A severe storm that moved through parts of the region on Tuesday afternoon – delivering a burst of heavy rain and small hail in some suburbs – was just a taste of what’s to come.

A severe weather warning for heavy rain and damaging winds was reissued late on Tuesday, as a low pressure system lined up the region. The system is expected to rapidly intensify as it moves over the coast during Wednesday.

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Bureau of Meteorology severe weather manager Simon Louis said the low was expected to cross the coast “somewhere between Sydney and Wollongong” before moving quickly offshore.

Intense rain and vigorous winds are expected in parts of the Illawarra and Greater Sydney. Mr Louis said “very intense falls” were expected “somewhere between around about Sydney, Wollongong or the Shoalhaven”.

“However, there is still some uncertainty around exactly where we’ll get the highest totals,” he said. The rain is likely to be heaviest on Wednesday morning and continue throughout the day, before easing in the late afternoon or evening.

Flash flooding is likely in parts of the Illawarra. The bureau has forecast between 120 and 150 millimetres of rain on Wednesday. However, localised rainfall totals of up to 200mm are possible.

Mr Louis said areas under the heaviest falls could see more than a month’s rain in the space of just a few hours.

Damaging winds – averaging 60 to 70km/h, with peak gusts in excess of 90 km/h – are likely along the Illawarra coast from late on Wednesday morning.  The system is also expected to whip up hazardous surf conditions.

A flood watch has been issued for the coastal rivers between between the Central Coast and St Georges Basin.

Coastal catchments in that area may see widespread localised flooding and minor to moderate riverine flooding.

NSW State Emergency Service (SES) director of operational response Assistant Commissioner Scott Hanckel said the organisation would likely have more than 3000 volunteers ready to respond in metropolitan Sydney alone.

Asst Comm Hanckel said the service’s southeast zone, which includes Illawarra units, was also “ramping up its response”.

Chief Inspector Phil Brooks, from the NSW Police Traffic and Highway Patrol Command, said roads would become “slippery and unpredictable”.

“We’re asking all road users to perhaps reconsider the need to be on the roads throughout what will be a severe rain event,” Chief Insp Brooks said.