East Asia and Western Pacific METEOROLOGY AND CLIMATE

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the west-northwest and swept across the islands of central Philippines
and southern Luzon on 17 May 1989. After entering the South China Sea
the following morning, it turned to a more northwestward course while
its forward speed was reduced by half. Brenda continued to intensify
during the process. It eventually attained typhoon strength on 19 May
with maximum sustained winds near its centre at the time estimated to be
about 120 km/h. It also accelerated slightly to a speed of about 18
km/h and at one stage seemed to be heading straight towards Hong Kong.
However, Brenda turned slightly to the west-northwest on 20 May, skirting
past at a distance of 130 km to the southwest. It finally made
landfall during the night over the coastal areas of western Guangdong
and dissipated rapidly over land in the morning.
A video tape on the life history of Typhoon Brenda has been prepared for
presentation using a special enhancement look-up table for tropical
cyclones. By observing the changes in cold tops and banding features
near its centre, forecasters can make reliable centre fixes and intensity
assessment. The observational aspect was covered in detail in the
video presentation. Discussion in this section will mainly concentrate
on the operational problems confronting the forecasters on the morning
of 19 May.
The provisional best track of Brenda along with forecasts and warnings
current at the time are shown in Fig. 7. JTWC (Joint Typhoon Warning
Centre, Guam) went for a basically northward track to eastern Guangdong.
ECMWF (European Centre for Medium-range Weather Forecasting) opted for a
gentle curve to the west-northwest in the general direction of western
Guangdong. Between the two extremes were the prognoses by ROLAM and the
analogue model. Both predicted a gentle curve to the north with landfall
position in the vicinity of Hong Kong. In terms of consistency,
ECMWF had been maintaining its scenario while JTWC had shifted from a
recurving scenario to a track that was further and further to the west.
Synoptically, there was a deep westerly trough moving out over eastern
China which provided some justification to the JTWC forecast. However,
ECMWF insisted that the trough would soon relax and a ridge would quickly
re-establish to the north of Brenda.
Therefore, it was a problem of assessing whether the westerly trough
would be able to pick up Brenda and the early part of 19 May was the
critical period if this should occur. Fig. 8 shows the visible GMS
picture received that morning. The cloud band extending to Japan was
associated with the westerly trough in question. It appeared to have
linked up already with the outer cloud bands of Brenda. However, subsequent
events as observed increasingly favoured those tracks which pointed
to the west of Hong Kong. Firstly, clouds previously clearing southeastern
China after the passage of the westerly trough had returned to
the region - an indication that the circulation of Brenda became more
dominant and the trough effect, if any, was on the decline. In fact,
when the picture shown in Fig. 8 was taken, the first of Brenda 1 s outer
rainbands had just reached Hong Kong, Secondly t Brenda intensified
further and an eye appeared for a short time. Good banding features
allowed a very reliable fix on Brenda's position on an hourly basis. It