More of the same
11 April, 2018, 12:00 am
FIJI can expect more devastation from rain and floods from this low category cyclone Keni, as the ground is fully saturated since the Easter floods over Fiji, and the fact that it is expected Tropical Cyclone Keni will be of a maximum Category 3 system as it passes southwest of Viti Levu.
The Madden-Julian Oscillation (MJO), which is a pulse of upper atmospheric waves going around the equatorial region longitudinally in a 30-90 days cycle, at 5 m/s, has been passing over us in the western Pacific, in a very enhanced form, giving us not only the Easter floods in Fiji and Vanuatu but also a regular spate of severe weather conditions to our nation since then.
The enhanced amplitude MJO hemispheric waves traversing in a west to east manner across us, towards the eastern Pacific is also flaring up cloud activity in the Wallis and Futuna, Samoa, Tonga, Cook Islands, and the French Polynesia as it progresses eastwards to the eastern Pacific and the Americas.
The MJO passage over the western Pacific has led to enhanced activity of the South Pacific Convergence Zone (SPCZ) which has spawned enough activity in the past through-four days leading to the formation of a tropical cyclone northwest of Fiji early Monday morning April 9, 2018 Fiji time. The Fiji Meteorological Service (FMS) named it TC Keni, a Category 1 system, showing a very good symmetric cyclonic cloud organisation with rainbands in-flowing into the centre.
As the tail end of the MJO is still over and east of us, this upper atmospheric phenomenon, has managed to control the dynamics of the weather and cyclonic activity over us — at least for the time being — which has managed to provide, energy, momentum and sustenance for the cyclone activity leading to the flaring up of TC Keri into at least a Category 2 system within a day or two.
Past the next eight-12 days from now, the western Pacific is expected to become much quieter and probably we are now seeing the last throes of high energy pulsating weather activity for the past two weeks or so, before the region becomes much quieter after the eastwards migration of the MJO signals.
By that time we will also be in transition, with the coming to an end of the wet season (November 1, 2017 to April 30, 2018), with a change to the dry season (May 1, 2018 to October 31, 2018). The transition will mean that the cool, dry southeast trade winds will become prevalent over Fiji and the Pacific Island nations, with great ventilation effect of bringing in much pleasant weather over us.
This is due to the west to east migrating anti-cyclones belt, in latitudinal manner, shifting much closer to the equatorial region; thus near Fiji region. This synoptic weather changes will also lead to a cut-off from the much humid laden air from the equatorial regions over our islands, to cooler winds driven via the trade winds from the New Zealand/Australia/Antarctic regions.
The last of the afternoon shower activity with humid conditions so prevalent in the tropics will subside within the next 3-4 weeks, when we should again experience fairly dry conditions with some major dry spells during June -October periods. There will be no cyclones over Fiji during the May to October period and most rains will be from passing upper air atmospheric troughs (upper air cyclonic wave features at 250 hPa) passing over us in four-six week intervals at 30,000-40,000 feet in the upper atmosphere.
Dry season rains over Fiji can be upwards of 80-120mm in short bursts of less than 24-hr periods, interspersed with dry conditions over four-six weeks. This would generally be the only rains received and should we be lucky with the passage of the MJO in an enhanced mode over us at that time, then we could get substantial rains for a day or two.
Now turning our attention to more immediate matters at home, according to the Special Weather Bulletin Number 12 for Fiji on TC Keni issued from the Regional Specialised Meteorological Centre (RSMC), Nadi at 2:40pm on Monday April 9, we now had a Tropical Cyclone Warning for Category -2, storm force winds for southwest Viti Levu from Nadi through Sigatoka to the Coral Coast.
A gale warning remained in force for the rest of Viti Levu, Yasawa and Mamanuca group, Kadavu and nearby smaller islands. A tropical cyclone alert remains in force for Lomaiviti and southern Lau group. A strong wind warning remained in force for the rest of Fiji.
TC Category-1 winds are 34-47 knots (10 minutes sustained) and often referred to as gale force winds. TC Category-2 winds are referred to as storm force winds, and are mean winds 48-63 knots (10 minutes sustained).
TC Keni has central pressure of 993 hPa and was a Category 1 system at 2.40pm on Monday and was located near latitude 16.4 degrees South and longitude 171.4 degrees East or about 590 km west of Viwa and about 660 km west-northwest of Nadi at midday. Keni was moving East-Southeast at 16 km/hr with average winds of 86 km/hr and momentary gusts of 120 km/her near the centre.
TC Keni was slowly intensifying and was expected to be located 400 km west of Nadi at midnight last night (Monday night -Tuesday morning) and 120 km southwest of Nadi at midday yesterday (Tuesday).
The FMS has forecast for southwest Viti Levu through Sigatoka to Coral Coast winds increasing to damaging gale force with average speed of 85 km/her and momentary gusts of 120km/her for early this morning (Tuesday) with winds strengthening to destructive storm force with average speed of 100 km/hr and momentary gusts to 140km/hr from mid-morning yesterday.
The weather office has further forecast periods of heavy rain with squally thunderstorms, becoming frequent. Flooding, including sea flooding of low lying areas and damaging heavy swells are also forecast for TC Keni as it passes southwest of Viti Levu around and after mid-day yesterday.
TC Keni is expected to strengthen to categories 2 and 3 and then to attain this strength for the following two days before weakening to Category 1 after that becoming extra-territorial. TC Keni is expected to pass on a very close south-western flank of Viti Levu, Kadavu, and Ono-i-Lau on its south eastwards track.
* Dr Sushil K Sharma is an associate professor of meteorology at the Fiji National University. These views are his, and not FNU’s or this newspaper’s.