are
most likely (45-50% chance) for the north and west of the
South Island.
Regional predictions for the January – March 2017 season
Northland, Auckland, Waikato,
Bay of Plenty
The table below shows the
probabilities (or percent chances) for each of three
categories: above average, near average, and below average.
In the absence of any forecast guidance there would be an
equal likelihood (33% chance) of the outcome being in any
one of the three categories. Forecast information from local
and global guidance models is used to indicate the deviation
from equal chance expected for the coming three month
period, with the following outcomes the most likely (but not
certain) for this region:
• Temperatures are equally
likely to be near average (40% chance) or above average (40%
chance).
• Rainfall totals are about equally likely to
be in the near normal (40% chance) or below normal (45%
chance) range.
• Soil moisture levels and river flows
are most likely to be below normal (50% chance).
The
full probability breakdown is:
Temperature Rainfall Soil
moisture River flows
Above average 40 15 10 10
Near
average 40 40 40 40
Below
average 20 45 50 50
Central
North Island, Taranaki, Whanganui, Manawatu,
Wellington
Probabilities are assigned in three
categories: above average, near average, and below average.
• Temperatures are most likely to be near average (40%
chance).
• Rainfall totals are equally likely to be in
the near normal (40% chance) or below normal range (40%
chance).
• Soil moisture levels and river flows are
about equally likely to be in the near normal (40% chance)
or below normal range (45% chance).
The full probability
breakdown is:
Temperature Rainfall Soil moisture River
flows
Above average 30 20 15 15
Near
average 40 40 40 40
Below
average 30 40 45 45
Gisborne,
Hawke’s Bay, Wairarapa
Probabilities are
assigned in three categories: above average, near average,
and below average.
• Temperatures are about equally
likely to be near average (40% chance) or above average (45%
chance).
• Rainfall totals are equally likely to be in
the near normal (40% chance) or below normal (40% chance)
range.
• Soil moisture levels and river flows are about
equally likely to be near normal (40% chance) or below
normal (45% chance).
The full probability breakdown
is:
Temperature Rainfall Soil moisture River
flows
Above average 45 20 15 15
Near
average 40 40 40 40
Below
average 15 40 45 45
Tasman,
Nelson, Marlborough, Buller
Probabilities are
assigned in three categories: above average, near average,
and below average.
• Temperatures are most likely to
be near average (40% chance).
• Rainfall totals are
about equally likely to be in the near normal range (40%
chance) or below normal (35%) range.
• Soil moisture
levels and river flows are most likely to be in the near
normal range (45% chance).
The full probability breakdown
is:
Temperature Rainfall Soil moisture River
flows
Above average 30 25 20 20
Near
average 40 40 45 45
Below
average 30 35 35 35
West
Coast, Alps and foothills, inland Otago,
Southland
Probabilities are assigned in three
categories: above average, near average, and below average.
• Temperatures are most likely to be near average (40%
chance).
• Rainfall totals are most likely to be in the
near normal (45% chance) range.
• Soil moisture levels
and river flows are most likely to be near normal (50%
chance) range.
The full probability breakdown
is:
Temperature Rainfall Soil moisture River
flows
Above average 30 30 15 15
Near
average 40 45 50 50
Below
average 30 25 35 35
Coastal
Canterbury, east Otago
Probabilities are
assigned in three categories: above average, near average,
and below average.
• Temperatures are about equally
likely to be near average (40% chance) or above average (35%
chance).
• Rainfall totals are most likely to be in the
near normal range (45% chance).
• Soil moisture levels
and river flows are about equally likely to be below normal
(45% chance) or near normal (40% chance).
The full
probability breakdown is:
Temperature Rainfall Soil
moisture River flows
Above average 35 30 15 15
Near
average 40 45 40 40
Below
average 25 25 45 45
Background
The tropical
Pacific continues to exhibit mainly ENSO-neutral conditions.
Sea surface temperatures (SSTs) in the central Equatorial
Pacific Ocean remain marginally below average, with a value
of -0.3oC in the NINO3.4 region, and thus do not exceed the
threshold used by NOAA’s Climate Prediction Centre (CPC)
to define La Niña events. In the sub-surface ocean, the
pockets of cooler than average temperatures that were
present in November 2016 have contracted and warmed. An
expanding tongue of warmer than average sub-surface ocean
temperatures is noted between about 160oE and 160oW. It
appears that any La Niña-like oceanic signal has peaked and
is subsiding back toward neutral.
The thirty-day
Southern Oscillation Index (SOI) trended in a weakly
positive direction (+0.2), and is currently in the
ENSO-neutral range. During December, stronger than normal
easterly trade winds continued in the central Pacific along
with enhanced rainfall over parts of the Maritime Continent.
Furthermore, the Intertropical Convergence Zone (ITCZ) was
displaced north of its climatological position along the
Equator in the central Pacific. These wind and convection
anomaly patterns are consistent with La Niña-like
conditions.
The South Pacific Convergence Zone (SPCZ) is
better defined than last month around Fiji, extending south
and east from there. It is displaced slightly south and
southwest of its climatological position east of the Date
Line. Consequently, the atmosphere reflects mixed ENSO
signals.
International guidance now strongly favours
ENSO-neutral conditions (77% chance) over the next three
month period (January - March 2017). By March-May 2017, the
chance for neutral conditions rises to 87% with a meagre 8%
chance for El Niño conditions and 5% chance for La Niña
conditions. In summary, ENSO-neutral conditions are likely
over the next 3-month period and should continue into
autumn.
Sea surface temperatures (SSTs) are warmer than
average to the east and north of New Zealand, while to the
west over the Tasman Sea they are slightly cooler than
normal. The dynamical model forecasts for SSTs indicate
that this pattern is likely to persist over the next three
month period (January – March 2017), with some warming
possible over the Tasman Sea. Thus, coastal waters around
the country are expected to be near or above normal.
The
2016-17 tropical cyclone season is expected to produce near
average activity across most islands of the southwest
Pacific. Refer to NIWA’s Tropical Cyclone outlook at https://www.niwa.co.nz/news/southwest-pacific-tropical-cyclone-outlook
for more information.
Notes to reporters and
editors
1. NIWA’s outlooks indicate the likelihood of
climate conditions being at, above, or below average for the
season as a whole. They are not ‘weather forecasts’. It
is not possible to forecast precise weather conditions three
months ahead of time.
2. The outlooks are the result of
the expert judgment of NIWA’s climate scientists. They
take into account observations of atmospheric and ocean
conditions and output from global and local climate models.
The presence of El Niño or La Niña conditions and the sea
surface temperatures around New Zealand can be a useful
indicator of likely overall climate conditions for a
season.
3. The outlooks state the probability for above
average conditions, near average conditions, and below
average conditions for rainfall, temperature, soil moisture,
and river flows. For example, for winter
(June–July–August) 2007, for all the North Island, we
assigned the following probabilities for temperature:
·
Above average: 60 per cent
· Near average: 30 per
cent
· Below average: 10 per cent
We therefore
concluded that above average temperatures were very
likely.
4. This three-way probability means that a random
choice would be correct only 33 per cent (or one-third) of
the time. It would be like randomly throwing a dart at a
board divided into three equal parts, or throwing a dice
with three numbers on it. An analogy with coin tossing (a
two-way probability) is not correct.
5. A 50 per cent
‘hit rate’ is substantially better than guesswork, and
comparable with the skill level of the best overseas climate
outlooks. See, for example, analysis of global outlooks
issued by the International Research Institute for Climate
and Society based in the US published in the Bulletin of the
American Meteorological Society (Goddard, L., A. G.
Barnston, and S. J. Mason, 2003: Evaluation of the IRI’s
“net assessment” seasonal climate forecasts 1997–2001.
Bull. Amer. Meteor. Soc., 84,
1761–1781).
6. Each month, NIWA publishes an analysis
of how well its outlooks perform. This is available online
and is sent to about 3500 recipients of NIWA’s
newsletters, including many farmers. See www.niwa.co.nz/our-science/climate/publications/all/cu
7. All
outlooks are for the three months as a whole. There will
inevitably be wet and dry days, and hot and cold days,
within a season. The exact range in temperature and rainfall
within each of the three categories varies with location and
season. However, as a guide, the “near average” or
middle category for the temperature predictions includes
deviations up to ±0.5°C for the long-term mean, whereas
for rainfall the “near normal” category lies between
approximately 80 per cent and 115 per cent of the long-term
mean.
8. The seasonal climate outlooks are an output of a
scientific research programme, supplemented by NIWA’s
Capability Funding. NIWA does not have a government contract
to produce these outlooks.
9. Where probabilities are
within 5% of one another, the term “about equally” is
used.
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