Number 100, January 2009
The Island
Climate Update
Collaborators
Pacific Islands National
Meteorological Services
Australian Bureau of
Meteorology
Meteo France
NOAA National
Weather Service
NOAA Climate
Prediction Centre
(CPC)
International Research
Institute for Climate
and Society
European Centre
for Medium Range
Weather Forecasts
UK Met Office
World Meteorological
Organization
MetService of
New Zealand
December’s climate
•
The South Pacific Convergence Zone (SPCZ) was displaced
southwest of its normal position.
•
Very suppressed convection near Western Kiribati and south of the
Equator from Nauru east to northern French Polynesia.
•
Above normal rainfall for few areas in the South Pacific, with a
record high in the Southern Cook Islands.
El Niño/Southern Oscillation (ENSO), seasonal
rainfall, and sea surface temperature forecasts
•
La Niña-like conditions exist in the tropical Pacific. Many climate
models project continuation of La Niña through to the end of
summer 2009.
•
Below normal rainfall is forecast for Western Kiribati, the
Marquesas, Tuvalu, Tokelau, the Northern Cook Islands, and the
Tuamotu archipelago.
•
Above normal rainfall is expected for New Caledonia, Fiji, Vanuatu,
Niue, Tonga, and the Southern Cook Islands.
•
Normal to above normal SSTs are forecast for the southwestern half
of the southwest Pacific region. Normal to below normal SSTs are
forecast for the northeast half of the southwest Pacific.
The Island Climate Update, No. 100, January 2009
Page 2
Climate developments in December 2008
Outgoing Long-wave Radiation (OLR) anomalies, in Wm
2
are represented
by hatched areas. High radiation levels (yellow) are typically associated
with clearer skies and lower rainfall, while cloudy conditions lower the OLR
(blue) and typically result in higher rainfall. The December 2008 position of
the South Pacific Convergence Zone (SPCZ) was contracted toward Papua
New Guinea, was displaced southwest of its normal position, and less
coherent than last month. The average position of the SPCZ is identified
by the dashed green line, which is based on mean January rainfall for the
South Pacific. Mean sea level (MSL) pressure anomalies (in hPa) are shown
as grey lines.
Soil moisture in December 2008
Estimated soil moisture conditions at the end of December 2008,
using monthly rainfall data. Soil moisture projections for individual
Pacific Island countries are dependent on data availability at the
time of publication.
E
stimates of soil moisture shown in the map (right) are
based on monthly rainfall for one station in each country.
Currently there are not many sites in the water balance model,
but more stations will be included in the future.
The information displayed is based on a simple water balance
technique to determine soil moisture levels. Addition of
moisture to the available water already in the soil comes
from rainfall, with losses via evapotranspiration. Monthly
rainfall and evapotranspiration are used to determine the
soil moisture level and its changes. These soil moisture
calculations were made at the end of the month, and for
practical purposes, generalisations were made about the
available water capacity of the soils at each site.
Nadi (Fiji), Hanan (Niue), Port Vila (Vanuatu), Rarotonga
(Southern Cook Islands), and Apia (Samoa) project moist
(at or near field capacity) soil moisture conditions. Soils are
moderate for the time of year at Nuku’alofa (Tonga).
T
he South Pacific Convergence Zone (SPCZ) activity was
displaced south and west of normal during December,
and less consolidated than last month. A region of enhanced
rainfall was observed during December 2008 over
southern Papua New Guinea and northeast Australia, and
to the southeast of New Caledonia. Suppressed convection
intensified during the month to the south of the Equator, and
encompassed the region northeast of the Solomon Islands,
Nauru, and Western Kiribati and extended across the
southwest Pacific to central French Polynesia. The regional
circulation for the month was characterised by more frequent
high pressure across the South Pacific from east of Papua
New Guinea to the Society Islands; and lower than normal
pressure near northern New Zealand and Eastern Kiribati.
Rainfall was near normal or below normal for many countries
in the southwest Pacific in December 2008. The exception
occurred in a swath that extended from southern Vanuatu
and west of Tonga southward through the Kermadec Islands,
and enhanced rainfall was also localised in northern and
central Australia. Lower than normal rainfall was recorded
at many stations in French Polynesia, with Tahiti in the
Society Islands receiving 106 mm of rainfall (30% of normal).
Elsewhere in the eastern half of the southwest Pacific, the
stations in the Tuamotu archipelago and the Austral Islands
all recorded normal or below normal rainfall, except Tubuai,
which received 354 mm (195% of normal)
Many stations in New Caledonia received well below normal
rainfall (30–60%) during December. Vanuatu experienced a
relatively dry month, with the northern part of the country
recording near or below normal rainfall. The Solomon
Islands also had a relatively dry month receiving 70–90% of
normal rainfall, except at Auki, which received 456 mm of
rain (159% of normal).
In Fiji, higher than normal rainfall occurred at Nadi Airport
(271 mm; 152% of normal). In Samoa, abundant rainfall
continued to fall in December, except at Maota. A regional
high monthly rainfall total was recorded at Afiamalu, which
received 751mm (129% of normal). In the western southwest
Pacific, rainfall totals were near to above normal in central
and eastern Australia.
Wet
Moderate
Dry
Wet
Moderate
Dry
Wet
Moderate
Dry
Wet
Moderate
Dry
December 2008 December 2007
Island Group
Location
Rainfall
(mm)
% of
avg
Comments
Southern Cook
Islands
Rarotonga
Airport
471
251
Record high
French
Polynesia
Tubuai
354
195
Very high
Samoa
Afiamalu
751
129
Highest monthly
total in the region
Tonga
Lupepau’u
27
21
Very low
Eastern Kiribati
Kanton
1
1
Very low
Australia
New Zealand
Fiji
New Caledonia
Vanuatu
Solomon Is
Samoa
Tonga
Niue
E Kiribati
Papua New Guinea
S Cook Is
N Cook Is
Society Is
W Kiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Tuamotu Is
Pitcairn
EQUATOR
The Island Climate Update, No. 100, January 2009
Page 3
Mean sea surface temperatures (ºC) for December 2008
Sea surface temperature anomalies (ºC) for December 2008
Forecast validation: October to December 2008
-3
-2
-1
0.5
2
3
Australia
New Zealand
Fiji
New Caledonia
Vanuatu
Solomon Is
Samoa
Tonga
Niue
E Kiribati
Papua New Guinea
S Cook Is
N Cook Is
Society Is
W Kiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Fed States of Micronesia
Tuamotu Is
Pitcairn
EQUATOR
Wallis & Futuna
10 12 14 16 18 20 22 24 26 28 30 32
Australia
New Zealand
Fiji
New Caledonia
Vanuatu
Solomon Is
Samoa
Tonga
Niue
E Kiribati
Papua New Guinea
S Cook Is
N Cook Is
Society Is
W Kiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Fed States of Micronesia
Tuamotu Is
Pitcairn
EQUATOR
Wallis & Futuna
El Niño/Southern Oscillation (ENSO)
D
uring December, La Niña conditions were
re–established in the equatorial Pacific Ocean,
with the tropical Pacific atmosphere exhibiting
moderate to strong La Niña characteristics. The SOI
has remained persistently positive with a December
value of +1.3 (OND mean +1.4), and easterly trade
winds have remained strong during December about
and west of the Date Line.
SST anomalies in December were below average
across the equatorial Pacific: The NINO3 anomaly
for December was –0.2°C (3–month mean +0.0°C),
and the NINO4 anomaly was –0.5°C (OND mean
0.2°C). A warmer ‘horseshoe’ has also formed in
the subtropics. Equatorial subsurface temperature
anomalies are now below average east of the Date
Line, with a –4°C anomaly centred near 140°W
below 100 m.
Tropical Pacific precipitation patterns continue a
La Niña signal, with the TRMM ENSO precipitation
index at –1.3 for December. OLR anomalies show
extremely suppressed equatorial convection about
and west of the Date Line for December as a whole,
with enhanced convection over the maritime
continent and northern Australia. A convective
pulse associated with the MJO was present east of
Indonesia during early January, but this is predicted
to dissipate by mid January as the convective region
approaches the Date Line. Thus, the evidence
suggests a redevelopment of a La Niña.
Several climate models assessed by NIWA indicate
cool SST anomalies for the late summer period and
La Niña conditions. However, the majority indicate
neutral conditions developing during autumn
2009. The NCEP draft discussion of 6 January
indicates La Niña conditions are likely to continue
into the Northern Hemisphere spring of 2009. The
IRI summary of 17 December projects a 50–55%
probability of ENSO-neutral conditions persisting
A
large region of suppressed convection was forecast to
encompass the Solomon Islands, and a region extending
southeast from Tuvalu to Pitcairn Island, including Tokelau,
Wallis & Futuna, Samoa, the Northern Cook Islands, and
most of French Polynesia, with average or below, or below
average rainfall for those countries. Enhanced convection
and above average rainfall was forecast for Papua New
Guine, Vanuatu, Eastern Kiribati, Tonga, and the Southern
Cook Islands. Near or above average rainfall was forecast for
Fiji, Niue, New Caledonia. No precipitation guidance was
offered for the Austral Islands or the Society Islands.
The rainfall outlook for the October–December 2008 period
was very good compared to our forecast, although this is
calculated for 17 island groups (two islands had a forecast of
‘climatology’, which is unscoreable and two did not report
values).The global station ‘hit’ rate was 71%, 7% higher than
average for forecasts made during October and 10% higher
than the average for all months combined. Rainfall totals
were slightly overestimated for parts of Samoa, Vanuatu, the
Southern Cook Islands, and Fiji.
Forecast statistics compiled over the last nine years indicate
the multi-model ensemble strike rate will continue to have
good skill throughout the summer.
over the coming season, and 45–50% for weak La Niña
conditions.
Tropical Cyclone Guidance
C
onditions in the tropical Pacific are likely to affect the chances of tropical cyclone (TC) activity for several countries
between January and May 2009. There is an increased risk of TC occurrence for countries west of the Date Line,
including Vanuatu, the Solomon Islands, and New Zealand, and a slight risk increase for New Caledonia. Reduced risk is
expected for Samoa, Tonga, and Niue. For more information go to
http://www.niwascience.co.nz/news/mr/2009/2009-01-09
The Island Climate Update, No. 100, January 2009
Page 4
Tropical Pacific rainfall – December 2008
Rainfall totalling 200% or more is considered well above average. Totals of 40% or less are normally well below average. Highlighted values are
new records.
Data are published as received and may be subject to change after undergoing quality control checks. N/A denotes data unavailability at the time
of publishing, and * denotes synoptic values.
Territory and
station station
name
December 2008
rainfall
total (mm)
December 2008
percent of
average
Australia
Cairns Airport
197
107
Townsville Airport
179
137
Brisbane Airport
63
50
Sydney Airport
54
71
Cook Islands
Penrhyn
83
26
Aitutaki
304
145
Rarotonga Airport
471
251
Fiji
Rotuma Island
138
48
Udu Point
309
117
Nadi Airport
271
152
Nausori
239
90
French Polynesia
Hiva Hoa, Atuona
58
58
Bora Bora
150
55
Tahiti – Faa’a
106
30
Tuamotu, Takaroa
105
48
Gambier, Rikitea
216
104
Tubuai
354
195
Rapa
112
53
Kiribati
Tarawa
194
92
Kanton
1
1
New Zealand
Kaitaia
83
86
Whangarei Airport
139
153
Auckland Airport
101
122
New Caledonia
Ile Art, Belep
109
83
Koumac
135
135
Ouloup
35
25
Ouanaham
78
45
Poindimie
93
41
La Roche
81
45
La Tontouta
85
116
Noumea
50
63
Moue
83
56
Territory and
station station
name
December 2008
rainfall
total (mm)
December 2008
percent of
average
Niue
Hanan Airport
149
88
Liku
188
116
North Tasman
Lord Howe Island
88
73
Norfolk Island
80
98
Raoul Island
142
105
Samoa
Faleolo Airport
393
152
Apia
365
99
Nafanua
N/A
N/A
Afiamalu
751
129
Maota
276
56
Solomon Islands
Taro
143
69
Munda
218
78
Auki
456
159
Honiara
N/A
N/A
Henderson
222
106
Kira Kira
214
70
Santa Cruz, Lata
360
97
Tonga
Niuafo’ou
N/A
N/A
Mata’aho Airport
85
32
Lupepau’u
67
27
Salote Airport
139
90
Nuku’alofa
80
49
Fua’amotu Airport
84
53
Tuvalu
Nanumea
N/A
N/A
Nui Island
N/A
N/A
Funafuti
N/A
N/A
Nuilakita
N/A
N/A
Vanuatu
Sola
213
55
Pekoa
241
89
Lamap
104
67
Port Vila
197
104
Tanna/Whitegrass
255
N/A
Aneityum
264
156
The Island Climate Update, No. 100, January 2009
Page 5
Rainfall outlook map for January to March 2009
Tropical rainfall and SST outlook: January to March 2009
NOTE: Rainfall and sea surface termperature estimates for Pacific Islands for the next three months are given in the tables below. The tercile probabilities (e.g.,
20:30:50) are derived from the averages of several global climate models. They correspond to the odds of the observed rainfall or sea surface temperatures being in
the lowest one third of the distribution, the middle one third, or the highest one third of the distribution. For the long term average, it is equally likely (33% chance)
that conditions in any of the three terciles will occur. *If conditions are climatology, we expect an equal chance of the rainfall being in any tercile.
D
uring the January–March 2009 forecast period, a
region of suppressed convection is likely to encompass
the central and eastern Southwest Pacific, extending from
Western Kiribati to Eastern Kiribati, including Tuvalu, Tokelau,
the Northern Cook Islands, and the Tuamotu archipelago.
Below normal rainfall is expected. Near–to–below normal
rainfall is expected for Samoa.
Enhanced convection is expected to extend southeast from,
Vanuatu and New Caledonia, to the Austral Islands, includ-
ing Tonga, Fiji, Wallis & Futuna, and Niue, with above aver-
age rainfall projected. No precipitation guidance is offered
for Pitcairn Island, Papua New Guinea, the Solomon Islands,
the Marquesas, or the Society Islands for the three-month
forecast period.
SSTs are expected to be above normal in a band extending
from near Papua New Guinea, southeast to Vanuatu and New
Caledonia, including the Solomon Islands, and above normal
SSTs are also expected for Niue and Tonga. Near–to–above
normal SSTs are forecast for Fiji, the Southern Cook Islands,
the Society Islands, the Austral Islands, and Pitcairn Island.
Below normal SSTs are forecast for the northeastern sector
of French Polynesia, including the Tuamotu archipelago and
the Society Islands, Tuvalu, Tokelau, and Eastern Kiribati.
Western Kiribati is projected to have normal–to–below
normal SSTs.
The confidence in the forecast model skill for this seasonal
rainfall outlook is moderately high for most Pacific Island
countries. In the past, the average region-wide hit rate for
forecasts issued in January is 56%, 5% lower than the long-
term average for all months combined. The SST forecast
confidence is moderate–to–high for this period.
Island Group
Rainfall Outlook
Outlook confidence
Tonga
20:30:50 (Above)
Moderate-High
Vanuatu
20:30:50 (Above)
Moderate-High
Wallis & Futuna
20:30:50 (Above)
Moderate-High
New Caledonia
20:35:45 (Above)
Moderate-High
Austral Islands
20:35:45 (Above)
Moderate-High
Cook Islands (Southern)
20:35:45 (Above)
Moderate-High
Fiji
20:35:45 (Above)
Moderate-High
Niue
20:35:45 (Above)
Moderate-High
Papua New Guinea
35:35:30 (Climatology)
Moderate
Pitcairn Island
30:35:35 (Climatology)
Moderate-High
Solomon Islands
30:35:35 (Climatology)
Moderate
Marquesas
30:35:35 (Climatology)
Moderate-High
Society Islands
30:35:35 (Climatology)
Moderate-High
Samoa
35:40:25 (Near or Below)
Moderate-High
Cook Islands (Northern)
45:35:20 (Below)
High
Kiribati (Eastern)
45:35:20 (Below)
High
Tuamotu Islands
45:35:20 (Below)
High
Kiribati (Western)
45:40:15 (Below)
Moderate-High
Tokelau
55:30:15 (Below)
High
Tuvalu
55:30:15 (Below)
High
Australia
New Zealand
Fiji
New Caledonia
Vanuatu
Solomon Is
Pitcairn
Samoa
Tonga
Niue
E Kiribati
Papua New Guinea
N Cook Is
S Cook Is
Society Is
W Kiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Fed States of Micronesia
Tuamotu Is
EQUATOR
Wallis & Futuna
SST outlook map for January to March 2009
Island Group
SST Outlook
Outlook confidence
New Caledonia
20:35:45 (Above)
Moderate
Niue
20:35:45 (Above)
Moderate
Papua New Guinea
20:35:45 (Above)
Moderate
Solomon Islands
20:35:45 (Above)
Moderate
Tonga
20:35:45 (Above)
Moderate
Vanuatu
20:35:45 (Above)
Moderate
Austral Islands
25:35:40 (Near or above)
Moderate
Fiji
25:35:40 (Near or above)
Moderate
Society Islands
25:35:40 (Near or above)
Moderate
Wallis & Futuna
20:40:40 (Near or above)
Moderate-High
Cook Islands (Southern)
25:40:35 (Near or above)
Moderate-High
Pitcairn Island
25:40:35 (Near or above)
Moderate-High
Cook Islands (Northern)
35:40:25 (Near or Below)
Moderate-High
Samoa
35:40:25 (Near or Below)
Moderate
Kiribati (Western)
40:35:25 (Near or Below)
Moderate
Tokelau
40:35:25 (Near or Below)
Moderate-High
Tuamotu Islands
40:35:25 (Near or Below)
Moderate
Tuvalu
40:35:25 (Near or Below)
Moderate-High
Kiribati (Eastern)
45:35:20 (Below)
Moderate-High
Marquesas
45:35:20 (Below)
Moderate-High
Australia
New Zealand
Fiji
New Caledonia
Vanuatu
Solomon Is
Pitcairn
Samoa
Tonga
Niue
E Kiribati
Papua New Guinea
N Cook Is
S Cook Is
Society Is
W Kiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Fed States of Micronesia
Tuamotu Is
EQUATOR
Wallis & Futuna
Below
Above
Near
or above
Near
or below
Near
normal
The Island Climate Update, No. 100, January 2009
Page 6
Acknowledgements
This bulletin is produced by NIWA and made possible
with financial support from the New Zealand Agency
for International Development (NZAID), with additional
support from the Pacific Islands Applied Geosciences
Commission (SOPAC) and the Secretariat for the
Pacific Regional Environmental Programme (SPREP).
This summary is prepared as soon as possible following the
end of the month, once the data and information are received
from the Pacific Island National Meteorological Services
(NMHS). Delays in data collection and communication
occasionally arise. While every effort is made to verify
observational data, NIWA does not guarantee the accuracy
and reliability of the analysis and forecast information
presented, and accepts no liability for any losses
incurred through the use of this bulletin and its content.
The contents of The Island Climate Update may be freely
disseminated, provided the source is acknowledged.
Requests for Pacific Island climate data should be directed
to the Meteorological Services concerned.
Cover Photo:
Wendy St George,
NIWA
Visit The Island Climate Update at:
www.niwascience.co.nz/ncc/icu
Your comments and ideas about The Island Climate
Update are welcome. Please contact:
Project Director: Dr Jim Salinger, NIWA,
Private Bag 99940, Newmarket, Auckland,
New Zealand. E-mail:
j.salinger@niwa.co.nz
Forecasts:
Dr. Andrew Lorrey (South Pacific rainfall and SST forecasts) and
the NIWA National Climate Centre (ENSO)
ICU Editors:
Andrew Lorrey Email:
a.lorrey@niwa.co.nz
Jim Salinger Email:
j.salinger@niwa.co.nz
Harriet Palmer Email:
h.palmer@niwa.co.nz
Sources of South Pacific rainfall data
This bulletin is a multi-national project, with important
collaboration from the following Meteorological Services:
American Samoa, Australia, Cook Islands, Fiji, French
Polynesia, Kiribati, New Caledonia, New Zealand, Niue,
Papua New Guinea, Pitcairn Island, Samoa, Solomon
Islands, Tokelau, Tonga, Tuvalu, Vanuatu, Wallis and
Futuna.
The Centennial Issue of the Island Climate Update:
Progress and success resulting from a multi-model ensemble forecast
Andrew Lorrey, Jim Salinger, and James Renwick (NIWA)
T
he strength of the Island Climate Update (ICU) forecast is drawn
from two primary sources: a regional discussion about local climate
information by Pacific Island Meteorological Services members each
month, and external input from international research organisations
which produce forecasts and interpretations of global climate
diagnostics. The discussion in the ICU monthly teleconference
and the collection of climate models compose the backbone of
the ICU three-month forecast. There are more than ten climate
models that are used to generate the rainfall outlook for the South
Pacific. In 2008, an additional ensemble of SST forecasts, which
include six models, were added to the ICU to provide an additional
layer of information that could be useful for planning purposes.
The capability of the ICU multi-model ensemble rainfall forecasts
have been tracked for more than eight years now, and there
are statistical data indicating when the technique has had good
‘skill’, or the ability to provide accurate climate projections. It is
very clear that the ICU has good skill for a majority of the year,
and not suprising that the strongest forecast periods are during
spring and summer, as well as mid
–
winter. The period of least
skill is during mid
–
to
–
late autumn, which corresponds to the
time when deterioration of ENSO events typically happens, and
as a result the associated strong (as well as predictable) regional
climate patterns that accompany these events are diminished.
Monthly average strike rate statistics for the ICU (January 2001-October
2008)
The Island
Climate Update
Long term trend in ICU strike rate, January 2001-present
Many of the island groups in the South Pacific have important
spatial contrasts in their rainfall patterns. East
–
west as well as
north
–
south differences in precipitation anomalies are often
observed from month to month. The ICU forecast strike rate
statistics indicate that the use of the multi-model ensemble
approach to provide an overall rainfall forecast for each island group
is, however, better than a coin toss. This suggests the multi-model
ensemble approach has value complementary to local forecast
information generated by Pacific Island Meteorological Services.
Moreover, the long-term trend in the ICU data indicates that the
average strike rate has gradually increased by nearly 10% over
the last eight years, at an average rate of about +1% each year.
Since the ICU inception in 2000, the practice has been to include
additional models that cover the South Pacific region as they come
on-line. These additions, along with continual improvements
made to models already in use, have likely improved the skill of
the regional-scale multi-model ensemble forecast. Key highlights
were achieving a global strike rate for the South Pacific of 90%
(August
–
October 2007) and 91% (September
–
November 2008).
Beginning in 2008, a detailed compilation of the strikerates for
the individual global climate models that are used in the ICU was
initiated. This was done to assist Pacific Island Meteorological
Services in their search for and refinement of the collection of
models that could be used for island-specific forecasts. Future
training sessions, selection of specific models, and discussions
about the multi-model ensemble are anticipated to increase the
skill of this powerful approach to regional climate forecasting
.
30
40
50
60
70
80
90
100
Jan-01
Jan-05
Jan-07
Jan-03
Jan-09
S
t
r
i
k
e r
a
t
e (
%
)
When forecast was produced
ICU rainfall forecast skill
45
50
55
60
65
70
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month forecast produced
Strike rate (%)