NIWA said sea surface temperatures in the central and eastern part of the ocean cooled substantially in October, while tradewinds in the west have been stronger than normal.
It said the tropical Pacific has consistent La Niña like signals in both the ocean and atmosphere.
However, if one does eventuate, it is likely to be weak and short-lived.
NIWA said Tonga, Samoa, Fiji and Niue can expect above normal rainfall, while rainfall in Tuvalu, eastern Kiribati, the northern Cook Islands, the Marquesas, central and western Kiribati and Nauru is forecast to be below normal.
Much of Kiribati is already in the grip of a developing drought.
Photo source SPREP