Tropical Cyclones (eBook)

James Terry is Head of the Department of Geography at the University of the South Pacific (USP), Fiji Islands. Previous positions include Associate Professor at the Research Centre for the Pacific Islands, Kagoshima University, Japan. In addition to his lecture and research experience, Dr. Terry has served as a geographer consultant for various governmental institutions.

Preface and Acknowledgements 6
Contents 8
I Tropical Cyclones in the South Pacific 12
Setting the Scene 13
1.1 Introduction 13
1.2 The Study Area 15
1.3 Regional Climatic Influences 18
1.3.1 The Southeast Trade Winds 18
1.3.2 The South Pacific Convergence Zone 20
1.3.3 The El Ni“o-Southern Oscillation 22
2.1 Principles and Controls 25
Tropical Cyclogenesis 25
2.2 Storm Formation and Development 2.2.1 Early Stages 26
2.2.2 Mature Stage 29
2.3 Storm Decay 2.3.1 Major Influences 30
2.3.2 Case Study Ò Decay by Vertical Shearing of Tropical Cyclone June in May 1997 33
Tropical Cyclone Structure 36
3.1 Shape and Size 36
3.2 Cloud Patterns 37
3.3 Eye of the Storm 39
3.4 Naming Tropical Cyclones 40
Tropical Cyclone Patterns and Behaviour 43
4.1 Numbers, Timing and Seasonality 43
4.2 Distribution of Origins and Activity 46
4.3 Identifying Storm Tracks 48
4.4 Environmental Steering 49
4.5 Speed of Advance 51
4.6 Track Directions 54
4.7 Storm Longevity 56
Meteorological Conditions 60
5.1 Low Pressure 60
5.2 Strong Winds 5.2.1 Wind Effects 62
5.2.2 Wind Strength 64
5.2.3 Wind Distribution 67
5.2.4 Wind Direction 70
5.2.5 Case Study Ò Intensity of Tropical Cyclone Ofa, February 1990 73
5.3 Storm Surge and Sea Flooding 5.3.1 Wind and Pressure Components 74
5.3.2 Cyclone and Coastline Influences 78
5.3.3 Case Study Ò Storm Surge Produced by Tropical Cyclone Gavin in Fiji, March 1997 81
5.4 Torrential Rainfall 5.4.1 Distribution and Controls 84
5.4.2 Case Study Ò Rainfall Distribution Across Fiji During Tropical Cyclone Gavin in March 1997 87
Future Tropical Cyclone Activity 89
6.1 Methodologies 89
6.2 Changes in Frequency 90
6.3 Changes in Intensity 91
6.4 Changes in Origins 93
6.5 Changes in Precipitation 93
6.6 Outlook 94
II Impacts of Tropical Cyclones 97
Introduction 97
Coastal Geomorphology 100
7.1 Coral Reefs 7.1.1 Reef Characteristics 100
7.1.2 Reef Damage and Recovery 101
7.2 Coastal Erosion 7.2.1 Erosional Features 105
7.2.2 Case Study Ò Coastal Erosion on Niue Island During Tropical Cyclone Heta in January 2004 108
7.3 Coastal Deposition 7.3.1 Reef- edge Megablocks 113
7.3.2 Gravel Sheets and Ramparts 114
7.3.3 Case Study Ò Rubble Ramparts Created on Upolu Island by Tropical Cyclone Ofa in February 1990 117
7.4 Changes on Coral Islands 7.4.1 Coral Island Types 118
7.4.2 Cay Migration and Redistribution 120
7.4.3 Case Study Ò Geomorphic Change on Tatafa Cay in Tonga During Tropical Cyclone Isaac in March 1982 120
7.4.4 Atoll Hoa 122
7.4.5 Motu Growth and Longevity 123
7.4.6 Case Study Ò New Land Created on Funafuti Atoll by Tropical Cyclone Bebe in October 1972 126
8.1 Slope Susceptibility to Failure 129
Slope Stability and Mass Movements 129
8.2 Failure Trigger Mechanisms 130
8.3 Landslide Geomorphology 8.3.1 Major Features 133
8.3.2 Case Study Ò the ÎGood Friday LandslidesÌ Triggered on Viti Levu Island by Tropical Cyclone Wally in April 1980 138
9.1 Introduction to Island Rivers 144
River Hydrology and Floods 144
9.2 Tropical Cyclone Floods 147
9.2.1 Influences on River Responses 148
9.2.2 Flood Analyses 152
9.2.3 Case Study Ò River Responses in Fiji to a Succession of Tropical Cyclones During the 1997 El Ni“o Event 153
9.2.4 Case Study Ò Exceptional River Flooding on Vanua Levu Island Caused by Tropical Cyclone Ami in January 2003 160
9.2.5 Flood Hazard Mitigation 165
10.1 Channel Adjustments 169
Fluvial Geomorphology 169
10.2 River Sediment Transport 173
10.3 Valley Aggradation 10.3.1 Features and Rates 176
10.3.2 Case Study Ò Catastrophic Valley Aggradation on Guadalcanal Island Caused by Tropical Cyclone Namu in May 1986 179
References 186
Appendix 197
Index 214