The dynamical models continue to indicate slightly drier conditions than normal in the far eastern Pacific south of the Equator, while the November 2013 to January 2014 period is forecast to be slightly wetter than normal in the western Pacific along and north of the Equator as well as in the central Pacific south of the Equator.
Near or above normal rainfall is forecast for Fiji, the Southern Cook Islands, the Federated States of Micronesia, Papua New Guinea and Tonga.
Near normal rainfall is expected for the Austral Islands, the Northern Cook Islands, New Caledonia, Niue, Samoa, the Society Islands, Tokelau, Vanuatu and Wallis & Futuna.
Normal or below normal rainfall is forecast for Western Kiribati, Pitcairn Island, Tuvalu, Eastern Kiribati, the Marquesas and the Tuamotu Archipelago.
The global model ensemble forecast for SST indicates that the region of higher than normal temperatures in the central and eastern Pacific that has been present over the past six months (see figure on page 2) is likely to persist over November 2013 – January 2014. Several models also forecast slightly warmer than normal SSTs in the equatorial western Pacific.
Near or above average SST is forecast for Fiji, Tonga, Niue, the Southern Cook Islands, Western Kiribati, Niue and the Federated States of Micronesia. Near normal sea surface temperatures are expected elsewhere.
The confidence for the rainfall outlook is generally high, except for Eastern Kiribati and Western Kiribati and Samoa, where uncertainty is greater. The average region–wide hit rate for rainfall forecasts issued in November is 66 %, 3 % higher than the long–term average for all months combined.
The confidence is generally high for the SST forecasts, expect for the far eastern Pacific, around Eastern Kiribati and the Marquesas.
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 2013 - January 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.
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 1998 – 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".
