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Island Climate Update 131 - August 2011

An overview of the present climate in the tropical South Pacific Islands, with an outlook for the coming months, to assist in dissemination of climate information in the Pacific region 

Introduction

El Niño/Southern Oscillation (ENSO)

  • La Niña in the equatorial Pacific region has ended, and conditions arein the neutral range. Many dynamical and statistical climate models suggest ENSO neutral conditions will exist during austral winter and into spring.

Summary of tropical cyclone activity for 2010-11 season

El Niño/Southern Oscillation (ENSO)

The tropical Pacific is in an ENSO–neutral state. TheNINO3 and NINO4 indices for July changed little from June, and were +0.4°C and +0.1°C respectively (3–month means +0.4 and 0.1°C).

Sub–surface temperature anomalies are positive in the top 50–100 m across the Equatorial Pacific, but have weakened slightly. The positive SST anomaly "horseshoe" from the recent La Niña is still evident at about 40 degrees latitude in both hemispheres at 160W. The former equatorial 'cold tongue' has itself become a 'horseshoe' as the equatorial SSTs have become slightly warmer than normal.

Summary of SW Pacific TC activity for the 2010 -11 season

The tropical cyclone season for 2010–11 has now closed.The ICU forecast for this season inidcated normal or above normal tropical cyclone (TC) activity for most islands west of the International Date Line in the southwest Pacific, with reduced activity east of the International Date Line due to La Niña conditions in the equatorial and tropical Pacific. A total of nine to 12 named TCs were forecast for the southwest Pacific (between 135°E to 120°W) for the period November 2010 through April 2010. 

Tropical rainfall and SST outlook: August to October 2011

Signals in the global climate models continue to showeasing of the rainfall anomalies associated with La Nina that existed earlier in the year. During August – October suppressed convection is expected in the southwest Pacific near Tuvalu, the Northern Cook Islands, and Pitcairn Island, which are expected to receive near normal or below normal rainfall. Above normal rainfall is forecast for Tonga, Niue, and Papua New Guinea. Near or above average rainfall is forecast for Vanuatu, Fiji, the Solomon Islands, the Austral Islands, New Caledonia, and the Southern Cook Islands.