Issued by the Director of Meteorology
The New Year began with great catastrophe, when one of the worst floods hit the Western Division on the 19th of the month followed by another of much less scale on 27th. Not yet recovered from the 1997/98 drought, these areas were struck with another disaster that caused devastation in Viti Levu's northwestern areas of Nadi, Lautoka, Ba and Tavua. Ba river level rose to 6.8 metres, while the Nadi river level rose to 7.25 metres. Residents in all these areas described the flooding as the worst ever in their living memory. Flooding also occurred in Labasa, Sigatoka and Rakiraki causing the closure of roads in these areas. Seven deaths occurred during the flood ordeal and four people were reported missing. Preliminary reports indicated damages to infrastructure, communications, homes and crops to be around F$5.4 Million.
Rainfall for the month was generally above average with sites in the northwestern part of Viti Levu experiencing three times their average rainfall for the month. Lautoka recorded a one-day maximum rainfall -of 391 mm on the 18th while Nadi recorded 356 mm for the same day, both replacing their previous records. Vatukoula Mine station reported a total fall of 650 mm for the 24 hours to 9 am on the 19th and a further 228 mm for the next day. Except for Nausori, Navua, Monasavu and Ono-I-Lau, the rest of the places recorded above average rainfall for the month.
Night-time temperatures were generally up to 0.9 C higher than average, while daytime temperatures varied. Matuku and Udu Point established new high daytime temperatures of 35.7 C and 33.8 C, respectively, replacing their previous records. Navua recorded a new low night-time temperature of 16.8 C on the 25th, 0.2 C lower than its previous low of 1983.
Sunshine at all recording sites was below average, with Nadi receiving only 64 percent of the normal sunshine for the month.
Weather during January was dominated by a series of westward-moving troughs that produced rain over most parts of the country.
A trough moving across the group from the east brought with it widespread rainfall at the start of the month, with some notable falls during the first two days. The western parts of the country received some heavy afternoon and evening showers.
As the trough moved to the southwest of Fiji on the 5th, heavy rain was experienced in Kadavu and parts of the Southern Lau. Also on the 5th, a second westward-moving trough, which later drifted to the north of the country, brought rain to the eastern part of Vanua Levu.
From the 8th to the 16th, a moist easterly wind flow resulted in showers and thunderstorms developing in the Interior of Viti Levu and Vanua Levu during the early afternoon, and drifting onto the western and the southern coastal areas later in the afternoon.
A third westward-moving trough approached the Lau Group late on the 16th. By the 17th, the trough was lying over the Lau Group and extending northwest towards Rotuma. It produced heavy rain over Rotuma and parts of the Lau group on this day. The trough continued to move westwards on the 18th with the South Pacific Convergence Zone (SPCZ) over Rotuma also drifting south. This low pressure system produced heavy rain during the day in most parts of Vanua Levu and Lomaiviti Group, resulting in severe flooding in Labasa.
During the night of the 18th, the trough drifted onto Viti Levu and stalled for nearly 12 hours causing strong convergence of winds and vigorous thunderstorm activity over the area. This resulted in very heavy rain overnight and during most of the following day over the northwestern part of Viti Levu with consequent severe flooding. Though the weather forecasts had indicated that flooding was expected in most areas, the extreme nature of flooding that occurred was obviously not well anticipated. The trough moved to the west of Fiji on the 21st with rain and floods easing.
From the 21st, a series of low pressure systems (mostly associated with Tropical Cyclones Dani, Olinda and Pete) moved towards Fiji from the west and became slow-moving just west of Viti Levu. Associated cloud and rain bands, some of which were originally feeder bands of cyclone Dani, affected the country during this time. Similar to previous week, there was convergence of the winds from the west (due to the trough) with the moist northerly flow that had been persistent for a while. Convection was enhanced as a result, especially in the western parts of the country during the 27th and 28th, eventuating in flooding again of rivers and low-lying areas. However, the scale of flooding was much less severe than that of the previous week.
A high pressure system extended onto Fiji from the southeast on the 29th bringing mostly fine weather conditions to most places for the remainder of the month. However, afternoon and evening showers continued about the larger islands due to somewhat moist conditions still persisting.
The SPCZ also affected Rotuma, together with shallow troughs of low pressure moving west across the island. These systems were responsible for the Island receiving almost one and a half times its average rainfall for January.
Lautoka recorded 1018 mm of total rainfall for the month, of which 391 mm fell on the 18th, Both these figures are new records for the station, the previous monthly total of 967 mm set in 1997. The one-day figure of 391 mm is also an all time record for the station, the previous record set during the passage of tropical cyclone Nigel on 19th of January 1985. Nadi Airport, recorded 981 mm of total rainfall for the month, out of which 356 mm fell on the 18th. The one-day figure is also an all time record for the station, the previous high being established during the passage of tropical cyclone Polly on the 26th of February 1993.
Matuku established a new high total rainfall for the month and also a new high daytime temperature on the 12th of 35.7 C, 1.8 C more than its previous record of 1977. The other place to record a new high daytime temperature was Udu Point. Navua recorded a new low night-time temperature of 16.8 C on the 25h, replacing its 1983 record.
Labasa's total rainfall was twice its average for the month while Laucala Bay recorded only slightly above average rainfall for the month.
Soils in Western Viti Levu, Navua and Monasavu had water-logged conditions for most of the month. Except for the outer Islands, where slightly dry soil conditions prevailed during midmonth, the remainder of the places had ample soil moisture throughout the month.
Runoffs occurred at all sites, but the highest amount recorded for the month was at Lautoka of 853 mm. Some of the other high runoffs were as follows: 812 mm at Nadi, 619 mm at Labasa, 587 mm at Penang, 495 mm at Matuku, and 437 mm at Monasavu.
Prospects for February/March
Southern Oscillation Index: The Southern Oscillation Index (SOI) for January was +16 (December at +13) with the five-month running mean (centred on November) at +13) (FIGURE D), confirming a La Niña event to be in place. Climate Models indicate that the La Niña event in the Tropical Pacific will continue through June 1999, with a further intensification of the condition possible thereafter.
FMS Rainfall Prediction Model: A computerised scheme for rainfall prediction, provided by the Bureau of Meteorology, Australia, is at present under trial by the Fiji Meteorological Service. This model uses combined historical monthly total rainfalls for the selected sites in the Divisions and the historical and current Southern Oscillation index values. It provides the probability of rainfall in 3 classes of below average, average and above average, for the following three months. At present probabilities are given for the Western and Northern divisions only. The model indicates that there is a slight bias towards wetter than normal conditions across the western and northern parts of the country. This means that above average rainfall is likely for the next three months; typical of the present La Niña event.
Prospects for February/March: Based on the above two indicators, it is likely that most parts of Fiji will continue to experience close to or above average rainfall in the next two months. With anticipated wetter than normal conditions for this time of the year, there is likely to be further incidences of flooding.