Northern and Northeastern Australia
Northern Australia (indicated by the boxed area in Fig.
62a) experiences a tropical climate with a well-defined rainy season that typically
begins during October and ends in April (Fig. 62c). Much of the
area receives more than 75% of its mean annual rainfall during this 7-month period, with
portions of extreme northern Australia recording more than 90%. This annual cycle is
modulated by the Southern Oscillation, with below- (above-) average rainfall often
observed during Pacific warm (cold) episodes (Ropelewski and Halpert 1987, 1989).
Overall, the October 1998April 1999 rainy season featured
above-average rainfall across the northern half of northern Australia (Fig. 62a), with record totals observed in portions of northwestern
Australia. In each of these regions, totals averaged more than 200 mm above-normal during
the season, with the locally extreme totals in some areas leading to significant flooding.
In northern Australia rainfall was above-average in every month of the season except
January (Fig. 62c, green bars), with particularly excessive
totals observed in NovemberDecember 1998 and in MarchApril 1999. The increased
rainfall in December, March, and April was partly associated with a series of five
tropical cyclones (TC), which included TC Thelma in December, TC Rona in February, TC
Vance in March, TC Elaine in March, and TC Gwenda in April. These systems, with the
exception of TC Rona, also produced copious rainfall totals over portions of western
At Darwin, Australia, indicated by the yellow dot in Fig. 62a, seasonal rainfall totals reached 2250 mm (Fig. 63a), which approached the record total of 2499 mm observed
during the previous record 1997/98 wet season (Bell et al., 1999). The largest rainfall
event during the 1998/99 season at this station was a 2-day total of 420 mm, in
association with Category-5 TC Thelma in December 1998 (Fig. 63b).
This single rainfall event contributed to more than half of the total seasonal anomaly of
750 mm. Darwin also recorded measurable rainfall nearly every day from January to
mid-April, with several substantial rain events (totals reaching 50 mm each) observed
during the period.
In northwestern Australia 1998/99 seasonal rainfall totals at Wittendom
Gorge (Fig. 64), location indicated by the red dot in Fig. 62a, reached 850 mm (Fig. 64a). This
total is 525 mm, and 260%, larger than the climatological mean. Most of this excess
rainfall resulted from three major precipitation events (Fig. 64b),
two of which occurred in February and one of which occurred in mid-March in association
with TC Elaine.
2) Southeastern Australia