The dynamical models forecasts indicate that the western equatorial Pacific as well as parts of the Maritime Continent are likely to experience normal or above-normal rainfall for the November 2014 - January 2015 season as a whole.
In contrast, parts of the south Pacific - from New Caledonia to Tonga - and the eastern Pacific from the northern Cook Islands to the Marquesas are expected to experience reduced rainfall.
Normal or below normal rainfall is forecast for the Northern Cook Islands, New Caledonia, Tonga, Fiji, the Marquesas and Vanuatu.
Normal or above normal rainfall is forecast for western Kiribati, Papua New Guinea, the Solomon Islands and the Austral Islands
Near normal rainfall is expected for the Southern Cook Islands, Niue, Pitcairn Island and Samoa.
No clear guidance is available for Eastern Kiribati, Tokelau, the Society Islands, the Tuamotu archipelago, Tuvalu and the Federated States of Micronesia.
The global model ensemble forecast for SSTs indicate higher than normal SSTs over the whole Equatorial Pacific, with maximum anomalies just west of the International Dateline.
Above normal SSTs are forecast for western Kiribati. Normal or above normal SSTs are forecast for the Austral Islands, eastern Kiribati, the Federated States of Micronesia, Papua New Guinea, Samoa, the Society Islands, the Solomon Islands, Tokelau and Tonga.
Near Normal SSTs are forecast elsewhere, except for Fiji, the northern Cook Islands, the southern Cook Islands, Tuvalu and Wallis & Futuna, for which no guidance is available (i.e. equal chances are given to each tercile).
The confidence for the rainfall outlook is moderate to high, but as usual moderate confidence is attached to the climatological forecasts.
The average region–wide hit rate for rainfall forecasts issued for the November - January season is 65 %, one point higher than the average for all months combined. Confidence for the SST forecasts is generally high.
The figure on the bottom right presents the last six months rainfall anomalies for each Island group alongside the latest ICU rainfall forecast for the November 2014 – January 2015 period.
The past 6 months rainfall anomalies are based on the near-real-time TRMM (Tropical Rainfall Measurement Mission) merged satellite product available from http://trmm.gsfc.nasa.gov. The data has been downloaded and available on the link below:
For each Island group, the monthly value is derived from the average of all grid-points (or "pixels") in the TRMM Dataset that intersect a coastline, to ensure that the values correspond as closely as possible to rainfall on land, and excluding rainfall falling on ocean surfaces.
The climatology used has been established over the 2001 – 2012 period. The categories ("Well-below", "Below", etc) are determined according to the percentage of the normal rainfall for that month. The thresholds are indicated in the colorbar at the bottom: to give an example, "Well-below" normal rainfall means the rainfall for that month was under 40 % of the normal rainfall, "Below" normal rainfall means that between 40 and 80 % of normal rainfall was received, etc.
IMPORTANT NOTE:
Please note that, while we use the same color-scheme for the past rainfall anomalies and the ICU forecast, the type of information presented is different. In the case of the past 6 months, actual rainfall has been estimated by satellite, and the categories are well-defined by monthly estimated rainfall compared to the long-term mean. The ICU forecast, on the other hand, is probabilistic: it indicates the likelihood (percentage chance) of rainfall being at, above, or below normal for the season as a whole. When the percentage chances in two categories are close to each other, we indicate both categories: for example if the forecast is for 35 % chance of receiving below rainfall, and 40 % chance of normal rainfall, the outcome is "Normal or below".
