Strong Positive Phase of the Indian Ocean Dipole Back in the Forecast

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Positive Phase Indian Ocean Dipole to Re-Intensify

Discussion: The Australian Bureau of Meteorology has updated their Indian Ocean Dipole outlook which indicates a robust positive phase evolving for AUG/SEP/OCT 2019 (Fig. 1). During the positive phase of the Indian Ocean dipole the central and western tropical Indian Ocean is warmer than normal which leads to anomalous thunderstorm activity in that region. Downstream from the convective currents fueling thunderstorms there is subsidence in the atmosphere having a drying effect on climate and coupled with cool waters just west and northwest of Australia a dry climate emerges (for Australia).

Fig. 1: The Australian Bureau of Meteorology Australia forecasts +IOD.

Recent analog years when +IOD has been in-place include 2006, 2012 and 2015. During AUG/SEP/OCT of the analog years the consensus upper air pattern across Asia featured a vigorous upper trough over West-central Russia (and a hot ridge over Europe) while an amplified ridge also affected Northeast Asia (Fig. 2). In Australia an intense upper ridge affected Southern Australia (Fig. 3) yielding anomalous warmth for much of the continent and dryness across eastern sections.

Summary: Given the weak ENSO regime which has evolved in recent weeks signaling an end to El Nino the influence of a developing robust positive phase of the Indian Ocean Dipole may reign as the leading climate influence for AUG/SEP/OCT on Asia and Australia. Based on analogs (+IOD in 2006, 2012 and 2015)  the prevailing climate across Asia features a cool trough over West-central Russia and amplified upper ridge over Northeast Asia. Cool temperatures are likely in Western Russia while upstream Europe sits beneath a hot upper ridge. Northeast Asia turns hot. In Australia an upper ridge pattern brings dryness to Eastern Australia and anomalous warmth everywhere but the far northern areas.

Fig. 2: The upper air projection across Asia based on influence of +IOD for AUG/SEP/OCT.

Fig. 3: The upper air projection across Australia based on influence of +IOD for AUG/SEP/OCT.