Illawarra storm season: what actually fails, and what to do about it

The Illawarra has two storm seasons, not one

The NSW SES defines the storm season as September to April, and adds that major storms can happen at any time of the year. That is the summer half: severe thunderstorms, short violent downpours, hail, damaging gusts.

But the Bureau of Meteorology says east coast lows are more common in late autumn and winter, with a maximum frequency in June. Look at the region’s worst days and the point makes itself. August 1998. June 2016. July 2022. All outside the official storm season. So preparing only for summer leaves you exposed for the half of the year when the longest, wettest events happen.

What an east coast low actually is

Not every bad coastal storm is one. The Bureau applies real criteria: a closed low pressure system, formed between 20 and 40 degrees south along the eastern Australian coast, lingering within about 200 kilometres of the coast for at least twelve hours, with a pressure gradient of at least 4 hectopascals per 100 kilometres.

What makes them destructive is usually not peak wind speed. It is that they are slow-moving or near-stationary, so the effects last far longer than a front or an ordinary low. Rain that a drainage system could shrug off for twenty minutes becomes a different problem when it runs for eighteen hours onto ground that is already saturated.

The local record, with the numbers

These are not scare figures. They are what has already happened here, and they are what we size stormwater work against.

• 17–18 August 1998. In the 24 hours to 9am on the 18th: Mt Ousley 445 mm, Bulli Pass 410 mm, Keiraville 337 mm, Wollongong 316 mm, Figtree 313 mm. Fifty homes flooded in north Wollongong, one death, mudslides on several roads including Bulli Pass, and around $40 million in insured losses in 1998 dollars.
• 21 March 2011. Flash flooding with more than 200 mm of daily rainfall around Shellharbour. Forty-five properties affected, one fatality.
• 4–7 June 2016. A textbook east coast low. Figtree recorded 320 mm; Robertson took 365 mm in 24 hours, a new daily record; 1,300 SES calls in the Illawarra; 81 people evacuated from the Oaklands Caravan Park at Windang. Kiama, Shellharbour and Wollongong were all named among significantly affected LGAs, and the Insurance Council estimated losses in excess of $304 million across NSW.
• 7 April 2022. The NSW SES took more than 680 calls and carried out 25 flood rescues across the Illawarra, South Coast and Greater Sydney. Lachlan Street at Thirroul became a torrent for the second time in a fortnight. A Woonona home on Nicholson Street took about an inch of water through the ground floor.
• 2 July 2022. The Illawarra recorded 200 mm in a single day against a July average of roughly 50 mm. Seven flood rescues statewide that day, five of them here.
• 8–9 February 2023. Bellambi took 116 mm, including 96 mm in one hour. More than 600 SES calls and 31 flood rescues.
• 6 April 2024. Upwards of 300 mm fell over Wollongong through the evening and early hours. Forty suburbs impacted. Thirty-one homes inundated and fourteen left uninhabitable. Council’s own recovery report notes Wollongong has had six natural disaster declarations since 2018. The federal declaration covering the event took in Wollongong, Kiama and Shellharbour.
• 30 June – 1 July 2025. A coastal low, forecast with the potential to develop into an east coast low, brought gusts of up to 110 km/h to Wollongong and the South Coast. The SES took 883 calls at its state operations centre in 28 hours.
• 17–18 January 2026. More than 2,300 SES incidents statewide and 25 flood rescues, with flash flooding and storm damage across the Illawarra. A woman died after being struck by a falling branch at Macquarie Pass.

Six natural disaster declarations in one LGA in six years is the number to sit with. This is not a once-in-a-lifetime problem to be prepared for in the abstract. It is a recurring operating condition.

Reading the warnings properly

The Bureau issues several products and they do not mean the same thing. Getting this right changes what you do with the hour you have.

Severe Thunderstorm Warning

Issued when a storm is producing, or likely to produce, one or more of: hail 2 cm or larger, wind gusts of 90 km/h or more, tornadoes, or heavy rainfall that may lead to flash flooding. The “very dangerous” thresholds are giant hail of 5 cm or more, destructive gusts of 125 km/h or more, or intense rainfall causing life-threatening flash flooding.

Severe Weather Warning

For hazardous weather not solely related to thunderstorms, tropical cyclones or bushfires. Damaging winds means sustained gale force of 63 km/h or more, or gusts of 90 km/h or more. Destructive winds means gusts of 125 km/h or more. It also covers heavy or intense rain that may lead to flash flooding. In an east coast low, this is usually the product you will see.

Flood Watch and Flood Warning

A Flood Watch is not a warning of imminent flooding. It is early advice of a developing situation, generally issued up to four days ahead. A Flood Warning comes when the Bureau is more certain, usually once rain has started, and is targeted at specific catchments with predictions of severity: Minor causes inconvenience and inundates low-lying land next to watercourses; Moderate may affect main traffic routes and some buildings above floor level; Major inundates extensive areas with many buildings affected above floor level.

What actually fails, in the order it fails

After a decade of these events, the sequence is remarkably consistent.

1. Gutters overflow first. Usually not because they are undersized, but because they are full of leaf litter, or the overflow provisions were never right, or a single downpipe is trying to serve too much gutter. Water then goes over the back edge into the eaves and down inside the wall, which is why the damage shows up as a ceiling stain rather than a wet garden.
2. Stormwater pits and charged lines back up. Silt and roots reduce capacity quietly over years, and nobody notices until the day it matters. Wollongong City Council thought conduit blockage important enough that its 2019 Hewitts Creek flood study revision was rewritten specifically to incorporate a Conduit Blockage Policy.
3. Surcharge gullies release. That is what they are for. An overflow relief gully is designed to let sewage escape outside at a level below your floor rather than come up through a shower. If yours is set too low, buried under a garden bed, or has had a paved area built up around it, it cannot do that job.
4. Sub-floor and slab-edge water. On the escarpment side this is often the real problem: ground water arriving laterally from uphill rather than falling on your roof at all.
5. The sewer surcharges. Worth knowing that the Illawarra network is explicitly designed around this. Sydney Water describes its Bellambi and Port Kembla plants as only receiving flow during storm events.

What to do before the season

The NSW SES publishes the householder list and it is a good one: clear gutters, downpipes and drains regularly; look for and repair roof damage including loose tiles, sheets and screws; check windows and doors seal properly; know how to shut off power, water and gas; clean up garden debris and trim overhanging branches; secure or store outdoor furniture and trampolines; park vehicles under cover away from trees; check your insurance is adequate; and keep an emergency kit with a battery or hand-crank radio, torch, first aid, medications and documents.

The plumbing half of that list is where we come in, and it is the part most people skip because none of it is visible:

• CCTV the stormwater lines, not just the sewer. Most people have never had their stormwater inspected. Silt, root intrusion and collapsed sections are common and invisible until the day the system is asked for full capacity.
• Check downpipe-to-gutter ratio. A single downpipe should not be serving an unreasonable run of gutter. More on the numbers in our guide to why gutters overflow.
• Check overflow provisions exist at all. Many older Illawarra houses have none, so the only overflow path is backwards into the eaves.
• Check the surcharge gully height and clearance. This is a five-minute check that prevents sewage in a bathroom.
• Test the sump pump before you need it, and know whether it has any backup if the power goes out, because in these events it usually does.
• Clear the pits. Not just the grate you can see. The one under the mulch too.

During, and afterwards

During a storm the safest place is inside, away from windows. Never drive through floodwater. Stay at least eight metres from fallen powerlines and out of storm drains and creeks.

For storm and flood assistance the number is NSW SES 132 500. For anything life-threatening it is 000. Those are the calls for trees on the house, structural roof damage in an active storm, sandbagging and rising water.

We handle the part the SES does not: blocked stormwater lines, surcharging gullies, sewer backing up into the house, roof leaks once it is safe to be up there, sub-floor water and sump pumps. In a real event you usually need both, in that order. If you are ringing us during a storm, we will tell you honestly on the phone whether it is a job for us, for the SES, or for an electrician first.

The insurance part, carefully

We are plumbers, not insurance advisers, so this is context rather than advice. Storm and flood are defined separately. Since 2012 a single legal definition of flood applies to prescribed insurance contracts, covering water that has escaped from a lake, river, creek or other natural watercourse, reservoir, canal or dam. Storm cover is generally broader, typically including rainwater run-off and water overflowing from stormwater drains, though the Insurance Council notes that some insurers will not cover run-off where the customer has declined flood cover. The product disclosure statement is the thing that governs, not the general rule.

On maintenance: yes, most storm policies contain wear-and-tear or lack-of-maintenance exclusions. No, that does not mean a claim is automatically dead because a gutter had leaves in it. The Australian Financial Complaints Authority applies a proximate cause test, and in its published case studies on maintenance and gradual deterioration exclusions it has repeatedly found insurers had not met the onus of establishing the exclusion applied. Two practical consequences: keep dated records and invoices for gutter cleaning, roof work and drainage maintenance, and if you are knocked back, free help exists through AFCA and the Financial Rights Legal Centre’s Insurance Law Service.

Where to start

If you do one thing before September, make it a CCTV inspection of the stormwater line and a look at the overflow provisions on the gutters. Those two together account for most of the ceiling damage we are called to after an Illawarra storm, and both are cheap to check and expensive to discover the hard way.

Related reading: why gutters overflow in Illawarra storms, what to do in the first hour of a roof leak, stormwater and drainage services, and gutter repairs.