The dynamical model forecasts indicate that the central equatorial as well as some parts of the southeast Pacific are likely to experience normal or above normal rainfall in February – April 2015. In contrast, regions in the southwest as well as east Pacific are expected to experience reduced rainfall. Normal or below normal rainfall is forecast for Fiji, the Marquesas, New Caledonia and Vanuatu.
Normal or above normal rainfall is forecast for Western Kiribati, Samoa, Tokelau, Tuvalu, the Austral Islands and the Society Islands. Near normal rainfall is expected for the Northern Cook Islands, the Southern Cook Islands, Eastern Kiribati, Niue, Pitcairn Island, Tonga, the Tuamotu archipelago, Wallis & Futuna and the Federated States of Micronesia. No clear guidance is available for Papua New Guinea and the Solomon Islands.
The global model ensemble forecast for SSTs indicates higher than normal SSTs over the equatorial Pacific, with maximum anomalies east of the International Dateline. Above normal SSTs are also forecast to persist in the Tasman sea. Normal or above normal SSTs are forecast for Western Kiribati, Eastern Kiribati, Tokelau and Tuvalu. Normal or below normal SSTs are forecast for Pitcairn Island.
Near normal SSTs are forecast for Fiji, the Marquesas, Niue, Papua New Guinea, Samoa, the Society Islands, Tonga, the Tuamotu archipelago and Vanuatu. No guidance is available for the Austral Islands, the Federated States of Micronesia, New Caledonia, the Northern Cook Islands, the Solomon Islands, the Southern Cook Islands and Wallis and Futuna.
The confidence for the rainfall outlooks is moderate to high. The average region–wide hit rate for rainfall forecasts issued for the February – April season is 63 %, one point higher than the average for all months combined. The confidence for the SSTs 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 June-August 2014 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".
