BOM:Weekly tropical Note 21.02.

[Crostorm]

Weekly Tropical Climate Note
Issued on Tuesday 21 February 2012
La Niña continues, but the Pacific warms
Sea surface temperatures (SSTs) in the tropical Pacific Ocean have continued to warm during the previous week. Despite this, the typical La Niña pattern remains, although weaker, with the NINO3.4 index currently at –0.5 °C.
The 30-day Southern Oscillation Index (SOI) also weakened over the past week dropping from last’s week +12.0 value to +8.0 on 18 February. The contributing atmospheric pressures were 0.9 hPa above normal at Tahiti and 0.7 hPa below normal at Darwin. The monthly SOI for January was +9.4. The 5-month running mean (centred on November) was +13.0.
Although both oceanic and atmospheric indices show signs of weakening, cloudiness near the Date Line continues to be below average, while convection across the South Pacific Convergence Zone (SPCZ) was greatly reduced over the past week. In contrast, enhanced convection was dominant over the South China and Philippines Seas.
Forecast models surveyed by the Bureau suggest this La Niña event will gradually decline over the coming months. However, it will continue to play a mayor role on Australian climate until the end of the north Australian wet season (end of April).
La Niña periods are typically associated with above average rainfall across northern Australia during the wet season. Tropical cyclone activity is usually above average between November and April, with six named systems across the Australian longitudes since November 2011.
See the Bureau's ENSO Wrap-Up which includes a compilation of ENSO computer model predictions.
The monsoon looms as drier conditions continue
Drier conditions continued over northern Australia as the North Australian Monsoon (NAM) remains in a break period. Agreement between the models continues, suggesting the MJO will remain strong over the next fortnight as it progresses across the Indian Ocean. Current guidance suggests it will not be back in Australian longitudes until the last few days in February or early March.
Over the next week and under the current scenario, drier than average conditions are expected to continue across northern Australia. Humidity levels across far northern Australia are expected to increase while daytime temperatures in central Australia continue to hit the high 30s and low 40s.
A weak trough is now developing over the southern Maritime Continent. A stronger signature of the NAM is expected to develop over the eastern Indian Ocean and the Coral Sea next week. With a developing NAM, the chance of tropical cyclones forming in the Australian longitudes is expected to increase over the next fortnight.
See the Bureau's MJO Monitoring for more information, including rainfall maps.
Next update expected by 28 February 2012 | Product Code IDCKGEWOOO

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