Number 104, May 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
April’s climate
•
The South Pacific Convergence Zone (SPCZ) shifted in April, with
only the eastern end positioned southwest of normal.
•
Very suppressed convection near Western Kiribati and south of the
Equator extending east through Nauru and Eastern Kiribati.
•
Mostly well above normal rainfall for Tuvalu and Niue.
El Niño/Southern Oscillation (ENSO), seasonal
rainfall, and sea surface temperature forecasts
•
La Niña-like conditions have existed in the tropical Pacific in
previous months, but most climate models project ENSO neutral
conditions for autumn and winter 2009.
•
Below normal rainfall is forecast for Tuvalu, Tokelau, and the
Northern Cook Islands.
•
Above normal rainfall is expected for Vanuatu, Fiji, Niue, the
Southern Cook Islands, and Papua New Guinea.
•
SST anomalies are expected to weaken in the region. Normal or
above normal SSTs are forecast for the southwestern half of the
southwest Pacific region. Normal or below normal SSTs are forecast
near the Tuamotu Archipelago.
The Island Climate Update, No. 104, May 2009
Page 2
Climate developments in April 2009
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 April 2009 position of the South Pacific Convergence Zone (SPCZ)
was partly displaced northeast and southwest of its normal position,
and exhibited coherent regions of high values near the Austral Islands.
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.
-90 -70 -50 -30 -20 -10 10 20 30 50 70 90
Australia
NewZealand
Fiji
NewCaledonia
Vanuatu
Solomon Is
Pitcairn
Samoa
Tonga
Niue
EKiribati
Papua NewGuinea
NCook Is
S Cook Is
Society Is
WKiribati
Line Is
Tuvalu
Marquesas Is
Austral Is
Marshall Is
Rawaki Is
Tokelau Is
Nauru
Fed States of Micronesia
Tuamotu Is
EQUATOR
Wallis & Futuna
Soil moisture in April 2009
Estimated soil moisture conditions at the end of April 2009, 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.
Hanan (Niue), Rarotonga (Southern Cook Islands), Apia
(Samoa) and Fua’amotu (Tonga) project moist (at or near field
capacity) soil moisture conditions. Soils are moderate for the
time of year at Nadi (Fiji), and dry at Tarawa (Kiribati).
T
he South Pacific Convergence Zone (SPCZ) shifted east
during April, with the northwestern part of the convective
spur moving northeast of normal. However the southeastern
portion of the SPCZ remained displaced southwest of its
normal position for the month, contributing to high rainfall
in the Austral Islands. A region of enhanced rainfall, partly
due to intensified convection, was also observed in the north
Tasman Sea and near New Caledonia last month. Suppressed
convection intensified near the Solomon Islands during April
and persisted in a zone including Western Kiribati, Nauru,
and Eastern Kiribati. There was also suppressed convection
localised near the Pitcairn Islands and Society Islands. The
regional circulation in April was characterised by more
frequent low pressure in the North Tasman Sea and to the
northeast of New Zealand, over the Austral Islands.
There were not many high precipitation totals concentrated
in any particular island group in the southwest Pacific
during April. In French Polynesia dry conditions occurred
over Tuamotu, Gambier, and the Society Islands, which
also experienced above normal pressures for the month.
A record daily maximum temperature was also recorded
at Rapa (30.3°C), located at the southeastern end of the
Austral Islands. Nearby in the Southern Cook Islands, near
normal rainfall occurred at Rarotonga. Most stations in Fiji
were normal or below normal for rainfall during April, the
exception being Ono–i–lau which received 403mm of
rainfall (257% of normal). Western Kiribati continued to have
dry conditions, and Butaritari, Tarawa, and Kanton all had
below normal rainfall during April.
There were also some localised high rainfall totals in the
central and southeastern parts of the southwest Pacific.
Northern New Zealand experienced a relatively dry month,
but the Far North of the country recorded well above normal
normal rainfall (257% of normal). Wallis and Futuna also
reported very high rainfall totals during April (see table
below). Lord Howe Island was one exception for month,
recording 515mm of rainfall (318% of normal) that was the
result of a sub-tropical low. In Tonga, nearly 200% of normal
rainfall fell at Lupepau’u. Monthly rainfall totals were also well
above normal in Tuvalu, which had 140 – 190% of normal
recorded at Nui and Funafuti, respectively. 610mm of rain
(263% of normal) fell at Rapa in the Austral Islands, which
was the second highest amount reported in the region last
Wet
Moderate
Dry
Wet
Moderate
Dry
Wet
Moderate
Dry
Wet
Moderate
Dry
April 2009
April 2008
Island Group
Location
Rainfall
(mm)
% of
avg
Comments
Wallis
Wallis Island
572
233
Record high
Futuna
Maopoopo
746
225
Highest monthly
total in the region
Tonga
Lupepau’u
413
198
High
Tuvalu
Nui Island
478
199
High
North Tasman
Lord Howe
Island
515
318
High
Austral Islands
Rapa
610
263
High
month. The high rainfall totals for these two island groups
was the result of SPCZ activity during April.
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. 104, May 2009
Page 3
Mean sea surface temperatures (ºC) for April 2009
Sea surface temperature anomalies (ºC) for April 2009
Forecast validation: February to April 2009
-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
10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0
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 April, the equatorial Pacific Ocean
returned to ENSO-neutral conditions, after
exhibiting a La Niña state since December 2008.
NINO3 and NINO4 SST anomalies are now close to
zero: +0.1°C and –0.1°C respectively (February –
April means both around –0.4°C). Sea surface height
anomalies still remain positive in the western Pacific,
but show a north–south banded structure in the east,
with positive anomalies along the Equator east of the
Date Line.
Equatorial subsurface ocean temperature anomalies
are now positive in the uppermost 100m near the
South American coast, as well as in the uppermost
200m west of the Date Line.The easterly trade winds
strengthened in April, west of the Date Line, but
eased late in the month, with westerly anomalies
evident at the end of April. Consistent with this, the
TRMM ENSO precipitation index strengthened to
–1.8 in April. However, tropical Pacific convection/
OLR does not exhibit a clear La Niña pattern, though
convection is suppressed near the Equator, east of
150°E.
The MJO was active in April, with an event
propagating steadily across the Maritime Continent
and the western Pacific in the last two weeks of
the month. This presumably contributed to the
strengthening of the SOI, which rose again in April to
+1.0, after falling to –0.2 in March (February – April
mean was +0.7). The MJO is expected to weaken
over the coming weeks.
The global climate model ensemble assessed by
NIWA indicate neutral conditions on average will
prevail during May – July. Almost all models show
warming over the next few months, with three
suggesting El Niño conditions later in 2009. The
NCEP discussion of 9 April suggests a transition to
neutral conditions during May, with La Niña-like
impacts lingering through June. The IRI summary
A
a region of suppressed convection was forecast to
encompass the central and eastern Southwest Pacific,
extending to the southeast from Western Kiribati and
including Tuvalu, Tokelau, the Northern Cook Islands,
and the Society Islands, where below normal rainfall is
expected. Near–to–below normal rainfall was expected for
Samoa, Eastern Kiribati, the Tuamotu archipelago, and the
Marquesas Islands. Enhanced convection was expected to
extend southeast from, Papua New Guinea, and include New
Caledonia, Tonga and Niue, where above normal rainfall
was expected. Near or above normal rainfall was forecast
for the Austral Islands, Fiji, the Southern Cook Islands, and
Pitcairn Island. No clear precipitation guidance was offered
for the Solomon Islands or Wallis & Futuna for the three-
month forecast period.
The February – April 2009 forecast validation was calculated
for 15 island groups (three countries did not report
rainfall values; two were forecast as climatology and were
unscorable). The global island group ‘hit’ rate was 85%, 22%
higher than average, and 24% higher than the average for all
months combined. Rainfall was overprojected for Tonga.
of 15 April indicates a 75% chance of neutral conditions
persisting through to June and remaining the most likely
ENSO state for the rest of 2009.
Tropical Cyclone Activity and Guidance
O
nly one Tropical Cyclone (TC) formed in the Southwest Pacific region during April. TC Lin formed on 4 April east of
Fiji and moved towards Tonga, passing over Tongatapu on 5 April. Sustained winds for TC Lin were estimated to be
55 knots with gusts up to 80 knots close to the storm centre. One significant tropical depression also occurred near Lord
Howe Island, and was active from 16-25 April. This system reached a Category One status on 19 April as it passed over the
island, with maximum wind gusts of 149km/h recorded at that time. A one day rainfall total of 230mm from this storm was
recorded on 20 April.
The Island Climate Update, No. 104, May 2009
Page 4
Tropical Pacific rainfall – April 2009
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
April 2009
rainfall
total (mm)
April 2009
percent of
average
Australia
Cairns Airport
134
71
Townsville Airport
51
82
Brisbane Airport
60
67
Sydney Airport
153
156
Cook Islands
Penrhyn
N/A
N/A
Aitutaki
N/A
N/A
Rarotonga Airport
199
94
Fiji
Rotuma Island
277
94
Udu Point
216
78
Nadi Airport
73
46
Nausori
157
44
French Polynesia
Hiva Hoa, Atuona
211
121
Bora Bora
99
54
Tahiti – Faa’a
31
27
Tuamotu, Takaroa
81
68
Gambier, Rikitea
72
48
Tubuai
187
103
Rapa
610
263
Kiribati
Tarawa
29
15
Kanton
3
2
New Zealand
Kaitaia
244
257
Whangarei Airport
87
74
Auckland Airport
41
43
New Caledonia
Ile Art, Belep
N/A
N/A
Koumac
106
163
Ouloup
54
56
Ouanaham
95
74
Poindimie
237
98
La Roche
69
51
La Tontouta
55
90
Noumea
85
83
Moue
200
163
Territory and
station station
name
April 2009
rainfall
total (mm)
April 2009
percent of
average
Niue
Hanan Airport
439
195
Liku
219
116
North Tasman
Lord Howe Island
515
318
Norfolk Island
86
61
Raoul Island
111
109
Samoa
Faleolo Airport
191
N/A
Apia
311
N/A
Nafanua
351
N/A
Afiamalu
477
N/A
Maota
N/A
N/A
Solomon Islands
Taro
304
90
Munda
108
38
Auki
270
106
Honiara
183
81
Henderson
179
112
Kira Kira
120
36
Santa Cruz, Lata
309
97
Tonga
Niuafo’ou
320
127
Mata’aho Airport
238
92
Lupepau’u
413
198
Salote Airport
N/A
N/A
Nuku’alofa
128
78
Fua’amotu Airport
249
157
Tuvalu
Nanumea
139
58
Nui Island
478
199
Funafuti
377
140
Nuilakita
250
104
Vanuatu
Sola
219
47
Pekoa
358
119
Lamap
223
113
Port Vila
N/A
N/A
Tanna/Whitegrass
55
N/A
Aneityum
156
81
The Island Climate Update, No. 104, May 2009
Page 5
Rainfall outlook map for May to July 2009
Tropical rainfall and SST outlook: May to July 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 May – July 2009, a region of suppressed convection
is likely in the southwest Pacific encompassing Tokelau,
Tuvalu, and the Northern Cook Islands, with below average
rainfall expected for those areas. Near to below average
rainfall is expected for Eastern Kiribati and the Marquesas.
Near normal rainfall is forecast for Pitcairn Island and Samoa.
Enhanced convection is likely in the area around Papua
New Guinea and Vanuatu, Fiji, Niue, and the Southern
Cook Islands, with above average rainfall anticipated for the
coming three month period. New Caledonia, Tonga, Wallis &
Futuna, and the Austral Islands are expected to receive near
or above average rainfall. No clear precipitation guidance
is offered for the Western Kiribati, the Solomon Islands, the
Tuamotu Archepelago and the Society Islands
Prominent SST anomalies that existed in the region during
that past months are now easing. Global models indicate
significant shifts to near-neutral SSTs during Austral winter,
but lingering anomalies related to the past La Nina event
may exist. Above average SSTs are expected for Papua
New Guinea, and near or above average SSTs are forecast
for Western Kiribati, the Solomon Islands, Vanuatu, Fiji,
Niue, New Caledonia, Tonga, Samoa, Niue, the Southern
Cook Islands, the Austral Islands, and Pitcairn Island. Near
normal SSTs are forecast for Samoa, Tokelau, Tuvalu, the
Northern Cook Islands, Wallis and Futuna, and the Society
Islands. Average to below average SSTs are expected for the
Tuamotu Archipelago. No clear SST guidance is provided for
the Marquesas or Eastern Kiribati.
The confidence in the multi-model ensemble forecast skill
for this seasonal rainfall outlook is moderately high for most
Pacific Island countries. In the past, the average region-
wide hit rate for rainfall forecasts issued in May is 53%, 8%
lower than the long-term average for all months combined.
Island Group
Rainfall Outlook
Outlook confidence
Cook Islands (Southern)
20:35:45 (Above)
Moderate-High
Vanuatu
20:35:45 (Above)
Moderate-High
Niue
20:35:45 (Above)
Moderate-High
Papua New Guinea
20:35:45 (Above)
Moderate-High
Fiji
25:35:40 (Near or Above)
Moderate-High
New Caledonia
25:35:40 (Near or Above)
Moderate-High
Tonga
25:35:40 (Near or Above)
Moderate-High
Austral Islands
25:35:40 (Near or Above)
Moderate-High
Wallis & Futuna
25:40:35 (Near or Above)
Moderate
Pitcairn Island
30:40:30 (Near normal)
Moderate
Samoa
30:40:30 (Near normal)
Moderate
Kiribati (Western)
30:35:35 (Climatology)
Moderate-High
Solomon Islands
30:35:35 (Climatology)
Moderate
Society Islands
35:35:30 (Climatology)
Moderate
Tuamotu Islands
35:35:30 (Climatology)
Moderate-High
Kiribati (Eastern)
40:40:20 (Near or Below)
Moderate-High
Marquesas
40:35:25 (Near or Below)
Moderate
Cook Islands (Northern)
45:35:20 (Below)
Moderate-High
Tokelau
45:35:20 (Below)
Moderate-High
Tuvalu
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
NO
FORECAST
SST outlook map for May to July 2009
Island Group
SST Outlook
Outlook confidence
Papua New Guinea
20:35:45 (Above)
Moderate-High
Austral Islands
25:35:40 (Near or Above)
Moderate-High
Cook Islands (Southern)
25:35:40 (Near or Above)
Moderate-High
Fiji
25:35:40 (Near or Above)
Moderate-High
New Caledonia
25:35:40 (Near or Above)
Moderate-High
Niue
25:35:40 (Near or Above)
Moderate-High
Solomon Islands
25:35:40 (Near or Above)
High
Vanuatu
25:35:40 (Near or Above)
Moderate-High
Kiribati (Western)
25:40:35 (Near or Above)
High
Pitcairn Island
25:40:35 (Near or Above)
High
Tonga
25:40:35 (Near or Above)
Moderate-High
Cook Islands (Northern)
30:40:30 (Near normal)
High
Samoa
30:40:30 (Near normal)
High
Society Islands
30:40:30 (Near normal)
High
Tokelau
30:40:30 (Near normal
)
High
Tuvalu
30:40:30 (Near normal
)
High
Wallis & Futuna
30:40:30 (Near normal)
High
Kiribati (Eastern)
35:35:30 (Climatology)
Moderate
Marquesas
35:35:30 (Climatology)
Moderate
Tuamotu Islands
35:40:25 (Near or 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
Below
Near or
below
Near
normal
Near or
above
Above
NO
FORECAST
The SST forecast confidence is moderate–to–high for this
period.
The Island Climate Update, No. 104, May 2009
Page 6
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.
Web links to ICU partners:
South Pacific Meteorological Services:
Cook Islands
http://www.cookislands.pacificweather.org/
Fiji
http://www.met.gov.fj
Kiribati
http://pi-gcos.org/index.php (follow link to PI Met
Services then Kiribati Met Service)
New Zealand
http://www.metservice.co.nz/
Niue
http://pi-gcos.org/index.php (follow link to to PI Met
Services then Niue Met Service)
Papua New Guinea
http://pi-gcos.org/index.php (follow link to to PI Met
Services then Papua New Guinea Met Service)
Samoa
http://www.mnre.gov.ws/meteorology/
Solomon Islands
http://www.met.gov.sb/
Tonga
http://www.met.gov.to/
Tuvalu
http://tuvalu.pacificweather.org/
Vanuatu
http://www.meteo.gov.vu/
International Partners
Meteo-France
New Caledonia: http://www.meteo.nc/
French Polynesia: http://www.meteo.pf/
Bureau of Meteorology (Australia)
http://www.bom.gov.au/
National Oceanographic and Atmospheric Administration
(USA)
National Weather Service: http://www.nws.noaa.gov/
Climate Prediction Center: http://www.cpc.noaa.gov/
The International Research Institute for Climate and
Society (USA):
http://portal.iri.columbia.edu/portal/server.pt
The UK Met Office
http://www.metoffice.gov.uk/
European Centre for Medium-term Weather Forecasts
http://www.ecmwf.int/
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:
Dr Andrew Lorrey, NIWA,
41 Market Place, Auckland, New Zealand
E-mail:
a.lorrey@niwa.co.nz
Forecasts:
Dr. Andrew Lorrey (South Pacific rainfall
and SST forecasts) and the NIWA National
Climate Centre (ENSO wrap)
ICU Editors:
Andrew Lorrey Email:
a.lorrey@niwa.co.nz
James Renwick Email:
j.renwick@niwa.co.nz
Harriet Palmer Email:
h.palmer@niwa.co.nz
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.
The Island
Climate Update