Storm News
and Chasing
[Index][Archives] 		Main Index Home Page Stock Weather Photos Australian Severe Weather Forum Storm News and Storm Chasing Reports Tropical Cyclones / Hurricanes / Typhoons Weather Data and Links Wild Fires / Bushfires Weather Observation Techniques Weather Picture Catalogue Tornado Pictures and Reports Stock Video Footage and DVDs for sale
East Coast Lows and Coastal Troughs: Autumn and Winter 1998
by Michael Bath

Introduction

The autumn and winter months for east coast residents from southeast Queensland to southeast Victoria will long be remembered weatherwise. Heavy rainfall, gales and floods have been regular features of the weather since a remarkable change in weather patterns that commenced on 10th April 1998. After months of hot and dry weather (and years since any major flooding), the persistent El-Nino finally waned.

At least 9 separate East Coast Low or Coastal Trough events have occurred in just over 4 months. This is a remarkable statistic for such a short period. In recent years, one or two lows at the most have developed in the six months between March and September. It would be interesting to have figures for the number of East Coast Lows from all past years of record. If anyone has this data, please make it available for Storm News.

Excerpts from "The Australian Weather Book" by Keith Colls and Richard Wittaker. East Coast lows are a phenomena that occur over southern Queensland and eastern New South Wales usually between the latitudes of 25S to 40 S. They occur typically in autumn or winter with an average frequency of one or two per year. They are characterised by their small size and often extremely rapid development. The formation of East Coast Lows usually occurs at night near the coast in a region of strong oceanic temperature gradients. Night time formation is preferred as continental cooling enhances the temperature gradients along the coast and a strong temperature gradient near the surface seems necessary to maintain the strength of the low. If East Coast Lows move away from the coast, they rapidly weaken. They usually form in the divergent poleward exit region of the subtropical jet and just downstream of a mid-level cold pool. There is usually significant convection and upslope precipitation on the poleward side of the low. The severe forms of the east coast low are usually warm cored in the lower troposphere - this results in a wind speed maximum at low levels, and in fact, spiral bands are formed in the cloud pattern and a distinct eye occurs just as in a tropical cyclone. Wind speeds often reach hurricane force.

Event Summaries

  • Event 1: Coastal Trough - 10th April 1998
  • Event 2: Trough and Coastal Lows - 22nd to 24th April 1998
  • Event 3: Coastal Trough ahead of an East Coast Low - 1st to 7th May 1998
  • Event 4: Trough then East Coast Low - 16th to 19th May 1998
  • Event 5: Persistent lows - 3rd to 14th June 1998
  • Event 6: Severe East Coast Low - 23rd June 1998
  • Event 7: East Coast Low - 1st July 1998
  • Event 8: Severe East Coast Low - 6th August 1998
  • Event 9: Coastal Trough and East Coast Low - 17th August 1998

    Event 1: Coastal Trough - 10th April 1998

    Synoptic Situation:
    A small but strong area of convergence in the upper air moved over the Sydney region during the morning on the 10th. At the surface a broad trough extended from central-eastern Queensland to across the NSW Mid-North Coast, where a small low pressure system formed during the early morning. This synoptic pattern persisted for almost 24 hours, after which time the trough dissipated. The small low off the NSW coast remained for a further 36 hours but had no significant affects on coastal weather.
    Charts and Satpics

    Weather that Occurred on the 10th
    Slow moving thunderstorm cells throughout the Sydney metropolitan area from dawn giving exceptional short duration rainfall totals. Flash flooding was widespread. In the greater Brisbane area, severe thunderstorms during the afternoon were accompanied with large hail and destructive winds.

    Notable Rainfall Totals
    24 hours to 9am 10th April:
    Randwick Racecourse 118, Mosman 76, Sydney Airport 75, Sydney 74, Rose Bay 71, Randwick Bowling Club 71, Point Perpendicular 170, Culburra, 130, Greenwell Point 68
    24 hours to 9am 11th April:
    Castle Cove 279, Belrose 263, Ingleside 250, Frenchs Forest 228, Cromer 190, Palm Beach 185, Gordon 166, Sydney 165, Pymble 163, Avalon 154, Riverview 142, Epping 140, Turramurra 129

    Further details of the Sydney flash floods can be found on Laurier Williams April 1998 News Page
    A full report of the Brisbane severe storms can be found on James Chambers SE Qld Storm Site

    Event 2: Trough and Coastal Lows - 22nd to 24th April 1998

    Synoptic Situation
    A slow moving cold front through NSW with a trough extending down from southern Queensland. Three small surface lows developed off and along the east coast during the 23rd, but only one persisted off the NSW central coast.
    Charts and Satpics

    Weather That Occurred
    Widespread moderate to heavy rainfall totals throughout NSW. Some minor flooding. Heavy thunderstorms in NW sloped late on the 23rd

    Notable Rainfall Totals
    24 hours to 9am 22nd April:
    Mudgee 59, Orange 68, Bourke Ap 57, Byrock 72, Carinda 75, Coonamble Ap 52, Girilambone 81, Narromine 64, Nyngan 80, Quambone 67, Trangie 72, Warren 83, Conowindra 55, Cudal 57, Dubbo 64, Dubbo Ap 72, Eugowra 60, Wellington 72, Manildra 52
    24 hours to 9am 23rd April:
    Clarence Town 50, Gosford 54, Gosford RN 87, Lostock Dam 58, Mangrove Mt 52, Nobbys Head 51, Norah Head 56, Wyong 54, Belrose 69, Mosman 50, Pymble 53, Turramurra 57
    24 hours to 9am 24th April:
    Breeza 75, Gunnedah 53, Quirindi 56, Somerton 64, Willow Tree 67, Ballina Ap 50, Cape Byron 58, Grafton 66, Mullumbimby 58, Bulahdelah 74, Coffs Harbour 73, Gloucester 50, Macksville 50, Smoky Cape 53

    Event 3: Coastal Trough ahead of an East Coast Low - 1st to 7th May 1998

    Synoptic Situation
    A trough developed along the central NSW coast extending back into southeastern Queensland on the 1st. With a large almost stationary high in the Bight, the trough persisted in the east-southeasterly flow for several days. A small surface low formed off the NSW mid north coast during the afternoon of the 3rd, but dissipated late on the 4th as a second trough intensified over central coastal Queensland, and the high pressure system pushed into the southern Tasman Sea. By the 5th a complex multi-centred low pressure had developed off the south Queensland coast. This rapidly deepened overnight into an East Coast Low, and quickly moved south along the NSW coast, before slowly heading SE over the next 36 to 48 hours.
    Charts and Satpics

    Weather That Occurred
    Heavy thunderstorms in SE Queensland late on the 1st, and very heavy rainfall around the Port Macquarie area in NSW during the afternoon and evening of the 2nd. Further heavy falls and thunderstorms during the 4th and 5th in southern Queensland with some flooding. Gales and moderate to heavy rainfalls affected the NSW coast on the 5th and 6th

    Notable Rainfall Totals in NSW
    24 hours in 9am 2nd May:
    Wyong 68
    24 hours to 9am 3rd May:
    Forster 60, Lorne 55, Port Macquarie 149, Taree 67, Taree Ap 85, Wauchope 76, Williamtown 73, Wyong 66
    24 hours to 9am 5th May:
    Burren Junction 58, Armidale Ap 52, Alstonville 52, Ballina 78, Woodburn 64, Gosford 64, Mangrove Mt 63, Nobbys Head 97, Williamtown 79, Wyong 65, Belrose 57, Frenchs Forest 57
    24 hours to 9am 6th May:
    Armidale Ap 56, Katoomba 53, Carrowbrook 51, Norah Head 55, Bellambi 57, Berry 68, Greenwell Point 58, Kiama 80, Robertson 86, Milton 52, Frenchs Forest 56

    Further details of this event can be found on Laurier Williams May 1998 News Page

    Event 4: Trough then East Coast Low - 16th to 19th May 1998

    Synoptic Situation
    A broad ridge of high pressure extending from northwest to southeast over the southern parts of the continent with several troughs active inland and offshore. Small surface low pressure centres formed on the 16th and 17th off the east coast. Early on the 18th an easterly dip from the north Tasman formed ahead of the east coast low. Multiple centres were analysed until the afternoon of the 18th when the low intensified into one centre near Sydney. During the 19th the low became elongated, and two centres were again apparent, one off the Sydney/Illawarra and the second off the north coast, NE of the first. The low was captured by a cold front on the 20th
    Charts and Satpics

    Weather That Occurred
    Heavy rainfall in NSW and SE Qld on the 16th with localised heavy coastal falls in NSW during the 17th, 18th and 19th. Gales occurred along the central NSW coast on the 18th and 19th with some trees and powerlines brought down. Some minor flooding occurred, particularly in Sydney.

    Notable Rainfall Totals
    24 hours to 9am 16th May:
    Coonamble 54, Gilgandra 51, Cape Byron 84, Tweed Heads 119
    24 hours to 9am 17th May:
    Mangrove Mt 50, Peats Ridge 74, Stroud 50
    24 hours to 9am 18th May:
    Upper Chichester 58, Wyong 88, Clarence Town 60, Avalon 101, Belrose 68, Frenchs Forest 65, Glenorie 58, Newport 82, Pymble 54, Turramurra 60
    24 hours to 9am 19th May:
    Kurrajong Heights 52, Carrowbrook 56, Clarence Town 51, Gosford 62, Lostock Dam 51, Mangrove Mt 100, Peats Ridge 74, Upper Chichester 68, Wyong 56, Bellambi 56, Berry 53, Darkes Forest 146, Robertson 125, Batemans Bay 50, Milton 60, Narooma 57, Pambula 56, Belrose 103, Berowra 127, Canterbury 70, Castle Hill 138, Fivedock 130, Frenchs Forest 91, Gordon 131, Granville 106, Schofields 115, Oakhurst 91, Homebush 90, Horsley Park 78, Liverpool 57, Lucas Heights 110, Mosman 107, Newport 55, Northbridge 116, Oatley 94, Parramatta 120, Pymble 135, Richmond AP 77, Riverview 129, Rose Bay 91, Seven Hills 118, Sydney AP 113, Tamarama 75, Turramurra 143, Sydney 109

    Further details of this event can be found on Laurier Williams May 1998 News Page

    Event 5: Persistent lows - 3rd to 14th June 1998

    Synoptic Situation
    A stagnating front along the NSW mid north coast developed into small low pressure cell early on the 4th. A blocking high in the south Tasman Sea maintained the low in the same general location while it slowly intensified over the next 36 hours, with multiple centres analysed. During the 6th the low weakened and moved away towards the southeast. The next cold front to approach from the southwest became cut-off on the 7th. This new low captured the first one and the two swirled around the southern Tasman for many days. The centre began to move northwest during the 10th, coming close to the NSW north coast before heading northeast and combining with several small lows in the north Tasman. The system eventually headed south and over New Zealand by the 14th.
    Charts and Satpics

    Weather That Occurred
    Localised heavy rainfalls early on the 3rd with some road closured from flooding around Port Macquarie. The low pressure had very little impact on the coast after it had developed, as its cloud band remained offshore. Heavy falls occurred on Lord Howe Is and Norfolk Is on the 4th and 6th respectively.

    Notable Rainfall Totals
    24 hours to 9am 3rd June:
    Laurieton 103, Lorne 60, Port Macquarie 140, Port Macquarie AWS 84, Taree 57, Darkes Forest 52, Bellambi 64, Milton 53
    24 hours to 9am 4th June:
    Lorne 50, Williamtown 72, Wyong 55,

    Event 6: Severe East Coast Low - 23rd June 1998

    Charts and Satpics

    Full details of this event can be found on Laurier Williams June 1998 News Page

    Event 7: East Coast Low - 30th June to 1st July 1998

    Synoptic Situation
    A cold front moved northeast through South Australia during the 29th June and became cut-off. The low combined with a surface trough over southern Queensland on the 30th and had moved off shore later that day. The low rapidly intensified on 1st July into a very large system and combined with a cold front to the south. It moved quickly away to the southeast after splitting into two centres.
    Charts and Satpics

    Weather That Occurred
    Instability on the western side on the low early on the 1st produced a tornado in the Port Stephens area. Rainfall totals were only light to moderate as the low quickly moved away from the coast.

    Event 8: Severe East Coast Low - 6th August 1998

    Charts and Satpics

    Full details of this event can be found on Laurier Williams August 1998 News Page

    Event 9: Coastal Trough and East Coast Low - 17th August 1998

    Charts and Satpics

    Refer to articles on this event:

  • Severe Flooding Isolates Wollongong
  • Michael Thompsons Chase Diary - Wollongong Floods
    Document: 9808-02.htm
    Updated: 14th January, 2003         		[Australian Severe Weather index] [Copyright Notice] [Email Contacts] [Search This Site]