Weekly Tropical Climate Note

Issued on Tuesday 22 July 2014

Third typhoon in northwest Pacific Ocean this month

Typhoon Matmo (Henry) formed over the Philippine Sea on 17 July and reached typhoon strength (average winds greater than 118 km/h) on 19 July, becoming the third typhoon in the northwest Pacific this month. Typhoon Neoguri (Florita) made landfall over southern Japan on 10 July and Typhoon Rammasun (Glenda) made landfall over both the Philippines and China within the past week. On average, 3.9 tropical storms (sustained winds greater than 64 km/h) including 2.5 typhoons form over the north-western Pacific in July (based on Joint Typhoon Warning Centre climatology from 1959-2012). Sea surface temperatures (SSTs) in the northwest Pacific Ocean are currently greater than 28°C, which provides an ideal environment for tropical cyclones to form.

The variability of the South-East Asian monsoon, including the formation of tropical cyclones, is usually influenced by the Madden-Julian oscillation (MJO). However, the MJO has been weak and at times indiscernible over the past five weeks and therefore is unlikely to have been a significant contributor to the recent typhoon activity. Most model forecast of the MJO predict it will remain weak for the next 10 to 14 days with only one model forecasting a strong MJO signal over the west Pacific this week.

See the Bureau's MJO Monitoring for more information on location and tracking of the MJO.

Indian Ocean Dipole event possible in 2014

The Indian Ocean is currently showing a negative Indian Ocean Dipole(IOD) like pattern, with warmer than normal SSTs in the east near the equator and cooler than normal SSTs in the tropical west. This pattern has been in place since mid-June. The Bureau's IOD index reflects this observed SST pattern and is currently below -0.4°C; if values of below -0.4°C; persist until early August, 2014 will be considered a negative IOD year. However, most climate models indicate the IOD index will return to neutral levels over the coming months. Only one model suggests a negative IOD event will develop fully.

Under favourable weather conditions tropical moisture from a warm Indian Ocean can be pulled over continental Australia producing bands of cloud over northwest and central Australia. The negative IOD like pattern in the Indian Ocean may have contributed to the above-average rainfall experienced in southeast Australia during June and over the Kimberley and Pilbara in July. It is also possible that the negative IOD pattern in the Indian Ocean has contributed to this season's weaker than usual southeast Indian monsoon.

El Niño remains on hold

Warming of the tropical Pacific Ocean over the past several months has primed the climate system for an El Niño in 2014. However, a general lack of atmospheric response over the last month has resulted in some cooling of the tropical Pacific Ocean. The majority of climate models surveyed by the Bureau still suggest El Niño remains likely for late 2014; however, most have eased their predicted strength. If an El Niño were to occur, it is increasingly unlikely to be a strong event.

The ENSO Tracker is currently at El Niño ALERT stage.

See the Bureau's ENSO Wrap-Up for official information about the current state of the El Niño-Southern Oscillation, and to learn more about El Niño.

Next update expected by 29 July 2014| Product Code IDCKGEW000

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