Weekly Tropical Climate Note at 1229 CST

Tuesday 11 February 2003

El Nino-Southern Oscillation Update The real-time SOI changed marginally from -3 to -2. Darwin's pressure anomaly rose slightly to +0.6 hPa [+0.5 last week], while Tahiti's rose to +0.2 hPa [-0.1 last week]. SSTs in the RSMC* tropical oceans are now close to the climatological norm. The warm SST anomalies in the equatorial Pacific are continuing to ease, with all anomalies less than the +2 degrees. The Nino 3.4, Nino 3 and 4 indices all show some falls in recent weeks and are close to zero. Weak westerly wind anomalies at lower levels and easterly anomalies in the upper levels are still found around the date-line near the equator.

Nine out of the 11 available model predictions updated during January indicate neutral conditions by June 2003 [five months lead]. These predictions are broadly consistent with the observations that El Nino tends to break down in late summer or autumn. Of the nine predictions available at eight months [September 2003], six favour neutral conditions with two indicating cool conditions. However, the skill of the forecasts is generally low between March and June. For a summary and links to individual models see http://www.bom.gov.au/climate/ahead/ENSO-summary.shtml.

Intra-Seasonal Patterns Active convection continues over the western part of the RSMC* and has developed over western Indonesia. TC Fiona formed near 110E, moving westward over the past 5 days. TC Beni redeveloped slightly off the coast of Queensland before crossing the coast as a rain depression. Activity near the date-line has moved further east with the development of TC Dovi near 170W. A good low level cross equatorial flow and a decent upper level divergent field persisted over the region. Weekly averaged OLR plots show increased activity extending into western Australian longitudes and weakening of activity east of 150E. Scattered convection has started in the past few days about the north Australian coastline after an extensive period of suppression. Synoptic charts maintain the near equatorial trough in the northern hemisphere, particularly east of 120E. The monsoon trough is clearly represented in the southern hemisphere westward of TC Fiona, with new development over western Indonisia in the past day as TC Fiona moves further westward.

Time-longitude plots of 200 hPa velocity potential in the southern and equatorial belts show a persistence of enhanced upper level divergence across the RSMC during the past week. BMRC 's coherent OLR mode displays [http://www.bom.gov.au/bmrc/clfor/cfstaff/matw/maproom] show an active MJO pulse extending between 80 and 110E, continuing to propagate eastwards. With the apparent well-behaved nature of the MJO in recent months, the inferred period for the MJO is around 35-40 days suggesting that the active pulse is likely to continue propagating eastwards reaching Australian longitudes during the next week. With an active MJO pulse propagating through the region an increased probability of tropical cyclone formation is expected.

* Darwin RSMC chart area extends from 40S to 40N, 70E to 180
The Weekly Tropical Climate Note is updated each Tuesday by about 0330 UTC. http://www.bom.gov.au/climate/tropnote/tropnote.shtml
For more information please contact climate.tropical@bom.gov.au