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close this bookSevere Tropical Storms Preparation and Response - Case Study Text (DHA/UNDRO - DMTP - UNDP, 1991, 58 p.)
close this folderPart Two: Disaster and Response
View the documentE. Detection and Warning of the Storm
View the documentF. Characteristics of the Threatened Area
View the documentG. Actions at the Provincial and Local Level in Response to Warning
View the documentH. Primary Impact
View the documentI. Secondary Effects
View the documentJ. Shortcomings in Management of the Response

E. Detection and Warning of the Storm

The Warning Network

The Republic of Salacca was widely reported to have one of the better meteorological departments in the region. It had an extensive network of traditional observation posts which reported surface and upper level observations round the clock throughout the year, using high frequency (HF) radio telephone. It also was able to draw upon geostationary meteorological satellite imagery for the region, and high resolution pictures from low orbit NOAA satellites, using terminals at its headquarters. The headquarters received colour digitised weather radar data by dedicated land-line from seven radar stations strategically located along the coastline and in the hinterland. The headquarters was linked into the Global Telecommunications System of the World Meteorological Organization’s World Weather Watch, using both satellite and cables, and had additional telex links with the main regional forecast centre 2000 km to the Southwest. There were additional HF radio links to airports throughout the region.

Staff were well selected and well trained. Specialist training was provided through World Meteorological Organization programmes, with additional bilateral support in some specialties. However, an on-going problem for the department was the low level of civil service salaries. Almost all the staff were forced to supplement their income in some way, and many of the professional staff had interests in a range of small businesses (including office equipment, fish-farming, computer software, and cosmetics, to name just some). Inevitably, many of those at work found it difficult to concentrate full-time on their jobs, although the level of professional skill remained high.

Detection of the Storm, and Issue of Warnings

A low pressure circulation was detected about 330 km east of Salacca early in the morning of September 30th. Satellite pictures showed an unstructured cloud mass, and on the basis of this data the forecasters in the national Meteorological department estimated that the low pressure area would intensify and move to the west. Five hours later, at around midday, the forecasting unit issued a warning advice, predicting widespread rain and flash flooding in the central provinces. Early the following morning (October 1st), at 3.30 am. the national forecasting centre issued a second warning advice, repeated at 11 am. This said that the low pressure area had intensified into an active depression, and was moving West North West. It forecast heavy rain, flash floods, and very rough seas.

A fourth warning was issued on the same day (October 1st) at 6.00 pm. It gave a likely impact point for the storm, but no estimate of wind speeds. That evening, the position of the depression shifted, and it started to move north at around 6 km/hr, intensifying over the next twenty hours.

The next warning was issued late in the afternoon of October 2nd. It reported that the depression had developed into a tropical storm moving northwest. Winds in the centre were reaching 70 km/hr. At this time it was about 230 km east of the coastline. The warning repeated that rough seas and flash floods could be expected, but gave no estimate of possible landfall. That evening, the storm was given the name Zelda, from the standard list issued by the Regional WMO committee.

The next warning was not issued by the Meteorological department for a further 18 hours, at around 11 am on the morning of October 3rd. It gave the storm’s position, 180 km from the coastline, moving northwest at 9 km/hr. The warning stated that maximum winds at the centre were now about 110 km/hr, with 10 metre waves. Possible landfall was specified as somewhere on a stretch of coastline 220 km long. Heavy rain and flash floods were again forecast. At around midday, satellite photographs showed the development of an “eye” in the centre of the storm, and the meteorologists estimated that the maximum winds would increase over the next 24 hours to at least 130 km/hr within 40 km of the centre.

Early on October 3rd, the weather radar on the coast picked up the storm and tracked it continuously thereafter. The seventh warning was issued from the Meteorological Office at midday on 3rd October. It said that the storm had intensified into a Cyclone, and was moving West North West at 8 km/hr. Maximum winds of 135 km/hr were expected. However, the shipping forecast issued that afternoon still specified wind speeds in the Cyclone area at 30 to 50 km/hr.

The next warning was delayed. The reasons for this are still unclear. The warning was not issued until 5 am on the morning of 4th October, when the centre of the storm was only 40 km from the coastline near the town of Grenora. Landfall was expected at 8 am. The warning message stated that strong winds and heavy rain were expected within 60 km of the centre, and that trees, telephone lines and power lines were likely to be damaged. A sudden rise in sea level, and flash floods, were both mentioned, but no further details were given. The same morning, one hour later, the national TV weather bulletins, prepared by the Meteorological Department early that morning, were still forecasting 25 to 50 km/hr winds, and moderate to rough seas.